SAR echo simulation system and method based on ground object scattering characteristics and speckle noise

Abstract

The invention relates to the technical field of radar system simulation, particularly discloses an SAR (Synthetic Aperture Radar) echo simulation system and method based on ground object scattering characteristics and speckle noise, and provides the SAR echo simulation system and method based on the ground object scattering characteristics and speckle noise simulation on the basis of simulating SAR echo signals based on gray images. On the basis of analyzing speckle noise characteristics in an SAR image, a ground real backscattering coefficient and SAR imaging related parameters are utilized to realize an SAR radar echo signal simulation method which is basically consistent with a real scene and contains speckle noise, accurate simulation of the SAR echo signal is realized in a semi-physical simulation test, and the simulation precision of the SAR echo signal is improved. According to the SAR echo signal simulation method based on gray level image simulation, the problem that in a traditional SAR echo signal simulation method based on gray level image simulation, speckle noise cannot be simulated, so that the simulation fidelity of the SAR echo signal is insufficient is solved, accurate simulation of the echo signal basically consistent with a real SAR echo signal is achieved, and the SAR echo signal simulation method based on gray level image simulation has good application and popularization value.

Description

Technical Field

[0001] The invention relates to the technical field of radar system simulation, and in particular discloses a SAR echo simulation system and method based on ground object scattering characteristics and coherent speckle noise. Background Art

[0002] Synthetic aperture radar (SAR), as an active sensor that uses microwaves for perception, has the ability to observe the earth in all weather and all day, and has become an important means of military reconnaissance. SAR imaging plays an important role in the field of military target detection, positioning and identification by performing high-resolution imaging of the target area. SAR radar effectively images the target area by transmitting broadband signals. The image can effectively display the scattering characteristics of the ground objects and the characteristics of the target, and then complete the target positioning through the target detection and recognition algorithm. At present, in order to effectively verify the performance of SAR imaging equipment, target echo simulation equipment is often used to generate SAR echo signals, and the echo is sent to the SAR imaging radar by radiation or injection to verify the imaging, target detection, identification and positioning performance of the equipment.

[0003] The fidelity of SAR echo signal simulation directly affects the performance of military target detection and positioning in the image. In the process of simulating SAR echo signals by target echo simulation equipment, traditional methods mostly pre-calculate and generate echo signals based on grayscale images, and transmit echo signals through pulse triggering. In this method, the grayscale image reflects the ground scattering characteristics, and the scene echo signal is calculated through the ground backscatter coefficient (RCS) and elevation data (DEM), but the coherent speckle characteristics in the echo signal are not considered. The coherent speckle is an internal process of ground scattering and is part of the entire scattering. It will affect the target detection performance in the actual SAR image. The traditional SAR echo signal based on grayscale image simulation ignores this influence, which makes the SAR echo signal simulation fidelity insufficient. Summary of the invention

[0004] In order to overcome the shortcomings in the background technology, the present invention discloses a SAR echo simulation system and method based on ground scattering characteristics and coherent speckle noise. The system and method utilize the ground's true backscattering coefficient and SAR imaging-related parameters to realize a SAR radar echo signal simulation method containing coherent speckle noise that is basically consistent with the real scene, and realizes accurate simulation of SAR echo signals in semi-physical simulation experiments.

[0005] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0006] The SAR echo simulation system based on ground object scattering characteristics and coherent speckle noise 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 transmission channel;

[0007] Simulation control and display are used to complete system control and related parameter settings, and monitor and display the working status of the entire system;

[0008] The radar signal receiving channel is used to receive the low-power radar transmission signal sent by the SAR radar system, down-convert the radar signal into an intermediate frequency radar signal, and send the signal to the intermediate frequency signal acquisition module after filtering, amplifying and power adjustment;

[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 and send it to the echo signal simulation module;

[0010] The echo signal simulation module completes the SAR echo signal simulation according to the received digital radar signal and related 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 up-convert the intermediate frequency SAR echo signal into a radio frequency SAR echo signal and send it to the SAR radar system.

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

[0014] The SAR echo simulation method based on ground object scattering characteristics and coherent speckle noise uses any one of the above SAR echo simulation systems based on ground object scattering characteristics and coherent speckle noise to realize SAR echo signal simulation. The specific steps are as follows:

[0015] 1) The system is powered on and self-checked, and the low-power radar transmission signal channel and echo signal receiving channel of the SAR radar system are connected to the radar signal receiving channel and echo signal transmission channel of the system through cables;

[0016] 2) Set the working center frequency of the SAR radar system, radar signal receiving channel gain, echo signal transmitting channel gain, SAR echo simulation multi-view coefficient, multiplicative noise ratio MNR 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 into an intermediate frequency radar signal, and sends the signal to the intermediate frequency signal acquisition module after filtering, amplifying, and power adjustment. The intermediate frequency signal acquisition module performs analog-to-digital conversion on the intermediate frequency radar signal to form a digital radar signal and sends it to the echo signal simulation module;

[0018] 4) After the echo signal simulation module receives the digital radar transmission signal and reads the relevant setting parameters, it calculates the SAR echo signal S0;

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

[0020]

