A radar calibration method and system for positioning and orienting an unmanned aerial vehicle based on GPS positioning

Abstract

This invention discloses a radar calibration method and system for a UAV based on a positioning and attitude locator and GPS positioning. The method includes: rigidly fixing the positioning and attitude locator to the base of the radar to be calibrated; planning at least three calibration paths; during flight, simultaneously collecting GPS positioning data of the UAV, detection data of the UAV by the radar to be calibrated, and attitude data of the positioning and attitude locator; calculating the true azimuth and true pitch angles of the UAV relative to the radar to be calibrated in the geodetic coordinate system; obtaining the radar system azimuth error and system pitch error corresponding to each calibration path; calculating the mechanical error correction amount of the radar to be calibrated, and the coordinate transformation matrix between the radar coordinate system and the positioning and attitude locator coordinate system; correcting the target detection data collected by the radar in real time, and then converting it into the true target attitude data in the geodetic coordinate system. This invention can accurately calibrate the mounting surface errors of the radar and the positioning and attitude locator, as well as the mechanical errors of the radar itself.

Description

Technical Field

[0001] This invention belongs to the field of radar calibration technology, and particularly relates to a radar calibration method and system for UAVs based on a positioning and attitude determination device and GPS positioning. Background Technology

[0002] With the widespread application of radar technology in low-altitude defense, regional security, environmental monitoring, and target tracking, increasingly higher demands are being placed on the angular accuracy and environmental adaptability of radar target positioning. The target azimuth and elevation angles output by radar detection are based on the radar's local coordinate system. When the radar is installed at an angle, not facing due north, or the mounting surface is not level, or when its attitude changes during use, the output target attitude data deviates from the true target attitude in the geodetic coordinate system. This makes it unsuitable for direct use in scenarios such as map display, multi-device linkage, and precise target tracking. Therefore, calibration is essential to compensate for radar system errors and perform coordinate system transformation to ensure detection accuracy.

[0003] Existing radar calibration technologies are mainly divided into two categories. One is the static calibration scheme based on a positioning and attitude determination device (PAD). This scheme obtains the radar's real-time attitude by installing a PAD on the radar, thereby completing the transformation from the radar's local coordinate system to the geodetic coordinate system. However, this scheme cannot guarantee the absolute parallelism between the PAD's mounting plane and the radar's zero-position plane. Without calibration, it can only reduce some errors through attitude data, but cannot eliminate system deviations caused by non-parallel mounting surfaces. Furthermore, it cannot compensate for the radar's own mechanical zero-position error or electromechanical coordination error. For systems with high accuracy requirements for target azimuth and elevation measurements, its residual error cannot meet the usage requirements. The other category is the calibration scheme based on fixed calibration facilities. This scheme completes radar calibration using targets with preset true values, such as calibration towers and fixed corner reflectors. However, this scheme has stringent site requirements, high deployment costs, and poor flexibility, making it unsuitable for rapid calibration needs in complex field environments.

[0004] To address the lack of flexibility in fixed calibration facilities, the industry has gradually developed radar calibration technology based on drones. Among them, Chinese invention patent application CN116359861A, entitled "An Automatic Radar Calibration Method and Device Based on Drones," discloses an automatic radar calibration scheme: This scheme uses a drone equipped with a high-precision RTK positioning system as the calibration target. First, the drone's positioning is used to obtain the reference coordinates of the radar station. During the drone's flight, the radar's tracking data of the drone and the drone's real-time RTK pose data are collected simultaneously. After completing the timestamp alignment and coordinate system unification of the multi-source data, the drone's RTK positioning data is used as the truth value to calculate the radar's ranging and angle measurement system errors, and finally, the radar system error is corrected.

[0005] However, the existing technology can only solve the angle measurement and ranging errors of the radar's basic system. It cannot simultaneously calibrate and compensate for the radar's own mechanical zero-position error and electromechanical coordination error. It can only achieve error correction within the angle range covered by the UAV flight. It cannot achieve 360° all-round high-precision calibration. The measurement error in the non-calibration range may even be amplified, which cannot meet the high-precision use requirements of radar omnidirectional detection. Summary of the Invention

[0006] The purpose of this invention is to provide a radar calibration method and system for UAVs based on a positioning and attitude locator and GPS positioning, which partially solves or alleviates the above-mentioned deficiencies in the prior art. It can accurately calibrate the mounting surface error of the radar and the positioning and attitude locator, as well as the mechanical error of the radar itself, and can achieve accurate output of target azimuth and pitch in all 360° directions.

