A method for acquiring electromagnetic scattering characteristics of a ship target by using an unmanned airborne radar

Abstract

The present application relates to a method for obtaining electromagnetic scattering characteristics of a ship target, and particularly relates to a method for obtaining electromagnetic scattering characteristics of a ship target by using an unmanned aerial vehicle radar, which solves the technical problem that the existing method for obtaining electromagnetic scattering characteristics of a ship target has a large error or is difficult to test electromagnetic scattering characteristics of a ship target at a large pitch angle. The present application can directly test electromagnetic scattering characteristics of a ship target by using an unmanned aerial vehicle radar system, improve the accuracy of the test result, and test electromagnetic scattering characteristics of a ship target at a large pitch angle. The signal-to-noise ratio of the echo of a calibration body is effectively improved by outdoor ground calibration of the calibration body, and the accuracy of the test result of the electromagnetic scattering characteristics of the ship target is further improved.

Description

Technical Field

[0001] This invention relates to a method for obtaining the electromagnetic scattering characteristics of ship targets, specifically a method for obtaining the electromagnetic scattering characteristics of ship targets using an unmanned aerial vehicle (UAV)-borne radar. Background Technology

[0002] Chinese patent CN101526611A discloses a method for detecting the radar cross section of ships. This method is based on graphic electromagnetic computation (GRECO) technology to calculate the radar cross section (RCS) distribution of ships. By modeling the ship and using the scattering equation of physical optics, combined with the graphic electromagnetic computation method of the graphics hardware interface (OpenGL) technology and its hidden line removal technology, the ship model is calculated to achieve the purpose of calculating the ship's radar cross section.

[0003] Although electromagnetic simulation methods can be used to calculate the scattering cross-section of ship targets, the results obtained by these methods have large errors, and the accuracy of the calculations still needs to be verified. At the same time, traditional scattering cross-section measurement methods, such as using scaled-down ship models, are not very accurate and are difficult to use to test the scattering cross-section distribution of ships at large pitch angles. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems that existing methods for obtaining the electromagnetic scattering characteristics of ships have large errors or are difficult to test the electromagnetic scattering characteristics of ships at large pitch angles, and to provide a method for obtaining the electromagnetic scattering characteristics of ship targets using UAV-borne radar.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for acquiring the electromagnetic scattering characteristics of ship targets using UAV-borne radar, characterized by the following steps:

[0007] Step 1: Set up the UAV-borne radar system so that the measurement radar of the UAV-borne radar system can always be aimed at the ship target during the test.

[0008] Step 2: Obtain the real-time position coordinates of the ship target center, and then plan the real-time circular flight trajectory of the UAV with the real-time position coordinates of the ship target center as the center.

[0009] Step 3: The UAV flies according to the real-time circular flight trajectory planned in Step 2. During the flight, the transmitting antenna of the measuring radar transmits test signals to the ship target. The test signals are reflected by the ship target and form target body echo signals, which are received by the receiving antenna of the measuring radar and then sent to the ground station.

[0010] Step 4: Perform outdoor ground calibration using a calibration body to obtain the power spectrum envelope of the calibration body echo signal;

[0011] Step 5: Based on the theoretical scattering cross-section of the calibration body and the power spectrum envelope of the calibration body echo signal obtained in Step 4, the ground station processes the target body echo signal obtained in Step 3 to obtain the electromagnetic scattering characteristics of the ship target.

[0012] Furthermore, step 5 specifically includes:

[0013] 5.1 Perform an inverse Fourier transform on the target body echo signal obtained in step 3 to obtain a one-dimensional image of the target body;

[0014] 5.2 Determine the range of the target area, and use a software distance gate to extract the target area echo from the one-dimensional image of the target body. Perform a Fourier transform on the extracted target area echo to obtain the target area echo in the frequency domain.

[0015] 5.3. Take the square of the modulus of the echo amplitude of the target region in the frequency domain to obtain the power spectrum data of the target body echo signal;

[0016] 5.4 Perform inverse Fourier transform on the power spectrum data of the target body echo signal, and then perform low-pass filtering to obtain the power spectrum envelope of the target body echo signal.

