Azimuth envelope aligned high-resolution moving ship SAR fine focusing method and system

Abstract

The present invention discloses a high-resolution moving ship SAR fine focusing method and system with azimuth envelope alignment, which belongs to the field of radar technology and includes the following steps: step 1, pre-processing, performing distance compression and translation compensation on the echo; step 2, extracting the special points, extracting the azimuth signals of two special points that are far apart in distance; step 3, difference frequency analysis, conjugate multiplying the azimuth signals of the two special points to obtain the difference frequency signal, and using IAA to perform time-frequency analysis on the difference frequency signal; step 4, peak extraction, extracting the peak of the time-frequency graph, and obtaining the change of the difference frequency with the azimuth time; step 5, resampling, resampling the signal after translation compensation according to the difference frequency; step 6, azimuth focusing, using azimuth Fourier transform to obtain a focused image. The present invention can complete the azimuth envelope alignment and achieve the best imaging effect when it is believed that the distance envelope alignment can be performed correctly.

Description

Technical Field

[0001] The invention belongs to the field of radar technology, and in particular relates to a high-resolution moving ship SAR fine focusing method and system with azimuth envelope alignment. Background Art

[0002] Synthetic Aperture Radar (SAR) is a radar technology that uses microwaves to image targets. SAR images the target through the relative motion between the target and the radar, and obtains the two-dimensional electromagnetic scattering characteristics of the target. Unlike traditional radar, it can obtain images of ground targets (such as buildings on the ground and ships on the sea) in all weather conditions and at all times of the day, and has important application value. SAR transmits linear frequency modulation signals and achieves high resolution in the distance direction through pulse compression. High resolution in the azimuth direction is obtained by coherently integrating the Doppler signals generated by the relative motion between the target and the radar.

[0003] SAR can also image non-cooperative targets, and the related technology is called Inverse Synthetic Aperture Radar (ISAR) technology. The steps for general SAR to finely focus on ships include: 1. Azimuth aperture expansion. Restore the ship image to a state where only pulse compression is performed in the range direction. 2. Range envelope alignment. Compensate for the envelope error caused by radial relative motion (translation). Use correlation method, centroid method or optimization method to translate the sampled signal pulse by pulse to align the range envelope. 3. Initial phase compensation. Compensate for phase changes caused by translation. It is inaccurate to compensate for the phase only by the translation amount, and initial phase compensation is required through self-focusing algorithms such as Phase Gradient Autofocus (PGA) and Doppler Center Tracking (DCT). 4. Azimuth focusing. Perform Fourier transform in the azimuth direction to obtain a finely focused ship SAR image. The above is the classic Range-Doppler (RD) algorithm of ISAR. The RD algorithm can only image a target that rotates steadily, and requires that the rotational angular velocity of the target relative to the radar is approximately constant.

[0004] With the demand for high-resolution imaging, a larger relative motion is required between the target and the radar, resulting in a larger synthetic angle. The coherent processing interval (CPI) needs to be further improved. When the CPI is increased, the non-stationarity of the target motion will significantly affect the RD imaging quality. The current pulse compression and translation compensation parts have been relatively well studied. However, the problem of azimuth focusing cannot be solved well at present. The current mainstream algorithm uses the range-instantaneous Doppler (RID) type algorithm for imaging. Find the optimal imaging time and use only part of the received data for imaging. In this short period of time, the target motion can be approximated as a smooth motion, and the RD algorithm can be used for imaging. The direct problem brought about by this is that the resolution is not enough, and imaging with a long CPI cannot be achieved.

[0005] RID methods can be divided into two categories. One is non-parametric methods, that is, imaging algorithms based on time-frequency distribution. Such as linear algorithms such as short time Fourier transform (STFT) and wavelet transform (Gabor representation), bilinear algorithms such as Wigner-Ville distribution (WVD), Born-Jordan distribution (BJD), Choi-Williams distribution (CWD), smoothed pseudo Wigner-Ville distribution (SPWVD), and reassigned pseudo Wigner-Ville distribution (RPWVD). The resolution of linear algorithms is not enough, and bilinear algorithms can tolerate certain non-stationary motion and use longer data segments for imaging to achieve higher resolution. Although the resolution can be increased, it will be affected by cross-terms, and a trade-off needs to be made between resolution and cross-terms.

