Imaging method and device based on calm water surface

Abstract

The invention belongs to the technical field of imaging, and relates to an imaging method and device based on a calm water surface. The method comprises the following steps: acquiring an observation scene of a calm water surface environment, and constructing an observation model of the calm water surface environment; according to the observation model of the calm water surface environment, a ray tracing method is adopted to calculate the propagation distance difference between the direct wave and the multipath signal so as to obtain a compensation phase; according to the compensation phase, moving the multi-path target to a real target position to obtain a compensation image; performing phase error correction on the compensation image by adopting a self-focusing algorithm based on weighted minimum entropy to obtain a corrected image; and when the image entropy of the corrected image meets a preset condition, taking the current image as an output image. According to the invention, the target positioning accuracy can be improved by using the multipath signal, and the target amplitude can be enhanced by using the multipath signal, so that the anti-noise capability of the target is improved, and the imaging quality of the target is improved.

Description

Technical Field

[0001] The present application relates to the field of imaging technology, and in particular to an imaging method and device based on a calm water surface. Background Art

[0002] In today's era, the widespread use of drones has brought many conveniences, but it is also accompanied by the increasingly serious phenomenon of "illegal flying". The so-called "illegal flying" refers to the flight of drones without permission or beyond the scope of permission, especially in important waters. This behavior not only threatens aviation safety and public safety, but may also cause serious ecological and military problems. The "illegal flying" behavior of drones has brought huge challenges to supervision due to its concealment and unpredictability. Traditional flight safety supervision methods are difficult to effectively control drones in complex electromagnetic environment scenarios in important waters, especially for those "illegal flying" drones that have not been legally declared.

[0003] Due to the low flying altitude, slow speed, weak heat signal and small size of drones, coupled with the complex low-altitude environment, it is difficult for them to be detected by traditional radio equipment (such as radar) and detection equipment. Therefore, the use of radio equipment for detection has become an effective technical means. Among them, Ku-band radio equipment has become an ideal choice for detecting drones due to its unique technical characteristics.

[0004] Ku-band radios operate at wavelengths below 3 cm, providing high-resolution and high-precision detection capabilities, which are essential for identifying "low, slow, and small" targets. Compared to other band radios, Ku-band radios have more precise positioning capabilities, but their range is relatively short. This short-wavelength radio is particularly suitable for short-range fire control radios, providing a 50-degree viewing angle up, down, left, and right, and can rotate 360 ​​degrees to detect targets in all directions. The high-frequency characteristics of Ku-band radios give them higher resolution when detecting small drones, which is essential for distinguishing targets from background noise in complex environments. In addition, the high resolution of Ku-band radios not only helps detect targets, but also provides accurate location and speed information of targets, which is essential for subsequent countermeasures. These characteristics of Ku-band radios make them an important part of drone detection and countermeasure systems, especially in scenarios that require accurate identification and rapid response.

[0005] Therefore, Ku-band radio equipment has the advantages of high resolution, high sensitivity, low cost and flexibility in detecting illegal drones, especially in the supervision of sensitive areas such as important waters. With the further development of technology, Ku-band radio equipment is expected to play a greater role in the field of drone detection and countermeasures in the future.

[0006] Multipath signal interference is a major challenge faced by radio equipment when detecting drones, especially in aquatic environments. The multipath effect refers to the signal interference and attenuation caused by different arrival times due to different path lengths when the signal reaches the receiving end through multiple paths during propagation. In aquatic environments, factors such as buildings, water surfaces, and terrain may become sources of signal reflections, increasing the complexity of the multipath effect and making it more difficult to detect and track drone signals.

[0007] Taking the lake environment as an example, the water flow of the lake is slow, and the lake surface reflection is more inclined to mirror reflection, which has strong multipath signal interference. During the detection process of radio equipment, the SAR two-dimensional image obtained often has multipath targets, which affects the imaging quality. If the position of the multipath target is not corrected and the multipath signal is not effectively used, it may cause problems such as blurred imaging results and unclear target numbers. Therefore, it is very important to study how to effectively use multipath signals to improve the imaging quality of radio equipment in multipath environments.