[0017] 5.5. Based on the theoretical scattering cross-section of the calibration body, the power spectrum envelope of the calibration body echo signal obtained in step 4, and the power spectrum envelope of the target body echo signal obtained in step 5.4, calculate the electromagnetic scattering cross-section of the ship target and obtain the electromagnetic scattering characteristics of the ship target.

[0018] Furthermore, in step 5.5, if the test distance of the target ship is the same as the test distance of the calibration object, the electromagnetic scattering cross-section of the ship target is calculated using the following formula:

[0019]

[0020] Where σ is the electromagnetic scattering cross-section of the ship target, σ0 is the theoretical scattering cross-section of the calibration object, P0 is the power spectral envelope of the calibration object's echo signal, and P T The power spectral envelope of the target body echo signal.

[0021] Furthermore, in step 5.5, if the test distance of the ship target differs from the test distance of the calibration target, it also includes:

[0022] The calibration body echo is compensated based on the test distance of the ship target to eliminate the distance error of the calibration body echo signal.

[0023] Further, in step 5.5, the electromagnetic scattering cross-section of the ship target is calculated using the following formula:

[0024]

[0025] Where σ is the electromagnetic scattering cross-section of the ship target, σ0 is the theoretical scattering cross-section of the calibration object, P0 is the power spectral envelope of the calibration object's echo signal, and P T R represents the power spectral envelope of the target body's echo signal. T R0 represents the test distance for the ship target, and R0 represents the test distance for the calibration object.

[0026] Furthermore, in step 4, the calibration body is a trihedral reflector.

[0027] Furthermore, step 4 specifically includes:

[0028] 4.1 Place the trihedral reflector horizontally and determine its horizontal orientation;

[0029] 4.2. Based on the trihedral reflector horizontal orientation obtained in step 4.1, plan the calibration circular trajectory of the UAV perpendicular to the ground;

[0030] 4.3 The UAV flies along a calibration circular trajectory perpendicular to the ground. During the flight, the pitch angle of the UAV relative to the trihedral reflector is adjusted. The transmitting antenna of the measuring radar transmits a test signal to the trihedral reflector. The test signal is reflected by the trihedral reflector, received by the receiving antenna of the measured radar, and sent to the ground station for processing. The distribution of the reflected power of the trihedral reflector as a function of the test pitch angle is obtained, and the UAV altitude and pitch angle corresponding to the peak reflected power of the trihedral reflector are recorded.

[0031] 4.4 Based on the distribution of the reflected power of the trihedral reflector with the test pitch angle obtained in step 4.3 and the UAV altitude and pitch angle corresponding to the peak reflected power, plan the calibration circular trajectory of the UAV parallel to the ground at the set distance.

[0032] 4.5 The UAV flies along a calibration circular trajectory parallel to the ground, performing a circular scan of the trihedral reflector. During the flight, the transmitting antenna of the measuring radar transmits a test signal to the trihedral reflector. The test signal is reflected by the trihedral reflector to form a calibration body echo signal, which is then received by the receiving antenna of the measuring radar and sent to the ground station for processing. The peak reflected power of the trihedral reflector in the calibration body echo signal is taken as the calibration data, and the power spectrum envelope of the calibration body echo signal is calculated.

[0033] Furthermore, in step 1, the UAV-borne radar system includes a UAV platform, a measurement radar, an optoelectronic camera, a gimbal, and a data transmission device;

[0034] The measuring radar and photoelectric camera are mounted on a pan-tilt unit, and their relative positions are fixed and they point in the same direction.

[0035] The gimbal is mounted on the UAV platform and is used to adjust the orientation of the measuring radar and photoelectric camera so that the measuring radar is always pointed at the target.

[0036] The data transmission device is installed on the UAV platform and is connected to the UAV platform, gimbal, measurement radar, and photoelectric camera respectively.

[0037] The photoelectric camera is used to capture images of the target and transmit them back to the ground station via a data transmission device, thereby adjusting the attitude of the gimbal.

