Non-cooperative bistatic SAR imaging system, processing method and device

Abstract

The invention provides a non-cooperative bistatic SAR imaging system, processing method and device, and relates to the technical field of radar systems, and the system comprises a satellite-borne irradiation source and a non-cooperative bistatic radar receiving and processing system. The non-cooperative bistatic radar receiving and processing system comprises an antenna subsystem, a receiving subsystem, a signal acquisition and processing subsystem and a display control terminal. The satellite-borne irradiation source is used for transmitting a direct wave signal; the antenna subsystem is used for simultaneously receiving a direct wave signal and an echo signal of an imaging area; the receiving subsystem is used for processing the direct wave signal and the echo signal and outputting a direct wave reference signal and a target echo detection signal; the signal acquisition and processing subsystem is used for performing bistatic SAR imaging processing on the direct wave reference signal and the target echo detection signal to obtain a bistatic SAR image; and the display control terminal is used for displaying the bistatic SAR image. According to the invention, the specific construction of the non-cooperative bistatic SAR imaging system is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of radar systems, and in particular to a non-cooperative bistatic SAR imaging system, a processing method and a device. Background Art

[0002] Bistatic radar is highly valued in the radar industry because of its long transmission and reception intervals and the fact that the receiving station does not emit electromagnetic waves, and therefore has good resistance to active directional interference and anti-radiation missiles.

[0003] Existing Synthetic Aperture Radar (SAR) bistatic imaging systems are mainly satellite-borne (satellite transmission-satellite reception) or airborne (aircraft transmission-aircraft reception), and are generally cooperative.

[0004] The concept of satellite-aircraft (or satellite-ground) joint bistatic SAR has brought about the possibility of non-cooperative SAR imaging, which is an advanced bistatic SAR mode. Therefore, it is necessary to study a non-cooperative bistatic SAR imaging system. Summary of the invention

[0005] In view of the defects existing in the prior art, the present invention provides a non-cooperative bistatic SAR imaging system, a processing method and a device, so as to solve the defect that the non-cooperative bistatic SAR imaging system in the prior art is difficult to implement, and realize the specific construction of the non-cooperative bistatic SAR imaging system.

[0006] The present invention provides a non-cooperative bistatic SAR imaging system, comprising: a satellite-borne illumination source and a non-cooperative bistatic radar receiving and processing system; the non-cooperative bistatic radar receiving and processing system comprises: an antenna subsystem, a receiving subsystem, a signal acquisition and processing subsystem and a display and control terminal; The satellite-borne illumination source is used to emit direct wave signals; The antenna subsystem is used to simultaneously receive the direct wave signal and the echo signal of the imaging area; The receiving subsystem is used to process the direct wave signal and the echo signal, and output a direct wave reference signal and a target echo detection signal; The signal acquisition and processing subsystem is used to perform bistatic SAR imaging processing on the direct wave reference signal and the target echo detection signal to obtain a bistatic SAR image; The display and control terminal is used to display the bistatic SAR image.

[0007] In some embodiments, the receiving subsystem includes: a multi-channel receiver and a clock; The multi-channel receiver is used to perform down-conversion, amplification, and filtering on the direct wave signal and the echo signal respectively to obtain the direct wave reference signal and the target echo detection signal; The clock is used to generate a reference clock signal.

[0008] In some embodiments, the multi-channel receiver includes: a low noise amplifier, an image rejection mixer, a front intermediate frequency amplifier, a first matching network, a first 30M filter, a first intermediate frequency amplifier, an attenuation network, a controllable gain amplifier, a second matching network, a second intermediate frequency amplifier, a power divider, a first matching output network, an oscilloscope, a second 30M filter, and a second matching output network; The input end of the low noise amplifier is used as the input end of the receiver, and the low noise amplifier, the image rejection mixer, the front intermediate frequency amplifier, the first matching network, the first 30M filter, the first intermediate frequency amplifier, the attenuation network, the controllable gain amplifier, the second matching network, the second intermediate frequency amplifier and the power divider are connected in sequence; The output end of the power divider is divided into two paths, one path is connected to the first matching output network and the oscilloscope in sequence, and the other path is connected to the second 30M filter and the second matching output network in sequence, and the output end of the second matching output network serves as the output end of the receiver.

