SAR echo simulation system and method based on ground feature scattering characteristics and coherent spot noise

Abstract

The application relates to the technical field of radar system simulation, and particularly discloses a SAR echo simulation system and method based on ground object scattering characteristics and speckle noise, which is based on simulation of a SAR echo signal based on a gray-scale image, and gives a SAR echo simulation system and method based on ground object scattering characteristics and speckle noise simulation. On the basis of analyzing the speckle noise characteristics in a SAR image, the SAR echo signal simulation method basically consistent with a real scene and containing speckle noise is realized by using real ground backscattering coefficients and SAR imaging related parameters. In a semi-physical simulation test, the SAR echo signal is accurately simulated, the problem that the traditional SAR echo signal simulation method based on a gray-scale image cannot simulate speckle noise and leads to insufficient simulation fidelity of the SAR echo signal is overcome, the echo signal accurate simulation basically consistent with the real SAR echo signal is realized, and the application has good popularization and application value.

Description

Technical Field

[0001] This invention relates to the field of radar system simulation technology, and specifically discloses a SAR echo simulation system and method based on ground object scattering characteristics and speckle noise. Background Technology

[0002] Synthetic Aperture Radar (SAR), an active sensor utilizing microwaves for perception, possesses all-weather, all-time Earth observation capabilities and has become an important tool for military reconnaissance. SAR imaging plays a crucial role in military target detection, location, and identification by providing high-resolution imaging of target areas. SAR radar effectively images target areas by transmitting broadband signals, and the images can effectively display information on the scattering characteristics of ground objects and target features, thereby enabling target location through target detection and identification algorithms. Currently, to effectively verify the performance of SAR imaging equipment, target echo simulation equipment is often used to generate SAR echo signals. These echoes are then transmitted to the SAR imaging radar through radiation or injection methods to verify the imaging, target detection, identification, and location performance of the equipment.

[0003] The realism of SAR echo signal simulation directly affects the performance of military target detection and positioning in images. In the process of simulating SAR echo signals using target echo simulation equipment, traditional methods mostly rely on grayscale images to pre-calculate and generate echo signals, and then use pulse triggering to transmit the echo signals. In this method, the grayscale image reflects the ground scattering characteristics, and the scene echo signal is calculated using the ground backscattering coefficient (RCS) and elevation data (DEM). However, the speckle characteristics in the echo signal are not considered. As an internal process of ground object scattering, speckle is part of the overall scattering and can affect target detection performance in actual SAR images. Traditional SAR echo signal simulation based on grayscale images ignores this influence, resulting in insufficient realism in SAR echo signal simulation. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention discloses a SAR echo simulation system and method based on ground object scattering characteristics and speckle noise. By utilizing the actual ground backscattering coefficient and SAR imaging related parameters, a SAR radar echo signal simulation method containing speckle noise that is basically consistent with the real scene is realized. The accurate simulation of SAR echo signal is achieved in a hardware-in-the-loop simulation experiment.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] A SAR echo simulation system based on ground object scattering characteristics and speckle noise includes a simulation control and display, a radar signal receiving channel, an intermediate frequency signal acquisition module, an echo signal simulation module, an intermediate frequency signal generation module, and an echo signal transmission channel.

[0007] Simulation control and display are used to control the system and set relevant parameters, and to monitor and display the working status of the entire system;

[0008] The radar signal receiving channel is used to receive low-power radar transmission signals sent by the SAR radar system, down-convert the radar signals to intermediate frequency radar signals, and send the filtered, amplified, and power-adjusted signals to the intermediate frequency signal acquisition module.

[0009] The intermediate frequency signal acquisition module is used to perform analog-to-digital conversion on the intermediate frequency radar signal to form a digital radar signal, which is then sent to the echo signal simulation module.

[0010] The echo signal simulation module completes the SAR echo signal simulation based on the received digital radar signal and relevant parameter settings;

[0011] The intermediate frequency signal generation module performs analog-to-digital conversion on the SAR echo digital signal to form an intermediate frequency SAR echo signal;

[0012] The echo signal transmission channel is used to upconvert intermediate frequency SAR echo signals into radio frequency SAR echo signals and send them into the SAR radar system.