[0007] To solve the aforementioned technical problems, the present invention specifically adopts the following technical solution: A first aspect of the present invention is to provide a radar calibration method for a UAV based on a positioning and attitude determination device and GPS positioning, comprising the following steps: The positioning and attitude determination device is rigidly fixed to the base of the radar to be calibrated, so that the positioning and attitude determination device and the radar to be calibrated maintain synchronous changes in position and attitude. At least three calibration paths are planned, each of which is a straight path, and the relative angle between each calibration path and the zero point of the radar array to be calibrated is different. Control the drone to fly along the calibration path; during the flight, simultaneously collect the drone's GPS positioning data, the detection data of the drone by the radar to be calibrated, and the attitude data of the positioning and attitude determination device; Based on the UAV's GPS positioning data, the true azimuth and true pitch angles of the UAV relative to the calibration radar in the geodetic coordinate system are calculated. By comparing the UAV's detection data with the radar to be calibrated using the true azimuth and true pitch angles, the radar system azimuth error and system pitch error corresponding to each calibration path are obtained; based on the system azimuth error and system pitch error of at least 3 calibration paths, the mechanical error correction amount of the radar to be calibrated, as well as the coordinate transformation matrix between the radar coordinate system and the positioning and attitude determination instrument coordinate system, are calculated. When the radar is calibrated for subsequent operations, the target detection data collected in real time by the radar is corrected based on the mechanical error correction amount, and then the corrected detection data is converted into the target's true pose data in the geodetic coordinate system through the coordinate transformation matrix.

[0008] Furthermore, the GPS positioning data of the UAV includes the acquisition time, longitude, latitude, and altitude; the detection data of the radar to be calibrated includes the acquisition time, target azimuth, target pitch angle, and target distance; and the attitude data of the positioning and attitude determination device includes the acquisition time, longitude, latitude, altitude, azimuth, roll angle, and pitch angle.

[0009] Furthermore, methods for solving the mechanical error correction amount and coordinate transformation matrix include: There are 3 calibration paths; for the nth calibration path, the system orientation error corresponding to that path is Δα. n The system pitch error is Δθ n Combined with the azimuth angle α' collected by the positioning and attitude determination device along this path n Pitch angle θ' n And the relative angle α between the calibration path and the zero point of the radar array. n Construct the matrix equation:

[0010] Where n is the index of the calibration path, n=1,2,3; Δ is the mechanical error correction amount of the radar to be calibrated; and T is the coordinate transformation matrix between the radar coordinate system and the positioning and attitude determination instrument coordinate system. Solve the matrix equation to obtain the mechanical error correction amount and coordinate transformation matrix.

[0011] Furthermore, after calculating the mechanical error correction amount and coordinate transformation matrix, the calibration result verification step is also included, specifically: The radar detection data is transformed by the mechanical error correction amount obtained through calculation and the coordinate transformation matrix to obtain the UAV's calculated pose data in the geodetic coordinate system. The calculated pose data is compared with the true GPS positioning data collected synchronously by the UAV to calculate the calibration error; If the calibration error meets the preset accuracy requirement, the calibration is considered successful; if the calibration error exceeds the preset accuracy requirement, the system azimuth error and system pitch error of the calibration path with the excessive positioning error are re-acquired until the calibration error meets the preset accuracy requirement.

[0012] Furthermore, methods for transforming the original target detection data based on mechanical error correction and coordinate transformation matrix include: Collect the original azimuth and original elevation angles of the target output by the radar to be calibrated; The original azimuth and elevation angles of the target are corrected by the mechanical error correction amount, and the corrected azimuth and elevation angles are obtained. Using the attitude data output by the positioning and attitude determination device, calculate the pitch angle of the positioning and attitude determination device corresponding to the azimuth angle of the current target; The corrected target pitch angle is transformed using a coordinate transformation matrix to obtain the target pitch angle in the positioning and attitude determination instrument coordinate system. The target pitch angle in the positioning and attitude determination instrument coordinate system is then superimposed with the positioning and attitude determination instrument pitch angle to obtain the target's true pitch angle in the geodetic coordinate system. Combined with the target distance detected by radar, the target's true longitude, latitude, and altitude in the geodetic coordinate system are calculated.

[0013] Furthermore, the pitch angle of the positioning and attitude determination device corresponding to the current target's relative azimuth angle is obtained using the formula:

[0014] Calculate; where, Let A be the pitch angle of the positioning and attitude determination device, and let A and B be the coefficients of the current plane equation Ax + By = 0 of the positioning and attitude determination device. The relative azimuth of the current target. Let azimuth angle of the current target in the radar coordinate system be the output of the radar to be calibrated. The heading angle of the self in the geodetic coordinate system as measured by the positioning and attitude determination instrument.

[0015] Furthermore, invalid data is removed and filtered from the collected GPS positioning data, radar detection data, and positioning and attitude determination device pose data.

[0016] Furthermore, methods for invalid data removal and filtering include: Based on the positioning status of the positioning and attitude determination device, invalid pose data during periods of satellite signal loss are filtered out; Based on the status bits of the drone's GPS positioning module, invalid positioning data is filtered out; if the drone uses a differential GPS positioning module, invalid positioning data during periods when it is out of differential positioning status is filtered out simultaneously. For the detection data of the radar to be calibrated under each calibration path, filtering and error calculation are performed respectively to determine the effective error threshold of the radar data under the corresponding calibration path, and invalid detection data exceeding the effective error threshold are filtered out.

[0017] Furthermore, it also includes: performing time interpolation on the UAV's GPS positioning data and radar detection data to align their timestamps.

[0018] The present invention also provides a radar calibration system for a UAV based on a positioning and attitude locator and GPS positioning, including a positioning and attitude locator, a UAV equipped with a GPS positioning module, and a data processing unit; The positioning and attitude determination device is rigidly fixed to the base of the radar to be calibrated and is used to collect the real-time position and attitude data of the radar to be calibrated; the UAV is used to fly along a preset calibration path and collect its own GPS positioning data; the radar to be calibrated collects detection data of the UAV during the flight of the UAV; the data processing unit is communicatively connected to the radar to be calibrated, the positioning and attitude determination device, and the UAV, and is used to execute the above-mentioned radar calibration method based on the positioning and attitude determination device and GPS positioning of the UAV.

