A method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles (UAVs)

Abstract

This invention discloses a method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles (UAVs). The technical solution involves constructing a shipborne radar calibration system composed of a UAV and a radar. The UAV is equipped with a DGPS navigation and positioning system, a first wireless communication system, and a first time unification system. The radar is equipped with a second wireless communication system, a DGPS positioning module, a target detection system, a calibration data acquisition module, a calibration data processing module, and a second time unification system. The two time unification systems synchronize the time. The radar sends the radar deployment point coordinates to the UAV, and the DGPS navigation and positioning system plans the UAV's movement path. The calibration data acquisition module collects raw calibration data. The calibration data processing module processes abnormal GPS positioning data, calculates radar measurement errors, and achieves radar measurement accuracy calibration. Using this invention can reduce the impact of calibration signal source position errors on the calibration results, improve calibration accuracy, and reduce the cost of shipborne radar calibration.

Description

Technical Field

[0001] This invention relates to the field of radar technology, and in particular to a method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles (UAVs). Background Technology

[0002] Shipborne radar is a general term for various types of radar equipped on surface vessels. It utilizes the principle of electromagnetic wave detection to measure the azimuth, elevation, and range data of targets on the sea surface and in the air, enabling target localization and tracking. It provides technical support for surface vessels to perform diverse missions such as cargo transport, firepower strikes, maritime and air surveillance, environmental monitoring, and guiding carrier-based aircraft flights and landings. Compared with existing visible light, infrared, and ultrasonic measurement equipment, shipborne radar can detect and track targets day and night, and is unaffected by adverse external factors such as fog, clouds, and rain, possessing the advantage of all-weather real-time measurement. It is widely used in military and... Shipborne radar has wide applications in the civilian sector. Measurement accuracy is one of the most important technical indicators of shipborne radar, directly determining the precision and effectiveness of data such as distance, azimuth, and elevation of detected targets. Typically, shipborne radar undergoes precise measurement and calibration before entering service. However, in actual use, as ships age, factors such as hull deformation, wear of mechanical parts, external impacts, and aging of electrical components inevitably cause drift in the horizontal, azimuth, and electrical zero points of the shipborne radar equipment, leading to deviations in target measurement data from the true values. Therefore, employing convenient, efficient, reliable, and accurate methods to calibrate the measurement accuracy of shipborne radar is of significant theoretical and practical value in effectively improving the precise positioning and tracking performance of surface vessels against surface and air targets, ensuring that surface vessels can better perform diverse missions such as cargo transport, battlefield situational awareness, and precision strikes against the enemy.

[0003] The main methods for calibrating the accuracy of shipborne radar currently include:

[0004] In their 2015 paper "Design and Implementation of Wind-Resistant Stabilization System for Signal Source of Calibration Tower" published in the journal Electronic Science and Technology, Wu Xin, Dai Guangming, Wei Zhongliang, Wang Leilei, and others addressed the issue of wind load disturbance causing swaying of the signal source at the top of the tower during the field radar calibration process, which affects the radar calibration accuracy. They designed a wind-resistant stabilization system based on a laser tracker and a two-dimensional stabilization platform as core components to stabilize the position of the signal source and improve the radar field calibration accuracy. The advantages of this method of using a fixed calibration tower for radar measurement error calibration are high accuracy and good repeatability; the disadvantages are: (1) The calibration tower is used in harsh environments and must be installed in open areas without obstruction. Otherwise, the strong reflective objects such as mountains, buildings and trees around the calibration tower will seriously affect the calibration accuracy of the radar; (2) The cost of measuring the true value of the position coordinates of the signal source at the top of the calibration tower is high. It generally requires high-precision laser rangefinders, theodolites and other equipment to accurately measure the position. The cost of using high-precision equipment is high, the equipment transfer and debugging process is complicated, and the measurement operation is complicated and time-consuming; (3) The calibration tower is a fixed building while the shipborne radar is a mobile radar. The actual working environment of the shipborne radar is rivers, lakes and oceans. The existing fixed calibration towers cannot meet the requirements for accurate calibration of the measurement error of the radar in the actual working environment.

[0005] Lin Sheng, Liu Junwei, Xu Wei, and others, in their 2018 paper "An ADS-B-Based Radar System Error Calibration Method" published in the journal *Ship Electronic Countermeasures*, utilized ADS-B (Automatic Dependent Surveillance-Broadcast) equipment to collect the position information of civil aviation aircraft within the radar's measurement range. They matched the radar's measured aircraft trajectory with the aircraft position information provided by the ADS-B equipment, interpolated the positions of the successfully matched points to obtain the true position of the points, and calibrated the radar's measurement accuracy based on this true position data. This method has advantages such as simplicity, speed, and low cost. However, its drawback is that it does not consider the potentially serious position errors that may exist in the aircraft position data provided by the ADS-B equipment. For high-precision radar calibration, these influences will introduce significant errors into the radar measurement accuracy calibration.

[0006] Qi Tao, Gao Yuchun, Zhang Xuefen, and others, in their 2020 Chinese invention patent application "A Weather Radar Calibration Method and System Based on Unmanned Aerial Vehicle (UAV)" (application number: CN202010349440.3), fixed the calibration source device on the UAV, controlled the UAV to fly to a predetermined area, and used the UAV's onboard GPS (Global Positioning System) positioning system to provide the position value of the calibration device to achieve radar measurement accuracy calibration. The method is flexible in use, low in cost, and can carry out calibration work in a near-real-world radar environment. However, the disadvantage is that the GPS positioning system is easily affected by external interference, which can lead to positioning anomalies. The presence of positioning anomalies can introduce a large deviation in the calibration of radar measurement accuracy.

[0007] Therefore, how to reduce the calibration cost of shipborne radar measurement accuracy, reduce the impact of calibration signal source position error on calibration results, and achieve convenient, efficient, reliable and accurate measurement accuracy calibration of radar under actual combat conditions remains a hot topic of great concern to those skilled in the art. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for calibrating the measurement accuracy of shipborne radar based on UAV, thereby reducing the calibration cost of shipborne radar, reducing the impact of calibration signal source position error on calibration results, and improving calibration accuracy.

[0009] The technical solution of this invention is:

[0010] The first step is to construct a shipborne radar calibration system based on unmanned aerial vehicles (UAVs). This system consists of one UAV and one radar.

[0011] The drone is equipped with a DGPS (Differential Global Position System, which is a system that uses differential technology on the basis of GPS to enable users to obtain higher positioning accuracy from the GPS system) navigation and positioning system, a first wireless communication system, and a first time unified system.

[0012] The first-time unified system is capable of providing GPS time (GPS time is the time reference for the operation of the GPS system; see details: [link to relevant documentation]). https: / / blog.csdn.net / jlf521521 / article / details / 120817150, June 30, 2022The general module for synchronizing information (based on GPS) requires the timing accuracy of the first time communication system to be better than 15ns, and the 24-hour timekeeping accuracy (timekeeping accuracy refers to the ratio of the time deviation of the time synchronization device to the running time of the time synchronization device; for details, refer to the paper "Research on the Timekeeping Algorithm of Digital Clock Based on GPS Calibration" published by Tian Ming and Wang Ruiqing in the journal "Computer and Digital Engineering" in 2011) to be better than 10us; the first time synchronization system is connected to the DGPS navigation and positioning system and the first wireless communication system, providing GPS time synchronization information to the DGPS navigation and positioning system and the first wireless communication system;

[0013] The DGPS navigation and positioning system is used to achieve UAV positioning and flight path planning, requiring a dynamic positioning accuracy better than 0.1m. The DGPS system is connected to a first wireless communication system and a first time synchronization system. The DGPS system receives GPS time synchronization information from the first time synchronization system to ensure that it operates on the same time reference as the first wireless communication system. The DGPS system receives the deployment point location information of the shipborne radar from the first wireless communication system and plans the UAV's flight path based on this information. The DGPS system achieves real-time GPS positioning of the UAV and transmits the UAV's GPS position information to the first wireless communication system.

[0014] The first wireless communication system is a general-purpose hardware module with communication functions, such as a Beidou communication terminal, a satellite communication terminal, and a data transmission radio. The effective communication distance of the first wireless communication system is recommended to be greater than 10km. The first wireless communication system is connected to the DGPS navigation and positioning system, the first time communication system, and the radar. The first wireless communication system receives the UAV's GPS position information from the DGPS navigation and positioning system and sends the UAV's GPS position information to the radar. The first wireless communication system receives the radar deployment point coordinates from the radar and sends the radar deployment point coordinates to the DGPS navigation and positioning system.

[0015] The shipborne radar is equipped with a second wireless communication system, a DGPS positioning module, a target detection system, a calibration data acquisition module, a calibration data processing module, and a second time unification system.

[0016] The second time unification system is a general-purpose module that provides GPS time synchronization information. It requires the second time communication system to have a timing accuracy better than 15ns and a 24-hour timekeeping accuracy better than 10us. The second time unification system is connected to the second wireless communication system, the DGPS positioning module, the target detection system, the calibration data acquisition module, and the calibration data processing module, and provides GPS time synchronization information to these components.

[0017] The second wireless communication system is a general-purpose hardware module with communication functions, such as a Beidou communication terminal, a satellite communication terminal, and a data transmission radio. The effective communication distance of the second wireless communication system is recommended to be greater than 10km. The second wireless communication system is connected to the DGPS positioning module, the calibration data acquisition module, the second time unification system, and the first communication system of the UAV. The second communication system receives the GPS time synchronization signal provided by the second time unification system and completes its own time synchronization. The second wireless communication system sends the radar deployment point coordinates provided by the DGPS positioning module to the first wireless communication system of the UAV and sends the UAV GPS position information provided by the first wireless communication system to the calibration data acquisition module.

[0018] The DGPS positioning module locates the radar deployment point, requiring a static single-point positioning accuracy better than 0.1m. The DGPS positioning module is connected to the second wireless communication system and the second time synchronization system. It receives GPS time synchronization information from the second time synchronization system, completes its own time synchronization, and ensures that it operates on the same time reference as the second wireless communication system, target detection system, calibration data acquisition module, and calibration data processing module on the shipborne radar. The DGPS positioning module then transmits the radar deployment point coordinates to the second wireless communication system.

[0019] The target detection system is used to measure the polar coordinate data of the UAV, acquiring its pitch, azimuth, and altitude data. Commonly used target detection systems for shipborne radar include Doppler radar, millimeter-wave radar, and meter-wave radar. The target detection system is connected to the calibration data acquisition module and the second time synchronization system. The target detection system receives GPS time synchronization information provided by the second time synchronization system, ensuring that the target detection system operates on the same time reference as the second wireless communication system, DGPS positioning module, calibration data acquisition module, and calibration data processing module on the shipborne radar. The target detection system sends the UAV's polar coordinate position information to the calibration data acquisition module.

