Ground moving target sar radio frequency echo simulation method and system for matching recognition

Abstract

The application relates to a SAR radio frequency echo simulation method and system for matching recognition of ground activity targets; the method comprises the following steps: a SAR echo simulator receives information sent by a simulation machine and an airborne SAR respectively; the SAR echo simulator calculates a system response function including a ground scene transfer function and an activity target transfer function according to the received information, and performs vector superposition to obtain the system response function; the system response function is convolved with a SAR excitation signal to generate a ground activity target SAR echo signal; the SAR echo simulator radiates the ground activity target SAR echo signal through an antenna array and a feed system in a microwave darkroom, so that the airborne SAR can receive a radio frequency echo signal in real time, generate a ground activity target SAR image after imaging processing, and then perform terrain matching and target recognition. The application overcomes the defects of the traditional method, such as static scene simulation, missing of the difference change of activity target scattering characteristics to the radar line-of-sight angle, and the like, and improves the accuracy and flexibility of the airborne SAR matching recognition radio frequency semi-physical simulation.

Description

Technical Field

[0001] This invention relates to the field of radio frequency simulation technology, and in particular to a method and system for simulating SAR radio frequency echoes of ground moving targets for matching identification. Background Technology

[0002] The basic principle of land target matching and identification technology is that the target and the radar generate relative motion, thereby obtaining an echo with linear frequency modulation properties that contains two dimensions. After imaging processing, this echo is matched with a complex ground background to identify the target. Different targets exhibit different scattering characteristics and different penetrating power, thus enabling the acquisition of high-resolution two-dimensional images, which is of great significance in geographic mapping, marine inspection, and global strategic reconnaissance of vegetation distribution.

[0003] Land target matching and recognition simulation can realize the relative motion relationship between the target and the detection platform in a laboratory environment through echo simulation. It uses a reference map to simulate target and scene features, and after processing by imaging algorithms, target matching and recognition can be achieved. This allows for repeated testing, significantly shortening the development cycle and reducing development costs, making it highly necessary. For SAR matching and recognition algorithm verification of fixed targets, scene updates can be achieved by changing the reference map. However, for airborne SAR moving target matching and recognition under the same flight path with multiple imaging operations, current commonly used simulation methods have two shortcomings: First, the target and scene are loaded in the form of a reference map, and the target is static and cannot change dynamically, failing to reflect the randomness of moving targets, i.e., it does not consider the scene differences caused by the motion characteristics of moving targets; second, it does not reflect the differences in the radar line-of-sight angle caused by the scattering characteristics of moving targets. Summary of the Invention

[0004] Based on the above analysis, this invention aims to disclose a method and system for simulating radio frequency echoes of SAR (Radar Radio Frequency Echo) for matching and identification of moving ground targets. It addresses the problems in SAR radio frequency echo simulation of moving ground targets, such as the dynamic changes in target position and attitude, and the correlation between target scattering characteristics and radar line-of-sight angle.

[0005] This invention discloses a ground-based moving target SAR radio frequency echo simulation method for matching and identification, comprising:

[0006] Step S1: The SAR echo simulator receives information from the simulator and the airborne SAR respectively; wherein, the simulator sends the latitude, longitude, altitude, speed and acceleration of the airborne platform, the latitude, longitude and altitude of the imaging area center and the image swath width, and the latitude, longitude and attitude angle information of the simulated moving target in real time according to the communication cycle; the airborne SAR sends radio frequency excitation signal, clock signal and pulse synchronization signal in real time.

[0007] Step S2: The SAR echo simulator calculates the ground scene transfer function and the moving target transfer function based on the received information, and performs vector superposition to obtain the system response function; the system response function is convolved with the SAR excitation signal to generate the ground moving target SAR echo signal.

[0008] Step S3: The SAR echo simulator radiates the SAR echo signal of the ground moving target in the microwave anechoic chamber through the antenna array and feeding system, so that the airborne SAR can receive the radio frequency echo signal in real time. After imaging processing, the SAR image of the ground moving target is generated, and then terrain matching and target identification are performed.

[0009] Further, step S2 includes:

[0010] Step S2-1: Calculate the position information of the airborne platform and the azimuth and elevation angles of the radar wave incident direction vector relative to the ground moving target;

[0011] Step S2-2: Calculate the ground scene transfer function based on the solved airborne platform position information and beam ground illumination area information; the beam ground illumination area information includes the position coordinates, scattering coefficients, and random phases of pixels within the beam ground illumination area.