[0019] Beneficial effects: Compared to existing calibration methods, this invention is based on a UAV equipped with GPS positioning and a positioning and attitude determination system rigidly connected to radar. Before processing the data, filtering and error calculations are performed on the data to eliminate all errors introduced by radar detection. Simultaneously, calculations are performed in three directions, thereby determining the error value of the mounting surface from all 360° omnidirectional perspective, thus achieving accurate omnidirectional calibration.

[0020] During each calibration, a set of GPS positioning data, radar data, and attitude control data is obtained. The GPS positioning data is used to obtain the target's azimuth and elevation angles in the geodetic coordinate system. These values ​​are then processed with the radar data to obtain the standard deviation of the azimuth error correction. Data values ​​exceeding the standard deviation are filtered out to prevent excessively large errors from interfering with the calibration results. Subsequently, the effective error in that direction is obtained. At the same time, the attitude sensor will collect the system's current attitude, process the data, and obtain the attitude value. Similarly, the data in the other two directions are processed.

[0021] Since the calibration scheme of this invention requires coordinate transformation based on the attitude sensor data, the result obtained by this invention is... Directional correction After correcting the zero pitch angles in the three calibration directions, the error correction amounts in the three directions should be obtained.

[0022] Zero pitch angle first needs to be corrected for mechanical error. The correction is obtained after solving the problem. And the transformation matrix T. After calibration, the raw radar data azimuth and elevation angles acquired each time are subsequently processed by error correction. After correction, the azimuth and pitch angles are obtained with the error correction amount. Then, the attitude data (azimuth, pitch, roll) collected by the current attitude instrument are acquired to calculate the current target's relative azimuth angle. pitch angle on the attitude instrument After the original pitch angle of the target is transformed by the transformation matrix T, the true pitch angle in the attitude sensor coordinate system can be obtained, which is then added to the pitch angle of the attitude sensor in that direction. This allows us to convert the actual pitch angle in the current direction, and then convert that into the actual latitude, longitude, and altitude of the target.

[0023] This invention enables radar calibration in complex environments. After calibration, even if the radar position and attitude are changed, it can be powered on and used without re-leveling.

[0024] Furthermore, this invention has extremely high precision, with the error value determined solely by the system error of the radar and attitude sensor. The algorithm does not introduce other errors and can calculate the target's true position and height based on the geodetic coordinate system. The algorithm's precision is high enough to satisfy high-precision systems such as photoelectric systems. The converted data is almost identical to the target's true position, and the target can be found almost near the center of the photoelectric system's field of view. In practical tests, traditional unidirectional and bidirectional calibration methods cannot achieve high-precision calibration in all directions. Unidirectional calibration can only solve the calibration problem in one direction, and the error in other directions may even be amplified. Bidirectional calibration cannot resolve the mechanical errors of the system itself, resulting in high accuracy only within the range of the two calibration directions. In contrast, this invention can eliminate the errors caused by the calibration algorithm in all directions, compressing the final calibration error to the level of the fixed system error of the positioning and attitude determination instrument and radar detection, thus achieving high-precision calibration in all directions. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. The elements or parts in the drawings are not necessarily drawn to scale. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0026] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] In this document, suffixes such as "module," "part," or "unit" used to denote elements are used only for the purpose of illustrative purposes and have no specific meaning in themselves. Therefore, "module," "part," or "unit" may be used interchangeably.

[0029] In this document, the terms "upper," "lower," "inner," "outer," "front," "rear," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the present invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] In this document, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] In this document, "and / or" includes any and all combinations of one or more of the listed related items.

[0032] In this article, "multiple" means two or more, that is, it includes two, three, four, five, etc.

[0033] Example 1: The calibration method of the present invention is based on a dedicated radar calibration system, which includes a radar to be calibrated, a positioning and attitude determination device, a calibration UAV equipped with a GPS positioning module, and a data processing unit.

[0034] In this embodiment, the detection radar is equipped with an azimuth turntable. The 0° position of the turntable is the normal direction of the radar array, which is defined as the azimuth zero position of the radar's local coordinate system.

[0035] The positioning and attitude determination device can output real-time data such as acquisition timestamp, longitude, latitude, altitude, azimuth (heading angle), roll angle, pitch angle, positioning status, and number of satellites. The device is rigidly fixed to the base of the radar to be calibrated using high-strength bolts, ensuring a secure and non-loose connection. After installation, there is no relative displacement between the device and the radar base. When the radar undergoes any attitude changes such as translation, rotation, or tilt, the device maintains completely synchronized attitude changes with the radar. After installation, the relative positional deviation between the measurement center of the device and the rotation center of the radar turntable is calibrated to ensure they are on the same vertical line, eliminating calculation errors caused by origin deviation.

[0036] The calibration drone can transmit data such as collection timestamp, longitude, latitude, altitude, positioning status bit, and differential status bit in real time.