[0013] Furthermore, the SAR echo simulation system based on ground object scattering characteristics and speckle noise also includes a local oscillator module that provides local oscillator and clock signals for the radar signal receiving channel and the echo signal transmitting channel.

[0014] The SAR echo simulation method based on ground object scattering characteristics and speckle noise uses any of the above-mentioned SAR echo simulation systems based on ground object scattering characteristics and speckle noise to simulate SAR echo signals. The specific steps are as follows:

[0015] 1) Power on the system and perform a self-test. Connect the low-power radar transmit signal channel and echo signal receive channel of the SAR radar system to the radar signal receive channel and echo signal transmit channel of this system via cables.

[0016] 2) Set the operating center frequency, radar signal receiving channel gain, echo signal transmitting channel gain, SAR echo simulation multi-view coefficient, and multiplicative noise ratio (MNR) of the SAR radar system through simulation control and display, and load the SAR echo simulation reference image.

[0017] 3) The radar signal receiving channel receives the low-power radar transmission signal sent by the SAR radar system, down-converts the radar signal to an intermediate frequency radar signal, and sends the filtered, amplified, and power-adjusted signal to the intermediate frequency signal acquisition module. The intermediate frequency signal acquisition module performs analog-to-digital conversion on the intermediate frequency radar signal to form a digital radar signal, which is then sent to the echo signal simulation module.

[0018] 4) After receiving the digital radar transmitted signal and reading the relevant setting parameters, the echo signal simulation module calculates the SAR echo signal S0;

[0019] 5) Quantize the echo signal according to the DAC's range. Assuming the DAC is 14-bit, the maximum amplitude output is A. max =2 14 -1, the quantification formula is:

[0020]

[0021] 6) The normalized SAR echo digital signal S0′ is converted from analog to digital using the intermediate frequency signal generation module to form an intermediate frequency SAR echo signal;

[0022] 7) The echo signal transmission channel upconverts the intermediate frequency SAR echo signal into a radio frequency SAR echo signal and sends it into the SAR radar system;

[0023] 8) While transmitting low-power radar signals, the SAR radar system receives SAR radio frequency echo signals and performs imaging, detection, and identification processing on the echo signals.

[0024] Furthermore, in the SAR echo simulation method based on ground object scattering characteristics and speckle noise, the calculation method for the SAR echo signal in step 4) is as follows:

[0025] 4.1 Read the reference image for SAR echo simulation. Assuming the reference image size for SAR echo simulation is 2048*2048, obtain the ground scattering coefficient matrix σ. n (n=1,2,...,2048 2 The ground scattering coefficient matrix characterizes the ideal, noise-independent RCS and reflects the backscattering characteristics of ground objects.

[0026] 4.2 Reading the SAR echo simulation multi-look coefficient N ds Multiplicative noise coefficient (MNR) is a multi-view coefficient that characterizes the non-coherent additive processing in SAR image processing. Its value is equal to the total number of frames in the multi-view image.

[0027] 4.3 Calculate the coherence speckle noise variance coefficient γ based on the multiplicative noise figure MNR. std The calculation formula is:

[0028]

[0029] 4.4. Generates with a mean coefficient of 1 and a variance coefficient of γ. std coherent speckle noise n i The noise figure length is equal to the multi-look coefficient N. ds ,but

[0030] n i =rand(1,γ) std N ds ), i = 1, 2, ..., N ds

[0031] Where rand represents the random number generation process;

[0032] 4.5 For each frame of the multi-view image, calculate the ground object scattering coefficient I with added speckle noise. n (n=1,2,...,2048 2 For any I n The formula is

[0033] I n =σ n ·n i i = randperm(1,2,...,N) ds )

[0034] Where: randperm randomly sorts i to simulate the random characteristics of speckle noise;

[0035] 4.6. Using the ground object scattering coefficient with added speckle noise and the SAR radar setting parameters, calculate the echo signal at each point in the SAR scene. The formula is as follows:

[0036]

[0037] Where: ω r Let τ be a rectangular window function, τ be the radar transmit signal pulse width, c be the speed of light, f0 be the carrier frequency, and K be the frequency. r R(n) represents the frequency modulation slope of the transmitted signal, and R(n) represents the distance from each pixel to the radar.