[0012] Step S2-3: Calculate the transfer function of the ground moving target based on the solved airborne platform position information and the azimuth and elevation angles of the radar wave incident direction vector relative to the body coordinate system;

[0013] Step S2-4: Vector superposition of the ground scene transfer function and the ground moving target transfer function to generate the system response function;

[0014] Step S2-5: Perform time-domain convolution between the system response function and the transmitted signal to generate radio frequency echoes of land-based moving targets.

[0015] Further, step S2-1 includes:

[0016] 1) Establish an imaging reference coordinate system and a moving target body coordinate system; the origin of the imaging reference coordinate system is the position of the airborne platform at the start of imaging; the origin of the moving target body coordinate system is the position of the centroid of the moving target.

[0017] 2) The position coordinates of the airborne platform in the imaging reference coordinate system at the current moment are obtained by recursively calculating the position of the airborne platform in the imaging reference coordinate system according to the internal clock cycle;

[0018] 3) Calculate the position coordinates of the center of the imaging area and the moving ground target in the imaging reference coordinate system, respectively;

[0019] 4) Based on the current position coordinates of the airborne platform and the ground moving target in the imaging reference coordinate system, perform coordinate transformation to obtain the position coordinates of the airborne platform in the target's body coordinate system;

[0020] 5) Based on the position coordinates of the airborne platform in the target coordinate system, calculate the azimuth and elevation angles of the radar wave incident direction vector relative to the target coordinate system.

[0021] Furthermore, the recursive formula for the location of the airborne platform is as follows:

[0022]

[0023] In the formula, (X n Y n Z n (X) represents the current position of the airborne platform in the imaging reference coordinate system. n-1 Y n-1 Z n-1 (v) represents the position of one clock cycle on the airborne platform. x v y v z (a) represents the speed of the airborne platform. x a y a z ) represents the acceleration of the airborne platform, and t represents the clock cycle length;

[0024] Coordinate transformation formula for airborne platform in target body coordinate system:

[0025]

[0026] Among them, (x r ,y r ,z r The position of the airborne platform in the target's body coordinate system, (x0, y0, z0) is the position of the ground moving target relative to the imaging reference coordinate system, and Λ is the coordinate transformation matrix, expressed as:

[0027]

[0028] in B = θ and C = φ are the angles by which the target rotates around the X, Y, and Z axes of the imaging reference coordinate system, respectively;

[0029] The azimuth angle ψ of the radar wave incident direction vector relative to the target's coordinate system. r and pitch angle θ r for:

[0030]

[0031]

[0032] Furthermore, in step S2-2, the process of calculating the transfer function of the ground scene within the beam illumination range includes:

[0033] 1) Obtain the position information of the pixels from the ground illumination area information of the beam, and calculate the slant distance and delay between the pixels and the airborne platform pixel by pixel according to the positional relationship between the airborne platform and each pixel of the scattering point in the imaging reference coordinate system.

[0034] 2) Calculate the phase value introduced by the distance;

[0035] 3) Perform phase modulation and scattering coefficient amplitude weighting on each pixel;

[0036] 4) Coherently superimpose pixels within the same distance gate to obtain the ground scene transfer function.

[0037] Furthermore, in the imaging reference coordinate system,

[0038] The coordinates of the airborne platform are (X) n ,Y n Z n );

[0039] The coordinates of the Lth pixel are: ((L rw ·δ X +x t ),H L ,(L cl ·δ Z +z t ));

[0040] Among them, H L Let L be the coordinate of pixel L on the Y-axis; (L rw ,L cl ) represents the pixel offset of pixel L in the imaging reference image relative to the center of the imaging region, (δ) X ,δ Z ) indicates the north and east resolution of the reference map; x t z t The X and Z coordinates of the center of the imaging region in the imaging reference coordinate system;

[0041] Pixel L and slant distance R between the airborne platform L and delay t L for:

[0042]

[0043]

[0044] t n The ground scene transmission function at any given time is:

[0045]

[0046] In the formula: M is the number of pixels falling within the distance gate, A L φ L T represents the scattering coefficient and random phase of the echo from pixel L within the distance gate. s Let λ be the sampling period of the system function, and λ be the wavelength of the radar signal.

