Bistatic radar multi-ship target separation imaging method and device

Abstract

The invention discloses a bistatic radar multi-ship target separation imaging method and device. The method comprises the following steps: acquiring echo signals containing a plurality of ship targets; performing range direction processing on the echo signal to obtain a range direction processing signal; distance unit screening is carried out according to the distance direction processing signals, a reference distance unit is determined through the screened distance units, and local entropy transformation is carried out on the distance direction processing signals at the reference distance unit to obtain an entropy value curve; solving the Doppler frequency modulation rate of each ship target according to the entropy curve; constructing a coarse focusing filter by using the Doppler frequency modulation rate, and performing coarse imaging on the distance direction processing signal according to the coarse focusing filter to obtain a coarse imaging result; and obtaining a special display point image according to the coarse imaging result, constructing a separation imaging filter by using a Doppler frequency modulation rate, and carrying out separation imaging on the coarse imaging result according to the special display point image and the separation imaging filter to obtain a separation imaging result of the ship target. According to the invention, the separation imaging result of the specific ship target can be accurately extracted.

Description

Technical Field

[0001] This invention belongs to the field of radar imaging technology, specifically relating to a bistatic radar multi-ship target separation imaging method and device. Background Technology

[0002] BFSAR (Bistatic Forward-Looking Synthetic Aperture Radar) is a radar imaging technology for imaging ship targets. It can be mounted on two independent flight platforms, such as aircraft, drones, or satellites. One platform transmits radar signals, while the other receives the echo signals from the target area. Multiple independently moving ship targets can exist in the target area. The receiver uses this technology to process the echo signals of these ship targets into a radar image. BFSAR technology enables radar receivers to perform all-weather, all-time, long-range, high-resolution imaging of ship targets in forward-looking target areas. It can be applied to the detection, imaging, and identification of ship targets, and has significant application value in maritime traffic monitoring, aircraft takeoff and landing, and other fields.

[0003] Existing methods mainly include ship target imaging based on short-time Fourier transform (SFT) and ship target imaging based on the Wegener-Weil distribution. SFT is a typical linear time-frequency analysis method that uses a local sliding window approach to acquire the time-frequency characteristics of the signal. The SFT-based ship target imaging method first transforms the echo signal to the time-frequency distribution domain using SFT; then, it uses Hough transform or Radon transform to detect the slope of the time-frequency ridge in the time-frequency distribution domain to estimate the Doppler modulation frequency of each ship target; finally, it uses the estimated Doppler modulation frequency of the ship target to construct an imaging filter and filter the echo signal to obtain the imaging result of the ship target. The Wegener-Weil distribution is a bilinear time-frequency analysis method with no window function limitation, enabling high-precision positioning of both time and frequency simultaneously. The ship target imaging method based on the Wegener-Weil distribution first transforms the echo signal into the time-frequency distribution domain using the high time-frequency resolution characteristic of the Wegener-Weil distribution. Then, the slope of the time-frequency ridge in the time-frequency distribution domain is detected using Hough transform or Radon transform to estimate the Doppler modulation frequency of each ship target. Finally, an imaging filter is constructed using the estimated ship target Doppler modulation frequency to filter the echo signal and obtain the imaging result of the ship target. Compared with the short-time Fourier transform, the Wegener-Weil distribution has higher Doppler modulation frequency estimation accuracy.

[0004] However, the aforementioned prior art has the following drawbacks: Disadvantage 1: Ship target imaging methods based on short-time Fourier transform suffer from poor Doppler frequency modulation estimation accuracy, making it impossible to achieve high-resolution imaging of ship targets.

[0005] According to the uncertainty principle, the product of the effective time width and effective bandwidth of the short-time Fourier transform (SFT) cannot be infinitely small. This means that its time-frequency resolution is easily affected by the length of the time-frequency window. When processing radar echo signals, the narrower the time-domain window, the worse the local spectral resolution. To improve local spectral resolution, the window length should be wider, but if the signal within the window exceeds the limit, it will not satisfy local stationarity and will instead worsen the signal's local spectral resolution. Therefore, the window width selection of the SFT is difficult to maintain a balance between the signal's time and frequency resolution, making it impossible to achieve high-precision Doppler frequency modulation estimation and thus hindering high-resolution imaging of ship targets. Furthermore, for multi-ship target imaging, the SFT, due to its low spectral resolution, cannot distinguish ship targets with small differences in Doppler frequency modulation, thus preventing multi-ship target imaging.

