Ship positioning method based on sequential multi-view radial distance combination

Abstract

The present invention discloses a ship positioning method based on sequential multi-perspective radial distance combination, which mainly solves the problem that the beam pointing error seriously affects the accuracy of ship position estimation in the existing angle measurement-based position estimation method, and the huge communication burden caused by the combination of multiple sensors. The implementation steps of the present invention are: using a single pulse radar on an airborne platform to measure the radial distance of a ship target under a sequential observation perspective, establishing the longitude and latitude coordinates of the airborne radar platform and the ship under a sequential perspective in the geodetic coordinate system according to the estimated value of the ship's speed and heading, estimating the radial distance between the airborne radar platform and each ship, and combining the radial distance measurement under multiple perspectives to estimate the position coordinates of the ship through the minimum mean square error method. The present invention significantly improves the estimation accuracy of the ship's position, and has a small amount of data and high reliability, and can achieve real-time positioning of ship targets under a high-density sea clutter background.

Description

Technical Field

[0001] The present invention belongs to the field of radar technology, and further relates to a method for ship positioning by combining sequential multi-view radial distance of airborne radar in the field of radar target tracking technology. The present invention can be applied to positioning of ships at sea by airborne radar, and the positioning of ship targets is achieved by using the radial distance between the radar and the ship target in multiple scanning cycles of a moving radar platform, combined with the least mean square estimation method. Background Art

[0002] Position information is an important feature of marine ship targets. High-precision sea surface target position calculation is of great significance to sea radar, which is conducive to improving the accuracy of tracking radar's tracking and scanning of targets. The existing ship positioning method obtains the target position through tracking filtering, and its performance depends on the spatial processing capability of the radar and is greatly affected by the radar beam pointing error.

[0003] Northwestern Polytechnical University disclosed a tracking filtering method based on αβ filtering that can be applied to ship positioning in its published patent document "A mathematical modeling method for tracking filtering of radar signal processor" (application number: 202111040428.5, application publication number CN 114117723 A). This method is aimed at the construction of a mathematical model of a radar signal processor for radar digital modeling and simulation, and fully considers the changes in target distance, Doppler shift, target azimuth and pitch angle parameters during target tracking and memory tracking states. The tracking filtering function of the radar signal processor is realized by mathematical calculation, and the target distance, target Doppler shift, target azimuth and target pitch angle are calculated according to the target distance measurement value, target Doppler shift measurement value, target azimuth measurement value and target pitch angle measurement value. The specific implementation steps of the method are as follows: first, determine whether the radar is in a tracking state, obtain the target radial distance measurement value, Doppler frequency shift measurement value, azimuth measurement value and pitch angle measurement value, and in the tracking state, consider the change of target parameters and update the target azimuth measurement value and pitch angle measurement value. Then, the target measurement value is filtered through an αβ filter to obtain the target radial distance, Doppler frequency shift, azimuth and pitch angle, so as to realize the ship target positioning and complete the radar platform tracking the target. However, the method still has the following shortcomings: the target positioning method is based on the target angle measurement. Due to the antenna jitter and the beam pointing error caused by the radar platform's long detection distance of the ship target at sea, the target azimuth and pitch angle measurement errors are caused, and the target positioning accuracy is reduced.

[0004] Shanghai Jiao Tong University disclosed a multi-station radar site location and joint tracking method that can be applied to ship positioning in its published patent document "Joint Multi-Sensor Registration and Multi-Target Tracking Method" (Application No.: 201810230699.9, Application Publication No. CN 108519595 A). This method models the distribution of multiple targets based on random finite sets and defines a new conditional complete data log-likelihood function. Under the framework of centralized processing, the maximum likelihood estimate of sensor bias and multi-target state is calculated using the mathematical method of expectation maximization. The position information of the radar is included in the joint likelihood function formed by using multiple radar measurements. The specific implementation steps of this method are as follows: First, the extended dimension measurement of multiple sensors is obtained, and the target state estimate is calculated under the condition of certain sensor bias using the measurement extended dimension Kalman filter. Then, the expectation of the log-likelihood function of the complete data is established, and the maximum likelihood estimate of the bias is obtained by using the expectation maximization method, and the bias estimate in the sense of minimum mean square error is obtained by Kalman filtering when the bias is time-varying. Finally, the probability density of the multi-target state distribution with deviation expansion is calculated, and then the target state estimation value is obtained to achieve target positioning and tracking. However, this method still has some shortcomings: this method combines multiple sensors and requires the establishment of a complete data log-likelihood function, and requires the collection of all measurement information from all radars, which will cause a huge communication burden in the high-density clutter environment of marine ship targets. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and propose a ship positioning method based on sequential multi-perspective radial distance combination, aiming to solve the problem that the beam pointing error seriously affects the accuracy of ship position estimation in the prior art position estimation method based on angle measurement, and the problem that the combination of multiple sensors causes a huge communication burden.