[0047] Furthermore, in steps S2-3, the ground moving target transfer function calculation process includes:

[0048] 1) Based on the positional relationship between the airborne platform and the ground moving target in the target body coordinate system, calculate the slant distance and delay between each scattering center and the airborne platform;

[0049] 2) Calculate the phase value introduced by the distance;

[0050] 3) Perform phase modulation and amplitude weighting of the scattering coefficients for each scattering center;

[0051] 4) Coherently superimpose the scattering centers within the same distance gate to obtain the transfer function of the ground moving target.

[0052] Furthermore, in the target body coordinate system,

[0053] The coordinates of the airborne platform are (x r ,y r ,z r );

[0054] The coordinates of the kth scattering center are (x k ,y k ,z k );

[0055] Then, the slant distance R′ between the scattering center k and the airborne platform k and delay t′ k for:

[0056]

[0057]

[0058] t n The ground activity target transfer function at time t is:

[0059]

[0060] In the formula, N is the number of scattering centers falling into the range gate, and A′ k and φ′ k T represents the scattering coefficient and phase of the k-th scattering center within the distance gate, respectively.s Let λ be the sampling period of the system function, and λ be the wavelength of the radar signal.

[0061] Furthermore, the position (x) of the kth scattering center k ,y k ,z k ), Amplitude A′ k and phase φ′ k Both are obtained from the established ground-based moving target scattering center model based on the azimuth angle ψ and elevation angle θ of the radar wave incident direction vector relative to the target's body coordinate system.

[0062] The present invention also provides a ground moving target SAR radio frequency echo simulation system for matching identification, including a simulator, an airborne SAR, a SAR echo simulator, an antenna array, and a feeding system;

[0063] The simulator sends the latitude, longitude, altitude, speed, and acceleration of the airborne platform, the latitude, longitude, altitude of the imaging area center, and the image width, as well as the latitude, longitude, and attitude angle information of the simulated moving target to the SAR echo simulator in real time according to the communication cycle.

[0064] The airborne SAR sends radio frequency excitation signals, clock signals, and pulse synchronization signals to the echo simulator in real time.

[0065] The SAR echo simulator executes the ground moving target SAR radio frequency echo simulation method for matching and identification as described above, generates simulated SAR echo signals, and radiates the SAR echo signals into the microwave anechoic chamber through the antenna array and feeding system, so that the airborne SAR receives the radio frequency echo signals in real time, generates ground moving target SAR images after imaging processing, and then performs terrain matching and target identification.

[0066] This invention can achieve one of the following beneficial effects:

[0067] The present invention discloses a ground moving target SAR radio frequency echo simulation method and system for matching identification. By introducing the motion and attitude changes of the moving target into the simulation loop, a dynamic scene is generated. At the same time, a scattering center model is used to accurately simulate the motion of the moving target and its own attitude changes to finely modulate the SAR imaging. SAR echoes that conform to the physical scattering mechanism are generated in real time according to the radar pulse sequence. This effectively overcomes the shortcomings of traditional methods such as static scene simulation and lack of understanding of the differences in radar line-of-sight angle changes in the scattering characteristics of moving targets. It greatly improves the accuracy and flexibility of airborne platform SAR matching identification radio frequency hardware-in-the-loop simulation. Attached Figure Description

[0068] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0069] Figure 1 This is a flowchart of the ground moving target SAR radio frequency echo simulation method for matching and identification in an embodiment of the present invention;

[0070] Figure 2 This is a flowchart of the method for generating SAR echo signals of ground moving targets in an embodiment of the present invention;

[0071] Figure 3 This is a block diagram showing the components and connections of the ground moving target SAR radio frequency echo simulation system for matching and identification in an embodiment of the present invention. Detailed Implementation

[0072] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0073] One embodiment of the present invention discloses a ground-based moving target SAR radio frequency echo simulation method for matching identification, such as... Figure 1 As shown, it includes:

[0074] Step S1: The SAR echo simulator receives information from the simulator and the airborne SAR respectively; wherein, the simulator sends the latitude, longitude, altitude, speed and acceleration of the airborne platform, the latitude, longitude and altitude of the imaging area center and the image swath width, and the latitude, longitude and attitude angle information of the simulated moving target in real time according to the communication cycle; the airborne SAR sends radio frequency excitation signal, clock signal and pulse synchronization signal in real time.