[0038] The measurement radar is used to transmit test signals, then receive target echo signals, and transmit them to the ground station through a data transmission device, thereby obtaining the electromagnetic scattering characteristics of the ship target.

[0039] The data transmission device is used to send images captured by the photoelectric camera and target echo signals received by the measurement radar, as well as to receive UAV platform control signals and gimbal control signals sent by the ground station.

[0040] Furthermore, in step 1, the signal emitted by the measuring radar is a linear frequency modulated signal.

[0041] Compared with the prior art, the present invention has the following beneficial technical effects:

[0042] The present invention provides a method for acquiring the electromagnetic scattering characteristics of ship targets using UAV-borne radar. By utilizing the UAV-borne radar system, the electromagnetic scattering characteristics of ship targets can be directly tested, improving the accuracy of the test results. Furthermore, it can test the electromagnetic scattering characteristics of ship targets at large pitch angles. By performing outdoor ground calibration on the calibration body, the signal-to-noise ratio of the calibration body echo can be effectively improved, further enhancing the accuracy of the test results for the electromagnetic scattering characteristics of ship targets. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the structure of the UAV-borne radar system used in the embodiments of the present invention;

[0044] Figure 2 This is a diagram of the real-time circular flight trajectory of the UAV planned in step 2 of this embodiment of the invention;

[0045] Figure 3 This is a schematic diagram illustrating the error between the observed actual flight trajectory of the UAV and the real-time circular flight trajectory of the UAV planned in step 2 in this embodiment of the invention.

[0046] Figure 4The waveform of the calibration body echo signal obtained in step 4 of this embodiment of the invention is shown.

[0047] Figure 5 This is a comparison chart of the calibration results in step 4 of this embodiment and the indoor standard values;

[0048] Figure 6 This is a graph showing the distribution of electromagnetic scattering characteristics of the ship target obtained in step 5 of this embodiment of the invention.

[0049] The annotations in the attached figures are explained as follows:

[0050] 1-Unmanned aerial vehicle platform, 2-Measurement radar, 3-Electro-optical camera, 4-Gimbal, 5-Data transmission device, 6-Ground station, 7-Ship target. Detailed Implementation

[0051] The method for acquiring the electromagnetic scattering characteristics of ship targets using an unmanned aerial vehicle (UAV)-borne radar, as proposed in this invention, will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are merely used to explain the technical principles of this invention and are not intended to limit the scope of protection of this invention.

[0052] A method for acquiring the electromagnetic scattering characteristics of ship targets using UAV-borne radar includes the following steps:

[0053] Step 1, set up as follows Figure 1 The UAV-borne radar system shown includes a UAV platform 1, a measurement radar 2, an electro-optical camera 3, a gimbal 4, and a data transmission device. The measurement radar 2 and the electro-optical camera 3 are mounted on the gimbal 4, and their relative positions are fixed with consistent pointing. The measurement radar 3 transmits a linear frequency modulated (LFM) signal and receives the target echo signal, transmitting it back to the ground station 6 to obtain the target's electromagnetic scattering characteristics. The electro-optical camera 3 captures images of the target and transmits them back to the ground station 6, thereby adjusting the attitude of the gimbal 4. The gimbal 4 is mounted on the UAV platform 1 and is used to adjust the pointing of the measurement radar 2 and the electro-optical camera 3, ensuring that the measurement radar 2 is always pointed at the target. The gimbal 4 is independently controlled. The data transmission device is mounted on the UAV platform 1 and connected to the UAV platform 1, the gimbal 4, the measurement radar 2, and the electro-optical camera 3. The data transmission device transmits images captured by the electro-optical camera 3 and target echo signals received by the measurement radar 2, as well as receiving control signals from the ground station for the UAV platform 1 and the gimbal 4. The signal transmitted by the measurement radar 2 is a LFM signal. The video signal captured by the photoelectric camera 3 is transmitted back in real time. The operator can use this video signal to adjust the azimuth and pitch of the pan-tilt unit 4 to achieve target alignment. The measured data and the video images captured by the camera are transmitted back to the ground station 6 in real time through the data transmission device 5.