[0006] The idea of ​​achieving the purpose of the present invention is as follows: the present invention calculates the radial distance between the radar platform and the target within the scanning period corresponding to a single observation angle, and then estimates the position of the ship by combining the radial distances under sequential multiple angles, without the need to measure the target angle, and the radial distance is a measurement that is not affected by beam pointing, thus avoiding the problem of beam pointing error affecting the accuracy of positioning estimation in the prior art. Since the present invention is based on a single radar system and a single measurement, the movement of the radar platform itself is used to obtain radial distance measurements under different observation geometries at different angles, without the need for communication between multiple radars and multiple sensors, thus solving the problem of communication burden in the prior art under the background of sea clutter.

[0007] The specific steps for achieving the purpose of the present invention are as follows:

[0008] Step 1: The airborne pulse radar periodically transmits pulses and receives signals:

[0009] The moving airborne platform is equipped with a single pulse radar, which divides the sea area to be detected into wave positions during the observation time, transmits periodic pulses to each wave position in turn to perform full-scene beam scanning of the detection area, and receives echo signals from the sea;

[0010] Step 2, using the echo pulse center estimation method to estimate the echo arrival time of the detected ship target in each observation period;

[0011] Step 3, calculating the radial distance measurement value of each ship target under the sequential observation perspective;

[0012] Step 4: Estimate the longitude and latitude coordinates of each ship target in the geodetic coordinate system under the sequential observation perspective:

[0013] Step 4.1, using a ship speed and heading estimation method based on multi-view radial velocity to estimate the speed and heading of each ship target;

[0014] Step 4.2, using the sequential perspective longitude and latitude iteration formula, estimate the longitude and latitude coordinates of each ship target in the geodetic coordinate system under the sequential observation perspective;

[0015] Step 5: Estimate the radial distance between the aircraft on the airborne radar platform and each ship target under sequential viewing angles:

[0016] Step 5.1, using the cosine calculation formula, calculate the cosine value of the angle between the line connecting the center of the earth and each ship target and the line connecting the center of the earth and the aircraft carried by the radar platform under the sequential observation perspective;

[0017] Step 5.2, using the radial distance calculation formula, estimate the radial distance between the aircraft carried by the airborne radar platform and each ship target under the sequential observation perspective;

[0018] Step 6: Estimate the initial longitude and latitude coordinates of each ship target in the geodetic coordinate system according to the following formula:

[0019]

[0020] in, It represents the estimated value of the initial position coordinates of the nth ship target in the geodetic coordinate system. Represents the initial longitude α of the nth target in the geodetic coordinate system s The coordinate estimate of (n), Represents the initial latitude β of the nth target in the geodetic coordinate system s The coordinate estimate of (n), Indicates the initial longitude α of the nth target s (n) and initial latitude β s (n) Minimum operation.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] First, the present invention calculates the radial distance between the radar platform and the target within the scanning period corresponding to a single observation angle, and estimates the ship position by combining the radial distances under sequential multi-angle views. The radial distance measurement is not affected by the beam pointing error, which overcomes the defect of the prior art that the beam pointing error affects the positioning estimation accuracy. The present invention estimates the ship position only by radial distance measurement, which significantly improves the estimation accuracy of the ship position.

[0023] Second, the present invention is based on a single radar system and a single measurement, and utilizes the movement of the radar platform itself to obtain radial distance measurements under different observation geometries at different viewing angles, thereby overcoming the defects of the prior art in the burden of multi-sensor communication under a clutter background. This enables the present invention to have the advantages of small data volume and high reliability, and can realize real-time positioning of ship targets under a high-density sea clutter background. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0025] The following is combined with Figure 1 The implementation steps of the present invention are further described with reference to the accompanying drawings and embodiments.

[0026] Step 1: The airborne pulse radar periodically transmits pulses and receives signals.