[0075] Step S2: The SAR echo simulator calculates the ground scene transfer function and the moving target transfer function based on the received information, and performs vector superposition to obtain the system response function; the system response function is convolved with the SAR excitation signal to generate the ground moving target SAR echo signal.

[0076] Step S3: The SAR echo simulator radiates the SAR echo signal of the ground moving target in the microwave anechoic chamber through the antenna array and feeding system, so that the airborne SAR can receive the radio frequency echo signal in real time. After imaging processing, the SAR image of the ground moving target is generated, and then terrain matching and target identification are performed.

[0077] Specifically, step S1 includes:

[0078] Step S1-1: In the SAR echo simulator, the airborne SAR pulse synchronization signal is detected through the control board. When the airborne SAR pulse synchronization signal is detected, the imaging control code is sent to control the SAR echo simulator to enter the imaging working mode; otherwise, the imaging control code is set to invalid.

[0079] Step S1-2: The SAR echo simulator encapsulates and packages data in real time via a lower-level machine. The lower-level machine receives the latitude, longitude, altitude, velocity, acceleration, sub-region center latitude, longitude, altitude, sub-map width, latitude, longitude, and rotation angle information of the airborne platform sent by the simulator in real time, and encapsulates and packages the data according to the internal protocol. After receiving the imaging control code command sent by the control board, the lower-level machine sends the data packet to the position relationship calculation module in the SAR echo simulator for position relationship calculation. It also updates the velocity value of the airborne platform in the data packet according to the communication cycle and executes step S2; otherwise, it returns to step S1-1.

[0080] Specifically, such as Figure 2 As shown, step S2 includes:

[0081] Step S2-1: Calculate the position information of the airborne platform and the azimuth and elevation angles of the radar wave incident direction vector relative to the ground moving target;

[0082] Step S2-2: Calculate the ground scene transfer function based on the solved airborne platform position information and beam ground illumination area information; the beam ground illumination area information includes the position coordinates, scattering coefficients, and random phases of pixels within the beam ground illumination area.

[0083] Step S2-3: Calculate the transfer function of the ground moving target based on the solved airborne platform position information and the azimuth and elevation angles of the radar wave incident direction vector relative to the body coordinate system;

[0084] Step S2-4: Vector superposition of the ground scene transfer function and the ground moving target transfer function to generate the system response function;

[0085] Step S2-5: Perform time-domain convolution between the system response function and the transmitted signal to generate radio frequency echoes of land-based moving targets.

[0086] Further, step S2-1 includes:

[0087] 1) Establish an imaging reference coordinate system and a moving target body coordinate system; the origin of the imaging reference coordinate system is the position of the airborne platform at the start of imaging; the origin of the moving target body coordinate system is the position of the centroid of the moving target.

[0088] In this system, the origin of the imaging reference coordinate system OXYZ is defined as the position of the airborne platform at the start of imaging, with X, Y, and Z representing the north-sky-east directions, respectively. The origin of the target body coordinate system oxyz is defined as the target's centroid, with ox along the target's axis of symmetry and pointing towards the head as the positive direction. oy is located within the longitudinal plane of symmetry of the airborne platform, perpendicular to ox and pointing upwards as the positive direction. oz is determined by the right-hand rule.

[0089] 2) The position coordinates of the airborne platform in the imaging reference coordinate system at the current moment are obtained by recursively calculating the position of the airborne platform in the imaging reference coordinate system according to the internal clock cycle;

[0090] The recursive formula for the location of the airborne platform is:

[0091]

[0092] In the formula, (X n Y n Z n (X) represents the current position of the airborne platform in the imaging reference coordinate system. n-1 Y n-1 Z n-1 (v) represents the position of one clock cycle on the airborne platform. x v y v z (a) represents the speed of the airborne platform. x a y a z ) represents the acceleration of the airborne platform, and t represents the clock cycle length;

[0093] 3) Calculate the position coordinates of the center of the imaging area and the moving ground target in the imaging reference coordinate system, respectively;

[0094] The position of the center of the imaging region in the imaging reference coordinate system is:

[0095] (x t ,y,z t )=Θ(λ R ,φ R H R ,λ BC ,φ BC H BC )