[0020] The calibration data acquisition module is used to acquire and stitch together the UAV's GPS position information and polar coordinate position information to obtain the original calibration dataset. The calibration data acquisition module is connected to the second wireless communication system, the target detection system, the second time unification system, and the calibration data processing module. The calibration data acquisition module receives GPS time synchronization information provided by the second time unification system, receives UAV GPS position information from the second wireless communication system, and receives UAV polar coordinate position information from the target detection system. It stitches together the UAV's GPS position coordinates and UAV polar coordinate position information at the same time to obtain the original calibration dataset, and sends the original calibration dataset to the calibration data processing module.

[0021] The calibration data processing module processes the original calibration dataset to calibrate the radar measurement accuracy. It is connected to the second time unification system and the calibration data acquisition module. The calibration data processing module receives GPS time synchronization information from the second time unification system, ensuring that it operates on the same time reference as the second wireless communication system, GPS positioning module, target detection system, and calibration data acquisition module. The calibration data processing module receives the original calibration dataset from the calibration data acquisition module and processes it, including coordinate transformation of the UAV's GPS position information, deletion of abnormal GPS position information, calculation of the error between the polar coordinate position information obtained from the UAV's GPS position information and the UAV's polar coordinate position information measured by the radar at the same time, and correction of the radar's measured azimuth, elevation, and range data based on the calculated average azimuth, elevation, and range errors, thereby calibrating the radar measurement accuracy.

[0022] The second step involves the first and second time unification systems completing GPS time synchronization, setting the calibration system's operating start time T, and outputting GPS time synchronization information. The method is as follows:

[0023] The first and second time unification systems utilize their onboard antennas to receive GPS signals, enabling GPS time synchronization between them and setting the starting time T for the calibration system. After GPS time synchronization is complete, the first time unification system provides GPS time synchronization information to the UAV's DGPS navigation and positioning system and first wireless communication system. The second time unification system provides GPS time synchronization information to the radar's second wireless communication system, DGPS positioning module, target detection system, calibration data acquisition module, and calibration data processing module, ensuring that all modules in the calibration system operate on the same time reference.

[0024] The third step involves the radar sending the coordinates of its deployment point to the drone. The drone's DGPS navigation and positioning system then plans its movement path based on these coordinates, as follows:

[0025] Step 3.1 The radar's DGPS positioning module provides the radar deployment point coordinates to the UAV's DGPS navigation and positioning system via a second wireless communication system:

[0026] Step 3.1.1 The radar's DGPS positioning module locates the radar's position and obtains the coordinates (L...) of the radar deployment point O. O B O HO ), where L O B O H O The system transmits the longitude, latitude, and altitude data of point O in the WGS84 coordinate system (WGS84 is short for the World Geodetic System, a geographic coordinate system used by GPS positioning systems; see: Xu Dengyun and Hao Lijuan's 2012 paper "Comparison of the 2000 National Geodetic Coordinate System with GRS80 and WGS84") to the second wireless communication system.

[0027] Step 3.1.2 The second wireless communication system sends the radar deployment point location coordinates (L) to the first wireless communication system of the UAV. O B O H O );

[0028] Step 3.1.3 The first wireless communication system sends the location coordinates of the radar deployment point to the DGPS navigation and positioning system;

[0029] Step 3.1.4 The UAV's DGPS navigation and positioning system receives the coordinates of point O (L... O B O H O );

[0030] Step 3.2 The UAV's DGPS navigation and positioning system plans the movement path, the method is as follows:

[0031] The planned movement path is circular, with point E (coordinates (L)) located at a height h directly above the radar deployment point O. E B E H E Let L be the center of the circular motion path. E B E H E Let E be the longitude, latitude, and altitude of point E in the WGS84 coordinate system, and let R be the radius of the circular path. The starting point is point S, located directly north of point E and at a distance R from point E (coordinates L). s B s H s )), L s B s H s These are the longitude, latitude, and altitude data of point S in the WGS84 coordinate system.

[0032] The fourth step involves the radar's calibration data acquisition module stitching together the UAV's GPS position information and the UAV's polar coordinate position information from the radar target detection system at the same time to obtain the original calibration dataset. The method is as follows:

[0033] Step 4.1 Let the current broadcast count of the drone be n = 1; set the drone's flight speed v, and the broadcast time interval Δt, with Δt recommended to be in the range of 1s to 3s. Then, the total number of broadcasts by the drone on one circular motion path is... The initial calibration data set J is initialized to be empty and is used to store the polar coordinate position information of the UAV collected by the radar target detection system; the coordinates (L) of the current position point W of the UAV are initialized according to equation (1). W B W H W ):

[0034]

[0035] Step 4.2 The UAV flies along a circular path; the UAV starts from its current position W at the initial time T and moves clockwise around point E at a constant speed v. During the flight, the DGPS navigation and positioning system broadcasts the UAV's GPS position information {L} to the radar's second wireless communication system through the first wireless communication system at time T+nΔt. n B n H n ,F n}, where L n For the longitude data of the UAV in the WGS84 coordinate system at time T+n△t, B n For the latitude data of the UAV in the WGS84 coordinate system at time T+n△t, H n Let F be the altitude data of the UAV in the WGS84 coordinate system at time T+n△t. n Let be the flight distance of the UAV at time T+n△t;

[0036] F n =n△tv (2)

[0037] Step 4.3 The radar's second wireless communication system receives the UAV's GPS location information from the first wireless communication system {L} n B n H n ,F n}, will {L n B n H n ,F n The data is sent to the calibration data acquisition module; simultaneously, the radar's target detection system measures the polar coordinate position information {θ} of the UAV at time T+n△t. n An , D n}, where θ n is the azimuth data, A n is the elevation data, D n is the distance data between the radar and the UAV. The polar coordinate position information {θ n , A n , D n} is sent to the calibration data acquisition module;

[0038] Step 4.4 The calibration data acquisition module of the radar receives the UAV GPS position information {L n , B n , H n , F n} at time T + nΔt from the second wireless communication system, and receives the polar coordinate position information {θ n , A n , D n} of the UAV at time T + nΔt from the target detection system. They are spliced into the original calibration data information J n = {L n , B n , H n , F n , θ n , A n , D n} at time T + nΔt. J n is saved in the set J and becomes the nth member of the set J;

[0039] Step 4.5 If n < N, update the coordinates (L W , B W , Z W ) of the current position point W according to formula (3):

[0040]

[0041] Let T = T + nΔt, n = n + 1, and go to Step 4.2; If n = N, it means that the UAV has flown to point S and completed a flight along a circular motion path; The shipborne radar has obtained a set of original calibration data sets J containing N data members, J = {J1, J2,..., J n ,..., J N}. The calibration data acquisition module sends the original calibration data set J to the calibration data processing module and goes to the fifth step.

[0042] The fifth step involves the radar's calibration data processing module processing the UAV's abnormal positioning data. This processing involves two steps: First, the UAV's GPS position information is converted to a station-centered rectangular coordinate system with the radar deployment point as the origin. (A station-centered rectangular coordinate system is a geodetic coordinate system with the station (such as a shipborne radar) as the origin; see details for further information.) https: / / baike.baidu.com / item / %E7%AB%99%E5%BF%83%E5%9D%90%E6%A0% 87%E7%B3%BB / 4542391? fr=aladdin, June 30, 2022 The positioning data (date) is then processed; the DGPS navigation and positioning system on the UAV is easily affected by external interference, leading to abnormal positioning data. To reduce the impact of abnormal GPS positioning data on radar calibration, this step divides the abnormal GPS positioning data into abnormal positioning data located on the circular motion path and abnormal positioning data not on the circular path, based on the characteristics of the UAV's circular motion path. Specifically: point A is the actual position of the UAV on the circular motion path, point A1 is the coordinate point of the abnormal positioning data located on the circular motion path, and point A2 is the coordinate point of the abnormal positioning data not on the circular motion path. The two types of abnormal positioning data are searched and deleted respectively. The method is as follows:

[0043] Step 5.1 The calibration data processing module receives the original calibration dataset J from the calibration data acquisition module, performs coordinate transformation on J, and converts the original calibration data information of the UAV in J into station-centered rectangular coordinate system data with radar deployment point O as the origin, thus obtaining the UAV positioning data set U in the station-centered rectangular coordinate system. The method is as follows:

[0044] Step 5.1.1 Initialize the UAV calibration data set U in the station-centered rectangular coordinate system as empty. U is used to store the UAV's positioning data in the station-centered rectangular coordinate system; set parameter n = 1;

[0045] Step 5.1.2 The calibration data processing module processes the nth original calibration data information J in J according to formula (4). n L in n B n H n The coordinates (X) are converted to a spatial geodetic rectangular coordinate system (a geodetic coordinate system with the Earth's center of mass as the origin; see: Zhai Yujian and Li Jing's 2020 paper "Conversion between the Geographic Coordinate System of a Stable Platform and the Spatial Geodetic Rectangular Coordinate System" published in the journal "Ship Electronic Countermeasures"). n Y n Z n ):

[0046]

[0047] Wherein, parameter V is the radius of the zonal circle, and parameter e is the first eccentricity of the Earth;

[0048] Step 5.1.3 The calibration data processing module converts the coordinates (X n , Y n , Z n ) of the UAV in the space geodetic rectangular coordinate system into the coordinates (x n , y n , z n ) in the local rectangular coordinate system with point O as the coordinate origin according to formula (5);

[0049]

[0050] Among them, {X O , Y O , Z O} are the coordinates of the radar in the space geodetic rectangular coordinate system, which are calculated by formula (6);

[0051]

[0052] The calibration data processing module combines (x n , y n , z n ) and {F n , θ n , A n , D n} into the nth transformed calibration data U n , that is, U n = {x n , y n , z n , F n , θ n , A n , D n}, and saves U n in the set U to become the nth member of the set U;

[0053] Step 5.1.4 If n < N, let n = n + 1, and go to step 5.1.2; otherwise, the conversion of the GPS positioning data of the UAVs in J is completed, and the transformed calibration data set U is obtained, U = {U1, U2,..., U n ,..., U N};