[0009] In some embodiments, the signal acquisition and processing subsystem includes: a signal acquisition unit, a signal processing unit, a main control unit and an interface unit; The signal acquisition unit is used to perform analog-to-digital conversion on the direct wave reference signal and the target echo detection signal, respectively, to obtain a baseband digital signal corresponding to the direct wave reference signal and a baseband digital signal corresponding to the target echo detection signal; The signal processing unit is used to perform bistatic SAR imaging processing on the baseband digital signal corresponding to the direct wave reference signal and the baseband digital signal corresponding to the target echo detection signal to obtain a bistatic SAR image; The main control unit is used to solve commands and parameters and control each subsystem to work normally according to the established sequence; The interface unit is used for external connection.

[0010] In some embodiments, the signal acquisition unit includes: a reference channel signal acquisition module and a monitoring channel signal acquisition module; The reference channel signal acquisition module is used to perform analog-to-digital conversion on the direct wave reference signal; The monitoring channel signal acquisition module is used to perform analog-to-digital conversion on the target echo detection signal.

[0011] The present invention also provides a non-cooperative bistatic SAR imaging processing method based on the above system, comprising: The received echo signal is processed in sequence by two-dimensional FFT, range bending correction and range compression, range FFT, cubic filtering, first azimuth IFFT, nonlinear frequency modulation scaling, azimuth FFT, azimuth compression, second azimuth IFFT and reference distance variation compensation to obtain a SAR image.

[0012] The present invention also provides a non-cooperative bistatic SAR imaging processing device, comprising: The processing module is used to perform two-dimensional FFT, range curvature correction and range compression, range FFT, cubic filtering, first azimuth IFFT, nonlinear frequency modulation scaling, azimuth FFT, azimuth compression, second azimuth IFFT and reference distance variation compensation on the received echo signal in sequence to obtain a SAR image.

[0013] The present invention also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the non-cooperative dual-base SAR imaging processing method as described above is implemented.

[0014] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the non-cooperative bistatic SAR imaging processing method as described in any one of the above is implemented.

[0015] The present invention also provides a computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the non-cooperative bistatic SAR imaging processing method described above is implemented.

[0016] The non-cooperative bistatic SAR imaging system, processing method and device provided by the present invention are through a satellite-borne illumination source and a non-cooperative bistatic radar receiving and processing system; the non-cooperative bistatic radar receiving and processing system includes: an antenna subsystem, a receiving subsystem, a signal acquisition and processing subsystem and a display and control terminal; the satellite-borne illumination source transmits a direct wave signal; the antenna subsystem simultaneously receives the direct wave signal and the echo signal of the imaging area; the receiving subsystem processes the direct wave signal and the echo signal, and outputs a direct wave reference signal and a target echo detection signal; the signal acquisition and processing subsystem performs bistatic SAR imaging processing on the direct wave reference signal and the target echo detection signal to obtain a bistatic SAR image; the display and control terminal displays the bistatic SAR image. The present invention realizes the specific construction of the non-cooperative bistatic SAR imaging system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is a schematic diagram of non-cooperative bistatic SAR imaging modeling; Figure 2 It is a structural schematic diagram of a non-cooperative bistatic SAR imaging system provided by the present invention; Figure 3 It is a structural schematic diagram of a multi-channel receiver provided by the present invention; Figure 4 It is a flow chart of the non-cooperative bistatic SAR imaging processing method provided by the present invention; Figure 5 It is a flow chart of the non-cooperative bistatic SAR imaging processing device provided by the present invention; Figure 6 It is a structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Bistatic radar has good anti-active directional interference and anti-radiation missile capabilities due to the long distance between transmission and reception and the fact that the receiving station does not emit electromagnetic waves. Therefore, it is highly valued in the radar industry. When using radio, television or satellite and other opportunistic illumination sources or friendly or even enemy non-cooperative radars to detect targets, there is no dedicated physical link between the receiving station and the transmitting station for signal synchronization processing. This situation is called non-cooperative bistatic radar.

[0021] Bistatic Synthetic Aperture Radar (BiSAR) is an important branch of the development of synthetic aperture radar. American researchers began to study airborne bistatic SAR imaging technology in the 1970s, making it the first country to conduct research on bistatic SAR. Similar to the research method of monostatic SAR imaging system, the research on bistatic SAR imaging technology is also carried out from two main application areas: airborne and satellite-borne. In addition, a new research field has emerged in the intersection of satellite-borne and airborne SAR, namely satellite-aircraft (or satellite-ground) joint bistatic SAR.