[0096] The position of the ground moving target in the imaging reference coordinate system is as follows:

[0097] (x0,y0,z0)=Θ(λ R ,φ R H R ,λ T ,φ T H T ),

[0098] Where, (λ R ,φ R H R ( ) represents the latitude and longitude of the airborne platform. The latitude, longitude, and altitude of the radar beam's ground illumination center; (λ) T ,φ T HT ) represents the latitude, longitude, and altitude of the target; the function Θ(·) is the transformation formula for converting latitude, longitude, and altitude to the North-East coordinate system, Θ(λ R ,φ R H R ,λ BC ,φ BC H BC ) represents (λ) R ,φ R H R (λ) is the reference point. BC ,φ BC H BC The positions of Θ(λ) to the north, sky, and east of the reference point. R ,φ R H R ,λ T ,φ T H T ) represents (λ) R ,φ R H R (λ) is the reference point. T ,φ T H T The position of the reference point in the north, sky, and east directions.

[0099] 4) Based on the current position coordinates of the airborne platform and the ground moving target in the imaging reference coordinate system, perform coordinate transformation to obtain the position coordinates of the airborne platform in the target's body coordinate system;

[0100] Coordinate transformation formula for airborne platform in target body coordinate system:

[0101]

[0102] Among them, (x r ,y r ,z r The position of the airborne platform in the target's body coordinate system, (x0, y0, z0) is the position of the ground moving target relative to the imaging reference coordinate system, and Λ is the coordinate transformation matrix, expressed as:

[0103]

[0104] in B = θ and C = φ are the angles by which the target rotates around the X, Y, and Z axes of the imaging reference coordinate system, respectively;

[0105] 5) Based on the position coordinates of the airborne platform in the target coordinate system, calculate the azimuth and elevation angles of the radar wave incident direction vector relative to the target coordinate system.

[0106] The azimuth angle ψ of the radar wave incident direction vector relative to the target's coordinate system. r and pitch angle θ r for:

[0107]

[0108]

[0109] Specifically, in step S2-2, the process of calculating the transfer function of the ground scene within the beam illumination range includes:

[0110] 1) Obtain the position information of the pixels from the ground illumination area information of the beam, and calculate the slant distance and delay between the pixels and the airborne platform pixel by pixel according to the positional relationship between the airborne platform and each pixel of the scattering point in the imaging reference coordinate system.

[0111] In the imaging reference coordinate system

[0112] The coordinates of the airborne platform are (X) n ,Y n Z n );

[0113] The coordinates of the Lth pixel are: ((L rw ·δ X +x t ),H L ,(L cl ·δ Z +z t ));

[0114] Among them, H L Let L be the coordinate of pixel L on the Y-axis; (L rw ,L cl ) represents the pixel offset of pixel L in the imaging reference image relative to the center of the imaging region, (δ) X ,δ Z ) indicates the north and east resolution of the reference map; x t z t The X and Z coordinates of the sub-region center in the imaging reference coordinate system;

[0115] Then, the slant distance R between pixel L and the airborne platform L and delay t L for:

[0116]

[0117]

[0118] C represents the speed of electromagnetic waves.

[0119] 2) Calculate the phase value introduced by the distance;

[0120] 3) Perform phase modulation and scattering coefficient amplitude weighting on each pixel;

[0121] 4) Coherently superimpose pixels within the same distance gate to obtain the ground scene transfer function;

[0122] Specifically, t n The ground scene transmission function at any given time is:

[0123]

[0124] In the formula: M is the number of pixels falling within the distance gate, A L R L and t L φ represents the scattering coefficient, distance, and delay of the echo from pixel L within the distance gate, respectively. L T represents the random phase of a pixel. s The sampling period of the system function.