[0027] The moving airborne platform is equipped with a single pulse radar. The sea area to be detected is divided into wave positions during the observation time, and periodic pulses are emitted to each wave position in turn to perform full-scene beam scanning of the detection area, and the sea echo signal is received. The sea area to be detected is determined by the specific task of the radar. The beam scans the entire detection area once and the number of periodic pulses emitted by each wave position simultaneously meets the false alarm rate and detection probability indicators in target detection and the positioning accuracy indicator in target tracking. The beam scanning time is defined as an observation cycle, the middle moment of an observation cycle is defined as the observation moment of the observation cycle, and the position of the airborne radar platform at the observation moment is defined as the observation angle of the observation cycle. In this way, the entire observation time is divided into multiple observation cycles, and the total number of observation cycles is constrained by the radar working time resources, ship target detection indicators and positioning accuracy. In the embodiment of the present invention, the total number of observation cycles is set to 40, and the observation angles arranged in chronological order during the entire observation time are called sequential observation angles. Since the time of an observation cycle is short, it can be considered that the position of the airborne radar platform and the ship target does not change in each observation cycle.

[0028] Step 2: Estimate the echo arrival time of the ship target in each observation period.

[0029] The echo pulse center estimation method is used to estimate the echo arrival time of the detected ship target in each observation cycle. That is, in each observation cycle, the sea echo signal received at each wave position is pulse accumulated, and the accumulated signal is divided into two paths, one of which is input into the comparator and compared with the threshold voltage for ship target detection. When a ship target is detected, the other signal is sequentially sent to the differential circuit and the zero-crossing detector to output a narrow pulse, and the time when the narrow pulse appears is estimated to obtain the arrival time of the ship target in the wave position. Due to the assumption of step 1, it can be considered that the target arrival time estimated in each observation cycle is the arrival time of the ship target under the observation perspective of the observation cycle.

[0030] Step 3: Calculate the radial distance measurement value of each ship target under the sequential observation perspective according to the following formula:

[0031]

[0032] Among them, r(k,n) represents the measured value of the straight-line distance between the nth ship target and the airborne radar platform at the kth observation angle in the sequential observation angle, k = 1, 2, ..., K, K represents the total number of observation cycles, c represents the propagation speed of light, and Δt(k,n) represents the arrival time of the nth ship target at the kth observation angle in the sequential observation angle.

[0033] Step 4: Estimate the longitude and latitude coordinates of each ship target in the geodetic coordinate system under the sequential observation perspective.

[0034] Since the detection distance between the airborne radar platform and the sea ship target is far, the aircraft and ship carrying the airborne radar platform are regarded as a point in the geodetic coordinate system.

[0035] Step 4.1, estimate the speed and heading of each ship target.

[0036] The following speed and heading estimation method is used to estimate the speed and heading of each ship target within the observation time. In the embodiment of the present invention, the observation time is set to 10 minutes.

[0037] Firstly, the radial velocity of the ship is estimated by Doppler peak search. Then, the standard deviation of the estimated radial velocity of the ship is calculated through Monte Carlo experiments. In addition, the standard deviation of the radial velocity compensation of the aircraft on the onboard radar platform is calculated according to the amplitude of the airborne radar antenna jitter. Finally, the radial velocities under multiple perspectives are combined to estimate the speed and heading of the ship by the maximum likelihood method.

[0038] Step 4.2, estimate the longitude and latitude coordinates of each ship target in the geodetic coordinate system under the sequential observation perspective according to the following formula:

[0039]

[0040] in, represents the estimated value of the longitude coordinate of the nth ship target in the geodetic coordinate system at the kth observation angle in the sequential observation angle, α s (n) represents the initial longitude coordinate of the nth ship target in the geodetic coordinate system, represents the estimated value of the speed of the nth ship target, sin{} represents the sine operation, represents the estimated value of the heading of the nth ship target, R represents the radius of the earth, cos{} represents the cosine operation, β s (n) represents the initial latitude coordinate of the nth ship target in the geodetic coordinate system, T k T1 represents the observation time of the observation cycle of the kth observation perspective in the sequential observation perspective, T2 represents the observation time of the observation cycle of the first observation perspective in the sequential observation perspective, and the K observation times satisfy T1<T2<T3···<T K , It represents the estimated value of the latitude coordinate of the nth ship target in the geodetic coordinate system at the kth observation perspective in the sequential observation perspective.

[0041] Step 5: Estimate the radial distance between the aircraft on the airborne radar platform and each ship target under sequential viewing angles:

[0042] Step 5.1, calculate the cosine value of the angle between the line connecting the center of the earth and each ship target and the line connecting the center of the earth and the aircraft carried by the radar platform under the sequential observation perspective according to the following formula:

[0043]

[0044] Among them, Θ k (n) represents the cosine value of the angle between the line connecting the center of the earth and the nth ship target and the line connecting the center of the earth and the aircraft on the radar platform at the kth observation angle in the sequential observation angle, β r (k) represents the latitude coordinate of the aircraft on the airborne radar platform in the geodetic coordinate system at the kth observation angle in the sequential observation angle, α r (k) represents the longitude coordinate of the aircraft carried by the airborne radar platform in the geodetic coordinate system at the kth observation angle in the sequential observation angle.