[0054] If the transmission signal power of measuring radar 2 is weak, the transmission power is increased by a power amplifier, and a low-noise amplifier is added at the receiver to improve the echo signal-to-noise ratio. Measuring radar 2 and the power amplifier are powered by the power supply on the UAV, continuously transmitting signals during flight. Since the attitude of the UAV may be affected by its flight, a gimbal 4 is used to mount the antenna, ensuring that the antenna beam center remains aligned with the target throughout the test.

[0055] Step 2: Obtain the real-time position coordinates of the center of ship target 7, and then plan the real-time circular flight trajectory of the UAV using the real-time position coordinates of the center of ship target 7 as the center. The real-time circular flight trajectory of the UAV is as follows: Figure 2 As shown, after GPS data was collected from the center of a ship target 7 with a length of 98m and a width of 32m, measurement parameters were set according to an elevation angle of 30°, vertical-vertical polarization, and a test frequency band of 15GHz. Simultaneously, the scattering amplitude of the ship target 7 was ensured to be relatively uniform, and the test was conducted within a 1dB beamwidth (11.7°) of the antenna. A circular flight path was planned from the measurement radar 2 to the center of the ship target 7, with a slant distance of 500m, an altitude of 250m, and a horizontal distance of 433m. The UAV flew at a speed of 8m / s, circling the ship with the bow at 0 degrees, and the antenna of the measurement radar 2 was adjusted via gimbal 4 to always fly towards the center of the ship and record the trajectory.

[0056] Step 3: The UAV flies according to the real-time circular flight trajectory planned in Step 2. During the flight, the transmitting antenna of the measuring radar 2 transmits a linear frequency modulated signal to the ship target 7. The linear frequency modulated signal is reflected by the ship target 7 and forms a target body echo signal, which is received by the receiving antenna of the measuring radar 2 and sent to the ground station 6.

[0057] In this step, the flight control module of UAV platform 1 also simultaneously collects the motion state and coordinate information of the UAV during flight, obtaining the UAV's real-time carrier phase (Real-Time Kinematic, RTK) information, and then sends it to ground station 6 via the RTCM protocol format. Ground station 6 processes the received UAV motion state and coordinate information in real time to obtain the observed value of the UAV's actual flight trajectory. The error between the observed value of the UAV's actual flight trajectory and the UAV's real-time circular flight trajectory planned in step 2 is as follows: Figure 3 As shown.

[0058] Because RCS testing is a high-precision test, it is highly sensitive to information such as the test angle and distance. Therefore, the UAV needs to maintain sufficient positional accuracy during flight. After acquiring the GPS point of the center of the ship target 7, a circular trajectory with a certain radius is planned around this point via a ground station. During flight, the UAV's flight control module encodes its motion state and coordinate information into RTCM protocol format and sends it to ground station 6 via data link. Ground station 6 receives and processes the data from the UAV in real time and controls the UAV accordingly. Simultaneously, it combines the information received by its differential GPS module to process differential observations in real time, achieving high-precision positioning. This is then used to match the angle and position with the target echo signal of ship target 7, ensuring the accuracy of the RCS test and laying the foundation for subsequent RCS reduction of the ship.

[0059] Step 4: Perform outdoor ground calibration using a trihedral reflector to obtain the power envelope of the calibration body echo signal, specifically:

[0060] 4.1 Place the trihedral reflector horizontally and determine its horizontal orientation;

[0061] 4.2. Based on the trihedral reflector horizontal orientation obtained in step 4.1, plan the calibration circular trajectory of the UAV perpendicular to the ground;

[0062] 4.3 The UAV flies along a calibration circular trajectory perpendicular to the ground. During flight, the pitch angle of the UAV relative to the trihedral reflector is adjusted. The transmitting antenna of the measuring radar transmits a linear frequency modulated signal to the trihedral reflector. The linear frequency modulated signal is reflected by the trihedral reflector, received by the receiving antenna of the measured radar, and sent to the ground station for processing. The distribution of the reflected power of the trihedral reflector according to the test pitch angle is obtained, and the UAV altitude and pitch angle corresponding to the peak reflected power of the trihedral reflector are recorded.