[0125] Specifically, in steps S2-3, the ground moving target transfer function calculation process includes:

[0126] 1) Based on the positional relationship between the airborne platform and the ground moving target in the target body coordinate system, calculate the slant distance and delay between each scattering center and the airborne platform;

[0127] In the target body coordinate system

[0128] The coordinates of the airborne platform are (x r ,y r ,z r );

[0129] The coordinates of the kth scattering center are (x k ,y k ,z k );

[0130] Then, the slant distance R′ between the scattering center k and the airborne platform k and delay t′ k ;

[0131] R′ k and t′ k This can be expressed as:

[0132]

[0133]

[0134] 2) Calculate the phase value introduced by the distance;

[0135] 3) Perform phase modulation and amplitude weighting of the scattering coefficients for each scattering center;

[0136] 4) Coherently superimpose the scattering centers within the same distance gate to obtain the transfer function of the ground moving target;

[0137] Specifically, t n The ground activity target transfer function at time t is:

[0138]

[0139] In the formula, N is the number of scattering centers falling into the range gate, and A′ k 、R′ k and t′ k Let φ′ represent the scattering coefficient, distance, and delay of the k-th scattering center within the distance gate, respectively. k T is the phase of the scattering center. s The sampling period of the system function.

[0140] In this embodiment, the scattering coefficient A′ of the k-th scattering center k Position (x) k ,y k ,z k ) and the phase φ′ of the scattering center k Both are obtained from the established ground-based moving target scattering center model based on the azimuth angle ψ and elevation angle θ of the radar wave incident direction vector relative to the target's body coordinate system.

[0141] The ground-based target scattering center model can be established by estimating scattering center parameters from SAR observation data, or by using ESPRIT to generate one-dimensional positions of scattering points from different angles, and then combining this with an improved random sampling consensus algorithm to generate all three-dimensional positions of the scattering center. The scattering amplitude is obtained by the least squares method.

[0142] After obtaining the ground scene transfer function and the ground moving target transfer function, vector superposition is performed to generate the system response function; the system response function is then convolved with the transmitted signal in the time domain to generate the radio frequency echo of the land moving target.

[0143] After generating radio frequency echoes of moving targets on land, the antenna and array control system radiates the signals in a microwave anechoic chamber, enabling the airborne SAR to receive the radio frequency echo signals in real time. After imaging processing, a SAR image of the moving targets on the ground is generated, followed by terrain matching and target identification.

[0144] Another embodiment of the present invention discloses a ground-based moving target SAR radio frequency echo simulation system for matching identification, such as Figure 3 As shown, it includes a simulator, airborne SAR, SAR echo simulator, antenna array, and feeding system;

[0145] The simulator sends the latitude, longitude, altitude, speed, and acceleration of the airborne platform, the latitude, longitude, altitude of the imaging area center, and the image width, as well as the latitude, longitude, and attitude angle information of the simulated moving target to the SAR echo simulator in real time according to the communication cycle.

[0146] The airborne SAR sends radio frequency excitation signals, clock signals, and pulse synchronization signals to the echo simulator in real time.

[0147] The SAR echo simulator executes the ground moving target SAR radio frequency echo simulation method for matching and identification as described in the previous embodiment, generates simulated SAR echo signals, and radiates the SAR echo signals into the microwave anechoic chamber through the antenna array and feeding system, so that the airborne SAR receives the radio frequency echo signals in real time, generates ground moving target SAR images after imaging processing, and then performs terrain matching and target identification.

[0148] More specifically, the SAR echo simulator includes a lower-level computer, a control board, a position relationship calculation module, a ground scene transfer function calculation module, a moving target transfer function calculation module, a system response function calculation module, and a baseband signal processing unit. Among these,

[0149] The control board is used for imaging control. When the control board detects the airborne SAR pulse synchronization signal, it sends an imaging control code to control the SAR echo simulator to enter the imaging working mode; otherwise, the imaging control code is set to invalid.

[0150] The lower-level machine is used to receive in real time the latitude, longitude, altitude, speed, acceleration, latitude, longitude, altitude of the sub-region center, width of the sub-map, latitude, longitude and rotation angle information of ground moving targets sent by the simulator. It encapsulates and packages the data according to the internal protocol and sends the data packets to the position relationship calculation module under the control of the imaging control code command. It also updates the speed value of the airborne platform in the data packets according to the communication cycle.

[0151] The positional relationship calculation module is used to calculate the positional relationship between the airborne platform and each pixel of the scattering point in the imaging reference coordinate system, and the positional relationship between the airborne platform and each scattering center of the moving target in the target body coordinate system.

[0152] The ground scene transfer function calculation module is used to calculate the ground scene transfer function based on the positional relationship between the airborne platform and each pixel of the scattering point in the imaging reference coordinate system.