[0006] Disadvantage 2: When processing echo signals from large ship targets or multiple ship targets, ship target imaging methods based on the Wegener-Weil distribution suffer from reduced imaging resolution or the appearance of false scattering points.

[0007] The Wegener-Weil distribution is a bilinear transformation with bilinear coupling. For the echo signals of large ship targets, the echo signals from multiple scattering points (mast, etc.) will produce cross terms, resulting in a spurious energy distribution in the time-frequency distribution. These cross terms not only fail to reflect the true signal characteristics but also mask the true target signal, leading to decreased accuracy in Doppler frequency modulation estimation or the appearance of false estimates, thus reducing the resolution of ship target imaging or introducing false scattering points. Furthermore, for multi-ship target imaging, the echo signals from each ship target are mutually coupled, resulting in even more severe cross terms in their Wegener-Weil distributions, making Doppler frequency modulation estimation impossible and hindering multi-ship target imaging. Summary of the Invention

[0008] To address the aforementioned problems in the existing technology, this invention provides a bistatic radar multi-ship target separation and imaging method and apparatus. The technical problem to be solved by this invention is achieved through the following technical solution: In a first aspect, embodiments of the present invention provide a bistatic radar multi-ship target separation and imaging method, the method comprising: Acquire echo signals from multiple independently moving ship targets in the target area; The echo signal is processed in the range direction to obtain the range-processed signal; A distance cell filtering operation is performed based on the distance processing signal. A reference distance cell is determined based on the filtered distance cells. A local entropy transformation is performed on the distance processing signal at the reference distance cell to obtain an entropy curve. The Doppler modulation frequency of each ship target is determined based on the entropy curve. A coarse focusing filter is constructed using the Doppler modulation frequency of each ship target. The range-oriented processing signal is then subjected to coarse imaging processing based on the coarse focusing filter to obtain the coarse imaging result of each ship target. For each ship target, the preprocessing process before performing separation imaging includes: constructing separation imaging filters between the ship target and other ship targets according to the Doppler modulation frequency of each ship target; and obtaining the corresponding highlight image based on the coarse imaging result of the ship target. Based on all the featured point images and all the constructed separation imaging filters, the coarse imaging results of each ship target are processed for separation imaging to obtain the corresponding ship target's separation imaging result.

[0009] In one embodiment of the present invention, range processing is performed on the echo signal to obtain a range-processed signal, including: Perform a range-direction Fast Fourier Transform on the echo signal to obtain a range-frequency domain signal; The range frequency signal is filtered using a range-oriented processing filter to obtain a range-oriented filtered signal; The range-filtered signal is subjected to a wedge transform to obtain the range-wedge-transformed signal; The range-direction wedge-transformed signal is subjected to a range-direction fast Fourier inverse transform to obtain the range-direction processed signal.

[0010] In one embodiment of the present invention, a range cell filtering operation is performed on the range-oriented processed signal, a reference range cell is determined based on the filtered range cells, and a local entropy transformation is performed on the range-oriented processed signal at the reference range cell to obtain an entropy curve, including: The range-processed signal is integrated in the azimuth direction to obtain the azimuth energy integration result; The distance cell threshold is calculated based on the azimuth energy integration result, and the distance cells whose azimuth energy integration result is greater than the distance cell threshold are filtered out. The filtered distance cells form a distance cell range, and the center of the distance cell range is used as the reference distance cell. A fractional Fourier transform is performed on the range-oriented processing signal at the reference range unit to obtain the fractional Fourier transform result; The fractional Fourier transform result is subjected to a local entropy calculation operation in the azimuth direction to obtain the entropy curve.

[0011] In one embodiment of the present invention, determining the Doppler modulation frequency of each ship target based on the entropy curve includes: Each ship target is determined based on the minimum point of the entropy curve, and the Doppler modulation frequency of the corresponding ship target is calculated using the minimum point of each ship target.

[0012] In one embodiment of the present invention, a corresponding coarse focusing filter is constructed using the Doppler modulation frequency of each ship target, as expressed by the formula: ; in, Indicates the first The coarse focusing filter corresponding to each ship target. , Indicates the number of ship targets. This represents the azimuth time-domain variable after range-to-wedge transformation. Represents the imaginary unit. Indicates the first Doppler tuning frequency of individual ship targets.

[0013] In one embodiment of the present invention, coarse imaging processing of the range-oriented processing signal based on the coarse focusing filter includes: The range signal is sequentially filtered and subjected to azimuth fast Fourier transform using the coarse focusing filter.

