Outdoor field large depression angle measurement method and system

Abstract

The present invention discloses a method and system for outdoor field large-angle measurement. The method comprises the following steps: S1. determining the position of a target to be measured, setting up a calibration ball and a positioning ball, determining the flight altitude of a drone, and setting a scanning path; S2. establishing a coordinate relationship between the calibration ball, the positioning ball, and the drone; S3. testing the calibration ball and the positioning ball in different orientations to obtain frequency domain data of a frequency-sweep echo at different orientations; S4. removing the calibration ball and setting up the target to be measured at the calibration ball's location; S5. testing the positioning ball and the target to be measured in different orientations to obtain frequency domain data of a frequency-sweep echo at different orientations; and S6. phase-compensating the measurement data using theoretical values of different distances from the positioning ball to a radar on the measurement path to obtain two-dimensional imaging data and RCS results of the target to be measured. The present invention is suitable for outdoor field measurement and can diagnose target scattering characteristics at large depression angles in complex environments such as land and sea, meet flexible deployment requirements, and reduce testing costs.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic scattering measurement and relates to an outdoor field large depression angle measurement method and system. Background Art

[0002] Electromagnetic scattering measurements primarily measure the radar cross section (RCS) of a target. Currently, RCS measurements are primarily categorized into far-field and near-field methods. Far-field measurement methods include indoor compressed-field measurement, outdoor static far-field measurement, and outdoor dynamic far-field measurement. Far-field measurement methods primarily involve illuminating the target with a plane wave, allowing the target's RCS to be directly measured using a measuring radar. While far-field measurements are more accurate, the plane wave implementation process is often complex, resulting in high construction and testing costs. Near-field measurement methods include indoor and outdoor near-field static measurements. Near-field measurement methods primarily involve setting up a simple measurement system within a relatively small test site to quickly acquire near-field scattering data from the target at different angles. RCS is then determined using a near-field to far-field transformation algorithm. For complex targets, near-field measurements may produce larger errors than far-field measurements, but they are less expensive, require a smaller site, and can be used to determine target scattering characteristics in certain application scenarios.

[0003] Currently, there are numerous test sites for measuring targets at low elevation angles, and the technology is mature. However, test sites for measuring targets at high elevation angles are rare. Currently available high-elevation-angle test sites employ large curved tracks constructed on the ground, onto which a measurement radar is mounted. An azimuth turntable is also installed at the center of the curved track to measure the target's near-field scattering characteristics at high elevation angles. As the target size increases, the curved track may require a larger size. However, these test sites are expensive to construct and lack flexibility in their transitions.

[0004] Therefore, in order to adapt to scattering measurements of different sizes, reduce the construction cost of measuring the scattering characteristics of targets at large depression angles, and have the flexibility of test transitions, it has become an urgent problem that the existing technology needs to solve. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide an outdoor field large depression angle measurement method and system, which can adapt to scattering measurements of different sizes, reduce the construction cost of large depression angle measurement target scattering characteristics, and have test transition flexibility.

[0006] The object of the present invention is to achieve the following technical solution: a method for measuring a large depression angle in an outdoor field, comprising the following steps:

[0007] S1. Determine the target's location within the test site, set up a calibration sphere and a positioning sphere, use the calibration sphere as the target, determine the drone's flight altitude, and set the scanning path.

[0008] S2. Using the calibration ball as the target, establish the coordinate relationship between the calibration ball, the positioning ball, and the UAV;

[0009] S3. Using the calibration sphere as the target, the test equipment is mounted on the drone. The test acquisition mode is triggered at equal intervals along the pre-set scanning path to simultaneously scan the calibration sphere and the positioning sphere. This allows for testing of the calibration sphere and positioning sphere in different orientations, acquiring frequency domain data of the swept echo at different orientations.