[0022] The concept of satellite-aircraft (or satellite-ground) joint bistatic SAR has brought about the possibility of non-cooperative SAR imaging. This is an advanced bistatic SAR mode. The non-cooperative radiation source can use the existing navigation, communication and broadcast satellite signals, or use the satellite-borne radar signals for imaging, which can effectively reduce the system cost and increase the concealment of the work. Since signals such as FM / TV or GPS are not specially designed for target detection and imaging, their signal power (effective range) and signal bandwidth (range resolution) are often not as good as radar signals. Therefore, the use of satellite-borne SAR radar signals has more potential advantages in high-resolution imaging than navigation, communication and broadcast satellite signals. Since the satellite-borne SAR radar signals basically adopt a pulse system, the system is also called a non-cooperative bistatic SAR system.

[0023] The non-cooperative bistatic SAR imaging system is a non-cooperative bistatic synthetic aperture radar based on a spaceborne SAR radar illumination source, which can perform remote sensing imaging in a passive manner without adding satellite equipment. The system has the following main advantages: 1) Such a passive system only requires the development of a receiver, which is relatively low cost; 2) The “transmit far away and receive near” working system is adopted, and the signal-to-noise ratio gain at the receiver end is considerable; 3) The receiver is carried on a variety of platforms (fixed stations, aircraft, balloons, airships, etc.), and the geometric configuration of the transceiver system is flexible, which can obtain the non-backscatter coefficient of the target; 4) Through technical upgrades, such as carrying multiple antennas, the functions of Interferometric Synthetic Aperture Radar (InSAR) and Ground Moving Target Indication (GMTI) can also be realized; 5) The dual-base SAR system can achieve effective forward-looking SAR imaging, which can enhance survivability in electronic warfare and meet the needs of special occasions such as SAR image navigation.

[0024] The non-cooperative bistatic SAR imaging system can use a relatively cheap receiving system to receive the radiation signals of the advanced radar built by the enemy at great expense to achieve the monitoring and imaging tasks of the enemy's battlefield area. Therefore, the system has important research value and good application prospects.

[0025] Figure 1 is a schematic diagram of non-cooperative bistatic SAR imaging modeling, such as Figure 1 As shown, the launch platform position is recorded as , the receiving station location is recorded as .

[0026] Assume that the transmitted signal is:

[0027] in, For quick time, is the envelope of the transmitted signal, is the distance modulation frequency, For the carrier frequency.

[0028] The echo signal of a point target can be expressed as:

[0029] In the formula, is the envelope of the azimuth beam, is the target’s position, The delay for the target, The target's position.

[0030] in,

[0031] In the formula, is the target’s position, is the transmission station movement speed, is the Y-axis coordinate corresponding to the center of the imaging area, is the corresponding Y-axis coordinate of the launch platform.

[0032]

[0033] In the formula, is the bistatic distance and, is the distance from the target to the receiving station, is the distance from the target to the transmitting station, For light beam.

[0034] Using the stationary phase principle, the expression of the echo signal in the range Doppler domain can be obtained as follows:

[0035] in,

[0036] In the formula, is the frequency corresponding to time t, is the gain constant, is the frequency modulation slope, is the sum of the bistatic distances corresponding to the shortest slant distance from the track to the target, is the equivalent frequency modulation slope, is the first gain coefficient, is the distance modulation frequency, is the second gain coefficient.

[0037] In the range Doppler domain, the target delay can be expressed as:

[0038] in,

[0039] In the formula, is the bistatic distance and, is the distance from the target to the receiving station, is the sum of the bistatic distances corresponding to the shortest slant distance from the track to the target.

[0040] From the expression of the echo signal in the range Doppler domain, it can be seen that the second phase term determines the azimuth modulation, while the third phase term determines the range modulation, where represents the range migration in the range Doppler domain. And due to the influence of the cross-coupling term, in the range Doppler domain, the range modulation frequency is not , the new equivalent modulation frequency Follow It can also be noted that the azimuth modulation and range migration are also related to about, that is The Doppler process of the target is determined by the SAR. This is because only the transmitter is moving in this system, and the Doppler is only contributed by it. Therefore, the key to imaging is to grasp the target's The distribution law in the echo data is then used to realize two-dimensional compression processing.

[0041] Figure 2 : is a schematic diagram of the structure of the non-cooperative bistatic SAR imaging system provided by the present invention, such as Figure 2As shown, the present invention provides a non-cooperative bistatic SAR imaging system, including: a satellite-borne illumination source and a non-cooperative bistatic radar receiving and processing system; the non-cooperative bistatic radar receiving and processing system includes: an antenna subsystem, a receiving subsystem, a signal acquisition and processing subsystem and a display and control terminal.