[0006] The second category is based on signal estimation algorithms. The signal of a single range gate is regarded as a multi-component high-order polynomial phase signal. When the signal order is considered to be second order, the center frequency and chirp rate of the signal can be estimated using algorithms such as fractional Fourier transform (FRFT), Radon-Wigner transform (RWT), Wigner-Hough transform (WHT), Radon-Ambiguity transform (RAT), and Lv's Distribution. When the signal order is considered to be third order, the product generalized cubic phase function (PGCPF), product high-order matched-phase transform (PHMPT), generalized scaled Fourier transform (GSCFT), and Keystone time-chirp rate distribution (KTCRD) can be used to estimate the high-order coefficients of the signal phase. Then the frequency and center frequency are swapped one by one to estimate. This type of algorithm is also affected by cross terms. These algorithms suppress cross terms through different methods, such as PGCPF and PHMPT suppress cross terms by multiplication, GSCFT suppresses cross terms by stretching data, and KTCRD breaks up cross term energy through KT transformation. Another problem with this type of algorithm is that it can only perform sparse imaging. No matter how many components can be estimated, they are limited. Only a limited number of independent and significant scattering points can be imaged within a range gate, and weak points will be covered by strong points.

[0007] How to suppress cross-terms while ensuring resolution is a problem that remains to be solved. With the development and application of modern digital signal processing theory, modern spectral analysis algorithms are gradually being used for non-cooperative target SAR imaging. Such as the multiple signal classification algorithm (MUSIC), the iterative adaptive amplitude phase spectrum estimation algorithm (IAA-APES), the Capon algorithm, and so on. These algorithms can use limited data to achieve imaging beyond the Rayleigh resolution, and there is no problem of cross-terms. But the problem is that the amplitude estimation is inaccurate, and the absolute amplitude and relative amplitude of the output result may be meaningless. As a result, although the position of the scattering point in the SAR image is accurate, the scattering coefficient has no practical meaning.

[0008] In summary, the current problem of SAR imaging of non-cooperative targets is that it is impossible to use longer data segments for imaging, and it is impossible to effectively achieve non-sparse long CPI imaging of distributed targets. It is urgent to study new SAR imaging algorithms that can extend the CPI of non-cooperative target imaging, completely suppress cross terms, and obtain accurate scattering coefficients of scattering points. Summary of the invention

[0009] In order to solve the above technical problems, the present invention proposes a high-resolution moving ship SAR fine focusing method and system with azimuth envelope alignment, the method includes: preprocessing, distance compression and translation compensation for echoes; special point extraction, extracting the azimuth signals of two special points that are far apart in distance; difference frequency analysis, conjugate multiplication of the azimuth signals of the two special points to obtain a difference frequency signal, and using an iterative adaptive amplitude phase spectrum estimation algorithm (IAA) to perform time-frequency analysis on the difference frequency signal; peak extraction, extracting the peak of the time-frequency graph to obtain the change of the difference frequency with azimuth time; resampling, resampling the signal after translation compensation according to the difference frequency; azimuth focusing, using azimuth Fourier transform to obtain a focused image. The present invention can complete the azimuth envelope alignment and achieve the best imaging effect when it is believed that the distance envelope alignment can be performed correctly.

[0010] In order to achieve the above object, the present invention adopts the following technical scheme:

[0011] A high-resolution moving ship SAR fine focusing method with azimuth envelope alignment comprises the following steps:

[0012] Step 1: Extract the ship slice in the SAR image, perform azimuth aperture expansion and translation correction, and obtain the equivalent turntable model signal , is the azimuth slow time, For distance to fast time;

[0013] Step 2: Select two prominent points whose distance in the range direction is greater than one-third of the range gate covered by the ship, and extract the azimuth signals respectively. and bearing signal ;

[0014] Step 3: Using the azimuth signal and bearing signal Get the difference frequency signal , for the difference frequency signal Perform time-frequency analysis to obtain a time-frequency diagram , is the azimuth frequency;

[0015] Step 4: Extract time-frequency graph The maximum value point of Slow time with direction changes;

[0016] Step 5: According to the difference frequency Equivalent turntable model signal Resample to obtain the echo signal aligned with the azimuth envelope ;

[0017] Step 6: Align the echo signal with the azimuth envelope Perform azimuth Fourier transform to obtain a finely focused ship SAR image at range Doppler .