[0010] S4. Remove the calibration ball and set up the target to be measured in the position of the calibration ball, ensuring that the center height of the target to be measured is consistent with the center height of the calibration ball;

[0011] S5. With the target being measured as the target, according to step S3, the positioning ball and the target being measured are scanned and tested to achieve positioning ball and the target being measured in different orientations, and obtain frequency domain data of the swept echo at different orientations;

[0012] S6. Phase compensation is performed on the measurement data using theoretical values of different distances from the positioning ball to the radar on the measurement path, and two-dimensional imaging data and RCS results of the measured target are obtained.

[0013] An outdoor field large depression angle measurement system, comprising: a UAV, a test device, a main control computer, an RTK positioning system and an auxiliary measurement system;

[0014] The test equipment includes a radar system, an antenna system and a test gimbal; the radar system is used to generate a pulse signal for scanning the target and the positioning ball when the test acquisition mode is triggered; the antenna system includes an antenna transmitting unit and an antenna receiving unit; the antenna transmitting unit is used to radiate the signal generated by the radar system to the target and the positioning ball, and the antenna receiving unit is used to receive the echo frequency domain data from the target and the positioning ball; the test gimbal is installed at the bottom of the UAV pod, and is used to carry the antenna system and align the antenna system with the target.

[0015] The auxiliary measurement equipment includes a positioning ball, a calibration ball and a fixed bracket; the fixed bracket is used to fix the positioning ball and the target; the target is the calibration ball or the target to be measured;

[0016] The UAV-mounted test equipment performs a scanning test on the positioning ball and the target according to a pre-set scanning path, obtains the frequency domain data of the sweep echo at different orientations, and transmits it to the main control computer;

[0017] The main control computer is used to establish the coordinate relationship between the calibration sphere, the positioning sphere, and the UAV through the RTK positioning system; perform phase compensation based on the theoretical values of different distances from the positioning sphere to the radar on the measurement path, and obtain two-dimensional imaging data and RCS results of the measured target.

[0018] The measurement system also includes a ground absorbing system and a communication system;

[0019] The ground absorbing system is composed of pyramidal absorbing materials and is laid flat on the ground to reduce coupling between the target being measured and the ground and electromagnetic wave multipath;

[0020] The communication system includes an airborne communication device mounted on a UAV and connected to the test equipment, and a ground communication device connected to a main control computer. Signal transmission between the test equipment and the main control computer is achieved through the airborne communication device and the ground communication device.

[0021] The beneficial effects of the present invention are: using a drone-mounted measurement radar to achieve large-angle alignment of the target, greatly reducing the cost of the test system; solving the problem of difficult site transfer of existing measurement systems, enhancing adaptability to the site, and the system has flexible construction and deployment characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Axis view layout diagram for the test scene;

[0023] Figure 2 This is the position relationship diagram of each unit when the test target is closest to the radar;

[0024] Figure 3 This is the relationship diagram between the measurement radar and the positioning ball when looking right;

[0025] Figure 4 is a flow chart of the method of the present invention;

[0026] Figure 5 Two-dimensional imaging after introducing positioning error for the UAV;

[0027] Figure 6 This is two-dimensional imaging after the drone position is corrected. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0029] like Figure 1 As shown, Figure 1 To test the scene axis view, the three-dimensional positional relationship between the measurement system, the target, and the positioning ball is characterized;

[0030] like Figure 4 As shown, a method for outdoor field large depression angle measurement includes the following steps:

[0031] S1. Determine the target's location within the test site, set up a calibration sphere and a positioning sphere, use the calibration sphere as the target, determine the drone's flight altitude, and set the scanning path.

[0032] Select a test site, design the target and locator placement, the drone's flight altitude, and the scanning path. Set up the locator and locator. The distance between the target and locator should be 2-3 times the maximum size of the target being measured. The locator should be placed close to the target, at a height of 1 / 2 to 3 / 4 the target's center height above the ground. The drone's flight altitude depends on the radar's relative pitch angle to the target and the horizontal distance between the drone and the target's center.