[0054] Step 5.2 The calibration data processing module searches for and deletes abnormal positioning data on non-circular motion paths in U; ​​based on the distance error distribution between the UAV's positioning data and the center coordinates, the Laida criterion (a classic outlier removal method, see the paper "Application of Laida Criterion in Traffic Survey Data Processing" published in the journal *Western Transportation Science and Technology* by Wang Tiansong, Zhang Jie, Sun Mingming et al., 2016) is used to search for and delete abnormal positioning data in U, as follows:

[0055] Step 5.2.1 Calculate the distance between the calibration data of the UAV on the circular motion path and the center E of the circular path, and generate the distance set RR. The method is as follows:

[0056] Step 5.2.1.1 Initialize the distance set RR to be empty, which is used to store the distance between the calibration data of the UAV on the circular motion path and the center E of the circle. Let the parameter n = 1;

[0057] Step 5.2.1.2 Calculate the nth calibration data U in U according to formula (7). n In the context RR={r1,r2,…,r n ,…,r N x of} n ,y n ,z n The distance r between the circular point E and the circular motion path n

[0058]

[0059] Among them, (x E ,y E ,z E Let (x) be the coordinates of point E in the station-centered rectangular coordinate system. E ,y E ,z E The coordinates of point E in the geodetic coordinate system (L) E B E H E The result is obtained by calculation using formulas (8) and (9), and the method is as follows:

[0060] Step 5.2.1.2.1 Based on the coordinates of point E in the WGS84 coordinate system (L... E B E H E The spatial geodetic rectangular coordinates (X, Y, F) of point E are calculated. E ,Y E Z E ):

[0061]

[0062] Step 5.2.1.2.2 Calculate the coordinates (x E , y E , z E ) of point E in the local rectangular coordinate system based on the geodetic rectangular coordinates (X E , Y E , Z E ) of point E:

[0063]

[0064] Save r n in set RR as the nth member of set RR.

[0065] Step 5.2.1.3 If n < N, let n = n + 1 and go to Step 5.2.1.2; otherwise, the calibration data processing module has completed the calculation of the distances between the N positioning data of the UAVs in the local rectangular coordinate system and point E, and obtained the distance set RR, RR = {r1, r2,..., r n ,..., r N};

[0066] Step 5.2.2 Calculate the variance s r of the N distances in the distance set RR according to formula (10):

[0067]

[0068] Step 5.2.3 The calibration data processing module searches for and deletes the abnormal positioning data on the non-circular motion path in set U to obtain the first calibrated data set U' after deleting the abnormal values; the method is as follows:

[0069] Step 5.2.3.1 Initialize the normal calibration data statistical parameter num = 0; initialize the first calibrated data set U' as empty, and U' is used to store the calibrated data remaining after deleting the abnormal values in data set U; set the parameter m to represent the number of the mth member in U', and initialize m = 1; let the parameter n = 1;

[0070] Step 5.2.3.2 Use the Raida criterion, i.e., formula (11), to judge and delete the abnormal positioning data on the non-circular motion path:

[0071] |r n - R| > 3s r (11)

[0072] If r n does not satisfy formula (11), it means that the nth calibration data U n in U is normal data, and assign U n to U' m: That is, let U' m = U n , save U' m into U', making it the m-th member of the dataset U'. Let num = num + 1, m = m + 1, and go to step 5.2.3.3; otherwise, U m is an outlier and is directly discarded, then go to step 5.2.3.3;

[0073] Step 5.2.3.3 If n < N, let n = n + 1 and go to step 5.2.3.2; otherwise, the judgment and deletion of N outlier data in U are completed, and the first calibrated dataset U' containing M normal data is obtained: U' = {U'1, U'2,..., U' m ,..., U' M}, where 1 < m < M, M = num, then go to step 5.3;

[0074] Step 5.3 The calibration data processing module searches for and deletes the abnormal positioning data on the circular motion path in the set U'; the UAV runs from the starting point S of the circular motion path along the arrow direction to the point S' (coordinates are (x m , y m , z m )). The flight distance between them is F m , that is, F m corresponds to the central angle β of the corresponding arc m , where (x m , y m , z m ) is the rectangular geocentric coordinate data of the UAV saved in the m-th member U' m of the set U', U' m = {x m , y m , z m , F m , θ m , A m , D m}; According to geometric principles, the central angle β of the circular path and the flight distance F m satisfy formula (12)

[0075]

[0076] In formula (12), the UAV flies in the airspace at altitude z = h, and the coordinates (x E , y E , z E ) of point E are fixed values, When (x m , y m , z m ) is the true value, The value is R. When (x m , y m , z m ) is an outlier, the value will deviate from R. In this step, according to the degree of deviation between the value and the radius R of the circular path, the Raida criterion is used to search for and delete the abnormal positioning data in U′. The method is as follows:

[0077] Step 5.3.1 According to the drone position coordinate data saved in U′, calculate the central angle of the broadcast position point of the drone on the circular motion path, and obtain the dataset JL of the ratio of the flight distance to the central angle. The method is as follows:

[0078] Step 5.3.1.1 Initialize the dataset JL of the ratio of the flight distance to the central angle to be empty. JL is used to store the ratio of the flight distance F m and the central angle data β m ; Let the parameter m = 1;

[0079] Step 5.3.1.2, calculate the central angle β m , y m , z m ) of the drone at the position (x m ;

[0080]

[0081] Let the m-th ratio Save JL m in the set JL and become the m-th element of JL:

[0082] Step 5.3.1.3 If m < M, let m = m + 1 and go to Step 5.3.1.2; if m = M, then the calculation of the ratio of the flight distance and the central angle of all the broadcast position points of the drone on the circular path is completed, and the dataset JL of the ratio of the flight distance and the central angle is obtained. JL = {JL1, JL2,..., JL m ,..., JL M}, go to Step 5.3.2;

[0083] Step 5.3.2 Calculate the variance s JL of the M members in the dataset JL according to Equation (14);

[0084]

[0085] Step 5.3.3 Use the Raida criterion to search for and delete the abnormal positioning data on the circular motion path. The method is:

[0086] Step 5.3.3.1 Initialize the second calibration data set dat as empty, which is used to save the valid positioning data in U′. Set the parameter i to represent the number of the i-th member in the set dat; set the parameter num3 as the statistical parameter of the valid calibration data in U′, and let i = 1, m = 1, num3 = 0;

[0087] Step 5.3.3.2 Use the Raida criterion, that is, formula (15), to judge and delete the outliers in the data set JL:

[0088] |JL m -R|>3s JL (15)

[0089] If JL m does not satisfy formula (15), then the m-th member U′ in U′ m is valid data. Let dat i =U′ m , save dat i in the set dat, which becomes the i-th member of the set dat. Let i = i + 1, num3 = num3 + 1, and go to Step 5.3.3.3; otherwise, U′ m is positioning outlier data, and directly go to Step 5.3.3.3;

[0090] Step 5.3.3.3 If m < M, let m = m + 1, and go to Step 5.3.3.2; otherwise, it means that the inspection and judgment of the M data in U′ are completed, and the second calibration data set dat containing I valid data is obtained. dat = {dat1, dat2, …, dat i ,…,dat I}, dat i = {x i , y i , z i , F i , θ i , A i , D i}, I = num3;

[0091] Sixth step, the calibration data processing module calculates the mean azimuth error, mean pitch error, and mean ranging error of the radar; it is mainly divided into two steps: First, the calibration data processing module performs coordinate transformation to convert the positioning data of the UAV in the local rectangular coordinate system to the positioning data in the local polar coordinate system with point O as the coordinate origin; second, according to the positioning data of the UAV in the polar coordinate system, calculate the mean azimuth error, mean pitch error, and mean ranging error of the radar. The method is:

[0092] Step 6.1. The data processing module converts the positioning data of the UAV in the local rectangular coordinate system into positioning data in the local polar coordinate system with point O as the coordinate origin (the local polar coordinate system is a geodetic coordinate system with the measuring station (such as shipborne radar) as the coordinate origin. For specific reference link: https: / / baike.baidu.com / item / %E7%AB%99%E5%BF%83% E5%9D%90%E6%A0%87%E7%B3%BB / 4542391? fr=aladdin, June 30, 2022 day):

[0093] Step 6.1.1 Initialize the calibration data set adat of the UAV in the polar coordinate system to be empty; let the parameter i = 1;

[0094] Step 6.1.2 According to formula (16), convert the coordinates (x i , y i , z i , F i , θ i , A i , D i} of the UAV in the local rectangular coordinate system in the i-th member dat i = {x i , y i , z i ) of the UAV in the local rectangular coordinate system into positioning data {D′ i , θ′ i , A′ i} in the local polar coordinate system with point O as the coordinate origin:

[0095]

[0096] Among them, D′ i is the distance of the UAV in the polar coordinate system, θ′ i is the azimuth angle of the UAV in the polar coordinate system, A′ i is the pitch angle of the UAV in the polar coordinate system; let adat i = {D′ i , θ′ i , A′ i , F i , θ i , A i , D i}, save adat i in the set adat and become the i-th member of the set adat;

[0097] Step 6.1.3 If i < I, let i = i + 1 and go to Step 6.1.2; if i = I, it means that the conversion of the UAV's local rectangular coordinate system data to local polar coordinate system data is completed, and the polar coordinate calibration data set of the UAV is obtained:

[0098] adat = {adat1, adat2,..., adat i,…, adat I};

[0099] Step 6.2 The calibration data processing module calculates the mean azimuth error, mean pitch error, and mean range error of the radar: The polar coordinate data {D′ i , θ′ i , A′ i} obtained by converting the GPS positioning data broadcast by the UAV into coordinates is used as the true value, and is compared with the polar coordinate data {θ i , A i , D i} of the UAV measured by the radar to find the error, and the mean range error, mean azimuth error, and mean pitch error are calculated according to the error. The specific method is as follows:

[0100] Step 6.2.1 Initialize the error set △E to be empty. The set △E is used to store the range error △D i of the radar measurement data, the azimuth error △θ i and the pitch error △A i ; Let the parameter i = 1;

[0101] Step 6.2.2 Calculate the error of the i-th member adat in adat according to formula (17): i of the radar measurement data:

[0102]

[0103] Let the i-th error data △E i = {△D i , △θ i , △A i}, and store △E i into the error set △E to become the i-th member of △E;

[0104] Step 6.2.3 If i < I, let i = i + 1, and go to Step 6.2.2; If i = I, complete the calculation of the radar measurement data error, and obtain the radar measurement error set △E = {△E1, △E2, …, △E i , …, △E I}, and go to Step 6.2.4;

[0105] Step 6.2.4 Calculate the mean range error △D ave , mean azimuth error △θ ave and mean pitch error △A ave in △E according to formula (18):

[0106]

[0107] Seventh step, the calibration data processing module uses △Dave , △θ ave , △A ave The calibration parameters, used to correct the radar's range, azimuth, and elevation measurement data, are used to obtain the target position data after error correction, thus completing the calibration of the shipborne radar.