[0042] The satellite-borne illumination source is used to transmit direct wave signals; The antenna subsystem is used to simultaneously receive the direct wave signal and the echo signal of the imaging area; The receiving subsystem is used to process the direct wave signal and the echo signal, and output the direct wave reference signal and the target echo detection signal; The signal acquisition and processing subsystem is used to perform bistatic SAR imaging processing on the direct wave reference signal and the target echo detection signal to obtain a bistatic SAR image; The display and control terminal is used to display dual-base SAR images.

[0043] Specifically, the non-cooperative bistatic SAR imaging system uses a spaceborne SAR radar as a non-cooperative illumination source. The bistatic SAR imaging system based on a spaceborne illumination source mainly includes: a spaceborne illumination source and a non-cooperative bistatic radar receiving and processing system.

[0044] The satellite-borne illumination source uses a low-orbit radar remote sensing satellite. The orbit altitude of a typical satellite-borne SAR sensor is about several hundred kilometers. The operating frequency band covers L, S, C and X bands. The mapping band width can range from tens of kilometers to hundreds of kilometers, and the resolution ranges from a dozen meters to several meters (the transmission bandwidth can vary with the operating mode).

[0045] The non-cooperative dual-base radar receiving and processing system can adopt a radar receiving system with the same frequency band as the satellite-borne radar. The receiving system has the indicators of high sensitivity, large dynamic range, and good channel consistency.

[0046] The satellite-borne illumination source transmits a direct wave signal, the antenna subsystem receives the direct wave signal and the echo signal of the imaging area simultaneously, the receiving subsystem processes the direct wave signal and the echo signal, and outputs the direct wave reference signal and the target echo detection signal, the signal acquisition and processing subsystem performs dual-base SAR imaging processing on the direct wave reference signal and the target echo detection signal to obtain a dual-base SAR image, and the display and control terminal realizes the control of the non-cooperative dual-base SAR system and the display of SAR imaging data.

[0047] The antenna subsystem uses an array antenna, which is a high-gain directional antenna. For the L-band spaceborne SAR radar illumination source, the antenna must have the ability to receive signals from 1 to 2 GHz.

[0048] The non-cooperative bistatic SAR imaging system provided by the present invention is through a satellite-borne illumination source and a non-cooperative bistatic radar receiving and processing system; the non-cooperative bistatic radar receiving and processing system includes: an antenna subsystem, a receiving subsystem, a signal acquisition and processing subsystem and a display and control terminal; the satellite-borne illumination source transmits a direct wave signal; the antenna subsystem simultaneously receives the direct wave signal and the echo signal of the imaging area; the receiving subsystem processes the direct wave signal and the echo signal, and outputs a direct wave reference signal and a target echo detection signal; the signal acquisition and processing subsystem performs bistatic SAR imaging processing on the direct wave reference signal and the target echo detection signal to obtain a bistatic SAR image; the display and control terminal displays the bistatic SAR image. The present invention realizes the specific construction of the non-cooperative bistatic SAR imaging system.

[0049] In some embodiments, Figure 2 As shown, the receiving subsystem includes: a multi-channel receiver and a clock.

[0050] The multi-channel receiver is used to down-convert, amplify and filter the direct wave signal and the echo signal respectively to obtain the direct wave reference signal and the target echo detection signal; The clock is used to generate a reference clock signal.

[0051] Specifically, the receiving subsystem includes a multi-channel receiver and a clock. The multi-channel receiver down-converts, amplifies, and filters the direct wave signal and the echo signal, respectively, and obtains the direct wave reference signal and the target echo detection signal, which are transmitted to the signal acquisition and processing subsystem, and the clock generates various reference clock signals.

[0052] The receiver subsystem needs to be designed for different frequency bands (such as L, S, C and X bands), and the receiver structures of different frequency bands are the same. The receiver has 4 receiving channels (BANK1~BANK4). The receiver can cover the frequency band of satellite radar signals by selecting different preselectors through frequency preselection. The intermediate frequency receiver has a tunable function and can convert the satellite radar signals to intermediate frequencies respectively.

[0053] The receiver processes the direct wave signal and the echo signal in parallel through two different channels to obtain the direct wave reference signal and the target echo detection signal.

[0054] In some embodiments, the multi-channel receiver includes: a low noise amplifier, an image rejection mixer, a front intermediate frequency amplifier, a first matching network, a first 30M filter, a first intermediate frequency amplifier, an attenuation network, a controllable gain amplifier, a second matching network, a second intermediate frequency amplifier, a power divider, a first matching output network, an oscilloscope, a second 30M filter, and a second matching output network; The input end of the low noise amplifier is used as the input end of the receiver, and the low noise amplifier, the image rejection mixer, the front intermediate frequency amplifier, the first matching network, the first 30M filter, the first intermediate frequency amplifier, the attenuation network, the controllable gain amplifier, the second matching network, the second intermediate frequency amplifier and the power divider are connected in sequence; The output end of the power divider is divided into two paths, one path is connected to the first matching output network and the oscilloscope in sequence, and the other path is connected to the second 30M filter and the second matching output network in sequence. The output end of the second matching output network serves as the output end of the receiver.