[0033] S2. Using the calibration ball as a target, establish a coordinate relationship between the calibration ball, the positioning ball, and the drone; Step S2 includes: using the RTK positioning system, with the ground projection of the drone trajectory as the Y axis, the X axis perpendicular to the Y axis and intersecting the center of the ground projection trajectory on the ground as the X axis, and the Z axis perpendicular to the ground and connecting the XY focal points as the Z axis, with the intersection point as O, to establish a three-dimensional rectangular coordinate system;

[0034] Take the calibration sphere as the target and obtain the height H of the drone above the ground, the height h1 of the positioning sphere, the height h2 of the target, the pitch angle theta of the test equipment illuminating the target, the distance R0 from the drone projection to the target center when the target and the test equipment are closest, the length L2 of the test path, and the distance L from the target center to the center of the positioning sphere.

[0035] according to Figure 2 Perform parametric design of site layout:

[0036] UAV height: H = 13m;

[0037] When the test target is closest to the radar, the distance between the drone projection and the target center is: R0 = 10m;

[0038] The distance from the center of the measured target to the center of the positioning ball: L = 3m;

[0039] Antenna irradiation target depression angle: theta = 45°;

[0040] Height of set piece: h1 = 1.5m;

[0041] Calibration ball height: h2 = 3m;

[0042] When the test target is closest to the radar, the distance from the drone projection to the center of the positioning ball is: R1 = R0-L;

[0043] according to Figure 3 Perform parametric design of site layout:

[0044] Test path length: L2 = 6m;

[0045] ΔL is the UAV movement distance, which is fed back by the UAV positioning system;

[0046] The distance between the drone and the center of the positioning ball when the test target is closest to the radar:

[0047] During the test, the distance from the radar to the center of the positioning ball was measured:

[0048] S3. Using the calibration sphere as the target, the test equipment is mounted on the drone. The test acquisition mode is triggered at equal intervals along the pre-set scanning path to simultaneously scan the calibration sphere and the positioning sphere. This allows for testing of the calibration sphere and positioning sphere in different orientations, acquiring frequency domain data of the swept echo at different orientations.

[0049] The test equipment includes a radar system, an antenna feed system and a test pan-tilt platform;

[0050] The radar system is used to generate a pulse signal for scanning the target and the positioning ball when triggering the test acquisition mode;

[0051] The antenna feed system comprises an antenna transmitting unit and an antenna receiving unit; the antenna transmitting unit is used to radiate the signal generated by the radar system toward the target and the positioning sphere, and the antenna receiving unit is used to receive the echo frequency domain data from the target and the positioning sphere; the depression angle theta of the calibration sphere illuminated by the test equipment refers to the angle between the line connecting the center of the antenna feed system and the center of the target and the horizontal plane; the target being closest to the test equipment means that the target is closest to the center of the antenna feed system;

[0052] The test gimbal is installed at the bottom of the UAV pod and is used to carry the antenna feed system and align the antenna feed system with the target.

[0053] The step S3 comprises:

[0054] S301. During each test, the azimuth angle of the current test is calculated according to the azimuth angle calculation formula:

[0055] phi=arctan((L2 / 2-ΔL) / R0)

[0056] Where L2 is the scanning path length; R0 is the distance between the UAV projection and the target center when the calibration sphere is closest to the radar; ΔL is the UAV movement distance, which gradually increases in equal intervals.

[0057] S302. During each test, the test equipment will send a pulse signal with a frequency sequence of f1, f1+Δf,..., f1+n*Δf, and at these frequencies, receive the swept frequency echo frequency domain data after the pulse signal is irradiated on the positioning ball and the calibration ball, and save it together with the azimuth angle of the test, that is, the swept frequency echo frequency domain data at different azimuths is obtained.