[0108]

[0109] Among them, D old θ old A old The data is divided into raw range measurement data, raw azimuth measurement data, and raw elevation angle measurement data acquired by the target detection system during a target measurement mission performed by the shipborne radar. new θ new A new These are the target distance measurement data, azimuth measurement data, and elevation angle measurement data after error correction.

[0110] The following technical effects can be achieved by using this invention:

[0111] (1) Existing radar calibration methods rely on high-precision GPS positioning equipment carried by airborne vehicles. When the GPS positioning system is interfered with, abnormal positioning values ​​are generated, which can introduce a large deviation in the calibration accuracy of radar measurements. This invention divides abnormal GPS positioning data into abnormal positioning data located on circular motion paths and abnormal positioning data on non-circular paths based on the characteristics of UAVs executing circular motion paths. It constructs search and deletion methods for the two types of abnormal values. Therefore, compared with existing radar calibration methods based on airborne vehicles and GPS positioning systems, this invention can effectively avoid the influence of abnormal positioning data of GPS positioning systems on radar calibration. This invention has obvious advantages in radar calibration accuracy.

[0112] (2) This invention does not require the construction of a land-based calibration tower, effectively avoiding the huge consumption of manpower, material resources and financial resources caused by the selection of a site for calibration tower construction and subsequent maintenance. Compared with the existing radar measurement accuracy calibration based on fixed calibration towers, this invention has obvious advantages in terms of usage cost. Calibration towers are fixed infrastructure, while surface ships usually perform diverse tasks far from land. Land-based calibration towers cannot complete the calibration work of radar in the actual working environment of shipborne radar. The method of this invention uses UAVs to calibrate shipborne radar. UAVs are easy to carry, deploy and retrieve. Ships can directly use the method of this invention to calibrate the measurement accuracy of shipborne radar in the actual working environment. Attached Figure Description

[0113] Figure 1 This is a logical structure diagram of a shipborne radar calibration system based on unmanned aerial vehicles (UAVs).

[0114] Figure 2 This is the overall flowchart of the present invention;

[0115] Figure 3 Circular motion path diagram;

[0116] Figure 4 Schematic diagram of abnormal positioning data from a UAV's DGPS navigation and positioning system;

[0117] Figure 5 Schematic diagram of flight distance and central angle. Detailed Implementation

[0118] Figure 2 This is the overall flowchart of the invention; as shown below. Figure 2 As shown, the present invention includes the following steps:

[0119] The first step is to construct a shipborne radar calibration system based on unmanned aerial vehicles (UAVs). This system consists of a quadcopter UAV and a pulse-Doppler shipborne radar, as detailed below. Figure 1 As shown:

[0120] The drone is equipped with a DGPS (Differential Global Position System, which is a system that uses differential technology on the basis of GPS to enable users to obtain higher positioning accuracy from the GPS system) navigation and positioning system, a first wireless communication system, and a first time unified system.

[0121] The first time synchronization system is a general-purpose module capable of providing GPS time (GPS time is the time reference for the operation of the GPS system; for details, see: https: / / blog.csdn.net / jlf521521 / article / details / 120817150, June 30, 2022) synchronization information. The system is required to have a timing accuracy better than 15ns and a 24-hour timekeeping accuracy better than 10us. This step uses a satellite synchronization clock module from Beijing Qianxing Time & Frequency Technology Co., Ltd., whose timing accuracy is better than 15ns and its 24-hour timekeeping accuracy is better than 5us. The first time synchronization system is connected to the DGPS navigation and positioning system and the first wireless communication system, providing GPS time synchronization signals to both systems.

[0122] The DGPS navigation and positioning system is used for UAV positioning and route planning, requiring a dynamic positioning accuracy better than 0.1m. The DGPS positioning module in this step uses the high-precision positioning board-P20 from Beijing UniStrong. The P20 achieves a positioning accuracy better than 0.04m when simultaneously receiving GPS signals and "China Precision" differential signals. ("China Precision" is a satellite-based wide-area differential correction service system independently developed by Beijing UniStrong. The system transmits differential data via L-band geostationary orbit communication satellites, providing users with enhanced positioning accuracy globally. For details on the "China Precision" differential system, please see the webpage.) https: / / www.unistrong.com / News / NewsShow.aspx?id =3136; June 29, 2022 For detailed parameters of the P20 device, please refer to the website of Beijing Hezhong Sizhuang Company. https: / / www.unistrong.com / Product / ProShow.aspx?proid=P20, June 23, 2022 (Day); The DGPS navigation and positioning system is connected to the first wireless communication system and the first time unification system. The DGPS navigation and positioning system receives the GPS time synchronization signal provided by the first time unification system to ensure that the DGPS navigation and positioning system and the first wireless communication system operate on the same time reference; the DGPS navigation and positioning system receives the deployment point location information of the shipborne radar from the first wireless communication system and plans the flight path of the UAV based on the deployment point location information of the shipborne radar; the DGPS navigation and positioning system realizes the real-time GPS positioning of the UAV and sends the GPS location information of the UAV to the first wireless communication system;

[0123] The first wireless communication system is a general-purpose hardware module with communication functions, such as a Beidou communication terminal, a satellite communication terminal, and a data transmission radio. This wireless communication system uses the E90-DTU (433L37-V8) data transmission radio from E-Best. The effective communication range of the E90-DTU (433L37-V8) data transmission radio is 20 kilometers. (For detailed parameters of the E90-DTU data transmission radio, please refer to the E-Best website.) https: / / www.ebyte.com / product-view-news.html?id=1857, 2022 June 30 (Day); The first wireless communication system is connected to the DGPS navigation and positioning system, the first time unified system, and the radar; The first wireless communication system receives the GPS location information of the UAV from the DGPS navigation and positioning system and sends the GPS location information of the UAV to the radar; The first wireless communication system receives the location coordinates of the radar deployment point from the radar and sends the location information of the radar deployment point to the DGPS navigation and positioning system.

[0124] The shipborne radar is equipped with a second wireless communication system, a DGPS positioning module, a target detection system, a calibration data acquisition module, a calibration data processing module, and a second time unification system.

[0125] The second time unification system is a general-purpose module that provides GPS time synchronization information. It requires the second time communication system to have a timing accuracy better than 15ns and a 24-hour timekeeping accuracy better than 10us. The time unification system in this step uses a satellite synchronization clock module from Beijing Qianxing Time and Frequency Technology Co., Ltd. The device has a timing accuracy better than 15ns and a 24-hour timekeeping accuracy better than 5us. The second time unification system is connected to the second wireless communication system, the DGPS positioning module, the target detection system, the calibration data acquisition module, and the calibration data processing module, and provides GPS time synchronization information to the second wireless communication system, the DGPS positioning module, the target detection system, the calibration data acquisition module, and the calibration data processing module.

[0126] The second wireless communication system is a general-purpose hardware module with communication functions, such as a Beidou communication terminal, a satellite communication terminal, and a data transmission radio. In this step, the wireless communication system uses the E90-DTU (433L37-V8) data transmission radio from E-Best. The second wireless communication system is connected to the DGPS positioning module, the calibration data acquisition module, the second time unification system, and the first communication system of the UAV. The second communication system receives GPS time synchronization information provided by the second time unification system and completes its own time synchronization. The second wireless communication system sends the radar deployment point location information provided by the DGPS positioning module to the first wireless communication system of the UAV, and sends the UAV's location information provided by the first wireless communication system to the calibration data acquisition module.

[0127] The DGPS positioning module locates the radar deployment point, requiring a static single-point positioning accuracy better than 0.1m. This step utilizes the high-precision positioning board P20 from Beijing Hezhong Sizhuang Company. The P20 achieves a positioning accuracy better than 0.04m when simultaneously receiving GPS signals and "China Precision" differential signals. The DGPS positioning module connects to the second wireless communication system and the second time unification system. It receives GPS time synchronization information from the second time unification system, completes its own time synchronization, and ensures that it operates on the same time reference as the second wireless communication system, target detection system, calibration data acquisition module, and calibration data processing module on the shipborne radar. The DGPS positioning module then transmits the radar deployment point coordinates to the second wireless communication system.

[0128] The target detection system is used to measure the polar coordinate data of the UAV, acquiring its pitch, azimuth, and altitude data. Commonly used target detection systems for shipborne radar include Doppler radar, millimeter-wave radar, and meter-wave radar. The target detection system is connected to the calibration data acquisition module and the second time synchronization system. The target detection system receives GPS time synchronization information provided by the second time synchronization system, ensuring that the target detection system operates on the same time reference as the second wireless communication system, DGPS positioning module, calibration data acquisition module, and calibration data processing module on the shipborne radar. The target detection system sends the UAV's polar coordinate data to the calibration data acquisition module.

[0129] The calibration data acquisition module is used to acquire and stitch together the UAV's GPS position information and polar coordinate position information to obtain calibration data. The calibration data acquisition module is connected to the second wireless communication system, the target detection system, the second time unification system, and the calibration data processing module. The calibration data acquisition module receives GPS time synchronization information provided by the second time unification system, receives the UAV's GPS position coordinates from the second wireless communication system, and receives the UAV's polar coordinate position information from the target detection system. It stitches together the UAV's GPS position coordinates and UAV's polar coordinate position information at the same time to obtain the original calibration dataset, and sends the original calibration dataset to the calibration data processing module.

[0130] The calibration data processing module processes the original calibration dataset to calibrate the radar measurement accuracy. It is connected to the second time unification system and the calibration data acquisition module. The calibration data processing module receives GPS time synchronization information from the second time unification system, ensuring that it operates on the same time reference as the second wireless communication system, GPS positioning module, target detection system, and calibration data acquisition module. The calibration data processing module receives the original calibration dataset from the calibration data acquisition module and processes it, including coordinate transformation of the UAV's GPS position information, deletion of abnormal GPS position information, and error calculation between the polar coordinate position information obtained from the UAV's GPS position information and the UAV's polar coordinate position information measured by the radar at the same time. Based on the calculated average azimuth error, average pitch error, and average ranging error of the radar, the measured azimuth, pitch, and range data are corrected to calibrate the radar measurement accuracy.

