A method for detecting moving targets using triangular wave modulated laser synthetic aperture radar

Abstract

The present disclosure provides a method for detecting moving targets of a laser synthetic aperture radar modulated by a triangular wave, including: obtaining synthetic aperture laser radar data of a triangular frequency modulated continuous wave; performing positive frequency modulation imaging and negative frequency modulation imaging on the synthetic aperture laser radar data; performing transformation processing on the positive frequency modulation imaging image and the negative frequency modulation imaging image to obtain a first signal and a second signal; performing interference multiplication on the first signal and the second signal to obtain an interference signal; and extracting the motion parameters of the moving target from the interference signal. The moving target detection and subsequent motion estimation method provided by the present disclosure does not require cross-correlation operations and upsampling interpolation, can reduce the operation process, reduce the amount of calculation, and extract motion parameters with high accuracy and precision.

Description

Technical Field

[0001] The present disclosure relates to the technical field of radar monitoring, and in particular to a method for detecting moving targets of a triangular wave modulated laser synthetic aperture radar. Background Art

[0002] The working principle of radar is to transmit electromagnetic waves to the target, and the target reflects the electromagnetic waves to the radar. The radar analyzes the echo and extracts information related to the target. Synthetic aperture technology uses a small moving antenna to radiate coherent signals along a predetermined trajectory, and performs coherent processing on the received echo to obtain a radar image with higher resolution.

[0003] In the field of remote sensing, synthetic aperture laser radar (SAL) is regarded as an extended application of synthetic aperture technology in the laser band, providing a new idea for obtaining high-resolution remote sensing images. The wavelength of laser is more than three orders of magnitude shorter than that of microwave. Therefore, SAL has ultra-high resolution and ultra-short synthetic aperture time compared with conventional microwave-based synthetic aperture radar (SAR), and can achieve fast and high-resolution fine imaging of targets. As an active imaging remote sensing device, SAL has the ability to work all day. Similar to SAR, SAL achieves high resolution in the range direction by emitting a large-bandwidth linear frequency modulation signal, and achieves high resolution in the azimuth direction through synthetic aperture technology. According to the different transmission signals, laser radar can be divided into two categories: one is the pulse system, and the other is the frequency modulation continuous wave system. Compared with the former, frequency modulation continuous wave (FMCW) laser radar has many advantages: large ranging range; high range resolution; good low intercept characteristics; low transmission power, easy engineering implementation, etc. Thanks to the above advantages, FMCW SAL has great application potential in power line inspection, agricultural remote sensing, target detection and identification, etc.

[0004] Moving target detection is a current research hotspot using radar detection technology. Radar systems can usually be divided into single-channel systems and multi-channel systems. The single-channel radar moving target detection method is mainly based on the echo characteristics of the moving target. The imaging of the moving target according to the conventional motion parameters and signal model will lead to blurred imaging results of the moving target, because it is difficult to effectively suppress strong clutter. In severe cases, it is impossible to distinguish, and it is even more difficult to extract relevant structural features and motion parameters. In comparison, the multi-channel system can simultaneously utilize information in both space and time dimensions, effectively suppress clutter, and highlight the moving target signal, especially the slow target. However, in order to increase the receiving channel, the hardware system structure is complex and the processing method is cumbersome.

[0005] Therefore, starting from the signal model, we consider solving the problem of moving target detection and subsequent motion estimation in SAL, and realizing the detection and estimation of weak moving targets. For linear frequency modulated continuous waves, there are two common wave types: sawtooth wave and triangle wave. Among them, the sawtooth wave modulation and processing method is simple and easy to implement, but it can only be used to measure the distance of stationary targets, and cannot obtain high-precision distance and speed information at the same time; the transmission and processing algorithm of the triangle wave signal is more complicated, but the highly symmetrical correlation relationship of the bilateral signals can be used to extract the parameter information of the moving target. However, in the field of imaging, the positive and negative frequency modulation signals of the triangle wave are usually separated and imaged independently according to the processing mode of the sawtooth wave echo signal. The correlation between the positive and negative frequency modulation signals cannot be utilized, and the moving target detection and motion parameter extraction cannot be completed.