[0037] The data processing unit uses an industrial control computer with built-in data acquisition module, data preprocessing module, calibration calculation module, and verification output module. It establishes communication connections with the radar to be calibrated, the positioning and attitude determination instrument, and the UAV ground station, respectively, and supports synchronous acquisition, real-time storage, parallel processing and calculation of multi-source data.

[0038] To ensure the clarity and feasibility of the technical solution, this invention unifies the definition of three types of coordinate systems, and all calculations are performed based on this coordinate system.

[0039] The geodetic coordinate system has the Earth's center as the origin, geographic north as the 0° azimuth reference, and the Earth's horizontal plane as the zero elevation reference. It is the absolute true coordinate system of this invention, and all final target pose data are converted to this coordinate system for output.

[0040] The origin of the radar's local coordinate system is the rotation center of the radar turntable. The normal direction of the radar array, i.e., the 0° position of the turntable, is the 0° azimuth reference. When the radar array is horizontal, the mounting plane is the zero elevation reference. The azimuth angle is positive when rotated clockwise, and the elevation angle is positive when raised upwards. All raw radar detection data are output based on this coordinate system.

[0041] The origin of the coordinate system of the positioning and attitude determination instrument is the measurement center of the instrument, which is on the same vertical line as the rotation center of the radar turntable. The heading angle of the positioning and attitude determination instrument is 0°, which is consistent with the due north direction of the geodetic coordinate system. The installation plane of the positioning and attitude determination instrument is the zero pitch reference. Because it is rigidly connected to the radar base, this coordinate system has a fixed installation deviation from the radar's own coordinate system, which is the core correction object of the calibration of this invention.

[0042] Based on the above hardware system, the specific steps of the radar calibration method for UAVs based on the positioning and attitude determination device and GPS positioning in this embodiment include: Step S1: Rigidly fix the positioning and attitude determination device to the base of the radar to be calibrated, so that the positioning and attitude determination device and the radar to be calibrated maintain synchronous changes in position and attitude.

[0043] The positioning and attitude determination device can simultaneously output the absolute position of the device in the geodetic coordinate system, including longitude, latitude, altitude, and three-dimensional attitude, including heading / azimuth, pitch angle, and roll angle. It serves as both a real-time measurement reference for the radar's overall position and attitude and an anchor point for the transformation between the radar coordinate system and the geodetic coordinate system.

[0044] The base of the radar to be calibrated specifically refers to the fixed main support base of the entire radar unit. It is the mechanical reference of the entire radar unit and has a fixed and unchanging geometric tolerance relationship with the rotation axis of the radar azimuth turntable and the zero position reference of the radar array. There is no relative movement throughout the entire process. It is prohibited to use moving parts or non-reference parts such as radar turntable, antenna array, equipment cover, etc. as the installation carrier.

[0045] The positioning and attitude determination device and the radar to be calibrated are rigidly connected by mechanical fasteners, without relative displacement, elastic deformation, movement gap, or hysteresis, so that the positioning and attitude determination device and the radar base are fixed as a single rigid body. This is different from flexible and detachable connections such as adhesive, magnetic attraction, cable ties, and buckles, which cannot guarantee the fixation of the relative position during long-term use and posture changes.

[0046] The positioning and attitude determination device maintains full-dimensional synchronization with the radar to be calibrated, meaning that when the radar undergoes any translational (changes in longitude, latitude, and altitude) or rotational (changes in heading, pitch, and roll angles), the positioning and attitude determination device will undergo completely consistent positional and attitude changes without difference, lag, or deviation. The relative position and attitude of the two devices are permanently fixed after calibration and are not affected by changes in the overall position and attitude of the radar.

[0047] Step S2: Plan at least 3 calibration paths. Each calibration path is a straight path, and the relative angle between each calibration path and the zero point of the radar array to be calibrated is different.

[0048] The purpose of this step is to plan a flight path that meets the calibration requirements, so as to ensure that the calibration parameters with high accuracy in 360° omnidirectional direction can be calculated subsequently.

[0049] At least three calibration paths need to be planned, and all paths must simultaneously meet the following requirements: Each calibration path is a horizontal straight path, and the horizontal projection of the path is a straight line. The altitude is constant throughout the flight, and the altitude fluctuation is ≤±1m to avoid pitch angle calculation errors caused by altitude changes. Each calibration path has a different relative angle with the radar array null position, and all calibration paths are not collinear, ensuring that the three paths can uniquely determine a plane, providing sufficient constraints for subsequent coordinate transformation matrix calculation. The straight-line distances between the start and end points of each calibration path and the center of the radar turntable are all within the radar's optimal detection range. In this embodiment, the distance between the start point and the radar is 1km, the distance between the end point and the radar is 3km, and the total path length is ≥2km, ensuring that enough continuous sampling points can be obtained to improve the statistical accuracy of error calculation. The flight path airspace is free from buildings and mountains, and there are no strong electromagnetic interference sources, ensuring that the radar can stably track the drone throughout the entire flight and that the drone's satellite signal is not lost.