[0131] The second step involves the first and second time unification systems completing GPS time synchronization, setting the start time T for the calibration system's operation, and outputting GPS time synchronization information. The method is as follows:

[0132] The first and second time synchronization systems utilize their onboard antennas to receive GPS signals, enabling GPS time synchronization between them and setting the starting time T for the calibration system. After completing GPS time synchronization, the first time synchronization system provides GPS time synchronization information to the UAV's DGPS navigation and positioning system and the first wireless communication system. The second time synchronization system provides GPS time synchronization information to the radar's second wireless communication system, DGPS positioning module, target detection system, calibration data acquisition module, and calibration data processing module, ensuring that all modules in the calibration system operate on the same time reference.

[0133] The third step involves the drone's DGPS navigation and positioning system planning its movement path, as follows:

[0134] Step 3.1 The radar's DGPS positioning module provides the radar deployment point coordinates to the UAV's DGPS navigation and positioning system via a second wireless communication system:

[0135] Step 3.1.1 as follows Figure 3 As shown, the radar's DGPS positioning module locates the radar's position and obtains the coordinates (L...) of the radar deployment point O. O B O H O ), where (L O B O H O The coordinates of point O in the WGS84 coordinate system are given as longitude, latitude, and altitude data, and the location coordinates of the radar deployment point are sent to the second wireless communication system.

[0136] Step 3.1.2 The second wireless communication system sends the radar deployment point coordinates to the first wireless communication system of the UAV;

[0137] Step 3.1.3 The first wireless communication system sends the location coordinates of the radar deployment point to the DGPS navigation and positioning system;

[0138] Step 3.1.4 The UAV's DGPS navigation and positioning system receives the coordinates of point O (L... O B O H O );

[0139] Step 3.2 The UAV's DGPS navigation and positioning system plans the movement path, the method is as follows:

[0140] The planned motion path is circular, such as... Figure 3 As shown, point E (with coordinates (L)) is located at a height h (in this step, the height h is set to 300m) directly above the radar deployment point O. EB E H E Let L be the center of the circular motion path. E B E H E Let E be the longitude, latitude, and altitude of point E in the WGS84 coordinate system. The radius of the circular path is R, which is set to 400m in this step. The starting point is point S, located directly north of point E and at a distance R from point E (coordinates (L...). s B s H s )), L s B s H s These are the longitude, latitude, and altitude data of point S in the WGS84 coordinate system.

[0141] The fourth step involves the radar's calibration data acquisition module stitching together the UAV's GPS position information and the UAV's polar coordinate position information from the radar target detection system at the same time to obtain the original calibration dataset. The method is as follows:

[0142] Step 4.1: Let n be the current number of broadcasts by the drone; set the drone's flight speed v, and the broadcast time interval Δt = 1s. Then, the total number of broadcasts by the drone on one circular motion path is: The initial calibration data set J is initialized to be empty and is used to store the polar coordinate position information of the UAV collected by the radar target detection system; the coordinates (L) of the current position point W of the UAV are initialized according to formula (1). W B W H W ):

[0143]

[0144] Step 4.2 The UAV flies along a circular path; the UAV starts from its current position W at the initial time T and moves clockwise around point E at a constant speed v. During the flight, the DGPS navigation and positioning system broadcasts the UAV's position information {L} to the radar's second wireless communication system via the first wireless communication system at time T+nΔt. n B n H n ,F n}, where L n For the longitude data of the UAV in the WGS84 coordinate system at time T+n△t, B n For the latitude data of the UAV in the WGS84 coordinate system at time T+n△t, H n For the altitude data of the UAV in the WGS84 coordinate system at time T+n△t, F n Let T+n△t be the distance the UAV flies.

[0145] F n =nΔtv (2)

[0146] Step 4.3 The second wireless communication system of the radar receives the GPS position information {L n ,B n ,H n ,F n} of the UAV from the first wireless communication system, and sends {L n ,B n ,H n ,F n} to the calibration data acquisition module; meanwhile, the target detection system of the radar measures the polar coordinate position information {θ n ,A n ,D n} of the UAV at the moment of T + nΔt, where θ n is the azimuth angle data, A n is the pitch angle data, D n is the distance data between the radar and the UAV, and sends the polar coordinate position information {θ n ,A n ,D n} to the calibration data acquisition module;

[0147] Step 4.4 The calibration data acquisition module of the radar receives the GPS position information {L n ,B n ,H n ,F n} of the UAV at the moment of T + nΔt from the second wireless communication system, and receives the polar coordinate position information {θ n ,A n ,D n} of the UAV at the moment of T + nΔt from the target detection system, splices them into the original calibration data information J n = {L n ,B n ,H n ,F n ,θ n ,A n ,D n} of the UAV at the moment of T + nΔt, saves J n in the set J and becomes the nth member of the set J;

[0148] Step 4.5, if n < N, update the coordinates (L W ,B W ,Z W ) of the current position point W according to formula (3):

[0149]

[0150] Let T = T + nΔt, n = n + 1, go to step 4.2; if n = N, it means that the UAV has flown to point S and completed one circular flight path; the shipborne radar obtained a set of original calibration dataset J with N data members, J = {J1, J2, ..., J...} n ,…J N The calibration data acquisition module sends the original calibration dataset J to the calibration data processing module, proceeding to step five.

[0151] The fifth step involves the radar calibration data processing module processing the UAV's abnormal positioning data. This processing is divided into two steps: First, the UAV's GPS position information is converted to a station-centered Cartesian coordinate system with point O as the origin. Then, the converted positioning data undergoes abnormal positioning data processing. The GPS navigation and positioning system onboard the UAV is susceptible to external interference, leading to abnormal positioning data. To reduce the impact of abnormal GPS positioning data on radar calibration, this step categorizes abnormal GPS positioning data based on the UAV's circular motion path: abnormal positioning data located on the circular motion path and abnormal positioning data on non-circular paths. Specifically... Figure 4 As shown: Point A is the actual location of the UAV on the circular motion path, point A1 is the coordinate point of the abnormal positioning data located on the circular motion path, and point A2 is the coordinate point of the abnormal positioning data on the non-circular motion path. The two types of abnormal positioning data are searched and deleted respectively; the method is as follows:

[0152] Step 5.1 The calibration data processing module receives the original calibration dataset J from the calibration data acquisition module, performs coordinate transformation on J, and converts the original calibration data information of the UAV in J into station-centered rectangular coordinate system data with point O as the coordinate center, to obtain the UAV's position data set U in the station-centered rectangular coordinate system. The method is as follows:

[0153] Step 5.1.1 Initialize the UAV calibration data set U in the station-centered rectangular coordinate system as empty. U is used to store the UAV's positioning data in the station-centered rectangular coordinate system; set parameter n = 1;

[0154] Step 5.1.2 The calibration data processing module processes the nth original calibration data information J of dataset J according to formula (4). n L in n B n H n Transform into coordinates X in a spatial geodetic rectangular coordinate system n Y n Z n ;

[0155]

[0156] Among them, the parameter V is the radius of the prime vertical circle, and the parameter e is the first eccentricity of the earth;

[0157] Step 5.1.3 The calibration data processing module converts the positioning data X of the UAV in the space geodetic rectangular coordinate system according to formula (5) n 、Y n 、Z n into the coordinates (x n , y n , z n ) in the local rectangular coordinate system with point O as the coordinate origin:

[0158]

[0159] Among them, {X O , Y O , Z O} are the coordinates of the radar in the space geodetic rectangular coordinate system, which are calculated by formula (6);

[0160]

[0161] The calibration data processing module combines (x n , y n , z n ) and {F n , θ n , A n , D n} into the nth transformed calibration data U n , that is, U n = {x n , y n , z n , F n , θ n , A n , D n}, and saves U n in the set U to become the nth member of the set U;

[0162] Step 5.1.4 If n < N, let n = n + 1; go to step 5.1.2; otherwise, the conversion of the GPS positioning data of the UAVs in J is completed, and the transformed calibration data set U is obtained, U = {U1, U2,..., U n ,..., U N};

[0163] Step 5.2 The calibration data processing module searches for and deletes the abnormal positioning data on the non-circular motion path in U; according to the distance error distribution between the positioning data of the UAV and the center coordinates, the Rida criterion of mathematical statistics is used to search for and delete the abnormal positioning data in U, and the method is as follows:

[0164] Step 5.2.1 Calculate the distance between the calibration data of the UAV on the circular motion path and the coordinates of the center E of the circular path, and generate the distance set RR. The method is as follows:

[0165] Step 5.2.1.1 Initialize the distance set RR to be empty, which is used to store the distance between the calibration data of the UAV on the circular motion path and the coordinates of the center E of the circle. Let the parameter n = 1;

[0166] Step 5.2.1.2 Calculate the nth calibration data U in U according to formula (7). n ={x n ,y n ,z n ,F n ,θ n A n D n The location data of the drone in} n ,y n ,z n The distance r between the circular point E and the circular motion path n :

[0167]

[0168] Among them, {x E ,y E ,z E Let {x} be the coordinates of point E in the station-centered rectangular coordinate system. E ,y E ,z E} The coordinates of point E in the geodetic coordinate system (L E B E H E The result is obtained by calculation using formulas (8) and (9), and the method is as follows:

[0169] Step 5.2.1.2.1 Based on the coordinates of point E in the WGS84 coordinate system (L... E B E H E The spatial geodetic rectangular coordinates (X, Y, F) of point E are calculated. E ,Y E Z E ):

[0170]

[0171] Step 5.2.1.2.2 Based on the spatial geodetic rectangular coordinates of point E {X E ,Y E Z E} Calculate the coordinates (x, y) of point E in the station center rectangular coordinate system. E ,yE , z E ):

[0172]

[0173] Save r n in the set RR and make it the n-th member of the set RR.