[0008] In the prior art, some use the inverse ray tracing method to locate the true position of the target according to the high-order multipath signal, and some use the music algorithm to estimate the delay under the influence of the multipath effect, so as to effectively distinguish the direct wave signal from the multipath signal.

[0009] However, the above methods are all aimed at the process of target positioning. Using multipath signals to locate the true position of the target will lose the target's detailed information, resulting in the loss of useful information. In tasks such as target identification, it may lead to erroneous analysis results and it is difficult to improve the accuracy of target positioning. Summary of the invention

[0010] Based on this, it is necessary to provide an imaging method and device based on a calm water surface to address the above-mentioned technical problems, which can utilize multipath signals to improve target positioning accuracy, and can also utilize multipath signals to enhance target amplitude to improve the signal-to-noise ratio, thereby improving the target's anti-noise ability, further improving target positioning accuracy, and improving target imaging quality.

[0011] A calm water surface imaging method, comprising: Obtain the observation scene of the calm water environment and construct the observation model of the calm water environment; According to the observation model of calm water environment, the ray tracing method is used to calculate the propagation distance difference between the direct wave and the multipath signal to obtain the compensation phase; according to the compensation phase, the multipath target is moved to the real target position to obtain the compensation image; The phase error of the compensation image is corrected by using the self-focusing algorithm based on weighted minimum entropy to obtain the corrected image. When the image entropy of the rectified image meets the preset conditions, the current image is used as the output image.

[0012] In one embodiment, when the image entropy of the corrected image does not meet the preset conditions, a self-focusing algorithm based on weighted minimum entropy is used to perform phase error correction on the corrected image to obtain the next corrected image until the image entropy of the next corrected image meets the preset conditions.

[0013] In one embodiment, according to the observation model of the calm water surface environment, a ray tracing method is used to calculate the propagation distance difference between the direct wave and the multipath signal to obtain the compensation phase, including: Determine the reflection path based on the observation model of the calm water environment; According to the reflection path, the direct wave and multipath signal are obtained, and the propagation distance difference between the direct wave and the multipath signal is calculated; According to the difference in propagation distance, the compensation phase is obtained.

[0014] In one embodiment, determining the reflection path according to the observation model of the calm water environment includes: According to the observation model of the calm water environment, the mirror image radio equipment of the radio equipment about the reflecting surface is obtained by the mirror symmetry; The first straight line defined by the radio device and the target point is the direct wave propagation distance, the second straight line defined by the mirror image radio device and the target point is the multipath signal propagation distance, and the intersection of the second straight line and the reflection surface is the reflection point; According to the length of the reflection point, when the reflection point is verified to be within the range of the reflection surface, the effective reflection point is obtained; While verifying that there are no obstructions between the radio device and the target and between the mirror radio device and the target, determine the reflection path based on the target point, the effective reflection point, the radio device, and the mirror radio device.

[0015] In one embodiment, when verifying that there is an obstruction between the radio device and the target or between the mirror radio device and the target, the mirror radio device of the radio device with respect to the reflecting surface is obtained by mirror symmetry, and the effective reflection point is obtained again until it is verified that there is no obstruction between the radio device and the target or between the mirror radio device and the target. In one embodiment, a self-focusing algorithm based on weighted minimum entropy is used to correct the phase error of the compensated image to obtain a corrected image, including: Perform azimuth Fourier transform on the compensated image to construct a phase error model; According to the phase error model, the least square estimation criterion is adopted to define the weighted entropy of the compensation image and obtain the phase error cost function; According to the phase error cost function, the compensated image is subjected to phase error correction and inverse Fourier transform to obtain a corrected image.

[0016] In one embodiment, the phase error model is:

[0017] In the formula, is the phase error model, For the The distance unit signal, For the The phase variance of the signal of the range unit is For the The distance unit signal, For the The phase variance of the signal of the range unit is For the The signal phase of the distance unit, For the The weighting coefficient of a distance unit is inversely proportional to the phase variance of the distance unit.

[0018] In one embodiment, the weighted entropy of the compensated image is:

[0019]

[0020] In the formula, To compensate for the weighted entropy of the image, For the A azimuth unit signal, is the pixel image density, is the pixel energy, is the total energy of the image.