[0050] Specific Path Planning Example: In this embodiment, three non-collinear calibration paths are planned to cover the radar's 360° azimuth range, ensuring uniform omnidirectional calibration accuracy. Specific parameters are as follows: The calibration path 1 has a relative angle α1 = 0° with the zero point of the radar array, meaning the path is parallel to the normal direction of the radar array, the flight altitude is constant at 100m, and the flight range is 1km to 3km north of the radar. The calibration path 2 has a relative angle α2 = 120° with the radar array zero point, a constant flight altitude of 100m, and a flight range of 1km to 3km in the direction of 120° north of east of the radar. The calibration path 3 has a relative angle α3 = 240° with the radar array zero point, a constant flight altitude of 100m, and a flight range of 1km to 3km in the direction of 120° north of the radar.

[0051] Step S3: Control the UAV to fly along the calibration path; during the flight, simultaneously collect the UAV's GPS positioning data, the detection data of the UAV by the radar to be calibrated, and the attitude data of the positioning and attitude determination device.

[0052] The drone is controlled to take off, climb to the constant altitude set on the calibration path, and hover at the starting position of the calibration path, awaiting data acquisition instructions. The data processing unit sends a synchronous acquisition start command to all devices. The calibration radar, positioning and attitude locator, and drone synchronously start data acquisition, and the sampling frequency of all devices is uniformly set to ensure matching sampling density.

[0053] The drone is controlled to fly at a constant speed of 10 m / s along a calibrated path. After smoothly reaching the endpoint, it immediately turns around and flies back to the starting point at a constant speed along the original path, completing one round trip. In this embodiment, each calibrated path is executed three times to obtain sufficient continuous sampling data, improving the statistical significance of error calculation. During the flight, the data processing unit simultaneously receives and stores three types of core data, all of which are timestamped to ensure traceability. In this embodiment, the UAV's GPS positioning data includes the acquisition timestamp, longitude, latitude, altitude, positioning status, and differential status. The radar's detection data includes the acquisition timestamp, target azimuth, target pitch angle, target slant range, signal strength, and tracking status. The positioning and attitude determination device's attitude data includes the acquisition timestamp, longitude, latitude, altitude, azimuth (heading angle), roll angle, pitch angle, positioning status, and number of satellites.

[0054] After completing all round-trip flights along the calibration path, the data processing unit issues a data acquisition stop command, completing the data acquisition and local storage for a single path.

[0055] After completing the data acquisition for a single calibration path, if it is necessary to adjust the radar attitude to adapt to the airspace, the radar to be calibrated and the positioning and attitude determination instrument can be treated as a whole and any attitude adjustment such as translation, rotation, and tilt can be performed. During the adjustment process, the rigid connection between the two must be maintained. After the adjustment is completed, there is no need to re-level the radar or re-initialize the positioning and attitude determination instrument. You can directly execute the data acquisition for the next calibration path.

[0056] Repeat the single-path data collection process described above to complete the data collection and storage for all three calibration paths, forming the original calibration dataset.

[0057] Step S4: Perform invalid data removal and filtering on the collected GPS positioning data, radar detection data, and positioning and attitude determination device pose data.

[0058] The purpose of this step is to remove invalid and abnormal data from the original data, filter random noise, and avoid abnormal data from interfering with the calibration calculation.

[0059] Based on the positioning status of the positioning and attitude determination instrument, invalid pose data during periods of satellite signal loss are filtered out.

[0060] Invalid positioning data is filtered out based on the status bits of the drone's GPS positioning module.

[0061] For the detection data of the radar to be calibrated under each calibration path, filtering and error calculation are performed respectively to determine the effective error threshold of the radar data under the corresponding calibration path, and invalid detection data exceeding the effective error threshold are filtered out.

[0062] Step S5: Perform time interpolation on the UAV's GPS positioning data and radar detection data to align their timestamps.

[0063] The purpose of this step is to eliminate timestamp misalignment in multi-source data and ensure that the radar measured values ​​and the GPS true values ​​correspond to the same data at the same time and spatial location.

[0064] The UAV GPS positioning data, radar detection data, and position and attitude data of the position and attitude indicator belong to three independent hardware systems, and there are inherent biases in their internal clocks. Therefore, in this embodiment, the GPS standard time is used as the unified time reference, and the timestamps of the radar detection data are all converted to GPS time to eliminate the time misalignment caused by time zones and hardware clock biases.

[0065] Specifically, taking the timestamp of the radar detection data as the reference node, a linear interpolation operation is performed on the UAV GPS positioning data. For each reference timestamp t0 of the radar, two adjacent UAV GPS sampling points t1 and t2 before and after t0 are selected to satisfy t1 < t0 < t2. Through the linear interpolation formula, the interpolation results of the longitude, latitude, and altitude of the UAV at the moment of t0 are calculated as the true value data of the UAV at this timestamp. After completing the interpolation alignment of all reference timestamps, a time synchronization calibration data set is constructed for subsequent true value calculation.

[0066] Step S6: Based on the UAV GPS positioning data, calculate the true azimuth and true pitch angles of the UAV relative to the radar to be calibrated in the geodetic coordinate system.

[0067] Specifically, in step S3, the GPS positioning data of the position and attitude indicator is collected, that is, the longitude, latitude, and altitude (Lon_Radar, Lat_Radar, Height_Radar) of the location where the radar is located are obtained. According to the longitude, latitude, and altitude (Lon_UAV, Lat_UAV, Height_UAV) of the UAV GPS data obtained at the current moment, based on the high-precision Vincenty formula, the true azimuth and true pitch angles of the UAV relative to the radar in the geodetic coordinate system can be obtained, and the accuracy can reach the micro-arcsecond level.