[0063] 4.4 Based on the reflection power of the trihedral reflector obtained in step 4.3, and according to the distribution of the test pitch angle change and the UAV altitude and pitch angle corresponding to the peak reflection power, plan the calibration circular trajectory of the UAV parallel to the ground at the set distance.

[0064] 4.5 The UAV flies along a calibration circular trajectory parallel to the ground, performing a circular scan of the trihedral reflector. During flight, the transmitting antenna of the measurement radar transmits a linear frequency modulated (LFM) signal to the trihedral reflector. This LFM signal is reflected by the trihedral reflector, forming a calibration echo signal, which is then received by the receiving antenna of the measurement radar and transmitted to the ground station for processing. The peak reflected power of the trihedral reflector is taken as the calibration data, and the power spectrum envelope and scattering cross-section of the calibration echo signal are calculated. The peak reflected power of the trihedral reflector is its maximum backscattered echo value, and this spatial location is inferred to be its scattering center. Therefore, the reflected power of the trihedral reflector can be used as calibration data for calculation.

[0065] In this embodiment, three trihedral corner reflectors with a side length of 500mm, a 15GHz frequency, and a center RCS value of 28dBsm are placed on the ground at equal intervals of 3m. The trihedral corner reflector located at the center of the array is calibrated at a distance of 80m from the radar to obtain the curve shown below. Figure 4 .from Figure 4 As can be seen, using a corner reflector for calibration results in a high signal-to-noise ratio and effectively reduces the influence of environmental background. Using a trihedral corner reflector at 80m and employing a 1m wide distance gate for data capture as calibration data improves the accuracy of target RCS acquisition.

[0066] Under vertical-vertical polarization and a frequency of 15 GHz, a 200 mm trihedral reflector (short side length) was used as the calibration body, and a 250 mm trihedral reflector was used as the target. Both were scanned and tested outdoors at a distance of 10 m, following the method in step 4, and the target RCS distribution as the horizontal angle changed was obtained. Simultaneously, in a darkroom environment, a turntable was used to test the targets in the same manner, and the results were compared. Figure 5 The comparison results are shown. (By...) Figure 5 It can be seen that this calibration method achieves an error of 0.4dB, demonstrating good calibration accuracy. Furthermore, its signal-to-noise ratio is higher than that of metal spheres, resulting in more accurate RCS inversion of the target. Therefore, this method can be used for outdoor calibration, solving problems such as low signal-to-noise ratio and difficulty in obtaining metal sphere echoes caused by aerial calibration.

[0067] Step 5: Based on the theoretical scattering cross-section of the calibration body and the power spectrum envelope of the calibration body echo signal obtained in Step 4, the ground station processes the received target echo signal to obtain the electromagnetic scattering characteristics of the ship target. The specific steps are as follows:

[0068] 5.1 Perform inverse Fourier transform on the target body echo signal to obtain a one-dimensional image of the target body;

[0069] 5.2 Determine the range of the target area, and use a software distance gate to extract the target area echo from the one-dimensional image of the target body. Perform a Fourier transform on the extracted target area echo to obtain the target area echo in the frequency domain.

[0070] 5.3. Take the square of the modulus of the echo amplitude of the target region in the frequency domain to obtain the power spectrum data of the target body echo signal.

[0071] 5.4 Perform inverse Fourier transform on the power spectrum data, and then perform low-pass filtering on the transformed result to obtain the power spectrum envelope of the target body echo signal.

[0072] 5.5. Based on the theoretical scattering cross-section of the calibration body, the power spectrum envelope of the calibration body echo signal obtained in step 4, and the power spectrum envelope of the target body echo signal obtained in step 5.4, the electromagnetic scattering cross-section of the ship target is calculated using the following formula to obtain the electromagnetic scattering characteristics of the ship target:

[0073]

[0074] Where σ is the electromagnetic scattering cross-section of the ship target, σ0 is the scattering cross-section of the calibration body echo signal, P0 is the power spectral envelope of the calibration body echo signal, and P T The power spectral envelope of the target body echo signal.