[0006] Furthermore, for synthetic aperture lidar, due to the extremely short wavelength of the laser, the energy of the moving target is likely to cross the range gate, and the estimation accuracy of the cross-correlation operation in the conventional method is easily affected by the target signal-to-noise ratio; secondly, in order to improve the estimation accuracy, interpolation is usually required, which will reduce processing efficiency; furthermore, for slow-moving targets, it is also possible that they will not cross the range gate within one triangular wave cycle, which will cause the existing cross-correlation processing method to fail. Summary of the invention

[0007] In order to solve the above technical problems, the present disclosure provides a method for detecting moving targets of a laser synthetic aperture radar using a triangular wave modulation, comprising:

[0008] Acquire triangular frequency modulated continuous wave synthetic aperture lidar data;

[0009] The synthetic aperture laser radar data will be subjected to positive frequency modulation imaging and negative frequency modulation imaging respectively;

[0010] Performing transformation processing on the positive frequency modulation imaging image to obtain a first signal, and performing transformation processing on the negative frequency modulation imaging image to obtain a second signal;

[0011] performing interference multiplication on the first signal and the second signal to obtain an interference signal; and

[0012] The motion parameters of the moving target are extracted from the interference signal.

[0013] According to some embodiments of the present disclosure, before transforming the positive frequency modulation image and the negative frequency modulation image, the method further includes:

[0014] The positive frequency modulation imaging image and the negative frequency modulation imaging image are subjected to window selection, and the window selection area includes all the interested areas to be detected or the positions where the moving target may exist.

[0015] According to some embodiments of the present disclosure, transforming a positive frequency modulation image to obtain a first signal, and transforming a negative frequency modulation image to obtain a second signal includes:

[0016] Decompressing the positive frequency modulation image and the negative frequency modulation image in azimuth direction respectively; and

[0017] The results of the azimuth decompression are respectively subjected to inverse Fourier transform in the range direction to obtain the first signal and the second signal.

[0018] According to some embodiments of the present disclosure, the image of the interference signal is a straight line, wherein the phases of the range information included in the first signal and the second signal cancel each other out.

[0019] According to some embodiments of the present disclosure, performing interference multiplication on the first signal and the second signal to obtain an interference signal includes:

[0020] s(K y ,X)=s + (K y ,X)·s - (K y ,X)

[0021] Among them, s(K y ,X) represents the interference signal, s + (K y ,X) represents the first signal, s - (K y ,X) represents the second signal, K y It represents the range beam parameter, Y represents the range coordinate axis, and X represents the azimuth coordinate axis.

[0022] According to some embodiments of the present disclosure, extracting the motion parameters of the moving target from the interference signal includes extracting phase information along the envelope of the interference signal, and calculating and obtaining the motion parameters of the moving target based on the phase information.

[0023] According to some embodiments of the present disclosure, the phase information includes an additional phase caused by motion and an inherent phase within a synthetic aperture when imaging a stationary target;

[0024] The calculating and obtaining the motion parameters of the moving target according to the phase information comprises:

[0025] An additional phase caused by target motion is calculated based on the inherent phase and the phase change, and a trajectory of the moving target is calculated based on the additional phase;

[0026] And the speed of the moving target is calculated according to the trajectory of the moving target.

[0027] According to some embodiments of the present disclosure, the additional phase caused by the target motion includes:

[0028]

[0029] Among them, φ e (X) represents the additional phase, φ AP (X) represents all phases extracted along the azimuth direction, AP represents the azimuth phase, and the position of the moving target is (r 0 ,x 0 ),K rc Indicates the distance to the beam center.

[0030] According to some embodiments of the present disclosure, calculating the trajectory of the moving target according to the additional phase includes:

[0031] as well as

[0032] Calculating the speed of the moving target based on the additional phase includes taking the derivative of the time based on the position.

[0033] According to some embodiments of the present disclosure, imaging methods for performing positive frequency modulation imaging and negative frequency modulation imaging on the synthetic aperture lidar data include range migration algorithm or range Doppler algorithm, etc.