[0068] The Vincenty algorithm is based on the earth's rotating ellipsoid, introduces the reduced latitude to correct the geodetic coordinates; by iteratively converging the longitude difference parameter, it solves the geodetic line arc distance and azimuth angle on the ellipsoid surface. Compared with the spherical approximation model, it effectively overcomes the inherent error caused by the earth's oblateness, and can achieve high-precision calculation of the distance and azimuth angle of the surface point position after iterative convergence. Its process is as follows: 1. Convert the longitude and latitude of the two points to radians and substitute them into the earth ellipsoid parameters (semi-major axis, oblateness). 2. Calculate the reduced latitude from the geodetic latitude to eliminate the influence of the earth ellipsoid oblateness, that is:

[0069] where is the earth's oblateness, and U1 and U2 are the reduced latitudes.

[0070] 3. Take the longitude difference between the two points as the initial value, iteratively correct the ellipsoid longitude difference, and loop until the numerical change is less than the set convergence threshold, that is:

[0071] Typically iterates to .

[0072] Where L is the difference in longitude between the two points, U m The average naturalized latitude, i.e. C is the ellipsoid correction factor. , The central angle between the two geodesics is denoted by . .

[0073] 4. Use the converged parameters to solve for the central angle of the ellipsoid geodesic. 5. Substitute into the arctangent formula to calculate the initial azimuth of the starting point and the geodetic distance between the two points. . 6. Output azimuth and ground distance to complete high-precision calculation, i.e.:

[0074]

[0075] Step S7: Calculate the calibration parameters.

[0076] The purpose of this step is to calculate the radar's mechanical error correction Δ and the coordinate transformation matrix T between the radar coordinate system and the positioning and attitude determination instrument coordinate system, based on the true value dataset.

[0077] Specifically, in this embodiment, the detection data of the UAV by the radar to be calibrated is compared with the actual azimuth angle and the actual pitch angle to obtain the radar system azimuth error and system pitch error corresponding to each calibration path; based on the system azimuth error and system pitch error of at least 3 calibration paths, the mechanical error correction amount of the radar to be calibrated and the coordinate transformation matrix between the radar coordinate system and the positioning and attitude determination instrument coordinate system are calculated.

[0078] For the nth calibration path (n=1,2,3), extract the original radar azimuth angle A_radar, the original elevation angle E_radar, and the corresponding true azimuth angle A_true and true elevation angle E_true for all sampling points along this path. Calculate the instantaneous azimuth error ΔA = A_radar - A_true and the instantaneous elevation error ΔE = E_radar - E_true for each sampling point. Remove outliers from the instantaneous azimuth and elevation errors, and take the arithmetic mean of the remaining effective error values ​​to obtain the system azimuth error Δα corresponding to this calibration path. n System pitch error Δθ n Extract the average azimuth angle α' collected by the positioning and attitude determination device along this calibration path. nMean pitch angle θ' n And the preset relative angle α between the calibration path and the zero position of the radar array. n This completes the extraction of error parameters for a single path.

[0079] The systematic errors in the three non-collinear directions are caused by the radar's own mechanical zero-position error and the parallelism error of the mounting surfaces of the radar and the positioning and attitude determination instrument. These errors can be fully vectorized using the mechanical error correction amount Δ and the coordinate transformation matrix T. The error samples in the three non-collinear directions can uniquely determine the optimal solutions for Δ and T. The constructed matrix equation is as follows:

[0080] Where n is the index of the calibration path, n=1,2,3; α1, α2, α3 are the relative angles between the three calibration paths and the radar array zero position, respectively; α'1, α'2, α'3 are the average azimuth angles collected by the positioning and attitude determination instrument under the three calibration paths, respectively; Δθ1, Δθ2, Δθ3 are the system elevation errors corresponding to the three calibration paths, respectively; Δ is the radar mechanical error correction amount to be solved, which is a 3×1 matrix, including the radar azimuth mechanical zero position error, elevation mechanical zero position error, and mounting surface tilt error; T is the coordinate transformation matrix between the radar coordinate system to be solved and the positioning and attitude determination instrument coordinate system, which is a 3×3 orthogonal rotation matrix.

[0081] The matrix equations are solved using the least squares method to obtain the global optimal solution for the mechanical error correction Δ and the coordinate transformation matrix T. After the solution is completed, Δ and T are stored in the data processing unit and the radar's main control system as core calibration parameters for subsequent radar detection data correction.

[0082] Step S8: Certification and daily application of calibration parameters.

[0083] After successful calibration, the mechanical error correction amount Δ and the coordinate transformation matrix T are stored in the radar's main control system. When the radar operates in any position and attitude, there is no need to readjust or recalibrate.

[0084] S81. Collect the original azimuth and original elevation angles of the target output by the radar to be calibrated.

[0085] When the radar is operating normally, it collects raw target detection data in real time, including the target's raw azimuth angle α. 目标 The system acquires the original elevation angle and target slant range R; simultaneously, a positioning and attitude determination device rigidly connected to the radar collects the radar's current attitude data in real time, including the azimuth angle α. 姿态仪 The roll angle, pitch angle, and coefficients A and B of the current positioning and attitude determination instrument plane equation Ax+By=0.