[0021] 6) Using the intermediate frequency signal generation module to perform analog-to-digital conversion on the normalized SAR echo digital signal S0′ to form an intermediate frequency SAR echo signal;

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

[0023] 8) The SAR radar system transmits low-power radar transmission signals while receiving SAR radio frequency echo signals, and then 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 coherent speckle noise, the calculation method of the SAR echo signal in step 4) is as follows:

[0025] 4.1. Read the reference image of SAR echo simulation. Assuming that the size of the reference image of SAR echo simulation is 2048*2048, obtain the ground scattering coefficient matrix σ n (n=1,2,...,2048 2 ), the ground scattering coefficient matrix represents the ideal RCS that is not affected by noise and reflects the backscattering characteristics of the ground objects;

[0026] 4.2. Read SAR echo simulation multi-view coefficient N ds , the multiplicative noise coefficient MNR, the multi-view coefficient characterizes the incoherent addition process in the SAR image processing, and its value is equal to the total number of frames of the multi-view image;

[0027] 4.3. Calculate the coherent speckle noise variance coefficient γ based on the multiplicative noise coefficient MNR std , the calculation formula is

[0028]

[0029] 4.4. Generate a mean coefficient of 1 and a variance coefficient of γ std The coherent speckle noise n i , the noise coefficient length is equal to the multi-view 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 coherent speckle noise added 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] Among them: randperm is to randomly sort i to simulate the random characteristics of coherent speckle noise;

[0035] 4.6. Using the ground scattering coefficient with added coherent speckle noise and the SAR radar setting parameters, the echo signal of each point in the SAR scene is calculated. The formula is:

[0036]

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

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

[0039] The present invention provides a SAR echo simulation system and method based on the simulation of SAR echo signals based on grayscale images, and based on the scattering characteristics of ground objects and the simulation of coherent speckle noise. On the basis of analyzing the coherent speckle noise characteristics in the SAR image, the present invention utilizes the real backscattering coefficient of the ground and the SAR imaging related parameters to realize a SAR radar echo signal simulation method containing coherent speckle noise that is basically consistent with the real scene, and realizes the accurate simulation of the SAR echo signal in a semi-physical simulation experiment, thereby overcoming the problem that the coherent speckle noise cannot be simulated in the traditional SAR echo signal simulation method based on grayscale image simulation, resulting in insufficient fidelity of the SAR echo signal simulation, and realizes the accurate simulation of the echo signal that is basically consistent with the real SAR echo signal. The present invention has a good value for popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0041] Figure 2 It is a flow chart of SAR echo signal simulation calculation in the present invention. DETAILED DESCRIPTION

[0042] The present invention is based on the SAR echo simulation system of ground object scattering characteristics and coherent 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 complete system control and related parameter settings, and monitor and display the working status of the entire system;

[0044] The radar signal receiving channel is used to receive the low-power radar transmission signal sent by the SAR radar system, down-convert the radar signal into an intermediate frequency radar signal, and send the signal to the intermediate frequency signal acquisition module after filtering, amplifying and power adjustment;

[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 and send it to the echo signal simulation module;

[0046] The echo signal simulation module completes the SAR echo signal simulation according to the received digital radar signal and related 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 up-convert the intermediate frequency SAR echo signal into a radio frequency SAR echo signal and send it to 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 coherent speckle noise uses any one of the above SAR echo simulation systems based on ground object scattering characteristics and coherent speckle noise to realize SAR echo signal simulation. The specific steps are as follows:

[0051] 1) The system is powered on and self-checked, and the low-power radar transmission signal channel and echo signal receiving channel of the SAR radar system are connected to the radar signal receiving channel and echo signal transmission channel of the system through cables;

[0052] 2) Set the working center frequency of the SAR radar system, radar signal receiving channel gain, echo signal transmitting channel gain, SAR echo simulation multi-view coefficient, multiplicative noise ratio MNR 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 into an intermediate frequency radar signal, and sends the signal to the intermediate frequency signal acquisition module after filtering, amplifying, and power adjustment. The intermediate frequency signal acquisition module performs analog-to-digital conversion on the intermediate frequency radar signal to form a digital radar signal and sends it to the echo signal simulation module;

[0054] 4) After the echo signal simulation module receives the digital radar transmission signal and reads the relevant setting parameters, it calculates the SAR echo signal S0, as shown in the attached figure. Figure 2 As shown, the calculation method of SAR echo signal is as follows:

[0055] 4.1. Read the reference image of SAR echo simulation. Assuming that the size of the reference image of SAR echo simulation is 2048*2048, obtain the ground scattering coefficient matrix σ n (n=1,2,...,2048 2 ), the ground scattering coefficient matrix represents the ideal RCS that is not affected by noise and reflects the backscattering characteristics of the ground objects;

[0056] 4.2. Read SAR echo simulation multi-view coefficient N ds , the multiplicative noise coefficient MNR, the multi-view coefficient characterizes the incoherent addition process in the SAR image processing, and its value is equal to the total number of frames of the multi-view image;

[0057] 4.3. Calculate the coherent speckle noise variance coefficient γ based on the multiplicative noise coefficient MNR std , the calculation formula is