[0021] In one embodiment, the phase error cost function is:

[0022] In the formula, is the error phase estimate, is the error phase.

[0023] An imaging device based on a calm water surface, comprising: An acquisition module is used to acquire the observation scene of the calm water surface environment and construct an observation model of the calm water surface environment; The compensation module is used to calculate the propagation distance difference between the direct wave and the multipath signal according to the observation model of the calm water surface environment by using the ray tracing method to obtain the compensation phase; according to the compensation phase, the multipath target is moved to the real target position to obtain the compensation image; A correction module, used for correcting the phase error of the compensation image by using a self-focusing algorithm based on weighted minimum entropy to obtain a corrected image; The output module is used to use the current image as the output image when the image entropy of the rectified image meets a preset condition.

[0024] The above-mentioned imaging method and device based on calm water surface, by constructing an observation model of calm water surface environment, adopts ray tracing method, calculates the propagation distance difference between direct wave and multipath signal, moves multipath target to the real target position, enhances target amplitude, and then focuses multipath target and target in azimuth through self-focusing algorithm based on weighted minimum entropy, effectively solves the problem of azimuth deviation of multipath target caused by diffuse reflection caused by fluidity of lake water, can improve target positioning accuracy by using multipath signal, and can also enhance target amplitude by using multipath signal, thereby improving target noise resistance and improving target imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic flow chart of an imaging method based on a calm water surface in an embodiment; Figure 2 A schematic diagram of modeling a measured scene to obtain an observation model in one embodiment; Figure 3 A schematic diagram of various parameters of a scene in an embodiment; Figure 4 is a two-dimensional single-view complex image in one embodiment; Figure 5 is a two-dimensional single-view complex image (i.e., compensated image) obtained after multipath distance compensation in one embodiment; Figure 6 is a two-dimensional single-view complex image (i.e., a corrected image) obtained after being processed by an autofocus algorithm in one embodiment; Figure 7 In one embodiment, Figure 4 Schematic diagram of azimuthal slice analysis; Figure 8 In one embodiment, Figure 4 Schematic diagram of distance slice analysis; Fig. 9 In one embodiment, Figure 5 Schematic diagram of azimuthal slice analysis; Fig.10 In one embodiment, Figure 5 Schematic diagram of distance slice analysis; Fig.11 In one embodiment, Figure 6 Schematic diagram of azimuthal slice analysis; Fig.12 In one embodiment, Figure 6 Schematic diagram of distance slice analysis; Fig.13 The figure is a structural block diagram of an imaging device based on a calm water surface in one embodiment. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application 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 application and are not intended to limit the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0027] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, "multiple groups" means at least two groups, such as two groups, three groups, etc., unless otherwise clearly and specifically defined.

[0028] In this application, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0029] In addition, the technical solutions between the various embodiments of the present application can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0030] This application provides an imaging method based on calm water surface, such as Figure 1 The flowchart shown, in one embodiment, includes: Step 101: Acquire an observation scene of a calm water surface environment and construct an observation model of the calm water surface environment.

[0031] Specifically: The observation scene of the calm water surface environment is obtained. Since the reflective surface is approximately a mirror reflection, the target, the mirror image radio equipment and the radio equipment are always in the same plane. The various parameters of the scene can be determined by the measured data, thereby constructing an observation model of the calm water surface environment.

[0032] In this step, how to specifically model the model belongs to the prior art and will not be described in detail here.

[0033] Step 102, based on the observation model of the calm water surface environment, the propagation distance difference between the direct wave and the multipath signal is calculated by using the ray tracing method to obtain a compensation phase; based on the compensation phase, the multipath target is moved to the real target position to obtain a compensated image.

[0034] Specifically: According to the observation model of the calm water surface environment, the reflection path is determined; according to the reflection path, the direct wave and the multipath signal are obtained, and the propagation distance difference between the direct wave and the multipath signal is calculated; according to the propagation distance difference, the compensation phase is obtained; according to the compensation phase, the multipath target is moved to the real target position to obtain a compensated image.