[0034] According to the method for detecting moving targets of the triangular wave modulated laser synthetic aperture radar of the above embodiment of the present disclosure, a coarse focusing image is obtained by processing the echoes of the positive and negative frequency modulation signals respectively, and then the two images are decompressed in azimuth and inverse Fourier transformed in distance, and then the interference image is obtained for the first signal and the second signal obtained, and the interference result is Fourier transformed in distance to achieve distance compression, and the phase is extracted along the envelope, and finally the relevant motion parameters are solved, avoiding the cross-correlation step in the conventional method, and the process is simple and easy to operate. Since upsampling interpolation is not required, the amount of calculation is small. For slow-moving targets, the accuracy and precision of the extracted motion parameters are very high, which has a strong engineering application value and is of great significance for expanding the application scenarios of SAL. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flowchart of a triangular wave modulated laser synthetic aperture radar moving target according to an embodiment of the present disclosure is schematically shown;

[0036] Figure 2 The synthetic aperture radar data processing flow of a moving target of a triangular wave modulated laser synthetic aperture radar according to an embodiment of the present disclosure is schematically shown; and

[0037] Figure 3The flowchart of obtaining the interference image of a moving target by a triangular wave modulated laser synthetic aperture radar according to an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0039] However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, the description of the known technology is omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0040] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The term "comprising" used herein indicates the existence of features, steps, operations, but does not exclude the existence or addition of one or more other features.

[0041] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0042] Where expressions such as "at least one of A, B, and C, etc." are used, they should generally be interpreted as those skilled in the art would normally understand the expressions. Where expressions such as "at least one of A, B, or C, etc." are used, they should generally be interpreted as those skilled in the art would normally understand the expressions.

[0043] Figure 1 The flowchart of the triangular wave modulated laser synthetic aperture radar moving target according to the embodiment of the present disclosure is schematically shown.

[0044] In order to solve the above technical problems, Figure 1 As shown, the present disclosure provides a method for detecting moving targets using a triangular wave modulated laser synthetic aperture radar, including operations S101 to S105.

[0045] According to some embodiments of the present disclosure, operation S101 includes: acquiring triangular frequency modulated continuous wave synthetic aperture lidar data.

[0046] According to some embodiments of the present disclosure, operation S102 includes: performing positive frequency modulation imaging and negative frequency modulation imaging on synthetic aperture lidar data respectively.

[0047] According to some embodiments of the present disclosure, operation S103 includes: performing transformation processing on the positive frequency modulation image to obtain a first signal, and performing transformation processing on the negative frequency modulation image to obtain a second signal.

[0048] According to some embodiments of the present disclosure, operation S104 includes: performing interference multiplication on the first signal and the second signal to obtain an interference signal.

[0049] According to some embodiments of the present disclosure, operation S105 includes: extracting motion parameters of the moving target from the interference signal.

[0050] According to some embodiments of the present disclosure, before the transformation processing is performed on the positive frequency modulation image and the negative frequency modulation image, the operation is also included: windowing and selecting the positive frequency modulation image and the negative frequency modulation image, and the windowed selected area includes all the areas of interest to be detected or the positions where the moving target may exist.

[0051] In this embodiment, the purpose of window selection is to reduce the negative impact of background noise on estimation. Optionally, a rectangular window is used for selection. First, the possible range of the target is preliminarily determined, and then the selected area is optimized according to the contrast, amplitude and other criteria so that the selected area contains all the energy of the target as much as possible.

[0052] According to some embodiments of the present disclosure, transforming a positive frequency-modulated image to obtain a first signal and transforming a negative frequency-modulated image to obtain a second signal comprises: performing azimuth decompression on the positive frequency-modulated image and the negative frequency-modulated image, respectively; and performing range inverse Fourier transform on the results of the azimuth decompression, respectively, to obtain the first signal and the second signal.

[0053] According to some embodiments of the present disclosure, the phases of the first signal and the second signal including the range information cancel each other out, and therefore, the image of the interference signal finally obtained is a straight line.

[0054] According to some embodiments of the present disclosure, performing interference multiplication on the first signal and the second signal to obtain an interference signal includes:

[0055] s(K y ,X)=s + (K y ,X)·s - (K y ,X)

[0056] Among them, s(K y ,X) represents the interference signal, s+ (K y ,X) represents the first signal, s-(K y , X) represents the second signal, K represents the range beam parameter, Y represents the range coordinate axis, and X represents the azimuth y

[0057] Coordinate axis.

[0058] According to some embodiments of the present disclosure, extracting the motion parameters of the moving target from the interference signal includes extracting phase information along the envelope of the interference signal, and calculating and obtaining the motion parameters of the moving target based on the phase information.