[0018] The present invention also provides a high-resolution moving ship SAR fine focusing system with azimuth envelope alignment, comprising the following modules:

[0019] Image extraction module, used to extract ship slices from SAR images, perform azimuth aperture expansion and translation correction, and obtain equivalent turntable model signals , is the azimuth slow time, For distance to fast time;

[0020] The azimuth signal extraction module is used to select two prominent points whose distance is greater than one-third of the range gate covered by the ship, and extract the azimuth signal respectively. and bearing signal ;

[0021] Time-frequency diagram analysis module, used to analyze the azimuth signal and bearing signal Get the difference frequency signal , for the difference frequency signal Perform time-frequency analysis to obtain a time-frequency diagram , is the azimuth frequency;

[0022] Difference frequency change acquisition module, used to extract time-frequency diagram The maximum value point of Slow time with direction changes;

[0023] The echo signal acquisition module is used to obtain the echo signal according to the difference frequency. Equivalent turntable model signal Resample to obtain the echo signal aligned with the azimuth envelope ;

[0024] Focused image acquisition module, used to align the echo signal with the azimuth envelope Perform azimuth Fourier transform to obtain a finely focused ship SAR image at range Doppler .

[0025] 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 steps of the above-mentioned azimuth envelope aligned high-resolution moving ship SAR fine focusing method are implemented.

[0026] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-mentioned azimuth envelope aligned high-resolution moving ship SAR fine focusing method.

[0027] Beneficial effects:

[0028] The present invention realizes non-parametric long synthetic aperture time non-sparse imaging of maneuvering targets, and is not limited by the nonlinear order of target motion and the specific manifestation of the generated azimuth signal. The present invention can achieve the theoretical highest resolution by using the maximum relative rotation angle of the target. The scattering point amplitude of the image obtained by the present invention can reflect the electromagnetic scattering characteristics of the target, and there is no distortion of the target in the image. Thanks to the high anti-noise performance of IAA, the present invention can image maneuvering targets at a lower signal-to-noise ratio, and can balance the anti-noise performance, calculation speed and calculation accuracy by setting the length of the data segment in a time-frequency analysis. The present invention is suitable for SAR imaging of various moving targets and various radar systems. No matter how the imaging plane changes during imaging, the present invention can achieve effective azimuth envelope alignment and obtain a focused image under the condition that the distance envelope alignment can be performed correctly. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a flow chart of the azimuth envelope aligned high-resolution moving ship SAR fine focusing method of the present invention;

[0030] Figure 2 It is a schematic diagram of the change of angular velocity and the focus position of the prominent point with azimuth time;

[0031] Figure 3 It is a comparison between the traditional time-frequency analysis method and the IAA time-frequency analysis method; where a is the traditional time-frequency analysis method, and b is the IAA time-frequency analysis method;

[0032] Figure 4 is a comparison diagram of the phase and frequency of two prominent points before and after resampling over time; wherein, a is a diagram of the phase and frequency of one prominent point before and after resampling over time, and b is a diagram of the phase and frequency of another prominent point before and after resampling over time;

[0033] Figure 5 is a comparison diagram of the target orientation envelope before and after using the present invention; wherein a is the target orientation envelope diagram before using the present invention, and b is the target orientation envelope diagram after using the present invention;

[0034] Figure 6 The processing results of the measured data by this method are compared with those of the traditional method; among them, a is the direct imaging of the first target RD, b is the imaging of the first target using this method, c is the direct imaging of the second target RD, and d is the imaging of the second target using this method. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inner", "outer", etc. used in the present invention to indicate the orientation or position relationship is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0037] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] like Figure 1 As shown, the present invention proposes a high-resolution moving ship SAR fine focusing method with azimuth envelope alignment, comprising the following steps:

[0039] Step 1: Extract the ship from the SAR image and perform azimuth aperture expansion and translation correction, including:

[0040] Extract the ship slices in the SAR image, perform azimuth aperture expansion and translation correction, and obtain the equivalent turntable model signal , is the azimuth slow time, expressed as , is the pulse repetition interval, is the number of pulses, is the distance-to-speed time, expressed as ,in, is the distance sampling interval, is the sampling start time, is the number of sampling points in the distance direction. The translation correction is completed accurately, and the echo signal generated by the equivalent turntable model has the rotation center at the center of gravity of the scattering point.

[0041] Step 2: Select two adjacent prominent points in range and extract their azimuth signals and ,include:

[0042] The equivalent turntable model signal Sum along the azimuth to get the signal , in the signal Before Find the maximum value among the sampling points , in the signal After Find the maximum value among the sampling points .

[0043] Extract range gates separately (i.e. the maximum value point) and range gate (maximum point) azimuth signal , as follows:

[0044] ;

[0045] ;

[0046] This extraction method extracts the range gate where the main energy of two prominent points that are far apart in the range direction (the distance is greater than one-third of the range gate covered by the ship) is located, as well as the signals of the two range gates before and after the range gate, and can tolerate a certain cross-range unit migration. Assume that the rotational angular velocity of the target relative to the radar is , the azimuth coordinates of the first prominent point are , the azimuth coordinates of the second prominent point are The focal positions of the two prominent points are and Slow time with direction The changes are , .in, is the signal carrier frequency, is the speed of light, Indicates phase. and The relationship between them is: , is the coefficient related to the azimuth coordinates of the two prominent points. Figure 2 As shown, the angular velocity of rotation , two special focus positions and The meaning of azimuth envelope is similar to that of range envelope. The change of the focus position of all scattering points of all range gates in the range direction with the azimuth slow time is the distance envelope, and the change of the focus position of all scattering points of all range gates in the azimuth with the azimuth slow time is the azimuth envelope.

[0047] Step 3: Pass and Get the difference frequency signal The time-frequency diagram is obtained by performing time-frequency analysis on the difference frequency signal. ,include:

[0048] The bearing signal and bearing signal Conjugate multiplication to obtain the difference frequency signal :

[0049] ;

[0050] in, Indicates direction signal If the azimuth signal With bearing signal Each contains only one frequency component, so the difference frequency signal obtained by conjugating and multiplying the two is The frequency of the azimuth signal With bearing signal The frequency difference of the signals involved.

[0051] The difference frequency signal is estimated using an iterative adaptive amplitude-phase spectrum estimation algorithm (IAA). Perform time-frequency analysis to obtain a time-frequency diagram IAA can also effectively estimate the signal when there is only a single snapshot, so IAA can be used to estimate the difference frequency signal. Perform time-frequency analysis. The principle of IAA is not described in detail in this invention, but for ease of representation, it is regarded as a time-frequency analysis function and defined as follows:

[0052] ;

[0053] ;

[0054] ;

[0055] in, Express The sequence is analyzed in time and frequency by an iterative adaptive amplitude-phase spectrum estimation algorithm. Represents the time series involved in time-frequency analysis, this sequence is a difference frequency signal part of the sequence, is the frequency amplitude distribution of IAA output, is the central time involved in the time-frequency analysis, The number of sampling points involved in a single time-frequency analysis needs to be set to an odd number. is the pulse repetition frequency, , is the frequency sampling interval. In the time-frequency analysis method based on Fourier transform, , but the IAA output resolution can exceed the Rayli resolution, so it can be Set to The above formula shows that IAA can input a time series and output the spectrum amplitude distribution of the time series. is the azimuth frequency.

[0056] The difference frequency signal The number of segments is related to the non-stationarity of the target motion. , then the step length between segments can be calculated . Therefore, in a time-frequency analysis, the input sequence is:

[0057] ;

[0058] ;

[0059] in, It is a segment index. Generally speaking , it is necessary to pad the original data with zeros before and after to avoid overflow.