[0058] S4. Remove the calibration ball and set up the target to be measured in the position of the calibration ball, ensuring that the center height of the target to be measured is consistent with the center height of the calibration ball;

[0059] S5. With the target being measured as the target, according to step S3, the positioning ball and the target being measured are scanned and tested to achieve positioning ball and the target being measured in different orientations, and obtain frequency domain data of the swept echo at different orientations;

[0060] S6. Perform phase compensation on the measurement data by using theoretical values of different distances from the positioning ball to the radar on the measurement path, and obtain two-dimensional imaging data and RCS results of the measured target.

[0061] Taking into account factors such as the overall jitter of the drone or inaccurate RTK positioning during the test, after obtaining all the measurement data, phase compensation is performed on the calibration body measurement data and the target measurement data using the theoretical values of different distances from the positioning ball to the radar on the measurement path;

[0062] The step S6 comprises:

[0063] S601. Perform inverse Fourier transform on the measured data to obtain a one-dimensional range image of the positioning ball, and find the actual distance R from the positioning ball to the measurement radar on the one-dimensional range image. 实 ;

[0064] S602. Calculate the theoretical distance between the positioning ball and the measurement radar at different orientations Where L2 is the test path length; ΔL is the UAV movement distance; H is the UAV height; h1 is the positioning ball height; R1 is the distance from the UAV projection to the positioning ball center when the target is closest to the radar;

[0065] S603. Calculate the difference between the actual distance of the positioning ball and the theoretical distance ΔL=R 实 -R 理 , the compensation is performed by multiplying the measured data by the formula exp(4πjΔRf / c) to obtain the compensated data, where j is the imaginary unit, c is the speed of light, π is the circumference of the circle, and f is the frequency sequence;

[0066] S604. When the target is a calibration sphere and a measured target, execute steps S601 to S603 respectively to obtain compensated data:

[0067] When the target is a calibration sphere, the measurement data in steps S601 and S603 adopt the frequency domain data of the swept echo at different orientations obtained in step S3 to obtain compensated data, which is recorded as first compensated data.

[0068] When the target is a measured target, the measurement data in step S601 and step S603 adopt the frequency domain data of the swept frequency echo at different orientations obtained in step S5 to obtain compensated data, which is recorded as second compensated data;

[0069] S604. Perform two-dimensional imaging processing on the second compensated data using any one of the range Doppler imaging algorithm, wavenumber domain imaging algorithm, or convolution back projection imaging algorithm to obtain the distribution of scattering points of the measured target and obtain two-dimensional imaging data of the measured target; obtain the distribution of scattering points of the measured target. The unphase-compensated two-dimensional imaging result is as follows: Figure 5 , the imaging results after phase compensation are as follows Figure 6 ;

[0070] S605. Perform near-field and far-field transformation on the first compensation data and the second compensation data by using a chain relationship or a spherical wave ring scattering algorithm, and obtain the near-field and far-field transformation result of the calibration sphere as FF 测c , the near-field and far-field transformation results of the measured target are FF 测t ; The theoretical RCS obtained by calibration through simulation (or Mie series) is recorded as FF 理c , the RCS result of the measured target FF 真t =FF 测t FF 理c / FF 测c .

[0071] The foregoing description shows and describes a preferred embodiment of the present invention. However, as previously mentioned, it should be understood that the present invention is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Instead, the present invention can be used in various other combinations, modifications, and environments and can be modified within the scope of the inventive concept described herein by the teachings above or by techniques or knowledge in the relevant art. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention are intended to be within the scope of the appended claims.