[0035] More specifically: According to the observation model of the calm water environment, the mirror image radio equipment of the radio equipment about the reflecting surface is obtained by the mirror symmetry; The first straight line defined by the radio device and the target point is the direct wave propagation distance, the second straight line defined by the mirror image radio device and the target point is the multipath signal propagation distance, and the intersection of the second straight line and the reflection surface is the reflection point; According to the length of the reflection point:

[0036] In the formula, is the horizontal distance between the reflection point and the target, is the width of the reflecting surface, is the target height, is the height of the radio equipment; When the reflection point is verified to be within the range of the reflection surface, a valid reflection point is obtained; if the reflection point is verified to be not within the range of the reflection surface, a new search is performed to obtain a valid reflection point. If the new searched reflection point is also not within the range of the reflection surface, it is a normal imaging, and the process ends here; After verifying that there are no obstructions between the radio device and the target and between the mirror radio device and the target, determine the reflection path based on the target point, the effective reflection point, the radio device, and the mirror radio device; When verifying that there is an obstruction between the radio device and the target or between the mirror radio device and the target, the mirror radio device of the radio device on the reflecting surface is obtained by mirror symmetry based on the observation model of the calm water surface environment, the reflection point is re-determined, and the effective reflection point is re-verified and obtained until it is verified that there is no obstruction between the radio device and the target or between the mirror radio device and the target; According to the reflection path, the direct wave and multipath signal are obtained, and the propagation distance difference between the direct wave and the multipath signal is calculated:

[0037] In the formula, is the propagation distance difference between the direct wave and the multipath signal, is the width of the reflecting surface, is the target height, is the height of the radio equipment vehicle (such as a radar vehicle); According to the propagation distance difference, the compensation phase is obtained:

[0038] In the formula, To compensate the phase, is an imaginary unit, The number of grids that need to be moved for multipath targets, is the distance-to-discrete time, is the distance to discrete Fourier transform length; According to the compensation phase, the multipath target is moved to the real target position to obtain a compensated image.

[0039] In this step, the multipath target is moved to the real target position to obtain a compensated image, which can enhance the real target amplitude and improve the signal-to-noise ratio.

[0040] Step 103, using a self-focusing algorithm based on weighted minimum entropy to correct the phase error of the compensated image to obtain a corrected image.

[0041] Specifically: The compensated image is subjected to azimuth Fourier transform to construct a phase error model; based on the phase error model, the least squares estimation criterion is used to define the weighted entropy of the compensated image and obtain the phase error cost function; based on the phase error cost function, the compensated image is subjected to phase error correction and inverse Fourier transform to obtain a corrected image.

[0042] More specifically: Perform azimuth Fourier transform on the compensated image and construct a phase error model:

[0043] In the formula, is the phase error model, For the The distance unit signal, For the The phase variance of the signal of the range unit is For the The distance unit signal, For the The phase variance of the signal of the range unit is For the The signal phase of the distance unit, For the The weighting coefficient of a distance unit is inversely proportional to the phase variance of the distance unit; According to the phase error model, the least squares estimation (WLS) criterion is used to define the weighted entropy of the compensated image:

[0044]

[0045] In the formula, To compensate for the weighted entropy of the image, For the A azimuth unit signal, is the pixel image density, is the pixel energy, is the total energy of the image; According to the weighted entropy of the compensated image, the phase error cost function is derived:

[0046] In the formula, is the error phase estimate, is the error phase; According to the phase error cost function, the compensated image is subjected to phase error correction and inverse Fourier transform to obtain a corrected image.

[0047] In this step, the autofocus algorithm based on weighted minimum entropy (WMEA) is used to further align the target and multipath target positions to improve the imaging quality.

[0048] Step 104: When the image entropy of the rectified image meets a preset condition, the current image is used as the output image.

[0049] Specifically: When the image entropy of the rectified image meets the preset conditions, the current image is used as the output image; When the image entropy of the corrected image does not meet the preset conditions, a self-focusing algorithm based on weighted minimum entropy is used to perform phase error correction on the corrected image to obtain the next corrected image until the image entropy of the next corrected image meets the preset conditions.

[0050] In this step, the preset condition means that the image entropy reaches a set threshold (the threshold is obtained by a phase error model, and how to obtain it is known in the art) or the number of iterations reaches a set upper limit.

