Method and system for measuring large depression angle of outdoor field

Abstract

The invention discloses an outdoor field large depression angle measurement method and system, and the method comprises the steps: S1, determining the position of a measured target, erecting a calibration ball and a positioning ball, determining the flight height of an unmanned plane, and setting a scanning path; s2, establishing a coordinate relationship among the calibration ball, the positioning ball and the unmanned aerial vehicle; s3, testing the calibration ball and the positioning ball in different directions, and acquiring frequency sweeping echo frequency domain data in different directions; s4, removing the calibration ball, and erecting a measured target at the position of the calibration ball; s5, testing the positioning ball and the tested target in different orientations, and acquiring frequency-sweeping echo frequency domain data in different orientations; and S6, performing phase compensation on the measurement data through theoretical values of different distances from the positioning ball to the radar on the measurement path, and obtaining two-dimensional imaging data and an RCS result of the measured target. The method is suitable for outdoor field measurement, target scattering characteristic diagnosis under complex environments such as large depression angle ground and sea can be realized, flexible deployment requirements can be realized, and the test cost is reduced.

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 measurement mainly measures the radar cross section (RCS) of the target. Currently, the measurement of RCS is mainly divided into far-field measurement method and near-field measurement method. The implementation of the far-field measurement method includes indoor compact field measurement, outdoor static far-field measurement and outdoor far-field dynamic measurement. The implementation method of the far-field measurement method is mainly to illuminate the target with a plane wave, and the target RCS can be directly measured by the measuring radar. The measurement results of the far-field method are more accurate, but the implementation process of the plane wave is often relatively complex, and the construction and testing costs are high. The implementation of the near-field measurement method includes indoor and outdoor near-field static measurement. The near-field measurement method mainly builds a simple measurement system in a relatively small test site, quickly obtains the near-field scattering data of the target in different angular domains, and then obtains the RCS through the near-far-field transformation algorithm. For complex targets, the measurement results of the near-field method have larger errors than the far-field method, but the construction cost is low, the required site is small, and the target scattering characteristics can be determined in certain application scenarios.

[0003] At present, there are many test sites for small pitch angles of targets, and the technology is very mature, but there are few test sites for large pitch angles of targets. The large pitch angle test sites that can be seen at present are to build a large arc track on the ground, and then install the measurement radar on the arc track, and install an azimuth turntable in the center of the arc track to achieve the large pitch angle near-field scattering characteristics of the target. As the size of the target to be measured increases, the size of the arc track may be larger. At the same time, the construction cost of this test site is high, and the flexibility of the transition is poor.

[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 prior art 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. In the test site, determine the position of the target to be measured, set up the calibration ball and positioning ball, use the calibration ball as the target, then determine the flight altitude of the drone and set the scanning path;

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

[0009] S3. The calibration ball is used as the target, and the test equipment is mounted on the drone. According to the pre-set scanning path, the calibration ball and the positioning ball are scanned and tested at the same time at equal intervals. The calibration ball and the positioning ball are tested in different directions, and the frequency domain data of the swept frequency echo at different directions are obtained;

[0010] S4. Remove the calibration ball, and set up the target to be measured at the location 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 to be measured as the target, according to step S3, the positioning ball and the target to be measured are scanned and tested to achieve different orientation tests of the positioning ball and the target to be measured, and the frequency domain data of the swept frequency echo at different orientations are obtained;

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

[0013] An outdoor field large depression angle measurement system, comprising: a drone, 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 a target and a positioning ball when triggering a test acquisition mode; 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 echo frequency domain data from the target and the positioning ball; the test gimbal is installed at the bottom of the drone 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 scanning tests on the positioning ball and the target according to a pre-set scanning path, obtains frequency domain data of the frequency sweep echo at different orientations, and transmits the data to the main control computer;

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

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

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

[0020] The communication system includes an airborne communication device mounted on a drone and connected to the test device, and a ground communication device connected to a main control computer. Signal transmission between the test device 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: a method of mounting a measurement radar on an unmanned aerial vehicle is used to achieve large depression angle alignment of the target, which greatly reduces the cost of the test system; the problem of difficulty in transition of the existing measurement system is solved, the adaptability to the site is enhanced, 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 is further described in detail below in conjunction with 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. In the test site, determine the position of the target to be measured, set up the calibration ball and positioning ball, use the calibration ball as the target, then determine the flight altitude of the drone and set the scanning path;

[0032] Select the test site, design the target and positioning ball placement, the UAV flight altitude, the scanning path, and set up the reference ball and positioning ball. The distance between the target and the positioning ball is 2 to 3 times the maximum size of the target to be measured. The positioning ball is designed to be placed closer to the target, and the positioning ball is placed at a height of 1 / 2 to 3 / 4 of the height of the target center from the ground; the UAV flight altitude depends on the radar relative to the target depression angle and the horizontal distance between the UAV and the target center.