Claims

1. A method for outdoor field large depression angle measurement, characterized by: The following steps are involved: S1. Determine the target's location within the test site, set up a calibration sphere and a positioning sphere, use the calibration sphere as the target, determine the drone's flight altitude, and set the scanning path. S2. Using the calibration ball as the target, establish the coordinate relationship between the calibration ball, the positioning ball, and the UAV; S3. Using the calibration sphere as the target, the test equipment is mounted on the drone. The test acquisition mode is triggered at equal intervals along the pre-set scanning path to simultaneously scan the calibration sphere and the positioning sphere. This allows for testing of the calibration sphere and positioning sphere in different orientations, acquiring frequency domain data of the swept echo at different orientations. S4. Remove the calibration ball and set up the target to be measured in the position of the calibration ball, ensuring that the center height of the target to be measured is consistent with the center height of the calibration ball; S5. With the target being measured as the target, according to step S3, the positioning ball and the target being measured are scanned and tested to achieve positioning ball and the target being measured in different orientations, and obtain frequency domain data of the swept echo at different orientations; S6. Phase-compensate the measurement data based on theoretical values of different distances from the positioning sphere to the radar along the measurement path, and obtain two-dimensional imaging data and RCS results of the measured target. The step S6 comprises: S601. Perform inverse Fourier transform on the measured data to obtain a one-dimensional range image of the positioning ball, and find the actual distance R from the positioning ball to the measurement radar on the one-dimensional range image. 实 ; S602. Calculate the theoretical distance between the positioning ball and the measurement radar at different orientations , where L2 is the test path length; ΔL is the UAV movement distance; H is the UAV height; h1 is the positioning ball height; R1 is the distance from the UAV projection to the positioning ball center when the target is closest to the radar; S603. Calculate the difference between the actual distance of the positioning ball and the theoretical distance ΔR = R 实 -R 理 , the compensation is performed by multiplying the measured data by the formula exp(4πjΔRf / c) to obtain the compensated data, where j is the imaginary unit, c is the speed of light, π is the circumference of the circle, and f is the frequency sequence; S604. When the target is a calibration sphere and a measured target, execute steps S601 to S603 respectively to obtain compensated data: When the target is a calibration sphere, the measurement data in steps S601 and S603 adopt the frequency domain data of the swept echo at different orientations obtained in step S3 to obtain compensated data, which is recorded as first compensated data. When the target is a measured target, the measurement data in step S601 and step S603 adopt the frequency domain data of the swept frequency echo at different orientations obtained in step S5 to obtain compensated data, which is recorded as second compensated data; S604. Perform two-dimensional imaging processing on the second compensation data to obtain two-dimensional imaging data of the measured target; S605. Perform near-field and far-field transformation on the first compensation data and the second compensation data to obtain the near-field and far-field transformation result of the calibration sphere as FF 测c The near-field and far-field transformation results of the measured target are FF 测t ; The theoretical RCS of the calibration sphere obtained through simulation is recorded as FF 理c , the RCS result of the measured target FF 真t =FF 测t FF 理c / FF 测c .

2. The outdoor field large depression angle measurement method according to claim 1, characterized in that: In step S1, a calibration ball is set at the position of the target to be measured, and the calibration ball is used as the target; The distance between the target and the positioning ball should be 2 to 3 times the maximum size of the target being measured; the positioning ball should be placed at a height of 1 / 2 to 3 / 4 of the height of the target center from the ground; The flight altitude H of the UAV depends on the pitch angle of the target illuminated by the test equipment and the horizontal distance R0 between the UAV and the center of the target, where H = R0tan(theta).

3. The outdoor field large depression angle measurement method according to claim 1, characterized in that: The step S2 comprises: establishing a three-dimensional rectangular coordinate system by using an RTK positioning system, with the ground projection of the drone trajectory as the Y axis, the X axis perpendicular to the Y axis and intersecting the center of the ground projection trajectory on the ground as the X axis, and the Z axis perpendicular to the ground and connecting the XY focal points as the Z axis, with the intersection point as O; Take the calibration sphere as the target and obtain the height H of the drone above the ground, the height h1 of the positioning sphere, the height h2 of the target, the pitch angle theta of the test equipment illuminating the target, the distance R0 from the drone projection to the target center when the target and the test equipment are closest, the length L2 of the test path, and the distance L from the target center to the center of the positioning sphere.