[0059] According to some embodiments of the present disclosure, the phase information includes an additional phase caused by motion and an inherent phase within a synthetic aperture when imaging a stationary target.

[0060] According to some embodiments of the present disclosure, calculating motion parameters of a moving target based on phase information includes: calculating an additional phase caused by the target motion based on the inherent phase and the phase change, calculating the trajectory of the moving target based on the additional phase; and calculating the speed of the moving target based on the trajectory of the moving target.

[0061] According to some embodiments of the present disclosure, the additional phase caused by the target motion includes:

[0062]

[0063] Among them, φ e (X) represents the additional phase, φ AP (X) represents all phases extracted along the azimuth direction, AP represents the azimuth phase, and the position of the moving target is (r 0 ,x 0 ),K rc Indicates the distance to the beam center.

[0064] According to some embodiments of the present disclosure, calculating the trajectory of the moving target according to the additional phase includes:

[0065] as well as

[0066] Calculating the velocity of the moving object based on the additional phase includes taking the derivative of the position with respect to time.

[0067] According to some embodiments of the present disclosure, after the speed of the moving target is obtained, the future trajectory of the moving target can be predicted.

[0068] According to some embodiments of the present disclosure, imaging methods for performing positive frequency modulation imaging and negative frequency modulation imaging on synthetic aperture lidar data include range migration algorithm or range Doppler algorithm, etc.

[0069] Figure 2 The synthetic aperture radar data processing flow of a triangular wave modulated laser synthetic aperture radar moving target according to an embodiment of the present disclosure is schematically shown.

[0070] According to some embodiments of the present disclosure, Figure 2 As shown, the synthetic aperture radar data processing flow includes two stages. The first stage is two parallel threads, including operations S211 to S241 and operations S212 to S242, and obtains a first signal and a second signal respectively; the second stage further processes the data obtained in the first stage to obtain motion parameters, including operations S250 to S280.

[0071] According to some embodiments of the present disclosure, in the first stage, coarse focusing imaging is performed on the SAL data, including operation S211 of positive frequency modulation coarse focusing imaging and operation S212 of negative frequency modulation coarse focusing imaging.

[0072] Then, the coarse focus imaging is further processed and optimized, including: windowing to select the region of interest (S221, S222), azimuth decompression (S231, S232), and range inverse Fourier transform (S241, S242) to obtain the optimized first signal and second signal.

[0073] According to some embodiments of the present disclosure, in the second stage, an interference signal is obtained based on the first signal and the second signal obtained in the first stage, and then the motion parameters of the moving target are extracted from the interference signal, including: operation S250, interference multiplication of the first signal and the second signal; operation S260, distance Fourier transform; operation S270, interference phase extraction; and, operation S280, motion parameter solution.

[0074] Figure 3 The flowchart of obtaining the interference image of a moving target by a triangular wave modulated laser synthetic aperture radar according to an embodiment of the present disclosure is schematically shown.

[0075] According to some embodiments of the present disclosure, the image of positive frequency modulation coarse focusing imaging and the image of negative frequency modulation coarse focusing imaging are both a curve after azimuth decompression. Figure 3 As shown, after the region of interest is windowed and selected, the azimuth direction is decompressed to obtain the image s + (Y,X) and image s - (Y,X).

[0076] For image s + (Y,X) and image s -(Y, X) are respectively subjected to inverse Fourier transform in the range direction and then interference multiplication is performed to obtain the interference signal. Since the phases of the first signal and the second signal containing the range information cancel each other, the obtained interference signal s(K y ,X) is a straight line.

[0077] According to the method for detecting moving targets of a triangular wave modulated laser synthetic aperture radar of the above embodiment of the present disclosure, a coarsely focused image is obtained by processing the echoes of the positive and negative frequency modulated signals respectively, and then the two images are decompressed in azimuth and inverse Fourier transformed in distance respectively, and then the interference image is obtained for the first signal and the second signal obtained, and the interference result is Fourier transformed in distance to achieve distance compression, and the phase is extracted along the envelope, and finally the relevant motion parameters are solved, thereby avoiding the cross-correlation step in conventional methods, and the process is simple and easy to operate. Since upsampling interpolation is not required, the amount of calculation is small. For slow-moving targets, the accuracy and precision of the extracted motion parameters are very high, and it has a strong engineering application value, which is of great significance for expanding the application scenarios of SAL.