[0058]

[0059] 4.4. Generate a mean coefficient of 1 and a variance coefficient of γ std The coherent speckle noise n i , the noise coefficient length is equal to the multi-view 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 coherent speckle noise added 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] Among them: randperm is to randomly sort i to simulate the random characteristics of coherent speckle noise;

[0065] 4.6. Using the ground scattering coefficient with added coherent speckle noise and the SAR radar setting parameters, the echo signal of each point in the SAR scene is calculated. The formula is:

[0066]

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

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

[0069]

[0070] 6) Using the intermediate frequency signal generation module to perform analog-to-digital conversion on the normalized SAR echo digital signal S0′ to form an intermediate frequency SAR echo signal;

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

[0072] 8) The SAR radar system transmits low-power radar transmission signals while receiving SAR radio frequency echo signals, and then performs imaging, detection and identification processing on the echo signals.

[0073] The present invention is based on the scattering characteristics of ground objects and the simulation of coherent speckle noise, and overcomes the problem that the coherent speckle noise cannot be simulated in the traditional SAR echo signal simulation method based on grayscale image simulation, resulting in insufficient fidelity of SAR echo signal simulation, and realizes 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 coherent 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 complete system control and related parameter settings, and monitor and display the working status of the entire system; The radar signal receiving channel is used to receive the low-power radar transmission signal sent by the SAR radar system, down-convert the radar signal into an intermediate frequency radar signal, and send the signal to the intermediate frequency signal acquisition module after filtering, amplifying and power adjustment; 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 and send it to the echo signal simulation module; The echo signal simulation module completes the SAR echo signal simulation according to the received digital radar signal and related 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 up-convert the intermediate frequency SAR echo signal into a radio frequency SAR echo signal and send it to the SAR radar system.

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

3. A SAR echo simulation method based on ground object scattering characteristics and coherent speckle noise is characterized by: The SAR echo simulation system based on ground object scattering characteristics and coherent speckle noise as described in claim 1 or 2 is used to realize SAR echo signal simulation, and the specific steps are as follows: 1) The system is powered on and self-checked, and the low-power radar transmission signal channel and echo signal receiving channel of the SAR radar system are connected to the radar signal receiving channel and echo signal transmission channel of the system through cables; 2) Set the working center frequency of the SAR radar system, radar signal receiving channel gain, echo signal transmitting channel gain, SAR echo simulation multi-view coefficient, multiplicative noise ratio MNR 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 into an intermediate frequency radar signal, and sends the signal to the intermediate frequency signal acquisition module after filtering, amplifying, and power adjustment. The intermediate frequency signal acquisition module performs analog-to-digital conversion on the intermediate frequency radar signal to form a digital radar signal and sends it to the echo signal simulation module; 4) After the echo signal simulation module receives the digital radar transmission signal and reads the relevant setting parameters, it calculates the SAR echo signal S0; 5) Quantize the echo signal according to the DAC range. Assuming the DAC is 14 bits, the maximum amplitude output is A max =2 14 -1, the quantization formula is: 6) Using the intermediate frequency signal generation module to perform analog-to-digital conversion on the normalized SAR echo digital signal S0′ to form an intermediate frequency SAR echo signal; 7) The echo signal transmission channel converts the intermediate frequency SAR echo signal into a radio frequency SAR echo signal and sends it to the SAR radar system; 8) The SAR radar system transmits low-power radar transmission signals while receiving SAR radio frequency echo signals, and then performs imaging, detection and identification processing on the echo signals.

4. The SAR echo simulation method based on ground object scattering characteristics and coherent speckle noise according to claim 3 is characterized in that: the calculation method of the SAR echo signal in step 4) is as follows: 4.

1. Read the reference image of SAR echo simulation. Assuming that the size of the reference image of SAR echo simulation is 2048*2048, obtain the ground scattering coefficient matrix σ n (n=1,2,...,2048 2 ), the ground scattering coefficient matrix represents the ideal RCS that is not affected by noise and reflects the backscattering characteristics of the ground objects; 4.

2. Read SAR echo simulation multi-view coefficient N ds , the multiplicative noise coefficient MNR, the multi-view coefficient characterizes the incoherent addition process in the SAR image processing, and its value is equal to the total number of frames of the multi-view image; 4.

3. Calculate the coherent speckle noise variance coefficient γ based on the multiplicative noise coefficient MNR std , the calculation formula is 4.

4. Generate a mean coefficient of 1 and a variance coefficient of γ std The coherent speckle noise n i , the noise coefficient length is equal to the multi-view 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; 4.

5. For each frame of the multi-view image, calculate the ground object scattering coefficient I with coherent speckle noise added 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 is to randomly sort i to simulate the random characteristics of coherent speckle noise; 4.

6. Using the ground scattering coefficient with added coherent speckle noise and the SAR radar setting parameters, the echo signal of each point in the SAR scene is calculated. The formula is: in: ω r is a rectangular window function, τ is the pulse width of the radar transmission signal, c is the speed of light, f0 is the carrier frequency, K r is the frequency modulation slope of the transmitted signal, and R(n) is the distance from each pixel point to the radar.

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