[0055] Specifically, Figure 3 is a schematic diagram of the structure of a multi-channel receiver provided by the present invention, such as Figure 3 As shown, the multi-channel receiver includes: a low noise amplifier (LNA), an image rejection mixer, a front intermediate frequency amplifier, a first matching network, a first 30M filter, a first intermediate frequency amplifier, an attenuation network, a controllable gain amplifier, a second matching network, a second intermediate frequency amplifier, a power divider, a first matching output network, an oscilloscope, a second 30M filter and a second matching output network.

[0056] The receiver operates at a frequency of f=X±30MHz, and uses an image rejection mixer for down-conversion. The selection of each frequency point (including the intermediate frequency and local oscillator frequency) should ensure that no harmonics or intermodulation occurs within the intermediate frequency band. The receiver receives the RF signal, outputs the intermediate frequency signal after mixing, amplification, and filtering, outputs one channel as a direct wave reference signal, outputs another channel for target echo detection, and also outputs a reference clock.

[0057] In order for the receiver to simultaneously output the direct wave reference signal and the target echo detection signal that meet the amplitude requirements, it must have a sufficiently large gain dynamic range. The indicator allocation and calculation of the receiving channel are as follows: The small signal gain requirement of the receiving link is 110-40=70dB, and the actual design gain is 80dB. According to actual needs, the temperature compensation attenuation or adjustment attenuation position can be added to achieve the required gain requirements. The receiving channel adopts a low-noise amplifier circuit to achieve the signal amplitude requirement of -110dBm to -20dBm; the input dynamic of the receiving channel is 90dB, and the output dynamic needs to be 40dB. The down-conversion channel is controlled by a two-stage digital attenuator, which can achieve 50dB dynamic control, and finally achieve the small signal -110dBm input, -40dBm output requirements, large signal -20dBm input, 0dBm output requirements.

[0058] In some embodiments, the signal acquisition and processing subsystem includes: a signal acquisition unit, a signal processing unit, a main control unit, and an interface unit; The signal acquisition unit is used to perform analog-to-digital conversion on the direct wave reference signal and the target echo detection signal, respectively, to obtain a baseband digital signal corresponding to the direct wave reference signal and a baseband digital signal corresponding to the target echo detection signal; The signal processing unit is used to perform bistatic SAR imaging processing on the baseband digital signal corresponding to the direct wave reference signal and the baseband digital signal corresponding to the target echo detection signal to obtain a bistatic SAR image; The main control unit is used to solve commands and parameters and control each subsystem to work normally according to the established sequence; The interface unit is used for external connection.

[0059] Specifically, the signal acquisition and processing subsystem includes a signal acquisition unit (AD), a signal processing unit, a main control unit, and an interface unit. The signal acquisition unit converts the baseband analog signals of the direct wave and the target echo into baseband digital signals respectively; the signal processing unit is responsible for completing signal processing tasks such as time-frequency synchronization and dual-base SAR imaging. The interface unit realizes the external connection of the system. The main control unit solves various commands and parameters and controls each subsystem to work normally according to the established timing.

[0060] The direct wave reference signal and the target echo detection signal are sent to the ADC chip for analog-to-digital conversion. The reference clock signal is used as the sampling reference clock for the ADC chip. The collected data is sent to the FPGA chip to realize the continuous collection and caching of dual-channel data, or to the DSP chip to complete the subsequent signal processing. In addition, in order to facilitate data recording and analysis, an SRIO interface is designed to connect the data recorder.

[0061] In some embodiments, the signal acquisition unit includes: a reference channel signal acquisition module and a monitoring channel signal acquisition module; The reference channel signal acquisition module is used to perform analog-to-digital conversion on the direct wave reference signal; The monitoring channel signal acquisition module is used to perform analog-to-digital conversion on the target echo detection signal.

[0062] The signal acquisition and processor uses the Artix-7 series FPGA XC7A200T launched by XILINX and the TI multi-core DSP TMS320C6678. The on-board DDR3 storage capacity reaches 2GB, which can achieve 1280GMACs fixed-point processing capabilities and 640GFLOPs floating-point processing capabilities, and can realize functions such as broadband signal reception, real-time processing, and transmission. The recording storage module uses flash chips from Spansion and Micron, providing a 1TB storage space, using a high-speed data interface SRIO to store external data in real time, upload the data to the host computer and form files, which can provide reliable protection for the system's high-speed real-time signal storage.