[0174] Step 5.2.1.3 If n < N, let n = n + 1, and go to Step 5.2.1.2; otherwise, the calibration data processing module has completed the calculation of the distances between the positioning data of N UAVs in the local rectangular coordinate system and the point E in the set U, and obtained the distance set RR;

[0175] Step 5.2.2, calculate the variance of the N distances in the distance set RR. The method is as follows:

[0176] Calculate the variance s of the N members in the distance set RR according to formula (10) r ;

[0177]

[0178] Step 5.2.3, the calibration data processing module searches for and deletes the abnormal positioning data on the non-circular motion path in the set U, and obtains the first calibrated data set U' after deleting the outliers. The method is as follows:

[0179] Step 5.2.3.1, initialize the normal calibration data statistical parameter num = 0; initialize the first calibrated data set U' to be empty. The first calibrated data set U' is used to store the calibrated data remaining after deleting the outliers in the data set U; set the parameter m to represent the number of the m-th member in U', and initialize m = 1; let the parameter n = 1;

[0180] Step 5.2.3.2, use the Raida criterion, that is, formula (11), to judge and delete the abnormal positioning data on the non-circular motion path:

[0181] |r n - R| > 3s r (11)

[0182] If r n does not satisfy formula (11), it means that the n-th calibration data U in U n is normal data. Assign U n to U': that is, let U' m = U m = U n m Save U' in U' and make it the m-th member of the data set U'. Let num = num + 1 and m = m + 1; go to Step 5.2.3.3; otherwise, U​m It is an outlier and is directly discarded. Go to step 5.2.3.3;

[0183] Step 5.2.3.3 If n < N, let n = n + 1 and go to step 5.2.3.2; otherwise, the determination and deletion of N abnormal data in the dataset U are completed, and the first calibrated dataset U′ containing M normal data is obtained: U′ = {U′1, U′2, …, U′ m , …, U′ M}, where 1 < m < M and M = num;

[0184] Step 5.3 The calibrated data processing module searches for and deletes the abnormal positioning data on the circular motion path in the set U′ = {U′1, U′2, …, U′ m , …, U′ M}; as shown in Figure 5 , the flight distance F between the starting point S of the circular motion path and the point S’ (coordinates (x m , y m , z m )) when the UAV flies from the starting point S along the arrow direction is F m , that is, Figure 5 the length of the solid arc in m is F m , and the central angle corresponding to the solid arc is β m , y m , z m ) is the rectangular geocentric coordinate data of the UAV saved in the m-th member U m ′ of the set U′; according to the geometric principle, the central angle β of the circular path and the flight distance L satisfy formula (12)

[0185]

[0186] In formula (12), the UAV flies in the airspace at height z = h, and the coordinates (x E , y E , z E ) of point E are fixed values, When (x m , y m , z m ) is the true value, the value is R. When (x m , y m , z m ) is an outlier, the value will deviate from R. In this step, according to the deviation degree of the value from the radius R of the circular path, the method of using the Raida criterion to search for and delete the abnormal positioning data in U′ is as follows:

[0187] Step 5.3.1 Calculate the central angle of the broadcast position points of the UAV on the circular motion path based on the UAV position coordinate data saved in U′, and obtain the dataset JL of the ratio of flight distance to central angle. The specific method is as follows:

[0188] Step 5.3.1.1 Initialize the dataset JL of the ratio of flight distance to central angle as empty. JL is used to store the ratio of the flight distance F m and the central angle data β m of Let the parameter m = 1;

[0189] Step 5.3.1.2 Calculate the central angle β of the UAV at the position (x m , y m , z m ) according to formula (13); m ;

[0190]

[0191] Let the m-th ratio Save JL m in the set JL and become the m-th element of JL:

[0192] Step 5.3.1.3 If m < M, let m = m + 1, and go to Step 5.3.1.2; if m = M, then the calculation of the ratio of flight distance and central angle of all broadcast position points on the UAV circular path is completed, and the dataset JL of the ratio of flight distance and central angle is obtained. JL = {JL1, JL2,..., JL m ,..., JL M}, and go to Step 5.3.2;

[0193] Step 5.3.2 Calculate the variance s of the M members in the dataset JL according to formula (14); JL ;

[0194]

[0195] Step 5.3.3 Use the Raida criterion to search for and delete abnormal positioning data on the circular motion path. The method is as follows:

[0196] Step 5.3.3.1 Initialize the second calibration data set dat as empty, which is used to save the valid positioning data in U′. Set the parameter i to represent the number of the i-th member in the set dat; set the parameter num3 as the statistical parameter of the valid calibration data in the set U′, and let i = 1, m = 1, num3 = 0;

[0197] Step 5.3.3.2 Use the Raida criterion, that is, formula (15), to judge and delete the outliers in the dataset JL:

[0198] |JL m -R|>3s JL (15)

[0199] If JL m does not satisfy formula (15), then the m-th data member U′ in the set U′ m is valid data. Let dat i =U′ im , save dat i in the set dat as the i-th member of the set dat, let i = i + 1, num3 = num3 + 1, and go to step 5.3.3.3; otherwise, U′ m is positioning abnormal data, and directly go to step 5.3.3.3;

[0200] Step 5.3.3.3 If m < M, let m = m + 1 and go to step 5.3.3.2; otherwise, it means that the inspection and judgment of the M data in the first calibrated data set U′ of the data set are completed, and I valid data are obtained and stored in the second calibrated data set datdat = {dat1, dat2,…, dat i ,…, dat I}, dat i = {x i , y i , z i , F i , θ i , A i , D i}, I = num3;

[0201] Sixth step, the calibrated data processing module calculates the mean azimuth error, mean pitch error, and mean ranging error of the radar; it is mainly divided into two steps: First, the calibrated data processing module performs coordinate transformation to convert the positioning data of the UAV in the local rectangular coordinate system to the positioning data in the local polar coordinate system with the radar as the origin; Second, according to the positioning data of the UAV in the polar coordinate system, calculate the mean azimuth error, mean pitch error, and mean ranging error of the radar. The method is:

[0202] Step 6.1. The data processing module converts the positioning data of the UAV in the local rectangular coordinate system to the positioning data in the local polar coordinate system with point O as the coordinate origin:

[0203] Step 6.1.1 Initialize the calibrated data set adat of the UAV in the polar coordinate system to be empty; let the parameter i = 1;

[0204] Step 6.1.2 According to formula (16), convert the i-th member dat i = {xi , y i , z i , F i , θ i , A i , D i} the x of the local rectangular coordinate system of the UAV in i , y i , z i is converted into the positioning data {D′ i , θ′ i , A′ i} in the local polar coordinate system with point O as the coordinate origin:

[0205]

[0206] Among them, D′ i is the distance of the UAV in the polar coordinate system, θ′ i is the azimuth angle of the UAV in the polar coordinate system, A′ i is the pitch angle of the UAV in the polar coordinate system; let adat i = {D′ i , θ′ i , A′ i , F i , θ i , A i , D i}, save adat i in the set adat and become the i-th member of the set adat;

[0207] Step 6.1.3 If i < I, let i = i + 1 and go to Step 6.1.2; if i = I, it means that the conversion of the local rectangular coordinate system data of the UAV to the local polar coordinate data is completed, and the polar coordinate calibration data set of the UAV is obtained:

[0208] adat = {adat1, adat2,..., adat i ,..., adat I};

[0209] Step 6.2 The calibration data processing module calculates the mean azimuth error, mean pitch error and mean distance error of the radar: The polar coordinate data {D′ i , θ′ i , A′ i} obtained by converting the GPS positioning data broadcast by the UAV is used as the true value, and compared with the polar coordinate data {θ i , A i , D i} Compare to find the error, and calculate the mean of the range error, the mean of the azimuth error, and the mean of the elevation error according to the error. The method is as follows:

[0210] Step 6.2.1 Initialize the error set △E to be empty. The set △E is used to store the range error △D of the radar measurement data i , the azimuth error △θ i and the elevation error △A i ; Let the parameter i = 1;

[0211] Step 6.2.2 Calculate the i-th member adat in the set adat according to formula (17) i The error of the radar measurement data:

[0212]

[0213] Let the i-th error data △E i ={△D i , △θ i , △A i}, and store △E i into the error set △E to become the i-th member of △E;

[0214] Step 6.2.3 If i < I, let i = i + 1, and go to Step 6.2.2; If i = I, complete the calculation of the radar measurement data error, and obtain the radar measurement error set △E = {△E1, △E2,..., △E i ,..., △E I}, and go to Step 6.2.4;

[0215] Step 6.2.4 Calculate the mean of the range error △D in △E according to formula (18) ave , the mean of the azimuth error △θ ave and the elevation error △A ave :

[0216]

[0217] Step 7, the radar calibration data processing system uses △D ave , △θ ave , △A ave as the calibration parameters of the radar measurement accuracy to correct the radar range, azimuth, and elevation measurement data, and obtain the target position data after error correction, thus completing the calibration of the shipborne radar measurement accuracy:

[0218]

[0219] where D old , θ old , A oldThe data is divided into raw range measurement data, raw azimuth measurement data, and raw elevation angle measurement data acquired by the target detection system during a target measurement mission performed by the shipborne radar. new θ new A new These are the target distance measurement data, azimuth measurement data, and elevation angle measurement data after error correction.

[0220] Table 1 shows the test results of the calibration accuracy using the method of the present invention described in the above embodiments. To accurately measure the measurement accuracy of the shipborne radar after calibration, an object with a known geographical location must be selected as the measurement target. The test scheme uses the signal source at the top of the shore-based fixed calibration tower as the measurement target. After the shore-based fixed calibration tower is built, the calibration signal source at the top of the tower will be measured using precision measuring equipment. Therefore, the geodetic coordinates of the signal source at the top of the tower are known values. The test scheme uses the DGPS high-precision positioning board-P20 from Beijing Hezhong Sizhuang Company to accurately locate the deployment position of the shipborne radar in the "China Precision" differential signal mode. Geodetic coordinates; the geodetic coordinates of the signal source at the top of the tower are converted into range, elevation, and azimuth data in a station-centered polar coordinate system with the radar deployment point as the origin. The range, elevation, and azimuth data of the signal source at the top of the tower in the station-centered polar coordinate system are compared with the range, elevation, and azimuth data of the signal source measured by the shipborne radar after calibration using the method of this invention to calculate the measurement error. Under this test scheme, the calibration accuracy of this invention and the calibration method in the invention patent "A Weather Radar Calibration Method and System Based on Unmanned Aerial Vehicle" (hereinafter referred to as the comparison method) are compared. The actual measurement results of the two calibration methods are shown in Table 1:

[0221] Table 1

[0222]

[0223] Note: Known reference data refers to the range, elevation, and azimuth data obtained by converting the geodetic coordinates of the signal source at the top of the tower into a station-centered polar coordinate system with the radar deployment point as the origin.

[0224] The comparison method did not search for and delete outliers in the GPS positioning device. As shown in Table 1, the positioning accuracy of the comparison method is significantly lower than that of the method of this invention. Specifically, the distance error of the comparison method is 502.33 - 500.23 = 2.13 m, while the distance measurement error of the method of this invention is 500.94 - 500.23 = 0.71 m. Compared to the comparison algorithm, the positioning accuracy of this invention is improved by (2.13 - 0.71) / 2.13 = 62%. The azimuth positioning error of the comparison method is 94.3 - 91.1 = 0.1 m. The azimuth error of this invention is 92.21° - 91.1° = 1.11°. Compared with the comparison algorithm, the azimuth measurement accuracy of this invention is improved by (3.22° - 1.11°) / 3.22° = 65%. The elevation angle error of the comparison method is 38.0° - 36.88° = 1.12°. The positioning error of this invention is 37.48° - 36.88° = 0.6°. Compared with the comparison method, the positioning accuracy of this invention is improved by (1.12° - 0.6°) / 1.12° = 46%.