[0014] In one embodiment of the present invention, separation imaging filters are constructed between the ship target and other ship targets, as expressed by the following formula: ; in, Indicates the first , Separate imaging filters for each ship target , Indicates the number of ship targets. Indicates the first Doppler modulation frequency of individual ship targets Indicates the first Doppler modulation frequency of individual ship targets , This represents the azimuth time-domain variable after range-to-wedge transformation. It represents the imaginary unit.

[0015] In one embodiment of the present invention, obtaining a corresponding highlighted point image based on the coarse imaging result of the ship target includes: Construct corresponding threshold values ​​for prominent points based on the coarse imaging results of the ship target; Signals smaller than the corresponding highlight threshold in the coarse imaging result of the ship target are set to 0 to obtain the highlight image of the ship target.

[0016] In one embodiment of the invention, it is applied to BFSAR.

[0017] Secondly, a bistatic radar multi-ship target separation and imaging device, the device comprising: The acquisition module is used to acquire echo signals from multiple independently moving ship targets in the target area; The processing module is used to perform range processing on the echo signal to obtain a range-processed signal; The filtering and transformation module is used to perform a range cell filtering operation based on the range processing signal, determine a reference range cell based on the filtered range cells, and perform a local entropy transformation on the range processing signal at the reference range cell to obtain an entropy curve. The solution module is used to solve for the Doppler modulation frequency of each ship target based on the entropy curve; The coarse imaging module is used to construct a corresponding coarse focusing filter using the Doppler modulation frequency of each ship target, and to perform coarse imaging processing on the range processing signal according to the coarse focusing filter to obtain the coarse imaging result of each ship target. The separation imaging preprocessing module is used to perform preprocessing procedures for each ship target before separation imaging, including: constructing separation imaging filters between the ship target and other ship targets according to the Doppler modulation frequency of each ship target; and obtaining the corresponding highlight image based on the coarse imaging result of the ship target. The separation imaging module is used to perform separation imaging processing on the coarse imaging results of each ship target based on all the featured point images and all the constructed separation imaging filters, so as to obtain the separation imaging results of the corresponding ship target.

[0018] The beneficial effects of this invention are: The bistatic radar multi-ship target separation imaging method proposed in this invention can achieve separation imaging of each ship target by processing the echo signals of multiple independently moving ship targets simultaneously. Specifically, it obtains the entropy curve through local entropy transformation, and then solves the Doppler modulation frequency of each ship target based on the entropy curve. This method is not affected by the existence of multiple scattering points and the coupling of echo signals from multiple ship targets, thus improving the estimation accuracy of the Doppler modulation frequency of the ship targets. This enables high-resolution imaging of the ship targets and obtains coarse imaging results for each ship target. Based on the coarse imaging results of each ship target, a highlight image is obtained. A separation imaging filter is constructed using the Doppler modulation frequency of each ship target estimated by local entropy transformation. Through the highlight image and the constructed separation imaging filter, the separation imaging result of a specific ship target is accurately extracted from the coarse imaging results of each ship target. This separation imaging result contains only one scattering point of the ship target and no defocus signals from other ship targets. This advantage is unattainable by any existing method. This invention can be applied to BFSAR to meet the needs of radar receiving platforms, such as satellites and aircraft, to perform high-resolution separation imaging of each ship target in the target area ahead. This enables aircraft / satellites to monitor ship targets in the target area and can also assist aircraft in landing on specific ship targets, etc., and has broad application prospects.

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating a bistatic radar multi-ship target separation and imaging method provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the spatial geometry configuration of a BFSAR provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the data matrix for range-oriented processing signals provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the azimuth energy integration results provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the entropy curve provided in an embodiment of the present invention; Figures 6(a) to 6(b) This is a schematic diagram of the coarse imaging results of ship target 1 and ship target 2 provided in an embodiment of the present invention; Figures 7(a) to 7(b) This is a schematic diagram of the separation imaging results of ship target 1 and ship target 2 provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the structure of a bi-base radar multi-ship target separation imaging device provided in an embodiment of the present invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0022] Please see Figure 1 This invention provides a bistatic radar multi-ship target separation imaging method that can be applied to BFSAR. The specific spatial geometry of BFSAR is as follows: Figure 2 As shown, the transmitter illuminates the target area, and the forward-looking receiver records the radar echoes scattered by the target scene, where multiple independently moving ship targets exist. The corresponding method specifically includes the following steps: S10. Acquire echo signals from multiple independently moving ship targets in the target area.