[0086] S82. Correct the original azimuth and pitch angles of the target by using mechanical error correction to obtain the corrected azimuth and pitch angles.

[0087] The mechanical error correction amount Δ obtained through calibration is used to correct the original azimuth angle α of the target. 目标 The original elevation angle is corrected to eliminate the radar's own mechanical null error, resulting in the corrected azimuth angle α. correct Corrected pitch angle E correct .

[0088] S83. Using the attitude data output by the positioning and attitude determination device, calculate the pitch angle of the positioning and attitude determination device corresponding to the azimuth angle of the current target.

[0089] Calculate the current target's relative azimuth angle, i.e., α. 目标 -α 姿态仪 Through the formula:

[0090] Calculate the pitch compensation angle of the positioning and attitude determination instrument at this relative azimuth angle; where, Let A and B be the pitch angle of the positioning and attitude determination instrument, and let B be the coefficients of the current plane equation Ax + By = 0 of the positioning and attitude determination instrument. These coefficients are calculated from the roll angle and pitch angle collected in real time by the positioning and attitude determination instrument. This plane equation represents the real-time tilt state of the radar mounting surface relative to the horizontal plane of the earth. The relative azimuth of the current target. Let azimuth angle of the current target in the radar coordinate system be the output of the radar to be calibrated. The heading angle of the self in the geodetic coordinate system as measured by the positioning and attitude determination instrument.

[0091] S84. Transform the corrected target pitch angle using a coordinate transformation matrix to obtain the target pitch angle in the positioning and attitude determination instrument coordinate system; superimpose the target pitch angle in the positioning and attitude determination instrument coordinate system with the positioning and attitude determination instrument pitch angle to obtain the target's true pitch angle in the geodetic coordinate system; combine the target distance detected by radar to calculate the target's true longitude, latitude, and altitude in the geodetic coordinate system.

[0092] Using the coordinate transformation matrix T obtained from the calibration, the corrected pitch angle E correct By performing a rotation transformation, the target pitch angle E in the coordinate system of the positioning and attitude determination instrument is obtained. pos .

[0093] The target pitch angle E in the coordinate system of the positioning and attitude determination instrument pos By superimposing the attitude pitch compensation angle θ, the true pitch angle E of the target in the geodetic coordinate system is obtained. trueBy combining the target slant range R detected by radar with the radar station reference coordinates collected in real time by the positioning and attitude determination instrument, the true longitude, latitude, and altitude of the target in the geodetic coordinate system can be calculated to achieve accurate target positioning. This can be directly used in scenarios such as electronic map display, multi-device linkage tracking, and target early warning.

[0094] Step S9: Verify calibration results.

[0095] After calculating the mechanical error correction amount and coordinate transformation matrix, the calibration result verification step is also included, specifically: S91. The radar detection data is converted by the mechanical error correction amount obtained through the solution and the coordinate transformation matrix to obtain the UAV's solved pose data in the geodetic coordinate system. S92. Compare the calculated pose data with the true GPS positioning data collected synchronously by the UAV, and calculate the calibration error; S93. If the calibration error meets the preset accuracy requirements, the calibration is considered successful. If the calibration error exceeds the preset accuracy requirements, the calibration path with the excessive positioning error will repeat steps S3 to S7 to re-obtain the system azimuth error and system pitch error of the calibration path until the calibration error meets the preset accuracy requirements.

[0096] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0097] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a computer terminal (which may be a mobile phone, computer, server, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0098] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A radar calibration method for unmanned aerial vehicles (UAVs) based on a positioning and attitude determination device and GPS positioning, characterized in that, Includes the following steps: The positioning and attitude determination device is rigidly fixed to the base of the radar to be calibrated, so that the positioning and attitude determination device and the radar to be calibrated maintain synchronous changes in position and attitude. At least three calibration paths are planned, each of which is a straight path, and the relative angle between each calibration path and the zero point of the radar array to be calibrated is different. Control the drone to fly along the calibration path; during the flight, simultaneously collect the drone's GPS positioning data, the detection data of the drone by the radar to be calibrated, and the attitude data of the positioning and attitude determination device; Based on the UAV's GPS positioning data, the true azimuth and true pitch angles of the UAV relative to the calibration radar in the geodetic coordinate system are calculated. By comparing the UAV's detection data with the radar to be calibrated using the true azimuth and true pitch angles, the radar system azimuth error and system pitch error corresponding to each calibration path are obtained; based on the system azimuth error and system pitch error of at least 3 calibration paths, the mechanical error correction amount of the radar to be calibrated, as well as the coordinate transformation matrix between the radar coordinate system and the positioning and attitude determination instrument coordinate system, are calculated. When the radar is calibrated for subsequent operations, the target detection data collected in real time by the radar is corrected based on the mechanical error correction amount, and then the corrected detection data is converted into the target's true pose data in the geodetic coordinate system through the coordinate transformation matrix.