[0060] The difference frequency signal After performing time-frequency analysis on all data segments, a complete time-frequency distribution diagram can be obtained. .like Figure 3 As shown in the figure, the time-frequency diagram generated by the IAA method is compared with the traditional time-frequency analysis method based on Fourier transform. It can be found that under the same time resolution and the same windowing, the frequency resolution of the time-frequency diagram generated by IAA is higher than that of the traditional method. Figure 3 a is the traditional time-frequency analysis method, Figure 3 b is the IAA time-frequency analysis method.

[0061] Step 4: Extraction The maximum value point is obtained Changes with time of position, including:

[0062] Frequency along azimuth Extracting time-frequency plots The maximum point is recorded as the difference frequency :

[0063] ;

[0064] ;

[0065] in, Represents the objective function The variable at the maximum value The value of .

[0066] After interpolation, we can get the complete curve of azimuth frequency versus azimuth time:

[0067] .

[0068] Step 5: According to Resampling the result obtained in step 1 to obtain an echo signal subjected to an azimuth envelope, including:

[0069] Position signal To resample:

[0070] First calculate the phase change caused by the difference frequency :

[0071] ;

[0072] in, Indicates the time of position Difference frequency phase The mapping function of .

[0073] Since we expect to achieve azimuth envelope alignment based on these two prominent points, that is, these two prominent points always remain unchanged in the azimuth envelope. After the autofocus algorithm in the translation compensation, the center of gravity of the azimuth envelope has remained unchanged. Now we only need to ensure that the distance between the two prominent points remains unchanged. So we have , for The expected value of is a constant that does not change with time. The positive and negative of the difference frequency remains unchanged, that is, the rotation direction of the equivalent turntable model remains unchanged, and the resolution can be increased by extending the coherent integration time (CPI). The maximum value of , then:

[0074] ; Among them, the last azimuth sampling time .

[0075] Then the constant for:

[0076] ;

[0077] New direction to slow time for:

[0078] ;

[0079] ;

[0080] in, is the phase step index, is the step phase between adjacent sampling points.

[0081] Slow down time in the new direction In, satisfied . Resample the data to obtain the echo signal aligned with the azimuth envelope :

[0082] ;

[0083] like Figure 4 As shown in the figure, the changes of phase and frequency (focus position) over time before and after resampling of two prominent points are compared. Figure 4 a is a graph showing the phase and frequency changes over time before and after resampling of a particular point. Figure 4 b is a graph showing the frequency / angular velocity variation over time of another prominent point before and after resampling; it can be found that after resampling, the linear phase of both prominent points has been restored. In fact, the phases of not only the two prominent points have been restored, but the phases of all the scattering points of the range gate have been restored at the same time through this resampling. At this point, the echo signals of all the scattering points can be coherently accumulated in the entire aperture and are correctly focused.

[0084] like Figure 5 As shown, The azimuth envelope and By comparing the azimuth envelope of The azimuth envelope of has been aligned. Among them, Figure 5 a is the target position envelope diagram before using the present invention, Figure 5 b is the target position envelope diagram after using the present invention;

[0085] Step 6: performing azimuth Fourier transform on the echo signal obtained in step 5 to obtain a finely focused ship SAR image, including:

[0086] right Perform azimuth Fourier transform to obtain a finely focused ship SAR image in the range Doppler domain (RD). , as follows:

[0087] ;

[0088] in, Indicates slow time in azimuth direction to perform Fourier transform. This is a finely focused image. The azimuth resolution of the scattering point corresponds to the maximum turning angle of the target relative to the radar. Figure 6 As shown in the figure, some measured data are selected to compare the processing results of the traditional method with those of this method. Figure 6 a is the first target RD direct imaging, Figure 6 b is the first target imaged using this method, Figure 6 c is the second target RD direct imaging, Figure 6 d is the second target imaged using this method. Accumulate time for coherence, The longer it is, the more difficult it is to focus. The first target and the second target are two bulk carriers in motion. It can be seen that when the first target and the second target are imaged using the traditional method, the target defocus is serious and it is difficult to identify the target features. The quality of the target image obtained by processing using the method of the present invention is significantly improved, the features are more obvious, and it is easier to identify. The present invention can effectively image non-stationary moving targets.