[0225] The above provides a detailed description of the shipborne radar calibration method based on unmanned aerial vehicles (UAVs) provided by this invention. This document elucidates the principles and implementation methods of this invention, and the above description is intended to aid in understanding the core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles (UAVs), characterized in that... Includes the following steps: The first step is to construct a shipborne radar calibration system based on unmanned aerial vehicles (UAVs). This system consists of one UAV and one radar. The drone is equipped with a DGPS navigation and positioning system, a first wireless communication system, and a first-time unified system; The first time synchronization system is a module that provides GPS time synchronization information. The first time synchronization system is connected to the DGPS navigation and positioning system and the first wireless communication system, and provides GPS time synchronization information to the DGPS navigation and positioning system and the first wireless communication system. The DGPS navigation and positioning system is used to achieve UAV positioning and flight path planning. The DGPS system is connected to the first wireless communication system and the first unified time system. The DGPS system receives GPS time synchronization information provided by the first unified time system to ensure that the DGPS system and the first wireless communication system operate on the same time reference. The DGPS system receives the deployment point location information of the shipborne radar from the first wireless communication system and plans the UAV's flight path based on this information. The DGPS system achieves real-time GPS positioning of the UAV and transmits the UAV's GPS position information to the first wireless communication system. The first wireless communication system is a general-purpose hardware module with communication functions; the first wireless communication system is connected to the DGPS navigation and positioning system, the first time communication system, and the radar; the first wireless communication system receives the UAV's GPS position information from the DGPS navigation and positioning system and sends the UAV's GPS position information to the radar; the first wireless communication system receives the radar deployment point coordinates from the radar and sends the radar deployment point coordinates to the DGPS navigation and positioning system. The shipborne radar is equipped with a second wireless communication system, a DGPS positioning module, a target detection system, a calibration data acquisition module, a calibration data processing module, and a second time unification system. The second time synchronization system is a general-purpose module that provides GPS time synchronization information. The second time synchronization system is connected to the second wireless communication system, the DGPS positioning module, the target detection system, the calibration data acquisition module, and the calibration data processing module, and provides GPS time synchronization information to the second wireless communication system, the DGPS positioning module, the target detection system, the calibration data acquisition module, and the calibration data processing module. The second wireless communication system is a general-purpose hardware module with communication functions; the second wireless communication system is connected to the DGPS positioning module, the calibration data acquisition module, the second time unification system, and the first communication system of the UAV; the second communication system receives GPS time synchronization information provided by the second time unification system and completes its own time synchronization; the second wireless communication system sends the radar deployment point location coordinates provided by the DGPS positioning module to the first wireless communication system of the UAV, and sends the UAV GPS location information provided by the first wireless communication system to the calibration data acquisition module. The DGPS positioning module locates the radar deployment point and is connected to the second wireless communication system and the second time unification system. The DGPS positioning module receives GPS time synchronization information provided by the second time unification system, completes its own time synchronization, and ensures that it operates on the same time reference as the second wireless communication system, target detection system, calibration data acquisition module, and calibration data processing module on the shipborne radar. The DGPS positioning module sends the radar deployment point coordinates to the second wireless communication system. The target detection system is used to measure the polar coordinate data of the UAV, acquiring its pitch, azimuth, and altitude data. The target detection system is connected to the calibration data acquisition module and the second time synchronization system. The target detection system receives GPS time synchronization information from the second time synchronization system, ensuring that the target detection system operates on the same time reference as the second wireless communication system, DGPS positioning module, calibration data acquisition module, and calibration data processing module on the shipborne radar. The target detection system sends the UAV's polar coordinate position information to the calibration data acquisition module. The calibration data acquisition module is used to acquire and stitch together the UAV's GPS position information and polar coordinate position information to obtain the original calibration dataset. The calibration data acquisition module is connected to the second wireless communication system, the target detection system, the second time unification system, and the calibration data processing module. The calibration data acquisition module receives GPS time synchronization information provided by the second time unification system, receives UAV GPS position information from the second wireless communication system, and receives UAV polar coordinate position information from the target detection system. It stitches together the UAV's GPS position coordinates and UAV polar coordinate position information at the same time to obtain the original calibration dataset, and sends the original calibration dataset to the calibration data processing module. The calibration data processing module processes the original calibration dataset to calibrate the radar measurement accuracy. It is connected to the second time unification system and the calibration data acquisition module. The calibration data processing module receives GPS time synchronization information from the second time unification system, ensuring that it operates on the same time reference as the second wireless communication system, DGPS positioning module, target detection system, and calibration data acquisition module. The calibration data processing module receives the original calibration dataset from the calibration data acquisition module and processes it, including coordinate transformation of the UAV's GPS position information, deletion of abnormal GPS position information, and error calculation between the polar coordinate position information obtained from the UAV's GPS position information and the UAV's polar coordinate position information measured by the radar at the same time. Based on the calculated average azimuth error, average pitch error, and average ranging error of the radar, the measured azimuth, pitch, and range data are corrected to calibrate the radar measurement accuracy. The second step involves the first and second time unification systems receiving GPS signals using their onboard antennas to synchronize their GPS time and set the starting time T for the calibration system. After GPS time synchronization, the first time unification system provides GPS time synchronization information to the UAV's DGPS navigation and positioning system and first wireless communication system. The second time unification system provides GPS time synchronization information to the radar's second wireless communication system, DGPS positioning module, target detection system, calibration data acquisition module, and calibration data processing module, ensuring that all modules in the UAV-based shipborne radar calibration system operate on the same time reference. The third step involves the radar sending the coordinates of its deployment point to the drone. The drone's DGPS navigation and positioning system then plans its movement path based on these coordinates, as follows: Step 3.1 The radar's DGPS positioning module provides the location coordinates of the radar deployment point O to the UAV's DGPS navigation and positioning system via the second wireless communication system. , These are the longitude, latitude, and altitude data of point O in the WGS84 coordinate system; Step 3.2 The UAV's DGPS navigation and positioning system plans the movement path, the method is as follows: The planned movement path is circular, with point E at a height h directly above the radar deployment point O as the center of the circular movement path. The coordinates of E are... ,in, These are the longitude, latitude, and altitude data of point E in the WGS84 coordinate system, and the radius of the circular motion path is... The starting point is located directly north of point E, at a distance of [distance from point E]. Point S at location S, with coordinates as follows: , These are the longitude, latitude, and altitude data of point S in the WGS84 coordinate system; The fourth step involves the radar's calibration data acquisition module stitching together the UAV's GPS position information and the UAV's polar coordinate position information from the radar target detection system at the same time to obtain the original calibration dataset. The method is as follows: Step 4.1 Set the current broadcast count of the drone to n=1; set the drone's flight speed. Broadcast interval The total number of broadcasts by the drone along a single circular path is . Initialize the original calibration data set. Empty, used to store the polar coordinate position information of the UAV collected by the radar target detection system; initialize the coordinates of the current position point W of the UAV according to equation (1). : ； Step 4.2 The UAV flies along a circular path; the UAV starts from its current position W at the initial time T and moves at a constant speed. The flight revolves around point E in a clockwise circular motion. During the flight, the DGPS navigation and positioning system... The UAV's GPS location information is constantly broadcast from the first wireless communication system to the radar's second wireless communication system. ,in, for Longitude data of the drone in the WGS84 coordinate system. for Latitude data of the drone in the WGS84 coordinate system. for Altitude data of the drone in the WGS84 coordinate system. For drones Flight distance at any given moment; ； Step 4.3 The radar's second wireless communication system receives the UAV's GPS location information from the first wireless communication system. ,Will The data is sent to the calibration data acquisition module; simultaneously, the radar's target detection system measures the UAV's position. Polar coordinate position information at time ,in, This is azimuth data. For pitch angle data, For the distance data between the radar and the drone, polar coordinate position information Send to the calibration data acquisition module; Step 4.4 The radar calibration data acquisition module receives data from the second wireless communication system. GPS location information of drones Received from the target detection system Polar coordinate position information of the drone splice them together Raw calibration data information of the drone ,Will Stored in a collection In, it becomes a set The nth member; Step 4.5 If Update the coordinates of the current position point W according to formula (3). : ； make If n=n+1, proceed to step 4.2; if This indicates that the UAV has flown to point S, completing one circular flight path; the shipborne radar has obtained a set of original calibration dataset J containing N data members. The calibration data acquisition module sends the original calibration dataset J to the calibration data processing module, proceeding to step five; The fifth step involves the radar's calibration data processing module processing the UAV's abnormal positioning data. The method is as follows: Step 5.1 The calibration data processing module receives the original calibration dataset J from the calibration data acquisition module, performs coordinate transformation on J, and converts the original calibration data information of the UAV in J into station-centered rectangular coordinate system data with radar deployment point O as the origin, thus obtaining the UAV positioning data set in the station-centered rectangular coordinate system. , , , ( () represents the coordinates of the UAV in a station-centered rectangular coordinate system with point O as the origin; Step 5.2 Calibration data processing module: search and delete. Anomaly positioning data on the circular motion path in Central Africa; based on the distance error distribution between the UAV's positioning data and the coordinates of the circle's center, the Laida criterion of mathematical statistics is used to analyze... The following methods are used to find and delete abnormal location data: Step 5.2.1 Calculate the distance between the calibration data of the UAV on the circular motion path and the center E of the circular path, and generate the distance set RR. , for The nth calibration data In The distance between the circular point E and the circular motion path; Step 5.2.2 Calculate the variance of the distance values ​​of the N distances in the distance set RR according to formula (10). : ； Step 5.2.3 The calibration data processing module uses the Laida criterion to find and delete sets. Anomaly localization data on the circular motion path in Central Africa were used to obtain the first calibration dataset after removing outliers. , , for Normal data in, M is The number of normal data points; Step 5.3 Calibration data processing module: search and delete. Anomaly localization data on the circular motion path; instruct the UAV to move from the starting point S of the circular motion path along the arrow direction to the coordinates... The flight distance between point S' is , The central angle corresponding to the arc is ,in, For set The mth member The station center rectangular coordinate data of the UAV stored in the database, ;according to The degree of deviation of the value from the radius R of the circular path is determined using the Laida criterion. The method for finding and deleting abnormal location data is as follows: Step 5.3.1 According to The saved UAV position coordinate data is used to calculate the central angle of the broadcast position point on the UAV's circular motion path, resulting in a dataset of the ratio of flight distance to central angle. , , ; Step 5.3.2 Calculate the dataset according to equation (14) Variance of M members ; ； Step 5.3.3 uses the Laida criterion to search for and delete abnormal positioning data on the circular motion path, obtaining the second calibration data set. The method is: Step 5.3.3.1 Initialize the second calibration data set Empty, used to store In the effective location data, the parameter i represents the set. The index of the i-th member in the set; set parameter num3 as the set Let i=1, m=1, num3=0 be the statistical parameters of the valid calibration data. Step 5.3.3.2 Apply the Laida criterion, i.e., formula (15), to the dataset. Identify and remove outliers in the data: ； if If equation (15) is not satisfied, then the set The m-th data member For valid data, let ,Will Stored in a collection , become a set For the i-th member, let i = i + 1, num3 = num3 + 1, and go to step 5.3.3.3; otherwise, To locate the abnormal data, proceed directly to step 5.3.3.3; Step 5.3.3.3 If m < M, let m = m + 1, and go to Step 5.3.3.2; otherwise, it means that the check and judgment of M data in the first calibration data set of the data set are completed, and I valid data are stored in the second calibration data set dat, and I valid data are stored in the second calibration data set dat, , , I = num3; The sixth step involves the calibration data processing module calculating the mean values ​​of the radar azimuth error, elevation error, and ranging error. The method is as follows: Step 6.1 The data processing module converts the UAV's positioning data in the station-centered rectangular coordinate system into positioning data in the station-centered polar coordinate system with point O as the origin, thus obtaining the UAV's polar coordinate calibration data set. , , , for middle( Convert the data into positioning data in the station-centric polar coordinate system with point O as the origin. Step 6.2 The calibration data processing module calculates the mean azimuth error, mean elevation error, and mean range error of the radar. The method is as follows: Step 6.2.1 Initialize the error set Empty, set Range error used to store radar measurement data Azimuth error and pitch angle error Let parameter i = 1; Step 6.2.2 Calculate according to formula (17) The i-th member Errors in radar measurement data: ； Let the i-th error data ,Will Store the error set ,become The i-th member; Step 6.2.3 If i < I, let i = i + 1, and go to Step 6.2.2; if i = I, complete the error calculation of the radar measurement data to obtain the radar measurement error set , and go to Step 6.2.4; Step 6.2.4 Calculate according to formula (18) Mean of mid-range error The mean of the azimuth error and the mean of pitch angle error : ； Step 7: The calibration data processing module adopts... , , The calibration parameters used to correct the radar range, azimuth, and elevation measurement data are used to obtain the target position data after error correction, thus completing the calibration of the shipborne radar's measurement accuracy. ； in, , , It is divided into raw range measurement data, raw azimuth measurement data, and raw elevation angle measurement data acquired by the target detection system during a target measurement mission performed by the shipborne radar. , , These are the target distance measurement data, azimuth measurement data, and elevation angle measurement data after error correction.