[0153] The moving target transfer function calculation module is used to calculate the ground moving target transfer function based on the positional relationship between the airborne platform and each scattering center of the moving target in the target body coordinate system.

[0154] The system response function calculation module is used to vector superimpose the ground scene transfer function and the ground moving target transfer function to generate the system response function.

[0155] The baseband signal processing unit is used to perform time-domain convolution between the system response function and the transmitted signal to generate radio frequency echoes of land-based moving targets.

[0156] In summary, the ground moving target SAR radio frequency echo simulation method and system for matching identification of the present invention introduces the motion and attitude changes of the moving target into the simulation loop to generate a dynamic scene. At the same time, it uses a scattering center model to accurately simulate the motion of the moving target and its own attitude changes to finely modulate the SAR imaging. It generates SAR echoes that conform to the physical scattering mechanism in real time according to the radar pulse sequence. It can effectively overcome the shortcomings of traditional methods such as static scene simulation and lack of understanding of the differences in radar line-of-sight angle changes in the scattering characteristics of moving targets. It greatly improves the accuracy and flexibility of radio frequency semi-physical simulation of SAR matching identification on airborne platforms.

[0157] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for simulating SAR radio frequency echoes of ground moving targets for matching identification, characterized in that, include: Step S1: The SAR echo simulator receives information from the simulator and the airborne SAR respectively; wherein, the simulator sends the latitude, longitude, altitude, speed and acceleration of the airborne platform, the latitude, longitude and altitude of the imaging area center and the image swath width, and the latitude, longitude and attitude angle information of the simulated moving target in real time according to the communication cycle; the airborne SAR sends radio frequency excitation signal, clock signal and pulse synchronization signal in real time. Step S2: The SAR echo simulator calculates the ground scene transfer function and the moving target transfer function based on the received information, and performs vector superposition to obtain the system response function; the system response function is convolved with the SAR excitation signal to generate the ground moving target SAR echo signal. Step S3: The SAR echo simulator radiates the SAR echo signal of the ground moving target in the microwave anechoic chamber through the antenna array and feeding system, so that the airborne SAR receives the radio frequency echo signal in real time. After imaging processing, the SAR image of the ground moving target is generated, and then terrain matching and target identification are performed. Step S2 includes: Step S2-1: Calculate the position information of the airborne platform and the azimuth and elevation angles of the radar wave incident direction vector relative to the ground moving target; Step S2-2: Calculate the ground scene transfer function based on the solved airborne platform position information and beam ground illumination area information; the beam ground illumination area information includes the position coordinates, scattering coefficients, and random phases of pixels within the beam ground illumination area. In step S2-2, the process of calculating the transfer function of the ground scene within the beam illumination range includes: 1) Obtain the position information of the pixels from the ground illumination area information of the beam, and calculate the slant distance and delay between the pixels and the airborne platform pixel by pixel according to the positional relationship between the airborne platform and each pixel of the scattering point in the imaging reference coordinate system. 2) Calculate the phase value introduced by the distance; 3) Perform phase modulation and scattering coefficient amplitude weighting on each pixel; 4) Coherently superimpose pixels within the same distance gate to obtain the ground scene transfer function; Step S2-3: Calculate the transfer function of the ground moving target based on the solved airborne platform position information and the azimuth and elevation angles of the radar wave incident direction vector relative to the body coordinate system; In steps S2-3, the ground moving target transfer function calculation process includes: 1) Based on the positional relationship between the airborne platform and the ground moving target in the target body coordinate system, calculate the slant distance and delay between each scattering center and the airborne platform; 2) Calculate the phase value introduced by the distance; 3) Perform phase modulation and amplitude weighting of the scattering coefficients for each scattering center; 4) Coherently superimpose the scattering centers within the same distance gate to obtain the transfer function of the ground moving target; Step S2-4: Vector superposition of the ground scene transfer function and the ground moving target transfer function to generate the system response function; Step S2-5: Perform time-domain convolution between the system response function and the transmitted signal to generate radio frequency echoes of land-based moving targets.