[0045] Step 5.2: Estimate the radial distance between the aircraft on the airborne radar platform and each ship target under the sequential observation perspective according to the following formula:

[0046]

[0047] in, represents the estimated radial distance of the nth ship target at the kth observation angle in the sequential observation angle, h r (k) represents the height coordinate of the aircraft carried by the airborne radar platform in the geodetic coordinate system at the kth observation angle in the sequential observation angle.

[0048] Step 6: Estimate the initial longitude and latitude coordinates of each ship target in the geodetic coordinate system according to the following formula:

[0049]

[0050] in, It represents the estimated value of the initial position coordinates of the nth ship target in the geodetic coordinate system. Represents the initial longitude α of the nth target in the geodetic coordinate system s The coordinate estimate of (n), Represents the coordinate estimate of the initial latitude of the nth target in the geodetic coordinate system, Indicates the initial longitude α of the nth target s (n) and initial latitude β s (n) Minimum operation.

[0051] The effects of the present invention are further described below in conjunction with simulation experiments.

[0052] 1. Simulation experiment conditions:

[0053] The hardware platform of the simulation experiment of the present invention is: the processor is Intel i7 8700k CPU, the main frequency is 3.20GHz, and the memory is 16GB.

[0054] The software platforms for the simulation experiment of the present invention are: Windows 10 operating system and Matlab2021a.

[0055] The initial longitude coordinate of the aircraft on the airborne radar platform used in the simulation experiment of the present invention in the geodetic coordinate system is 118.618°, the initial latitude coordinate in the geodetic coordinate system is 35°, the flight altitude is 8km, the movement speed is 200m / s, and the movement angle is 0°; the bandwidth of the radar transmitted pulse signal is 3MHz, the pulse repetition frequency is 1500Hz, and the carrier frequency is 9.1GHz; the jitter amplitude of the radar antenna is 0.05°; the radar observation time is 10min, each observation cycle is 15s, the speed of the ship target during the entire observation time is 10m / s, the heading angle is 60°, the initial longitude coordinate of the ship target in the geodetic coordinate system is 121°, and the initial latitude coordinate in the geodetic coordinate system is 36.8852°.

[0056] 2. Simulation content and results analysis:

[0057] The simulation experiment of the present invention adopts the method of the present invention and an existing technology (αβ tracking filter method) to estimate the position of the ship respectively, and obtains the root mean square error of the ship position estimation.

[0058] In the simulation experiment, the existing αβ tracking filtering method used is:

[0059] Northwestern Polytechnical University proposed a tracking filtering method based on αβ filtering that can be applied to ship positioning in its published patent document "A mathematical modeling method for tracking filtering of a radar signal processor" (application number: 202111040428.5, application publication number CN 114117723 A), referred to as the αβ tracking filtering method.

[0060] The effects of the present invention are further described below in conjunction with the simulation results table in Table 1.

[0061] An evaluation index (root mean square error RMSE) is used to evaluate the positioning results of the two methods. The root mean square error RMSE of the position estimation is calculated using the following formula, and the calculation results are plotted in Table 1:

[0062] Root mean square error RMSE = (estimated value of the initial position of the ship - actual value of the initial position of the ship) 2

[0063] Table 1 Quantitative analysis of the ship positioning results of the present invention and the prior art in the simulation experiment

[0064] Method of the present invention αβ tracking filter method Root mean square error RMSE (km) 0.039 0.328 Total number of observation cycles 40 40

[0065] It can be seen from Table 1 that the root mean square error of ship positioning of the method of the present invention is 0.039, which is lower than that of the prior art method, proving that the present invention can obtain higher ship target positioning accuracy.

[0066] The above simulation experiments show that: the present invention uses the movement of the radar platform itself to calculate the radial distance between the radar platform and the target under different observation geometries at the observation angles of multiple observation periods, and then estimates the ship position by combining the radial distances under sequential multi-angle views. There is no need to communicate between multiple radars and multiple sensors, which solves the problem of communication burden in the prior art under the background of sea clutter. There is no need to measure the target angle, and the radial distance is a measurement that is not affected by beam pointing, which avoids the problem of beam pointing error in the prior art affecting the positioning estimation accuracy. It is a very practical ship target positioning method.