[0023] The embodiments of the present invention use the receiver's offline point Establish a Cartesian right-handed coordinate system with the origin at the origin. With the ground as the XY plane, the transmitter's position is... The location of the receiver is Define the transmitter speed as The receiver speed is Define any ship target within the target area. At the time of the synthesis aperture center, it is located Its speed is The reference point for the center of the target area is... Then the ship target The two-way distance journey can be expressed as: (1); in, Let be the azimuth time domain variable. It is evident that the two-way distance history is expressed in the form of double square roots, which is not conducive to subsequent derivation. Therefore, it needs to be approximated using a Taylor series, and can be expressed as: (2); in: (3); in, Indicates to beg Derivative. Therefore, when the transmitter transmits a linear frequency modulated signal, the receiver receives information about the ship target. The echo signal can be represented as: (4); in, For distance in the time domain, the corresponding distance in the frequency domain is: , For the frequency modulation of the transmitted signal, At the speed of light, The carrier wavelength of the transmitted signal is given by [symbol missing], and its corresponding carrier frequency is [symbol missing]. , and These are the distance time-domain window function and the azimuth time-domain window function, respectively. It is the imaginary unit.

[0024] If there are multiple independently moving ship targets in the target area, the echo signal received by the receiver in the target area can be represented as the sum of the echo signals of these ship targets. Assume there are a number of ship targets in the target area. If there are 1, then the echo signal of the target area can be expressed as: (5); S20. Perform range processing on the echo signal to obtain the range-processed signal.

[0025] This invention provides a range-direction processing method for echo signals to obtain a range-direction processed signal. The method includes: performing a range-direction Fast Fourier Transform (FSFT) on the echo signal to obtain a range-frequency domain signal; filtering the range-frequency signal using a range-direction processing filter to obtain a range-direction filtered signal; performing a wedge transform on the range-direction filtered signal to obtain a range-direction wedge-transformed signal; and performing an inverse range-direction FFT on the range-direction wedge-transformed signal to obtain the range-direction processed signal. More specifically: First, perform a range-direction Fast Fourier Transform on the echo signal. Then, use the stationary phase method to obtain the corresponding range-frequency domain signal, as shown in the following expression: (6); in, It is a distance-frequency domain window function. .

[0026] Let the range-direction processing filter be: (7); in, , and These are reference points for the center of the target area. Similar to ship targets of , and The value of .

[0027] Multiplying formulas (6) and (7) yields the range-processed filtered signal, expressed as: (8); in: (9); Then process and filter the distance-oriented signal. Perform a wedge transformation, which can be written as: (10); in, The azimuth time-domain variable is the result of the wedge transformation.

[0028] The signal after the wedge transform can be written as: (11); because ,exist: (12); Therefore, formula (11) can be rewritten as: (13); In formula (13), the first exponential term The second exponential term represents the distance to the focal position and the remaining distance of migration. This represents the azimuth modulation term. In BFSAR, residual range migration and cubic azimuth modulation terms are usually negligible, while the quadratic azimuth modulation term cannot be ignored. Therefore, [the following is a more detailed explanation of the azimuth modulation term:] Performing a range-direction inverse fast Fourier transform to the time domain, the expression for the range-direction processed signal is obtained as follows: (14); in, , , Indicates the first Doppler frequency of individual ship targets Indicates the first Doppler modulation frequency of individual ship targets .

[0029] S30. Perform a range cell filtering operation based on the range processing signal, determine a reference range cell based on the filtered range cells, and perform a local entropy transformation on the range processing signal at the reference range cell to obtain the entropy curve.

[0030] This invention embodiment performs a range cell filtering operation on the range-oriented processed signal, determines a reference range cell based on the filtered range cells, and performs a local entropy transformation on the range-oriented processed signal at the reference range cell to obtain an entropy curve, including: The range-processed signal is integrated in the azimuth direction to obtain the azimuth energy integral result. A range cell threshold value is calculated based on the azimuth energy integral result, and range cells whose azimuth energy integral result is greater than the threshold value are selected. These selected range cells form a range cell range, and the center of the range cell range is used as the reference range cell. A fractional Fourier transform is performed on the range-processed signal at the reference range cell to obtain the fractional Fourier transform result. The azimuth local entropy is calculated on the fractional Fourier transform result to obtain the entropy curve. More specifically: A schematic diagram of the data matrix for range-oriented signal processing is shown below. Figure 3 As shown, Figure 3 This displays the range and azimuth directions of the range-processed signal. The range unit represents all units at the same range, for example... Figure 3 The 8th range cell in the range direction. In step S30, a range cell filtering operation needs to be performed on the range-processed signal. First, the azimuth energy is integrated on the range-processed signal to obtain the azimuth energy integration result, which can be expressed as: (15); in, Indicates the modulo value. Indicates the time for synthesizing the aperture.