[0033] S2. Take the calibration ball as the target and establish the coordinate relationship between the calibration ball, the positioning ball and the drone; the step S2 comprises: 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 ball as the target, and obtain the height H between the drone and the ground, the height h1 of the positioning ball, the height h2 of the target, the pitch angle theta of the test equipment irradiating the target, the distance R0 from the drone projection to the target center when the target is closest to the test equipment, the length L2 of the test path, and the distance L from the target center to the positioning ball center in this coordinate system.

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

[0036] Drone height: H = 13m;

[0037] When the test target is closest to the radar, the distance from the drone projection to 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 ball: 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 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 from the drone to 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. The calibration ball is used as the target, and the test equipment is mounted on the drone. According to the pre-set scanning path, the calibration ball and the positioning ball are scanned and tested at the same time at equal intervals. The calibration ball and the positioning ball are tested in different directions, and the frequency domain data of the swept frequency echo at different directions are obtained;

[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 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 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 equipment illuminates the calibration ball depression angle theta, which refers to the angle between the line connecting the center of the antenna system and the center of the target and the horizontal plane; the target is closest to the test equipment, which means that the target is closest to the center of the antenna system;

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

[0053] The step S3 comprises:

[0054] S301. In 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 from the drone projection to the target center when the calibration sphere is closest to the radar; ΔL is the movement distance of the drone, 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 irradiates the positioning ball and the calibration ball, and save it together with the azimuth of the test, thus obtaining the swept frequency echo frequency domain data at different azimuths.

[0058] S4. Remove the calibration ball, and set up the target to be measured at the location 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 to be measured as the target, according to step S3, the positioning ball and the target to be measured are scanned and tested to achieve different orientation tests of the positioning ball and the target to be measured, and the frequency domain data of the swept frequency echo at different orientations are obtained;

[0060] S6. By using the theoretical values ​​of different distances from the positioning ball to the radar on the measurement path, phase compensation is performed on the measurement data, and the two-dimensional imaging data and RCS results of the measured target are obtained.

[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, the phase compensation of the calibration body measurement data and the target measurement data is performed through 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 measuring radar on the one-dimensional range image. 实 ;

[0064] S602. Calculate the theoretical distance between the positioning ball and the measuring radar at different orientations Among them, L2 is the length of the test path; ΔL is the movement distance of the UAV; H is the height of the UAV; h1 is the height of the positioning ball; R1 is the distance from the UAV projection to the center of the positioning ball 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 a circle, and f is the frequency sequence;

[0066] S604. When the target is a calibration ball 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 step S601 and step S603 adopt the frequency domain data of the swept frequency echo at different orientations obtained in step S3 to obtain compensated data, which is recorded as the 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 by using any one of the range Doppler imaging algorithm, the wavenumber domain imaging algorithm or the convolution back projection imaging algorithm to obtain the distribution of scattering points of the measured target and obtain the two-dimensional imaging data of the measured target; obtain the distribution of scattering points of the measured target. The two-dimensional imaging result without phase compensation is as follows: Figure 5 , the imaging result after phase compensation is as follows Figure 6 ;

[0070] S605. Perform near-field and far-field transformation processing on the first compensation data and the second compensation data through 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 is FF 真t =FF 测t FF 理c / FF 测c .