[0063] In the translation-invariant mode, the transceiver platform keeps moving at the same speed and direction, so it is not difficult to carry out long-term strip mapping. However, in wartime or other special circumstances, the transceiver platform may not be able to keep flying at the same speed and direction. At this time, it will be very difficult for the bistatic SAR working in the translation-variant mode to carry out long-term strip mapping of a large area, which requires detailed spatial configuration and parameter design.

[0064] Figure 4 FIG. 5 is a flow chart of the non-cooperative bistatic SAR imaging processing method provided by the present invention. Figure 4 As shown, based on the above non-cooperative bistatic SAR imaging system, the present invention provides a non-cooperative bistatic SAR imaging processing method, comprising: The received echo signal is processed in sequence by two-dimensional FFT, range bending correction and range compression, range FFT, cubic filtering, first azimuth IFFT, nonlinear frequency modulation scaling, azimuth FFT, azimuth compression, second azimuth IFFT and reference distance variation compensation to obtain a SAR image.

[0065] Specifically, assume that the bistatic SAR transmits an LFM pulse signal with a signal modulation frequency of k. After the transmitted signal is reflected by a point target and demodulated by the receiver, the received echo signal is (ignoring the signal amplitude information):

[0066] Where:

[0067] in, is the echo signal, is the distance time, is the azimuth time, is the center frequency, is the speed of light, is the reference distance from the point target to the receiver, For point target, is the minimum oblique distance from the reference point to the receiver, is the reference distance change from the point target to the receiver, is the receiver movement speed, is the azimuth time, is the route angle, is the receiving beam squint angle, is the distance between the transmitter and the target, is the transmit beam squint angle, is the transmitter movement speed, is the azimuth coordinate of the target point.

[0068] Using the stationary phase method, the echo signal is transformed by two-dimensional fast Fourier transform (FFT):

[0069] in,

[0070] in, is the two-dimensional fast Fourier transform spectrum of the echo signal, is the distance frequency, is the azimuth frequency, is the azimuth Doppler modulation frequency of the bistatic SAR, is the bistatic SAR azimuth Doppler center frequency, is the bistatic distance and, is the wavelength of the transmitted signal, The frequency of the azimuth The distance from the affected target to the receiver.

[0071] The expression shows that the azimuth modulation rate of the shifting bistatic SAR echo signal is not only affected by the oblique distance from the target to the carrier, but also by the change in the azimuth distance of the target relative to the reference point. Therefore, the shift-variant bistatic SAR echo signal has spatial variability in both distance and azimuth.

[0072] It should be noted that the purpose of receiving the direct wave signal is to assist in completing the distance compression processing of the echo signal and provide the reference signal required for the compression cross-correlation processing.

[0073] After performing the secondary range compression algorithm (SRC), range curvature correction and range compression in the frequency domain, the echo signal after range compression is obtained, and the azimuth information is written out separately:

[0074] Since the accuracy of range motion correction and secondary range compression will seriously affect the subsequent azimuth focusing processing, in order to achieve range motion correction more efficiently without interpolation, the imaging selects the chirp scaling (CS) algorithm. The change of range motion with distance is not large and can even be ignored. The superiority of the range motion correction method in the CS algorithm is reflected in compensating for the spatial variability introduced by receiver coupling. According to the above analysis, the range motion correction is achieved by multiplying the phase of the perturbation function, thus avoiding interpolation. The compensation of the algorithm for secondary range compression ignores the change with distance, but this method solves this problem well.

[0075] According to the above analysis, the imaging algorithm uses the principle of nonlinear variable scaling to compensate for the azimuth-varying characteristics of the echo signal, and extends the application of the nonlinear variable scaling algorithm to the field of shift-varying bistatic SAR.

[0076] Cubic filter function

[0077] in, is the cubic filter function, is the coefficient to be determined in the cubic filter function, is the azimuth frequency, is the azimuth Doppler center frequency of the bistatic SAR.

[0078] Then transform back to the azimuth time domain, we get:

[0079] in, is the azimuth time domain signal, is the cubic coefficient, Frequency tuning for azimuth The first derivative of .

[0080] Nonlinear frequency modulation scaling function

[0081] in, is the nonlinear frequency modulation scaling function, and is the coefficient to be determined in the nonlinear frequency modulation scaling function, is the nonlinear frequency modulation scaling factor, and its value should be as close to 1 as possible.