[0038] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0039] This invention, based on grayscale image simulation of SAR echo signals, presents a SAR echo simulation system and method based on ground object scattering characteristics and speckle noise simulation. By analyzing the speckle noise characteristics in SAR images and utilizing the actual ground backscattering coefficient and SAR imaging parameters, a method for simulating SAR radar echo signals including speckle noise that is essentially consistent with the real scene is achieved. Accurate simulation of SAR echo signals is realized in a hardware-in-the-loop simulation experiment. This overcomes the problem of insufficient realism in traditional grayscale image-based SAR echo signal simulation methods, which cannot simulate speckle noise. This invention achieves accurate simulation of echo signals that are essentially consistent with real SAR echo signals and has significant potential for widespread application. Attached Figure Description

[0040] Figure 1 This is a block diagram of the SAR echo simulation system based on ground object scattering characteristics and speckle noise of the present invention;

[0041] Figure 2 This is a flowchart of the SAR echo signal simulation calculation in this invention. Detailed Implementation

[0042] This invention provides a SAR echo simulation system based on ground object scattering characteristics and speckle noise, such as... Figure 1 As shown, it includes simulation control and display, radar signal receiving channel, intermediate frequency signal acquisition module, echo signal simulation module, intermediate frequency signal generation module, echo signal transmission channel and local oscillator module;

[0043] Simulation control and display are used to control the system and set relevant parameters, and to monitor and display the working status of the entire system;

[0044] The radar signal receiving channel is used to receive low-power radar transmission signals sent by the SAR radar system, down-convert the radar signals to intermediate frequency radar signals, and send the filtered, amplified, and power-adjusted signals to the intermediate frequency signal acquisition module.

[0045] The intermediate frequency signal acquisition module is used to perform analog-to-digital conversion on the intermediate frequency radar signal to form a digital radar signal, which is then sent to the echo signal simulation module.

[0046] The echo signal simulation module completes the SAR echo signal simulation based on the received digital radar signal and relevant parameter settings;

[0047] The intermediate frequency signal generation module performs analog-to-digital conversion on the SAR echo digital signal to form an intermediate frequency SAR echo signal;

[0048] The echo signal transmission channel is used to upconvert intermediate frequency SAR echo signals into radio frequency SAR echo signals and send them into the SAR radar system.

[0049] The local oscillator module provides local oscillator and clock signals for the radar signal receiving channel and the echo signal transmitting channel.

[0050] The SAR echo simulation method based on ground object scattering characteristics and speckle noise uses any of the above-mentioned SAR echo simulation systems based on ground object scattering characteristics and speckle noise to simulate SAR echo signals. The specific steps are as follows:

[0051] 1) Power on the system and perform a self-test. Connect the low-power radar transmit signal channel and echo signal receive channel of the SAR radar system to the radar signal receive channel and echo signal transmit channel of this system via cables.

[0052] 2) Set the operating center frequency, radar signal receiving channel gain, echo signal transmitting channel gain, SAR echo simulation multi-view coefficient, and multiplicative noise ratio (MNR) of the SAR radar system through simulation control and display, and load the SAR echo simulation reference image.

[0053] 3) The radar signal receiving channel receives the low-power radar transmission signal sent by the SAR radar system, down-converts the radar signal to an intermediate frequency radar signal, and sends the filtered, amplified, and power-adjusted signal to the intermediate frequency signal acquisition module. The intermediate frequency signal acquisition module performs analog-to-digital conversion on the intermediate frequency radar signal to form a digital radar signal, which is then sent to the echo signal simulation module.