[0031] For example, the azimuth energy integral result is as follows Figure 4 As shown. The distance unit threshold value can be set according to the following formula. : (16); in, For distance sampling duration, This is the distance unit threshold coefficient, which can usually be set to 0.01.

[0032] Then, the azimuth energy integration results are filtered using a range cell threshold value, and range cells exceeding the range cell threshold value are selected as the range cell range where the ship target signal is located. Here, the center of the range cell range is selected as the reference range cell, which is denoted as . .

[0033] After selecting the reference range cell, a local entropy transform operation is performed on the range-processed signal at the reference range cell. First, a fractional Fourier transform is performed on the range-processed signal at the reference range cell, which can be expressed as: (17); in: (18); in, Represents the fractional Fourier transform. It is of fractional order. For azimuth frequency domain variables, For the time to synthesize the pore size, It is an integer. This represents the impulse function.

[0034] Then, the fractional Fourier transform results The operation of calculating the local entropy in the direction of orientation can be represented as: (19); in: (20); in, This is the pulse repetition frequency.

[0035] The entropy curve can be obtained by performing the operation of calculating the local entropy in the azimuth direction. .

[0036] The local entropy transform proposed in this invention utilizes the fractional Fourier transform, which is recognized for its higher Doppler frequency modulation estimation accuracy than the short-time Fourier transform. Based on the fractional Fourier transform, an azimuth-direction local entropy operation is performed, transforming the result of the fractional Fourier transform into an entropy curve, further improving the estimation accuracy of the Doppler frequency of subsequent ship targets, ultimately resulting in higher resolution ship target imaging. The local entropy transform proposed in this invention is a linear transform with no cross terms, enabling simultaneous estimation of the Doppler frequency of multiple ship targets, unaffected by the coupling of echo signals from multiple ship targets.

[0037] S40. Solve for the Doppler modulation frequency of each ship target based on the entropy curve.

[0038] This invention embodiment calculates the Doppler modulation frequency of each ship target based on the entropy curve, including: Each ship target is identified based on the minimum point of the entropy curve, and the corresponding Doppler modulation frequency is calculated using the minimum point of each ship target. More specifically: For example, the entropy curves of the echo signals from two independent ship targets after processing in step 30 are as follows: Figure 5 As shown, from Figure 5 As can be seen, each obvious local minimum point corresponds to a ship target, and the x-coordinate of each obvious local minimum point represents the fractional order of the corresponding ship target.

[0039] Assuming ship target The fractional order is The ship target can then be determined using the following formula. Doppler frequency modulation : (twenty one); in, This represents the number of sampling points in the azimuth direction.

[0040] S50. Construct a coarse focusing filter corresponding to each ship target using the Doppler modulation frequency, and perform coarse imaging processing on the range direction processing signal according to the coarse focusing filter to obtain the coarse imaging result of each ship target.

[0041] This invention utilizes the Doppler modulation frequency of each ship target to construct a corresponding coarse focusing filter, expressed by the formula: (twenty two); in, Indicates the first The coarse focusing filter corresponding to each ship target. , Indicates the number of ship targets. This represents the azimuth time-domain variable after range-to-wedge transformation. Represents the imaginary unit. Indicates the first Doppler tuning frequency of individual ship targets.

[0042] This invention embodiment performs coarse imaging processing on the range-oriented processed signal based on a coarse focusing filter, including: sequentially filtering the range-oriented processed signal and performing a fast Fourier transform in the azimuth direction based on the coarse focusing filter. (Using a ship target...) For example, using ship targets The corresponding coarse focusing filter is used to obtain the ship target. The coarse imaging result can be expressed as: (twenty three); in, Represents the Sink function, For the azimuth frequency domain window function, Similar to It can be obtained by formula (3).