[0071] The above description shows and describes a preferred embodiment of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for measuring large depression angles in an outdoor field, characterized in that: The following steps are involved: S1. In the test site, determine the position of the target to be measured, set up the calibration ball and positioning ball, use the calibration ball as the target, then determine the flight altitude of the drone and set the scanning path; S2. Take the calibration ball as the target and establish the coordinate relationship between the calibration ball, the positioning ball and the UAV; S3. The calibration ball is used as the target, and the test equipment is mounted on the drone. According to the pre-set scanning path, the calibration ball and the positioning ball are scanned and tested at the same time at equal intervals. The calibration ball and the positioning ball are tested in different directions, and the frequency domain data of the swept frequency echo at different directions are obtained; S4. Remove the calibration ball, and set up the target to be measured at the location 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 to be measured as the target, according to step S3, the positioning ball and the target to be measured are scanned and tested to achieve different orientation tests of the positioning ball and the target to be measured, and the frequency domain data of the swept frequency echo at different orientations are obtained; S6. By using the theoretical values ​​of different distances from the positioning ball to the radar on the measurement path, phase compensation is performed on the measurement data, and the two-dimensional imaging data and RCS results of the measured target are obtained.

2. The outdoor large depression angle measurement method according to claim 1, characterized in that: In the 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 is 2 to 3 times the maximum size of the target to be measured; the positioning ball is placed at a height of 1 / 2 to 3 / 4 of the height of the target center from the ground; The flying height 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 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 track as the Y axis, the X axis perpendicular to the Y axis and intersecting the center of the ground projection track 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 ball as the target, and obtain the height H between the drone and the ground, the height h1 of the positioning ball, the height h2 of the target, the pitch angle theta of the test equipment irradiating the target, the distance R0 from the drone projection to the target center when the target is closest to the test equipment, the length L2 of the test path, and the distance L from the target center to the positioning ball center in this coordinate system.

4. The outdoor large depression angle measurement method according to claim 3 is 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 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 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 equipment illuminates the calibration ball with a depression angle theta, which 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 is closest to the test equipment, which means that the target is closest to the center of the antenna feed system; The test gimbal is installed at the bottom of the drone pod and is used to carry the antenna system and align the antenna system with the target.

5. The outdoor field large depression angle measurement method according to claim 1 is characterized in that: In step S3, the calibration ball is used as the target, and the test equipment mounted on the drone follows the preset trajectory and triggers the test acquisition mode to scan the calibration ball and the positioning ball at equal intervals to test the calibration ball and the positioning ball in different directions. The frequency domain data of the frequency sweep echo at different directions includes: S301. In 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 from the drone projection to the target center when the calibration sphere is closest to the radar; ΔL is the movement distance of the drone, 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 irradiates the positioning ball and the calibration ball, and save it together with the azimuth of the test, thus obtaining the swept frequency echo frequency domain data at different azimuths.

6. The outdoor field large depression angle measurement method according to claim 1, characterized in that: 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 measuring radar on the one-dimensional range image. 实 ; S602. Calculate the theoretical distance between the positioning ball and the measuring radar at different orientations Among them, L2 is the length of the test path; ΔL is the movement distance of the UAV; H is the height of the UAV; h1 is the height of the positioning ball; R1 is the distance from the UAV projection to the center of the positioning ball when the target is closest to the radar; 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 a circle, and f is the frequency sequence; S604. When the target is a calibration ball 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 step S601 and step S603 adopt the frequency domain data of the swept frequency echo at different orientations obtained in step S3 to obtain compensated data, which is recorded as the 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 processing on the first compensation data and the second compensation data, 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 result of the measured target is FF 测t ; The theoretical RCS obtained by simulation and calibration is recorded as FF 理c , the RCS result of the measured target is FF 真t =FF 测t FF 理c / FF 测c .

7. The outdoor field large depression angle measurement method according to claim 6 is 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.

8. The outdoor field large depression angle measurement method according to claim 6 is characterized in that: The near-field to far-field transformation process is performed by a chain relationship or a spherical wave ring scattering algorithm.

9. An outdoor field large depression angle measurement system, using the method described in any one of claims 1 to 8 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 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; The UAV mounted test equipment performs scanning tests on the positioning ball and the target according to a pre-set scanning path, obtains frequency domain data of the frequency sweep echo at different orientations, and transmits the data to the main control computer; The main control computer is used to establish the coordinate relationship between the calibration ball, the positioning ball, and the UAV through the RTK positioning system; and to perform phase compensation through theoretical values ​​of different distances from the positioning ball to the radar on the measurement path, and to obtain two-dimensional imaging data and RCS results of the measured target.

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

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