2. The method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles as described in claim 1, characterized in that... The timing accuracy of both the first and second time unification systems is better than 15ns, and the 24-hour timekeeping accuracy is better than 10us; the dynamic positioning accuracy of the DGPS navigation and positioning system is better than 0.1m; the first and second wireless communication systems are any one of Beidou communication terminals, satellite communication terminals, and data transmission radios, and the effective communication distance is required to be greater than 10km; the static single-point positioning accuracy of the DGPS positioning module is better than 0.1m; the target detection system refers to any one of Doppler radar detection system, millimeter-wave radar detection system, and meter-wave radar detection system.

3. The method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles as described in claim 1, characterized in that... The method described in step 3.1 for the radar's DGPS positioning module to provide the radar deployment point coordinates to the UAV's DGPS navigation and positioning system via a second wireless communication system is as follows: Step 3.1.1 The radar's DGPS positioning module locates the radar's position and obtains the coordinates of the radar deployment point O. ,Will Send to the second wireless communication system; Step 3.1.2 The second wireless communication system sends the radar deployment point coordinates to the first wireless communication system of the UAV. ; Step 3.1.3 The first wireless communication system transmits the coordinates of the radar deployment point. Send to the DGPS navigation and positioning system; Step 3.1.4 The UAV's DGPS navigation and positioning system receives... .

4. The method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles as described in claim 1, characterized in that... Step 4.1 Broadcast time interval The value range is 1s to 3s.

5. The method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles as described in claim 1, characterized in that... Step 5.1 describes the calibration data processing module performing coordinate transformation on J, converting the original calibration data of the UAV in J into station-centered rectangular coordinate system data with the radar deployment point as the coordinate center, thus obtaining the UAV's positioning data set in the station-centered rectangular coordinate system. The method is: Step 5.1.1 Initialize the UAV calibration data set in the station-centered rectangular coordinate system Empty Used to store the positioning data of the UAV in the station-centered rectangular coordinate system; Let parameter n=1; Step 5.1.2 The calibration data processing module is used to process the data according to formula (4). The nth original calibration data information In Convert to coordinates in a spatial geodetic rectangular coordinate system ( , , ): ； Among them, parameters The radius of the circle is 50° and the parameter is 60°. It is the first eccentricity of the Earth; Step 5.1.3 The calibration data processing module calculates the coordinates of the UAV in the spatial geodetic rectangular coordinate system according to formula (5). , , Transform the coordinates into a station-centered rectangular coordinate system with point O as the origin. ); ； in, The coordinates of the radar in the space geodetic rectangular coordinate system are calculated by formula (6); ； The calibration data processing module will ( )and Combined into the nth transformed calibration data ,Right now ,Will Stored in a collection In, it becomes a set The nth member; Step 5.1.4 If ,make Proceed to step 5.1.2; otherwise, The conversion of GPS positioning data from the UAV is completed, resulting in the converted calibration dataset. , .

6. The method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles as described in claim 1, characterized in that... The method described in step 5.2.1 for calculating the distance between the calibration data of the UAV on the circular motion path and the center E of the circular path, and generating the distance set RR, is as follows: Step 5.2.1.1 Initialize the distance set RR to be empty, which is used to store the distance between the calibration data of the UAV on the circular motion path and the center E of the circle. Let the parameter n=1; Step 5.2.1.2 Calculate according to formula (7) The nth calibration data coordinates in The distance between the circular point E and the circular motion path , ； in, Let E be the coordinates of point E in the station center rectangular coordinate system. The coordinates of point E in the geodetic coordinate system The results are obtained through formulas (8) and (9), and the method is as follows: Step 5.2.1.2.1 Based on the coordinates of point E in the WGS84 coordinate system The spatial geodetic rectangular coordinates of point E were calculated. : ； Step 5.2.1.2.2 Based on the spatial geodetic rectangular coordinates of point E Calculate the coordinates of point E in the station center rectangular coordinate system. : ； Will It is stored in the set RR and becomes the nth member of the set RR; Step 5.2.1.3 If n < N, let n = n + 1, and go to Step 5.2.1.2; otherwise, the calibration data processing module has completed the calculation of the distances between the positioning data of the N drone station center rectangular coordinate systems in the set and point E, obtaining the distance set RR, and obtained the distance set RR, .

7. The method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles as described in claim 1, characterized in that... Step 5.2.3 The data processing module uses the Laida criterion to find and delete sets. Anomaly localization data on the circular motion path in Central Africa were used to obtain the first calibration dataset after removing outliers. The method is: Step 5.2.3.1: Initialize the normal calibration data statistical parameter num=0; initialize the first calibration dataset. Empty Used to store datasets The calibration data remaining after deleting outliers; Setting parameter m represents The index of the m-th member is initialized to m=1; the parameter n=1. Step 5.2.3.2: Use the Laida criterion, i.e., formula (11), to judge and delete abnormal positioning data on non-circular motion paths: ； like If formula (11) is not satisfied, it means The first in calibration data For normal data, Assign to Immediately ,Will Save to In, it becomes a dataset For the m-th member, let num = num + 1, m = m + 1, and go to step 5.2.3.3; otherwise, If the value is outlier, discard it and proceed to step 5.2.3.3; Step 5.2.3.3 If n < N, let n = n + 1, and go to Step 5.2.3.2; otherwise, it is completed. The judgment and deletion of N abnormal data in obtain a first calibration data set containing M normal data : , where 1 < m < M, , and go to Step 5.

3.

8. The method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles as described in claim 1, characterized in that... According to step 5.3.1 The saved UAV position coordinate data is used to calculate the central angle of the broadcast position point on the UAV's circular motion path, resulting in a dataset of the ratio of flight distance to central angle. The method is: Step 5.3.1.1 Initialize the dataset of flight distance to central angle ratio Empty Used to store the flight distance of drones and central angle data ratio ; Let parameter m = 1; Step 5.3.1.2, calculate the location of the UAV according to formula (13). central angle at the point ; ； Let the m-th ratio ,Will Stored in a collection In the middle, it became The m-th element; Step 5.3.1.3 If m < M, let m = m + 1, and go to Step 5.3.1.2; if m = M, then the calculation of the ratio of the flight distance to the central angle for all the position points of the UAV circular path broadcast is completed, and a dataset of the ratio of the flight distance to the central angle is obtained , .

9. The method for calibrating the measurement accuracy of shipborne radar based on unmanned aerial vehicles as described in claim 1, characterized in that... The method described in step 6.1 for the data processing module to convert the UAV's positioning data in the station-centered rectangular coordinate system into positioning data in the station-centered polar coordinate system with point O as the origin is as follows: Step 6.1.1 Initialize the UAV calibration data set in polar coordinates. Empty; Let parameter i = 1; Step 6.1.2 Apply formula (16) to The i-th member The coordinates of the UAV in the station-centered rectangular coordinate system ( Convert the data into positioning data in the station-centered polar coordinate system with point O as the origin. : ； in, The distance of the drone in the polar coordinate system. The azimuth angle of the UAV in the polar coordinate system. Let be the pitch angle of the UAV under polar mounting; ,Will Stored in a collection In, it becomes a set The i-th member; Step 6.1.3 If ,make Proceed to step 6.1.2; if, This demonstrates the successful conversion of the UAV's station-centered rectangular coordinate system data to station-centered polar coordinate system data, resulting in the UAV's polar coordinate calibration data set. , .

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