[0043] As can be seen in formula (23), the ship target The coarse imaging results not only contain ship targets The imaging signal itself also contains other... The imaging signals of these other ship targets can severely interfere with the imaging of the ship target. Image recognition. For example, given coarse imaging results of two ship targets, such as... Figures 6(a) to 6(b)As shown, Figure 6(a) is the coarse imaging result of processing the range signal using the coarse focusing filter corresponding to ship target 1, and Figure 6(b) is the coarse imaging result of processing the range signal using the coarse focusing filter corresponding to ship target 2. It can be seen from Figures 6(a) to 6(b) that there are defocused signals of other ship targets in the coarse imaging results.

[0044] S60. For each ship target, the preprocessing process before separation imaging includes: constructing separation imaging filters between the ship target and other ship targets according to the Doppler modulation frequency of each ship target; and obtaining the corresponding highlight image based on the coarse imaging result of the ship target.

[0045] This embodiment of the invention obtains a corresponding highlighted point image based on the coarse imaging result of the ship target, including: A threshold value for prominent points is constructed based on the coarse imaging result of each ship target; signals in the coarse imaging result of each ship target that are less than the corresponding threshold value are set to 0, thus obtaining the prominent point image of each ship target. More specifically: In this embodiment of the invention, a highlighting point selection operation is first performed on each coarse imaging result, which is similar to the range cell selection operation in S30. Assume the... The threshold value of the distinctive points corresponding to the coarse imaging result of a ship target is It can be written as: (twenty four); in, This is the threshold coefficient for the special point, which can usually be set to 0.05.

[0046] The first In the coarse imaging results of a ship target, weak signal points smaller than the prominent point threshold are set to 0, thus obtaining the first... A highlighted image of a ship target, denoted as _____. , .

[0047] Then, in this embodiment of the invention, a corresponding separation imaging filter is constructed using the Doppler frequency modulation of each ship target. Assuming that for the first... Separate imaging of individual ship targets, the first The Doppler modulation frequency of the individual ship targets is . No. Remove the first one from the coarse imaging results of the ship targets. The formula for the separation imaging filter for individual ship targets is expressed as: (25); in, Indicates the first , Separate imaging filters for each ship target , Indicates the number of ship targets. Indicates the first Doppler modulation frequency of individual ship targets Indicates the first Doppler modulation frequency of individual ship targets , This represents the azimuth time-domain variable after range-to-wedge transformation. This represents the imaginary unit. The numbers can be obtained using formula (25). Individual ship targets and others Separate imaging filters between individual ship targets.

[0048] S70. Based on all the featured point images and all the constructed separation imaging filters, perform separation imaging processing on the coarse imaging results of each ship target to obtain the separation imaging results of the corresponding ship target.

[0049] In this embodiment of the invention, all the featured point images obtained in S60 and all the constructed separation imaging filters are used to perform separation imaging processing on the coarse imaging results of each ship target. Assuming that for the first... Separating and imaging individual ship targets can be written as: (26); in, Indicates the first Separation imaging results of individual ship targets, and These represent the azimuth-directed Fast Fourier Transform and the inverse azimuth-directed Fast Fourier Transform, respectively. For the first A highlighting image of a single ship target. For the first , Separate imaging filters for each ship target.

[0050] Separate imaging processing is performed sequentially on the coarse imaging results of all ship targets to obtain the separated imaging results of all ship targets. For example, the separated imaging results obtained after processing the echo signals of two ship targets via S60 are as follows: Figures 7(a) to 7(b) As shown, Figures 7(a) to 7(b) The separation imaging results are obtained by processing the coarse imaging results of ship target 1 and ship target 2 using the separation imaging filters corresponding to them. As can be seen from Figures 7(a) to (b), the separation imaging results of ship target 1 and ship target 2 do not have the defocus signal of the other ship target, which can improve the detection and recognition probability of ship targets.

[0051] This invention proposes a ship target separation imaging method using the solved Doppler modulation frequency of each ship target. This method constructs a separation imaging filter, and after separation imaging processing, it can obtain the separation imaging results of each ship target. Furthermore, experiments have demonstrated that this separation imaging method can separate the individual imaging results of each ship target from coarse imaging results where multiple ship targets overlap and intertwine. Figures 6(a) to 6(b) The coarse imaging results of two overlapping and intertwined ship targets are processed by this separation imaging method to obtain the separation imaging results of the two ship targets as follows: Figures 7(a) to 7(b) As shown, the defocus signal of another ship target is not present in the separation imaging results of each ship target.