[0082] Nonlinear frequency modulation function Azimuth and time domain Multiply them to get the signal after nonlinear frequency modulation and scaling , and then Transform to frequency domain:

[0083] in, For signal The spectrum of for The first derivative of azimuth time, is the nonlinear frequency modulation scaling factor, and its value should be as close to 1 as possible.

[0084] Azimuth Compression Function

[0085] The first term in the expression is a linear phase term, which represents the azimuth position of a point target. The last two terms are constants for fixed points and do not affect azimuth compression. It is irrelevant and can be compressed using a unified orientation matching function.

[0086]

[0087] in, is the orientation matching function.

[0088] Reference distance variation compensation function

[0089] Since the transmitter route has a certain angle with respect to the reference route, the reference distance from the point target to the receiver will change with the azimuth coordinates of the target point, and the change is After the focusing process is completed, the image data is converted back to the range-Doppler-azimuth time domain and then multiplied by the inverse linear range-walk correction function:

[0090] in, is the linear distance movement correction function.

[0091] The change in reference distance can be compensated, and finally the processed data can be converted back to the time domain to complete the entire signal processing process.

[0092] According to the spatial configuration characteristics of the shifting bistatic SAR, this imaging processing method enables the shifting bistatic SAR system to perform strip mapping, and extends the nonlinear variable scaling algorithm to this working mode. In the system design of the shifting bistatic SAR, the flexibility of the bistatic configuration is fully utilized. If the movement speed, heading angle and beam pointing of the transceiver platform meet certain constraints, the spatial synchronization of the transceiver beam can be achieved; in the processing of the echo signal, the nonlinear variable scaling principle is used to solve the azimuth spatial variability of the echo signal, which is an effective method.

[0093] The non-cooperative bistatic SAR imaging processing device provided by the present invention is described below. The non-cooperative bistatic SAR imaging processing device described below and the non-cooperative bistatic SAR imaging processing method described above can be referred to each other.

[0094] Figure 5 FIG. 1 is a flow chart of a non-cooperative dual-base SAR imaging processing device provided by the present invention. Figure 5 As shown, the present invention provides a non-cooperative bistatic SAR imaging processing device, comprising: The processing module 510 is used to perform two-dimensional FFT, range curvature correction and range compression, range FFT, cubic filtering, first azimuth IFFT, nonlinear frequency modulation scaling, azimuth FFT, azimuth compression, second azimuth IFFT and reference distance variation compensation on the received echo signal in sequence to obtain a SAR image.

[0095] It should be noted here that the above-mentioned non-cooperative dual-base SAR imaging processing device provided by the present invention can implement all the method steps implemented by the above-mentioned method embodiment, and can achieve the same technical effect. The parts and beneficial effects that are the same as those in the method embodiment will not be specifically described here.

[0096] Figure 6 is a schematic diagram of the structure of the electronic device provided by the present invention, such as Figure 6 As shown, the electronic device may include: a processor 610, a communication interface 620, a memory 630 and a communication bus 640, wherein the processor 610, the communication interface 620 and the memory 630 communicate with each other through the communication bus 640. The processor 610 may call the logic instructions in the memory 630 to execute the non-cooperative bistatic SAR imaging processing method, which includes: performing two-dimensional FFT, range warp correction and range compression, range FFT, cubic filtering, first azimuth IFFT, nonlinear frequency modulation scaling, azimuth FFT, azimuth compression, second azimuth IFFT and reference distance variation compensation processing on the received echo signal in sequence to obtain a SAR image.

[0097] In addition, the logic instructions in the above-mentioned memory 630 can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when it is sold or used as an independent product. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0098] On the other hand, the present invention also provides a computer program product, which includes a computer program. The computer program can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the non-cooperative dual-base SAR imaging processing method provided by the above-mentioned methods. The method includes: performing two-dimensional FFT, range curvature correction and range compression, range FFT, cubic filtering, first azimuth IFFT, nonlinear frequency modulation scaling, azimuth FFT, azimuth compression, second azimuth IFFT and reference distance variation compensation processing on the received echo signal in sequence to obtain a SAR image.

[0099] On the other hand, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, it is implemented to execute the non-cooperative dual-base SAR imaging processing method provided by the above-mentioned methods. The method includes: performing two-dimensional FFT, range curvature correction and range compression, range FFT, cubic filtering, first azimuth IFFT, nonlinear frequency modulation scaling, azimuth FFT, azimuth compression, second azimuth IFFT and reference distance variation compensation processing on the received echo signal in sequence to obtain a SAR image.