[0075] If the test distance of the ship target is different from the test distance of the calibration body, the calibration body echo is compensated according to the test distance of the ship target to eliminate the distance error of the calibration body echo signal.

[0076] In this case, the electromagnetic scattering cross-section of the ship target is calculated using the following formula:

[0077]

[0078] Among them, R T R0 represents the test distance for the ship target, and R0 represents the test distance for the calibration object.

[0079] like Figure 6 As shown, after range compensation according to the radar equation, the RCS of the ship target 7 at 15 GHz with vertical-vertical polarization is obtained based on the calibration data and the echo data of the ship target 7. Large peaks are observed at the bow, stern, port center, and starboard center, with the largest RCS value (60.2 dBsm) at the stern position, consistent with the theoretical RCS distribution of ships. Therefore, this invention can effectively obtain the RCS distribution of ship targets.

[0080] After acquiring the GPS data of the ship's center, this invention uses an unmanned aerial vehicle (UAV)-borne radar to plan a circular trajectory centered on the ship's target 7 from a specific overhead angle, and then flies at a constant speed along this trajectory. During flight, the antenna beam center of the measuring radar 2 is always aligned with the target, and signals are transmitted through the transmitting antenna of the measuring radar 2. After the signals illuminate the target, they scatter in all directions, and the receiving antenna of the measuring radar 2 receives the backscattered signals. Simultaneously, differential GNSS positioning at the UAV and ground ends is used as navigation information to accurately record the UAV's flight status. To obtain the RCS of the ship's target 7, the UAV-borne radar performs a two-dimensional spatial scan of a trihedral reflector placed in any orientation on the ground, finding the peak value of the backscattered signal from the trihedral reflector as calibration data. After calibration, the radar cross section of the ship's target 7 is obtained. This method can effectively improve the signal-to-noise ratio of the calibration body echo, thereby improving the accuracy of the target's RCS value.

Claims

1. A method for acquiring the electromagnetic scattering characteristics of ship targets using unmanned aerial vehicle (UAV)-borne radar, characterized in that, Includes the following steps: S1. Build an unmanned aerial vehicle (UAV)-borne radar system, ensuring that its measurement radar is always pointed at the ship target during the test. S2. Obtain the real-time position coordinates of the ship target center, and then plan the real-time circular flight trajectory of the UAV with it as the center. S3. The UAV flies along a real-time circular flight trajectory. During the flight, the transmitting antenna of the measuring radar transmits test signals to the ship target. The test signals are reflected by the ship target, forming target body echo signals, which are received by the receiving antenna of the measuring radar and sent to the ground station. S4. Perform outdoor ground calibration using a calibration body to obtain the power spectral envelope of the calibration body echo signal. The calibration body is a trihedral reflector. 4.1 Place the trihedral reflector horizontally and determine its horizontal orientation; 4.

2. Based on the horizontal orientation of the trihedral reflector, plan the calibration circular trajectory of the UAV perpendicular to the ground; 4.3 The UAV flies along a calibration circular trajectory perpendicular to the ground. During the flight, the pitch angle of the UAV relative to the trihedral reflector is adjusted. The transmitting antenna of the measuring radar transmits a test signal to the trihedral reflector. The test signal is reflected and received by the receiving antenna of the measuring radar and sent to the ground station for processing. The distribution of the reflected power of the trihedral reflector as a function of the test pitch angle is obtained, and the height of the UAV and the pitch angle corresponding to the peak reflected power of the trihedral reflector are recorded. 4.4 Based on the distribution of the reflected power of the trihedral reflector with the test pitch angle and the UAV altitude and pitch angle corresponding to the peak reflected power, plan the calibration circular trajectory of the UAV parallel to the ground at the set distance; 4.5 The UAV flies along a calibration circular trajectory parallel to the ground and performs a circular scan of the trihedral reflector. During the flight, the transmitting antenna of the measuring radar transmits a test signal to the trihedral reflector. The test signal is reflected to form a calibration body echo signal, which is received by the receiving antenna of the measuring radar and sent to the ground station for processing. The peak reflected power of the trihedral reflector in the calibration body echo signal is taken as the calibration data, and the power spectrum envelope of the calibration body echo signal is calculated. S5. Based on the theoretical scattering cross-section of the calibration body and the power spectrum envelope of the calibration body's echo signal, the target body's echo signal is processed to obtain the electromagnetic scattering characteristics of the ship target: 5.1 Perform inverse Fourier transform on the target body echo signal to obtain a one-dimensional image of the target body; 5.2 Determine the target area range, use a software distance gate to extract the target area echo from the one-dimensional image of the target body, and perform a Fourier transform on it to obtain the target area echo in the frequency domain; 5.