[0052] In summary, the dual-base radar multi-ship target separation imaging method proposed in this invention can achieve separation imaging of each ship target by processing the echo signals of multiple independently moving ship targets simultaneously. Specifically, it obtains the entropy curve through local entropy transformation, and then solves the Doppler modulation frequency of each ship target based on the entropy curve. This method is unaffected by the existence of multiple scattering points and the coupling of echo signals from multiple ship targets, thus improving the estimation accuracy of the Doppler modulation frequency of the ship targets. This enables high-resolution imaging of the ship targets and obtains coarse imaging results for each ship target. Based on the coarse imaging results of each ship target, a highlight image is obtained. A separation imaging filter is constructed using the Doppler modulation frequency of each ship target estimated by local entropy transformation. Through the highlight image and the constructed separation imaging filter, the separation imaging result of a specific ship target is accurately extracted from the coarse imaging results of each ship target. This separation imaging result contains only one scattering point of the ship target and no defocus signals from other ship targets. This advantage is unattainable by any existing method. This invention can be applied to BFSAR to meet the needs of radar receiving platforms, such as satellites and aircraft, to perform high-resolution separation imaging of each ship target in the target area ahead. This enables aircraft / satellites to monitor ship targets in the target area and can also assist aircraft in landing on specific ship targets, etc., and has broad application prospects.

[0053] Secondly, please see Figure 8 This invention provides a bistatic radar multi-ship target separation imaging device, which includes: The acquisition module is used to acquire echo signals from multiple independently moving ship targets in the target area; The processing module is used to perform range processing on the echo signal to obtain the range-processed signal; The filtering and transformation module is used to perform range cell filtering operations based on the range processing signal, determine the reference range cell based on the filtered range cell, and perform local entropy transformation on the range processing signal at the reference range cell to obtain the entropy curve. The solver module is used to solve for the Doppler modulation frequency of each ship target based on the entropy curve; The coarse imaging module is used to construct a corresponding coarse focusing filter using the Doppler modulation frequency of each ship target, and to perform coarse imaging processing on the range direction processing signal according to the coarse focusing filter to obtain the coarse imaging result of each ship target. The separation imaging preprocessing module is used to perform preprocessing procedures for each ship target before separation imaging, including: constructing separation imaging filters between the ship target and other ship targets according to the Doppler modulation frequency of each ship target; and obtaining the corresponding highlight image based on the coarse imaging result of the ship target. The separation imaging module is used to perform separation imaging processing on the coarse imaging results of each ship target based on all the featured point images and all the constructed separation imaging filters, so as to obtain the separation imaging results of the corresponding ship target.

[0054] As the apparatus embodiment of the second aspect is basically similar to the method embodiment of the first aspect, the description is relatively simple, and relevant details can be found in the description of the method embodiment of the first aspect.

[0055] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0056] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the specification and accompanying drawings, will understand and implement other variations of the disclosed embodiments in carrying out the claimed invention. In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. While certain measures are described in different embodiments, this does not mean that these measures cannot be combined to produce good results.

[0057] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A bistatic radar method for separating and imaging multiple ship targets, characterized in that, The method includes: Acquire echo signals from multiple independently moving ship targets in the target area; The echo signal is processed in the range direction to obtain the range-processed signal; A distance cell filtering operation is performed based on the distance processing signal. A reference distance cell is determined based on the filtered distance cells. A local entropy transformation is performed on the distance processing signal at the reference distance cell to obtain an entropy curve. The Doppler modulation frequency of each ship target is determined based on the entropy curve. A coarse focusing filter is constructed using the Doppler modulation frequency of each ship target. The range-oriented processing signal is then subjected to coarse imaging processing based on the coarse focusing filter to obtain the coarse imaging result of each ship target. For each ship target, the preprocessing process before performing separation imaging includes: constructing separation imaging filters between the ship target and other ship targets according to the Doppler modulation frequency of each ship target; and obtaining the corresponding highlight image based on the coarse imaging result of the ship target. Based on all the featured point images and all the constructed separation imaging filters, the coarse imaging results of each ship target are processed for separation imaging to obtain the corresponding ship target's separation imaging result.

2. The bistatic radar multi-ship target separation and imaging method according to claim 1, characterized in that, The echo signal is processed in the range direction to obtain a range-processed signal, including: Perform a range-direction Fast Fourier Transform on the echo signal to obtain a range-frequency domain signal; The range frequency signal is filtered using a range-oriented processing filter to obtain a range-oriented filtered signal; The range-filtered signal is subjected to a wedge transform to obtain the range-wedge-transformed signal; The range-direction wedge-transformed signal is subjected to a range-direction fast Fourier inverse transform to obtain the range-direction processed signal.