[0054] 4) After receiving the digital radar transmitted signal and reading the relevant setting parameters, the echo signal simulation module calculates the SAR echo signal S0, as shown in the attached diagram. Figure 2 As shown, the calculation method for SAR echo signals is as follows:

[0055] 4.1 Read the reference image for SAR echo simulation. Assuming the reference image size for SAR echo simulation is 2048*2048, obtain the ground scattering coefficient matrix σ. n (n=1,2,...,2048 2 The ground scattering coefficient matrix characterizes the ideal, noise-independent RCS and reflects the backscattering characteristics of ground objects.

[0056] 4.2 Reading the SAR echo simulation multi-look coefficient N ds Multiplicative noise coefficient (MNR) is a multi-view coefficient that characterizes the non-coherent additive processing in SAR image processing. Its value is equal to the total number of frames in the multi-view image.

[0057] 4.3 Calculate the coherence speckle noise variance coefficient γ based on the multiplicative noise figure MNR. std The calculation formula is:

[0058]

[0059] 4.4. Generates with a mean coefficient of 1 and a variance coefficient of γ. std coherent speckle noise n i The noise figure length is equal to the multi-look coefficient N. ds ,but

[0060] n i =rand(1,γ) std N ds ), i = 1, 2, ..., N ds

[0061] Where rand represents the random number generation process;

[0062] 4.5 For each frame of the multi-view image, calculate the ground object scattering coefficient I with added speckle noise. n (n=1,2,...,2048 2 For any I n The formula is

[0063] I n =σ n ·n i i = randperm(1,2,...,N) ds )

[0064] Where: randperm randomly sorts i to simulate the random characteristics of speckle noise;

[0065] 4.6. Using the ground object scattering coefficient with added speckle noise and the SAR radar setting parameters, calculate the echo signal at each point in the SAR scene. The formula is as follows:

[0066]

[0067] Where: ω r Let τ be a rectangular window function, τ be the radar transmit signal pulse width, c be the speed of light, f0 be the carrier frequency, and K be the frequency. r R(n) represents the frequency modulation slope of the transmitted signal, and R(n) represents the distance from each pixel to the radar.

[0068] 5) Quantize the echo signal according to the DAC's range. Assuming the DAC is 14-bit, the maximum amplitude output is A. max =2 14 -1, the quantification formula is:

[0069]

[0070] 6) The normalized SAR echo digital signal S0′ is converted from analog to digital using the intermediate frequency signal generation module to form an intermediate frequency SAR echo signal;

[0071] 7) The echo signal transmission channel upconverts the intermediate frequency SAR echo signal into a radio frequency SAR echo signal and sends it into the SAR radar system;

[0072] 8) While transmitting low-power radar signals, the SAR radar system receives SAR radio frequency echo signals and performs imaging, detection, and identification processing on the echo signals.

[0073] This invention, based on the scattering characteristics of ground objects and speckle noise simulation, overcomes the problem that traditional SAR echo signal simulation methods based on grayscale image simulation cannot simulate speckle noise, resulting in insufficient realism of SAR echo signal simulation. It achieves accurate simulation of echo signals that are basically consistent with real SAR echo signals.