4. The outdoor field large depression angle measurement method according to claim 3, characterized in that: The test equipment includes a radar system, an antenna feed system and a test pan-tilt platform; The radar system is used to generate a pulse signal for scanning the target and the positioning ball when triggering the test acquisition mode; The antenna feed system includes an antenna transmitting unit and an antenna receiving unit; The antenna transmitting unit is used to radiate the signal generated by the radar system toward the target and the positioning sphere, and the antenna receiving unit is used to receive the echo frequency domain data from the target and the positioning sphere; the depression angle theta of the calibration sphere illuminated by the test equipment refers to the angle between the line connecting the center of the antenna feed system and the center of the target and the horizontal plane; the target being closest to the test equipment means that the target is closest to the center of the antenna feed system; The test gimbal is installed at the bottom of the UAV pod and is used to carry the antenna feed system and align the antenna feed system with the target.

5. The outdoor field large depression angle measurement method according to claim 1, characterized in that: In step S3, the calibration ball is used as the target, and the test equipment mounted on the drone follows a pre-set trajectory and triggers the test acquisition mode to scan the calibration ball and the positioning ball at equal intervals, so as to achieve different orientation tests of the calibration ball and the positioning ball. The frequency domain data of the frequency sweep echo at different orientations includes: S301. During each test, the azimuth angle of the current test is calculated according to the azimuth angle calculation formula: phi=arctan((L2 / 2-ΔL) / R0) Where L2 is the scanning path length; R0 is the distance between the UAV projection and the target center when the calibration sphere is closest to the radar; ΔL is the UAV movement distance, which gradually increases in equal intervals. S302. During each test, the test equipment will send a pulse signal with a frequency sequence of f1, f1+Δf,..., f1+n*Δf, and at these frequencies, receive the swept frequency echo frequency domain data after the pulse signal is irradiated on the positioning ball and the calibration ball, and save it together with the azimuth angle of the test, that is, the swept frequency echo frequency domain data at different azimuths is obtained.

6. The outdoor field large depression angle measurement method according to claim 5, characterized in that: The method of two-dimensional imaging data includes any one of a range Doppler imaging algorithm, a wavenumber domain imaging algorithm or a convolution back projection imaging algorithm.

7. The outdoor field large depression angle measurement method according to claim 5, characterized in that: The near-far field transformation process is performed by a chain relationship or a spherical wave ring scattering algorithm.

8. An outdoor field large depression angle measurement system, which uses the method according to any one of claims 1 to 7 for measurement, characterized in that: include: UAV, test equipment, main control computer, RTK positioning system and auxiliary measurement system; the test equipment includes radar system, antenna feed system and test gimbal; The auxiliary measurement system includes a positioning ball, a calibration ball and a fixed bracket; the fixed bracket is used to fix the positioning ball and the target; the target is the calibration ball or the target to be measured; The UAV-mounted test equipment performs a scanning test on the positioning ball and the target according to a pre-set scanning path, obtains the frequency domain data of the sweep echo at different orientations, and transmits it to the main control computer; The main control computer is used to establish the coordinate relationship between the calibration sphere, the positioning sphere, and the UAV through the RTK positioning system; perform phase compensation based on the theoretical values of different distances from the positioning sphere to the radar on the measurement path, and obtain two-dimensional imaging data and RCS results of the measured target.

9. The outdoor large depression angle measurement system according to claim 8, characterized in that: The measurement system also includes a ground absorbing system and a communication system; The ground absorbing system is composed of pyramidal absorbing materials and is laid flat on the ground to reduce coupling between the target being measured and the ground and electromagnetic wave multipath; The communication system includes an airborne communication device mounted on a UAV and connected to the test equipment, and a ground communication device connected to a main control computer. Signal transmission between the test equipment and the main control computer is achieved through the airborne communication device and the ground communication device.

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