3. The bistatic radar multi-ship target separation and imaging method according to claim 1, characterized in that, The range-processed signal is subjected to a range cell filtering operation. A reference range cell is determined based on the filtered range cells. A local entropy transformation is then performed on the range-processed signal at the reference range cell to obtain an entropy curve, including: The range-processed signal is integrated in the azimuth direction to obtain the azimuth energy integration result; The distance cell threshold is calculated based on the azimuth energy integration result, and the distance cells whose azimuth energy integration result is greater than the distance cell threshold are filtered out. The filtered distance cells form a distance cell range, and the center of the distance cell range is used as the reference distance cell. A fractional Fourier transform is performed on the range-oriented processing signal at the reference range unit to obtain the fractional Fourier transform result; The fractional Fourier transform result is subjected to a local entropy calculation operation in the azimuth direction to obtain the entropy curve.

4. The bistatic radar multi-ship target separation and imaging method according to claim 1, characterized in that, The Doppler modulation frequency of each ship target is determined based on the entropy curve, including: Each ship target is determined based on the minimum point of the entropy curve, and the Doppler modulation frequency of the corresponding ship target is calculated using the minimum point of each ship target.

5. The bistatic radar multi-ship target separation and imaging method according to claim 1, characterized in that, Construct a coarse focusing filter using the Doppler modulation frequency of each ship target, as expressed by the formula: ； in, Indicates the first The coarse focusing filter corresponding to each ship target. , Indicates the number of ship targets. This represents the azimuth time-domain variable after range-to-wedge transformation. Represents the imaginary unit. Indicates the first Doppler tuning frequency of individual ship targets.

6. The bistatic radar multi-ship target separation and imaging method according to claim 1, characterized in that, The range-oriented processing signal is subjected to coarse imaging processing based on the coarse focusing filter, including: The range signal is sequentially filtered and subjected to azimuth fast Fourier transform using the coarse focusing filter.

7. The bistatic radar multi-ship target separation and imaging method according to claim 1, characterized in that, The separation imaging filters between this ship target and other ship targets are constructed separately, and the formula is expressed as follows: ； in, Indicates the first , Separate imaging filters for each ship target , Indicates the number of ship targets. Indicates the first Doppler modulation frequency of individual ship targets Indicates the first Doppler modulation frequency of individual ship targets , This represents the azimuth time-domain variable after range-to-wedge transformation. It represents the imaginary unit.

8. The bistatic radar multi-ship target separation and imaging method according to claim 1, characterized in that, Based on the coarse imaging results of the ship target, the corresponding highlighted point image is obtained, including: Construct corresponding threshold values ​​for prominent points based on the coarse imaging results of the ship target; Signals smaller than the corresponding highlight threshold in the coarse imaging result of the ship target are set to 0 to obtain the highlight image of the ship target.

9. The bistatic radar multi-ship target separation and imaging method according to claim 1, characterized in that, It is applied in BFSAR.

10. A bistatic radar multi-ship target separation and imaging device, characterized in that, The device includes: The acquisition module is used to acquire echo signals from multiple independently moving ship targets in the target area; The processing module is used to perform range processing on the echo signal to obtain a range-processed signal; The filtering and transformation module is used to perform a range cell filtering operation based on the range processing signal, determine a reference range cell based on the filtered range cells, and perform a local entropy transformation on the range processing signal at the reference range cell to obtain an entropy curve. The solution module is used to solve for the Doppler modulation frequency of each ship target based on the entropy curve; The coarse imaging module is used to construct a corresponding coarse focusing filter using the Doppler modulation frequency of each ship target, and to perform coarse imaging processing on the range processing signal according to the coarse focusing filter to obtain the coarse imaging result of each ship target. The separation imaging preprocessing module is used to perform preprocessing procedures for each ship target before separation imaging, including: constructing separation imaging filters between the ship target and other ship targets according to the Doppler modulation frequency of each ship target; and obtaining the corresponding highlight image based on the coarse imaging result of the ship target. The separation imaging module is used to perform separation imaging processing on the coarse imaging results of each ship target based on all the featured point images and all the constructed separation imaging filters, so as to obtain the separation imaging results of the corresponding ship target.

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