2. The radar calibration method for a UAV based on a positioning and attitude determination device and GPS positioning as described in claim 1, characterized in that, The GPS positioning data of the UAV includes the acquisition time, longitude, latitude, and altitude; the detection data of the radar to be calibrated includes the acquisition time, target azimuth, target pitch angle, and target distance; the attitude data of the positioning and attitude determination device includes the acquisition time, longitude, latitude, altitude, azimuth, roll angle, and pitch angle.

3. The radar calibration method for a UAV based on a positioning and attitude determination device and GPS positioning as described in claim 1, characterized in that, Methods for calculating mechanical error corrections and coordinate transformation matrices include: There are 3 calibration paths; for the nth calibration path, the system orientation error corresponding to that path is Δα. n The system pitch error is Δθ n Combined with the azimuth angle α' collected by the positioning and attitude determination device along this path n Pitch angle θ' n And the relative angle α between the calibration path and the zero point of the radar array. n Construct the matrix equation: Where n is the index of the calibration path, n=1,2,3; Δ is the mechanical error correction amount of the radar to be calibrated; and T is the coordinate transformation matrix between the radar coordinate system and the positioning and attitude determination instrument coordinate system. Solve the matrix equation to obtain the mechanical error correction amount and coordinate transformation matrix.

4. The radar calibration method for a UAV based on a positioning and attitude determination device and GPS positioning as described in claim 3, characterized in that, After calculating the mechanical error correction amount and coordinate transformation matrix, the calibration result verification step is also included, specifically: The radar detection data is transformed by the mechanical error correction amount obtained through calculation and the coordinate transformation matrix to obtain the UAV's calculated pose data in the geodetic coordinate system. The calculated pose data is compared with the true GPS positioning data collected synchronously by the UAV to calculate the calibration error; If the calibration error meets the preset accuracy requirements, the calibration is considered successful. If the calibration error exceeds the preset accuracy requirement, the system azimuth error and system pitch error of the calibration path with the excessive positioning error will be re-acquired until the calibration error meets the preset accuracy requirement.

5. The radar calibration method for a UAV based on a positioning and attitude determination device and GPS positioning as described in claim 1, characterized in that, Methods for transforming raw target detection data based on mechanical error correction and coordinate transformation matrix include: Collect the original azimuth and original elevation angles of the target output by the radar to be calibrated; The original azimuth and elevation angles of the target are corrected by the mechanical error correction amount, and the corrected azimuth and elevation angles are obtained. Using the attitude data output by the positioning and attitude determination device, calculate the pitch angle of the positioning and attitude determination device corresponding to the azimuth angle of the current target; The corrected target pitch angle is transformed using a coordinate transformation matrix to obtain the target pitch angle in the positioning and attitude determination instrument coordinate system. The target pitch angle in the positioning and attitude determination instrument coordinate system is then superimposed with the positioning and attitude determination instrument pitch angle to obtain the target's true pitch angle in the geodetic coordinate system. Combined with the target distance detected by radar, the target's true longitude, latitude, and altitude in the geodetic coordinate system are calculated.

6. The radar calibration method for a UAV based on a positioning and attitude determination device and GPS positioning as described in claim 5, characterized in that, The pitch angle of the positioning and attitude locator corresponding to the current target's relative azimuth angle is calculated using the following formula: Calculate; where, Let A be the pitch angle of the positioning and attitude determination device, and let A and B be the coefficients of the current plane equation Ax + By = 0 of the positioning and attitude determination device. The relative azimuth of the current target. Let azimuth angle of the current target in the radar coordinate system be the output of the radar to be calibrated. The heading angle of the self in the geodetic coordinate system as measured by the positioning and attitude determination instrument.

7. The radar calibration method for a UAV based on a positioning and attitude determination device and GPS positioning as described in claim 1, characterized in that, Invalid data is removed and filtered from the collected GPS positioning data, radar detection data, and positioning and attitude determination instrument pose data.

8. A radar calibration method for a UAV based on a positioning and attitude determination device and GPS positioning as described in claim 7, characterized in that, Methods for invalid data removal and filtering include: Based on the positioning status of the positioning and attitude determination device, invalid pose data during periods of satellite signal loss are filtered out; Based on the status bits of the drone's GPS positioning module, invalid positioning data is filtered out. For the detection data of the radar to be calibrated under each calibration path, filtering and error calculation are performed respectively to determine the effective error threshold of the radar data under the corresponding calibration path, and invalid detection data exceeding the effective error threshold are filtered out.

9. A radar calibration method for a UAV based on a positioning and attitude determination device and GPS positioning as described in claim 1, characterized in that, Also includes: Time interpolation is performed on the UAV's GPS positioning data and radar detection data to align their timestamps.

10. A radar calibration system for a UAV based on a positioning and attitude determination device and GPS positioning, characterized in that, This includes a positioning and attitude determination device, a drone equipped with a GPS positioning module, and a data processing unit; The positioning and attitude determination device is rigidly fixed to the base of the radar to be calibrated and is used to collect the real-time position and attitude data of the radar to be calibrated; the UAV is used to fly along a preset calibration path and collect its own GPS positioning data; the radar to be calibrated collects detection data of the UAV during the flight of the UAV; the data processing unit is communicatively connected to the radar to be calibrated, the positioning and attitude determination device, and the UAV, and is used to execute the radar calibration method based on the positioning and attitude determination device and GPS positioning of the UAV as described in any one of claims 1 to 9.

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