3. Take the square of the modulus of the echo amplitude of the target region in the frequency domain to obtain the power spectrum data of the target body echo signal; 5.4 Perform inverse Fourier transform on the power spectrum data of the target body echo signal and perform low-pass filtering to obtain the power spectrum envelope of the target body echo signal; 5.

5. Based on the theoretical scattering cross-section of the calibration body, the power spectrum envelope of the calibration body echo signal, and the power spectrum envelope of the target body echo signal, calculate the electromagnetic scattering cross-section of the ship target and obtain the electromagnetic scattering characteristics of the ship target.

2. The method for acquiring the electromagnetic scattering characteristics of ship targets using UAV-borne radar according to claim 1, characterized in that: In step 5.3, if the test distance of the ship target is the same as the test distance of the calibration object, the electromagnetic scattering cross-section of the ship target is calculated using the following formula: ； Where σ is the electromagnetic scattering cross-section of the ship target, σ0 is the theoretical scattering cross-section of the calibration object, P0 is the power spectral envelope of the calibration object's echo signal, and P T The power spectral envelope of the target body echo signal.

3. The method for acquiring the electromagnetic scattering characteristics of ship targets using UAV-borne radar according to claim 1, characterized in that, In step 5.3, if the test distance of the ship target differs from the test distance of the calibration target, then the following steps are also included: The calibration body echo is compensated based on the test distance of the ship target to eliminate the distance error of the calibration body echo signal.

4. The method for acquiring the electromagnetic scattering characteristics of ship targets using UAV-borne radar according to claim 3, characterized in that: In step 5.3, the electromagnetic scattering cross-section of the ship target is calculated using the following formula: ； Where σ is the electromagnetic scattering cross-section of the ship target, σ0 is the theoretical scattering cross-section of the calibration object, P0 is the power spectral envelope of the calibration object's echo signal, and P T R represents the power spectral envelope of the target body's echo signal. T R0 represents the test distance for the ship target, and R0 represents the test distance for the calibration object.

5. The method for acquiring the electromagnetic scattering characteristics of ship targets using UAV-borne radar according to claim 2 or 4, characterized in that: In step 1, the UAV-borne radar system includes a UAV platform, a measurement radar, an optoelectronic camera, a gimbal, and a data transmission device; The measuring radar and photoelectric camera are mounted on a pan-tilt unit, and their relative positions are fixed and they point in the same direction. The gimbal is mounted on the UAV platform and is used to adjust the pointing of the measuring radar and the photoelectric camera, so that the measuring radar is always pointed at the target; the data transmission device is mounted on the UAV platform and is connected to the UAV platform, the gimbal, the measuring radar, and the photoelectric camera respectively. The photoelectric camera is used to capture images of the target and transmit them back to the ground station via a data transmission device, thereby adjusting the attitude of the gimbal. The measurement radar is used to transmit test signals, then receive target echo signals, and transmit them to the ground station through a data transmission device, thereby obtaining the electromagnetic scattering characteristics of the ship target. The data transmission device is used to send images captured by the photoelectric camera and target echo signals received by the measurement radar, as well as to receive UAV platform control signals and gimbal control signals sent by the ground station.

6. The method for acquiring the electromagnetic scattering characteristics of ship targets using UAV-borne radar according to claim 5, characterized in that: In step 1, the signal emitted by the measuring radar is a linear frequency modulated signal.

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