[0089] The present invention also provides a high-resolution moving ship SAR fine focusing system with azimuth envelope alignment, comprising the following modules:

[0090] Image extraction module, used to extract ship slices from SAR images, perform azimuth aperture expansion and translation correction, and obtain equivalent turntable model signals , is the azimuth slow time, For distance to fast time;

[0091] The azimuth signal extraction module is used to select two prominent points whose distance is greater than one-third of the range gate covered by the ship, and extract the azimuth signal respectively. and bearing signal ;

[0092] Time-frequency diagram analysis module, used to analyze the azimuth signal and bearing signal Get the difference frequency signal , for the difference frequency signal Perform time-frequency analysis to obtain a time-frequency diagram , is the azimuth frequency;

[0093] Difference frequency change acquisition module, used to extract time-frequency diagram The maximum value point of Slow time with direction changes;

[0094] The echo signal acquisition module is used to obtain the echo signal according to the difference frequency. Equivalent turntable model signal Resample to obtain the echo signal aligned with the azimuth envelope ;

[0095] Focused image acquisition module, used to align the echo signal with the azimuth envelope Perform azimuth Fourier transform to obtain a finely focused ship SAR image at range Doppler .

[0096] 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 steps of the above-mentioned azimuth envelope aligned high-resolution moving ship SAR fine focusing method are implemented.

[0097] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-mentioned azimuth envelope aligned high-resolution moving ship SAR fine focusing method.

[0098] It should be understood by those skilled in the art that the embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The solutions in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and interpreted scripting language JavaScript, etc.

[0099] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0100] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0101] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0102] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0103] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A high-resolution moving ship SAR fine focusing method with azimuth envelope alignment, characterized in that: The steps include: Extract the ship slices in the SAR image, perform azimuth aperture expansion and translation correction, and obtain the equivalent turntable model signal , is the azimuth slow time, For distance to fast time; Select two prominent points whose distance in the range direction is greater than one-third of the range gate covered by the ship, and extract the azimuth signal respectively. and bearing signal ; Via bearing signal and bearing signal Get the difference frequency signal , for the difference frequency signal Perform time-frequency analysis to obtain a time-frequency diagram , is the azimuth frequency; Extracting time-frequency plots The maximum value point of Slow time with direction changes; According to the difference frequency Equivalent turntable model signal Resample to obtain the echo signal aligned with the azimuth envelope ; For echo signals aligned with azimuth envelope Perform azimuth Fourier transform to obtain a finely focused ship SAR image at range Doppler .

2. The high-resolution moving ship SAR fine focusing method with azimuth envelope alignment according to claim 1 is characterized in that: The ship slices in the SAR image are extracted, and the azimuth aperture expansion and translation correction are performed to obtain the equivalent turntable model signal. include: Azimuth Slow Time It is expressed as: ,in, is the pulse repetition interval, is the number of pulses, is the distance-to-speed time, expressed as: ,in, is the distance sampling interval, is the sampling start time, is the number of sampling points in the distance direction; equivalent turntable model signal Accurately complete the translation correction, and generate the echo signal for the equivalent turntable model, with the rotation center at the center of gravity of the scattering point.

3. The high-resolution moving ship SAR fine focusing method with azimuth envelope alignment according to claim 2 is characterized in that: The method selects two distinct points whose distance in the range direction is greater than one third of the range gate covered by the ship, and extracts the azimuth signal respectively. and bearing signal include: The equivalent turntable model signal Sum along the azimuth to get the signal , in the signal Before Find the maximum value among the sampling points , in the signal After Find the maximum value among the sampling points ; Extract the maximum value points respectively The direction signal and maximum point The direction signal : ； 。 4. The high-resolution moving ship SAR fine focusing method with azimuth envelope alignment according to claim 3 is characterized in that: The passing position signal and bearing signal Get the difference frequency signal , for the difference frequency signal Perform time-frequency analysis to obtain a time-frequency diagram include: The bearing signal and bearing signal Conjugate multiplication to obtain the difference frequency signal , expressed as: ； in, express conjugation of; Iterative adaptive amplitude-phase spectrum estimation algorithm is used to estimate the difference frequency signal For time-frequency analysis, the iterative adaptive amplitude-phase spectrum estimation algorithm is regarded as a time-frequency analysis function and is defined as follows: ； ； ； in, Represents the time series involved in time-frequency analysis. This sequence is a signal part of the sequence, is the frequency amplitude distribution of IAA output, is the central time involved in the time-frequency analysis, is the number of sampling points involved in the time-frequency analysis at a time, set to an odd number. is the pulse repetition frequency, , is the frequency sampling interval; IAA represents the iterative adaptive amplitude phase spectrum estimation algorithm; The difference frequency signal Perform time-frequency analysis to obtain a complete time-frequency diagram .