[0100] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0101] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A non-cooperative bistatic SAR imaging system, It is characterized in that include: Onboard illumination source and non-cooperative bistatic radar receiving and processing system; The non-cooperative bistatic radar receiving and processing system comprises: an antenna subsystem, a receiving subsystem, a signal acquisition and processing subsystem and a display and control terminal; The satellite-borne illumination source is used to emit direct wave signals; The antenna subsystem is used to simultaneously receive the direct wave signal and the echo signal of the imaging area; The receiving subsystem is used to process the direct wave signal and the echo signal, and output a direct wave reference signal and a target echo detection signal; The signal acquisition and processing subsystem is used to perform bistatic SAR imaging processing on the direct wave reference signal and the target echo detection signal to obtain a bistatic SAR image; The display and control terminal is used to display the bistatic SAR image.

2. The non-cooperative bistatic SAR imaging system according to claim 1, It is characterized in that The receiving subsystem includes: a multi-channel receiver and a clock; The multi-channel receiver is used to perform down-conversion, amplification, and filtering on the direct wave signal and the echo signal respectively to obtain the direct wave reference signal and the target echo detection signal; The clock is used to generate a reference clock signal.

3. The non-cooperative bistatic SAR imaging system according to claim 2, It is characterized in that The multi-channel receiver comprises: a low noise amplifier, an image rejection mixer, a front intermediate frequency amplifier, a first matching network, a first 30M filter, a first intermediate frequency amplifier, an attenuation network, a controllable gain amplifier, a second matching network, a second intermediate frequency amplifier, a power divider, a first matching output network, an oscilloscope, a second 30M filter and a second matching output network; The input end of the low noise amplifier is used as the input end of the receiver, and the low noise amplifier, the image rejection mixer, the front intermediate frequency amplifier, the first matching network, the first 30M filter, the first intermediate frequency amplifier, the attenuation network, the controllable gain amplifier, the second matching network, the second intermediate frequency amplifier and the power divider are connected in sequence; The output end of the power divider is divided into two paths, one path is connected to the first matching output network and the oscilloscope in sequence, and the other path is connected to the second 30M filter and the second matching output network in sequence, and the output end of the second matching output network serves as the output end of the receiver.

4. The non-cooperative bistatic SAR imaging system according to claim 1, It is characterized in that The signal acquisition and processing subsystem includes: a signal acquisition unit, a signal processing unit, a main control unit and an interface unit; The signal acquisition unit is used to perform analog-to-digital conversion on the direct wave reference signal and the target echo detection signal, respectively, to obtain a baseband digital signal corresponding to the direct wave reference signal and a baseband digital signal corresponding to the target echo detection signal; The signal processing unit is used to perform bistatic SAR imaging processing on the baseband digital signal corresponding to the direct wave reference signal and the baseband digital signal corresponding to the target echo detection signal to obtain a bistatic SAR image; The main control unit is used to solve commands and parameters and control each subsystem to work normally according to the established sequence; The interface unit is used for external connection.

5. The non-cooperative bistatic SAR imaging system according to claim 4, It is characterized in that The signal acquisition unit comprises: a reference channel signal acquisition module and a monitoring channel signal acquisition module; The reference channel signal acquisition module is used to perform analog-to-digital conversion on the direct wave reference signal; The monitoring channel signal acquisition module is used to perform analog-to-digital conversion on the target echo detection signal.

6. A non-cooperative bistatic SAR imaging processing method based on the system of claim 1, It is characterized in that include: The received echo signal is processed in sequence by two-dimensional FFT, range bending correction and range compression, range FFT, cubic filtering, first azimuth IFFT, nonlinear frequency modulation scaling, azimuth FFT, azimuth compression, second azimuth IFFT and reference distance variation compensation to obtain a SAR image.

7. A non-cooperative bistatic SAR imaging processing device, It is characterized in that include: The processing module is used to perform two-dimensional FFT, range curvature correction and range compression, range FFT, cubic filtering, first azimuth IFFT, nonlinear frequency modulation scaling, azimuth FFT, azimuth compression, second azimuth IFFT and reference distance variation compensation on the received echo signal in sequence to obtain a SAR image.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, It is characterized in that When the processor executes the program, the non-cooperative bistatic SAR imaging processing method according to claim 6 is implemented.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, It is characterized in that When the computer program is executed by a processor, the non-cooperative bistatic SAR imaging processing method according to claim 6 is implemented.

10. A computer program product comprising a computer program, It is characterized in that When the computer program is executed by a processor, the non-cooperative bistatic SAR imaging processing method according to claim 6 is implemented.

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