Claims

1. A SAR echo simulation system based on ground object scattering characteristics and speckle noise, characterized by: It includes simulation control and display, radar signal receiving channel, intermediate frequency signal acquisition module, echo signal simulation module, intermediate frequency signal generation module, and echo signal transmitting channel; Simulation control and display are used to control the system and set relevant parameters, and to monitor and display the working status of the entire system; The radar signal receiving channel is used to receive low-power radar transmission signals sent by the SAR radar system, down-convert the radar signals to intermediate frequency radar signals, and send the filtered, amplified, and power-adjusted signals to the intermediate frequency signal acquisition module. The intermediate frequency signal acquisition module is used to perform analog-to-digital conversion on the intermediate frequency radar signal to form a digital radar signal, which is then sent to the echo signal simulation module. The echo signal simulation module completes the SAR echo signal simulation based on the received digital radar signal and relevant parameter settings; The intermediate frequency signal generation module performs analog-to-digital conversion on the SAR echo digital signal to form an intermediate frequency SAR echo signal; The echo signal transmission channel is used to upconvert intermediate frequency SAR echo signals into radio frequency SAR echo signals and send them into the SAR radar system. The calculation method for SAR echo signals is as follows: a) Read the reference image for SAR echo simulation. Assuming the reference image size for SAR echo simulation is 2048*2048, obtain the ground scattering coefficient matrix σ. n n = 1, 2, ..., 2048 2 The ground scattering coefficient matrix characterizes the ideal, noise-independent RCS and reflects the backscattering characteristics of ground objects. b) Read the SAR echo simulation multi-look coefficient N ds Multiplicative noise coefficient (MNR) is a multi-view coefficient that characterizes the non-coherent additive processing in SAR image processing. Its value is equal to the total number of frames in the multi-view image. c) Calculate the speckle noise variance coefficient γ based on the multiplicative noise figure MNR. std The calculation formula is: d) Generate data with a mean coefficient of 1 and a variance coefficient of γ. std coherent speckle noise n i The noise figure length is equal to the multi-look coefficient N. ds ,but n i =rand(1,γ std ,N ds ),i=1,2,...,N ds Where rand represents the random number generation process; e) For each frame of the multi-view image, calculate the ground object scattering coefficient I with added speckle noise. n n = 1, 2, ..., 2048 2 For any I n The formula is IN n =σ n ·n i ,i=margin binding(1,2,...,N ds ) Where randperm randomly sorts i to simulate the random characteristics of speckle noise; f) Using the ground object scattering coefficients with added speckle noise and the SAR radar setting parameters, calculate the echo signal at each point in the SAR scene, using the formula: Where: ω r Let τ be a rectangular window function, τ be the radar transmit signal pulse width, c be the speed of light, f0 be the carrier frequency, and K be the frequency. r R(n) represents the frequency modulation slope of the transmitted signal, and R(n) represents the distance from each pixel to the radar.

2. The SAR echo simulation system based on ground object scattering characteristics and speckle noise according to claim 1, characterized in that: It also includes a local oscillator module that provides local oscillator and clock signals for the radar signal receiving channel and the echo signal transmitting channel.

3. A SAR echo simulation method based on ground object scattering characteristics and speckle noise, characterized by: The SAR echo signal simulation system based on ground object scattering characteristics and speckle noise, as described in claim 1 or 2, is implemented through the following specific steps: 1) Power on the system and perform a self-test. Connect the low-power radar transmit signal channel and echo signal receive channel of the SAR radar system to the radar signal receive channel and echo signal transmit channel of this system via cables. 2) Set the operating center frequency, radar signal receiving channel gain, echo signal transmitting channel gain, SAR echo simulation multi-view coefficient, and multiplicative noise ratio (MNR) of the SAR radar system through simulation control and display, and load the SAR echo simulation reference image. 3) The radar signal receiving channel receives the low-power radar transmission signal sent by the SAR radar system, down-converts the radar signal to an intermediate frequency radar signal, and sends the filtered, amplified, and power-adjusted signal to the intermediate frequency signal acquisition module. The intermediate frequency signal acquisition module performs analog-to-digital conversion on the intermediate frequency radar signal to form a digital radar signal, which is then sent to the echo signal simulation module. 4) After receiving the digital radar transmitted signal and reading the relevant setting parameters, the echo signal simulation module calculates the SAR echo signal S0; 5) Quantize the echo signal according to the DAC's range. Assuming the DAC is 14-bit, the maximum amplitude output is A. max =2 14 -1, the quantification formula is: 6) The normalized SAR echo digital signal S0′ is converted from analog to digital using the intermediate frequency signal generation module to form an intermediate frequency SAR echo signal; 7) The echo signal transmission channel upconverts the intermediate frequency SAR echo signal into a radio frequency SAR echo signal and sends it into the SAR radar system; 8) While transmitting low-power radar signals, the SAR radar system receives SAR radio frequency echo signals and performs imaging, detection, and identification processing on the echo signals.

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