5. The high-resolution moving ship SAR fine focusing method with azimuth envelope alignment according to claim 4 is characterized in that: The extracted time-frequency diagram The maximum value point of Slow time with direction The changes include: In azimuth frequency Direction Extraction Frequency Graph The maximum value point of The change over time is expressed as: ； ； in, Represents the objective function The variable at the maximum value The value of represents the inter-segment step length in time-frequency analysis, is the number of segments in the time-frequency analysis; After interpolation, we get the complete curve of azimuth frequency versus azimuth time: 。 6. The high-resolution moving ship SAR fine focusing method with azimuth envelope alignment according to claim 5 is characterized in that: The difference frequency Equivalent turntable model signal Resample to obtain the echo signal aligned with the azimuth envelope include: according to Equivalent turntable model signal To resample, first calculate the difference frequency The phase change caused : ； in, Indicates the time of position With phase change The mapping function of set up for The objective function is , is a constant that does not change with time; set up The positive and negative of remains unchanged, that is, the rotation direction of the equivalent turntable model remains unchanged, and the coherent accumulation time is extended to increase the resolution; The phase change caused by the difference frequency The maximum value of , then: ； Among them, the last azimuth sampling time ; Then the constant for: ； New direction to slow time for: ； ； in, is the phase step index, is the step phase of adjacent sampling points, Slow down time in the new direction In, satisfied ; in, Slow down time for a new orientation The difference frequency; Resample the data to obtain an echo signal aligned with the azimuth envelope : 。 7. The high-resolution moving ship SAR fine focusing method with azimuth envelope alignment according to claim 6 is characterized in that: The pair of echo signals aligned by azimuth envelope Perform azimuth Fourier transform to obtain a finely focused ship SAR image at range Doppler include: For echo signals aligned with azimuth envelope Perform azimuth Fourier transform to obtain a finely focused ship SAR image in the range Doppler domain , as follows: ； in, Indicates slow time in position direction to perform Fourier transform.

8. A high-resolution moving ship SAR fine focusing system with azimuth envelope alignment, characterized in that: Includes the following modules: Image extraction module, used to extract ship slices from SAR images, perform azimuth aperture expansion and translation correction, and obtain equivalent turntable model signals , is the azimuth slow time, For distance to fast time; The azimuth signal extraction module is used to select two prominent points whose distance is greater than one-third of the range gate covered by the ship, and extract the azimuth signal respectively. and bearing signal ; Time-frequency diagram analysis module, used to analyze the azimuth signal and bearing signal Get the difference frequency signal , for the difference frequency signal Perform time-frequency analysis to obtain a time-frequency diagram , is the azimuth frequency; Difference frequency change acquisition module, used to extract time-frequency diagram The maximum value point of Slow time with direction changes; The echo signal acquisition module is used to obtain the echo signal according to the difference frequency. Equivalent turntable model signal Resample to obtain the echo signal aligned with the azimuth envelope ; Focused image acquisition module, used to align the echo signal with the azimuth envelope Perform azimuth Fourier transform to obtain a finely focused ship SAR image at range Doppler .

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps of the azimuth envelope aligned high-resolution moving ship SAR fine focusing method according to any one of claims 1 to 7 are implemented.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the azimuth envelope aligned high-resolution moving ship SAR fine focusing method as described in any one of claims 1 to 7 are implemented.

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