2. The method for simulating SAR radio frequency echoes of ground moving targets according to claim 1, characterized in that, Step S2-1 includes: 1) Establish an imaging reference coordinate system and a moving target body coordinate system; the origin of the imaging reference coordinate system is the position of the airborne platform at the start of imaging; the origin of the moving target body coordinate system is the position of the centroid of the moving target. 2) Obtain the current position coordinates of the airborne platform in the imaging reference coordinate system by recursively calculating the airborne platform's position in the imaging reference coordinate system according to the internal clock cycle; 3) Calculate the position coordinates of the center of the imaging area and the moving ground target in the imaging reference coordinate system, respectively; 4) Based on the current position coordinates of the airborne platform and the ground moving target in the imaging reference coordinate system, perform coordinate transformation to obtain the position coordinates of the airborne platform in the target's body coordinate system; 5) Based on the position coordinates of the airborne platform in the target coordinate system, calculate the azimuth and elevation angles of the radar wave incident direction vector relative to the target coordinate system.

3. The method for simulating SAR radio frequency echoes of ground moving targets according to claim 2, characterized in that, The recursive formula for the location of the airborne platform is: ； In the formula, ( X n , Y n , Z n ) represents the current position of the airborne platform in the imaging reference coordinate system. X n-1 , Y n-1 , Z n-1 ) represents the position of one clock cycle on the airborne platform, ( v x , v y , v z ) indicates the speed of the airborne platform, ( a x , a y , a z This indicates the acceleration of the airborne platform. t Indicates the length of the clock cycle; Coordinate transformation formula for airborne platform in target body coordinate system: ； in, The position of the airborne platform in the target's coordinate system. This represents the position of the moving ground target relative to the imaging reference coordinate system. The coordinate transformation matrix is ​​represented as follows: ； in , , These are the target around the imaging reference coordinate system. , , The angle of rotation of the axis; The azimuth angle of the radar wave incident direction vector relative to the target's coordinate system. and pitch angle for: ； 。 4. The method for simulating SAR radio frequency echoes of ground moving targets according to claim 1, characterized in that, In the imaging reference coordinate system The coordinates of the airborne platform are ( , , ); No. L The coordinates of the pixels are: (( ), , ); in, For pixels L Coordinates on the Y-axis; Represents a pixel in the imaging reference image. L Pixel offset relative to the center of the imaging area Indicates the north and east resolution of the reference map; , The X and Z coordinates of the center of the imaging region in the imaging reference coordinate system; Pixel L Slant distance from the airborne platform R L and delay t L for: ； ； The ground scene transmission function at any given time is: In the formula: M The number of pixels falling into the gate at that distance. A L , This indicates the distance to the pixel inside the gate. L The scattering coefficient and random phase of the echo, T s The sampling period of the system function. The wavelength of the radar signal.

5. The method for simulating SAR radio frequency echoes of ground moving targets according to claim 1, characterized in that, In the target body coordinate system The coordinates of the airborne platform are ; No. k The coordinates of the scattering centers are ; Then, the scattering center k Slant distance from the airborne platform and delay for: ； ； The ground activity target transfer function at time t is: In the formula, N The number of scattering centers falling into this distance gate. and These represent the distances within the gate, respectively. k The scattering coefficient and phase of each scattering center T s The sampling period of the system function. The wavelength of the radar signal.

6. The method for simulating SAR radio frequency echoes of ground moving targets according to claim 5, characterized in that, The first k The location of each scattering center Amplitude and phase Both are based on the azimuth angle of the radar wave incident direction vector relative to the target's coordinate system. and pitch angle Obtained from the established model of the scattering center of ground-based active targets.

7. A ground-based moving target SAR radio frequency echo simulation system for matching and identification, characterized in that, This includes simulators, airborne SAR, SAR echo simulators, antenna arrays, and feeding systems; The simulator sends the latitude, longitude, altitude, speed, and acceleration of the airborne platform, the latitude, longitude, altitude of the imaging area center, and the image width, as well as the latitude, longitude, and attitude angle information of the simulated moving target to the SAR echo simulator in real time according to the communication cycle. The airborne SAR sends radio frequency excitation signals, clock signals, and pulse synchronization signals to the echo simulator in real time. The SAR echo simulator executes the ground moving target SAR radio frequency echo simulation method for matching and identification as described in any one of claims 1-6, generates simulated SAR echo signals, and radiates the SAR echo signals into a microwave anechoic chamber through an antenna array and a feeding system, enabling the airborne SAR to receive the radio frequency echo signals in real time. After imaging processing, a ground moving target SAR image is generated, and then terrain matching and target identification are performed.

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