Claims

1. A ship positioning method based on sequential multi-view radial distance combination, characterized in that: The radial distance of the ship target is measured by using a single pulse radar carried by an airborne platform under sequential observation angles, and the position coordinates of the ship are estimated by the minimum mean square error method by combining the radial distance measurements under multiple angles. The steps of the method include the following: Step 1: The airborne pulse radar periodically transmits pulses and receives signals: The moving airborne platform is equipped with a single pulse radar, which divides the sea area to be detected into wave positions during the observation time, transmits periodic pulses to each wave position in turn to perform full-scene beam scanning of the detection area, and receives echo signals from the sea; Step 2, using the echo pulse center estimation method to estimate the echo arrival time of the detected ship target in each observation period; Step 3, calculating the radial distance measurement value of each ship target under the sequential observation perspective; Step 4: Estimate the longitude and latitude coordinates of each ship target in the geodetic coordinate system under the sequential observation perspective: Step 4.1, using a ship speed and heading estimation method based on multi-view radial velocity to estimate the speed and heading of each ship target; Step 4.2, using the sequential perspective longitude and latitude iteration formula, estimate the longitude and latitude coordinates of each ship target in the geodetic coordinate system under the sequential observation perspective; Step 5: Estimate the radial distance between the aircraft on the airborne radar platform and each ship target under sequential viewing angles: Step 5.1, using the cosine calculation formula, calculate the cosine value of the angle between the line connecting the center of the earth and each ship target and the line connecting the center of the earth and the aircraft carried by the radar platform under the sequential observation perspective; Step 5.2: Use the radial distance calculation formula to estimate the radial distance between the aircraft on the airborne radar platform and each ship target under the sequential observation perspective. Step 6: Estimate the initial longitude and latitude coordinates of each ship target in the geodetic coordinate system according to the following formula: in, It represents the estimated value of the initial position coordinates of the nth ship target in the geodetic coordinate system. Represents the initial longitude α of the nth target in the geodetic coordinate system s The coordinate estimate of (n), Represents the initial latitude β of the nth target in the geodetic coordinate system s The coordinate estimate of (n), Indicates the initial longitude α of the nth target s (n) and initial latitude β s (n) Minimum operation, r(k,n) represents the measured value of the straight-line distance between the nth ship target and the airborne radar platform at the kth observation angle in the sequential observation angle, k = 1, 2, ..., K, K represents the total number of observation cycles, It represents the estimated radial distance of the nth ship target at the kth observation angle in the sequential observation angle.

2. The ship positioning method based on sequential multi-view radial distance combination according to claim 1 is characterized in that: The radial distance measurement value r(k,n) of each ship target under the sequential observation angle described in step 3 is obtained by the following formula: Where c represents the propagation speed of light, and Δt(k,n) represents the arrival time of the nth ship target at the kth observation perspective in the sequential observation perspective.

3. The ship positioning method based on sequential multi-view radial distance combination according to claim 1 is characterized in that: The sequential perspective latitude and longitude iteration formula described in step 4.2 is as follows: in, represents the estimated value of the longitude coordinate of the nth ship target in the geodetic coordinate system at the kth observation angle in the sequential observation angle, α s (n) represents the initial longitude coordinate of the nth ship target in the geodetic coordinate system, represents the estimated value of the speed of the nth ship target, sin{·} represents the sine operation, represents the estimated value of the heading of the nth ship target, R represents the radius of the earth, cos{·} represents the cosine operation, β s (n) represents the initial latitude coordinate of the nth ship target in the geodetic coordinate system, T k T1 represents the observation time of the observation cycle of the kth observation perspective in the sequential observation perspective, T2 represents the observation time of the observation cycle of the first observation perspective in the sequential observation perspective, and the K observation times satisfy T1<T2<T3···<T K , It represents the estimated value of the latitude coordinate of the nth ship target in the geodetic coordinate system at the kth observation perspective in the sequential observation perspective.

4. The ship positioning method based on sequential multi-view radial distance combination according to claim 3 is characterized in that: The cosine calculation formula described in step 5.1 is as follows: Among them, Θ k (n) represents the cosine value of the angle between the line connecting the center of the earth and the nth ship target and the line connecting the center of the earth and the aircraft on the radar platform at the kth observation angle in the sequential observation angle, β r (k) represents the latitude coordinate of the aircraft on the airborne radar platform in the geodetic coordinate system at the kth observation angle in the sequential observation angle, α r (k) represents the longitude coordinate of the aircraft carried by the airborne radar platform in the geodetic coordinate system at the kth observation angle in the sequential observation angle.

5. The ship positioning method based on sequential multi-view radial distance combination according to claim 4 is characterized in that: The radial distance calculation formula described in step 5.2 is as follows: Among them, h r (k) represents the height coordinate of the aircraft carried by the airborne radar platform in the geodetic coordinate system at the kth observation angle in the sequential observation angle.

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