[0078] So far, the embodiments of the present disclosure have been described in detail in conjunction with the accompanying drawings. It should be noted that the implementation methods not shown or described in the drawings or the body of the specification are all forms known to ordinary technicians in the relevant technical field and are not described in detail. In addition, the above definitions of each component are not limited to the various specific structures, shapes or methods mentioned in the embodiments, and ordinary technicians in the field can simply change or replace them.

[0079] It should also be noted that, in the specific embodiments of the present disclosure, unless otherwise indicated, the numerical parameters in the present specification and the appended claims are approximate values ​​and can be changed according to the desired characteristics obtained through the content of the present disclosure. Specifically, all numbers used in the specification and claims to express the size, range conditions, etc. of the composition should be understood to be modified by the term "about" in all cases. In general, the meaning of the expression refers to the change of ±10% in some embodiments, ±5% in some embodiments, ±1% in some embodiments, and ±0.5% in some embodiments by a specific number.

[0080] It will be appreciated by those skilled in the art that the features described in the various embodiments and / or claims of the present disclosure may be combined and / or combined in a variety of ways, even if such combinations and / or combinations are not explicitly described in the present disclosure. In particular, the features described in the various embodiments and / or claims of the present disclosure may be combined and / or combined in a variety of ways without departing from the spirit and teachings of the present disclosure. All of these combinations and / or combinations fall within the scope of the present disclosure.

[0081] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A method for detecting moving targets using a triangular wave modulated laser synthetic aperture radar, characterized in that: include: Acquire triangular frequency modulated continuous wave synthetic aperture lidar data; The synthetic aperture laser radar data will be subjected to positive frequency modulation imaging and negative frequency modulation imaging respectively; Performing transformation processing on the positive frequency modulation imaging image to obtain a first signal, and performing transformation processing on the negative frequency modulation imaging image to obtain a second signal; Perform interference multiplication on the first signal and the second signal to obtain an interference signal, wherein an image of the interference signal is a straight line, and phases of the first signal and the second signal including range information cancel each other out; Performing interference multiplication on the first signal and the second signal to obtain an interference signal includes: in, represents the interference signal, Indicates the first signal, Indicates the second signal, represents the range beam parameter, represents the distance axis, represents the azimuth coordinate axis; and Extracting the motion parameters of the moving target from the interference signal includes: extracting phase information along the envelope of the interference signal, and calculating and obtaining the motion parameters of the moving target according to the phase information; The phase information includes the additional phase caused by motion and the inherent phase within the synthetic aperture when imaging a stationary target; The calculating and obtaining the motion parameters of the moving target according to the phase information comprises: An additional phase caused by target motion is calculated based on the inherent phase and the phase change, and a trajectory of the moving target is calculated based on the additional phase; And calculating the speed of the moving target according to the trajectory of the moving target; The additional phases caused by the target motion include: in, represents the additional phase, represents all phases extracted along the azimuth direction, Indicates the azimuth phase, and the position of the moving target is , Indicates the distance to the beam center; Calculating the trajectory of the moving target according to the additional phase includes: ,as well as Calculating the speed of the moving target based on the additional phase includes taking the derivative of the time based on the position.

2. The detection method according to claim 1, characterized in that: Before transforming the positive frequency modulation image and the negative frequency modulation image, the method further includes: The positive frequency modulation imaging image and the negative frequency modulation imaging image are subjected to window selection, and the window selection area includes all the interested areas to be detected or the positions where the moving target may exist.

3. The detection method according to claim 1, characterized in that: The step of transforming the positive frequency modulation image to obtain the first signal and transforming the negative frequency modulation image to obtain the second signal comprises: Decompressing the positive frequency modulation image and the negative frequency modulation image in azimuth direction respectively; and The results of the azimuth decompression are respectively subjected to inverse Fourier transform in the range direction to obtain the first signal and the second signal.

4. The detection method according to claim 1, characterized in that: The imaging methods for performing positive frequency modulation imaging and negative frequency modulation imaging on the synthetic aperture laser radar data include range migration algorithm or range Doppler algorithm.

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