[0051] The above-mentioned imaging method based on calm water surface constructs an observation model of calm water surface environment, adopts ray tracing method, calculates the propagation distance difference between direct wave and multipath signal, moves multipath target to the real target position, enhances target amplitude, and then focuses multipath target and target in azimuth through self-focusing algorithm based on weighted minimum entropy, which effectively solves the azimuth deviation problem of multipath target caused by diffuse reflection caused by the fluidity of lake water, can improve target positioning accuracy by using multipath signal, and can also enhance target amplitude by using multipath signal, thereby improving target noise resistance and improving target imaging quality.

[0052] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0053] In a specific embodiment, the method of the present application is verified using measured data, and the measured scene is modeled (a multipath environment observation model is constructed) to obtain a schematic diagram of the observation model as shown in FIG. Figure 2 As shown in the figure, A is a hovering drone and O is a river dam. Since the reflection surface is approximately a mirror reflection, the radio equipment, propagation signal and target are in the same plane. Therefore, the model is further simplified. The schematic diagram of the scene parameters is shown in the figure. Figure 3 As shown, A is a hovering drone with coordinates , B is the on-board radio equipment, with coordinates , C is the mirror image vehicle radio equipment, the coordinates are , R 1 is a direct wave, R 2 is a multipath signal,F is the normal line, and the angles of incidence and refraction are , L is the width of the lake, L 1 is the length of the reflection point, and the simulation parameters are shown in Table 1.

[0054] Table 1: Simulation parameters

[0055] The data obtained from the radio equipment car is used to obtain a two-dimensional single-view complex image using a back-projection algorithm, such as Figure 4 The ray tracing method is used to calculate the multipath signal propagation distance of the scene. Substituting the measured data, the multipath signal propagation distance is 612m. According to the difference of 1.3m between the multipath signal and the direct wave propagation distance, the multipath target is moved to the target position. After multipath distance compensation, the two-dimensional single-view complex image is obtained as shown in the figure below. Figure 5 As shown in the figure, the azimuth deviation of multipath targets caused by diffuse reflection due to the fluidity of lake water will lead to a certain widening of the target azimuth and a decrease in azimuth resolution. The application of weight coefficients in the WMEA algorithm can effectively reduce the impact of clutter and noise caused by the movement of multipath targets, thereby achieving better focusing effects. The reason is that the WMEA algorithm performs weighted processing according to the phase variance of each distance unit, so that high-quality samples play a leading role in the convergence of entropy values. In addition, the WMEA algorithm uses weighted entropy to establish a cost function and estimates the error phase through an iterative algorithm to achieve motion error compensation. Compared with the traditional minimum entropy autofocus algorithm (MEA), WMEA can effectively improve the convergence speed of iteration. For large scene models, the efficiency has been effectively improved. The two-dimensional single-view complex image obtained after processing by the above autofocus algorithm is shown in the figure below. Figure 6 shown.

[0056] right Figure 4 , Figure 5 , Figure 6 Slice analysis (including azimuth slice analysis and distance slice analysis) was performed separately. The results are as follows: Figures 7 to 12 As shown in the figure, it can be seen that the three index parameters of the range slice are improved. This is because the multipath target is moved to the target, which improves the signal-to-noise ratio of the target, enhances the anti-noise ability, and improves the amplitude, which is consistent with the previous theoretical derivation; after being processed by the autofocus algorithm, the target impulse response width, integral sidelobe ratio and peak sidelobe ratio are significantly improved, which is consistent with the theoretical analysis.

[0057] The present application also provides an imaging device based on a calm water surface, such as Fig.13As shown, in one embodiment, it includes: an acquisition module 1301, a compensation module 1302, a correction module 1303 and an output module 1304, wherein: An acquisition module 1301 is used to acquire an observation scene of a calm water surface environment and construct an observation model of the calm water surface environment; The compensation module 1302 is used to calculate the propagation distance difference between the direct wave and the multipath signal according to the observation model of the calm water surface environment by using the ray tracing method to obtain a compensation phase; according to the compensation phase, the multipath target is moved to the real target position to obtain a compensation image; The correction module 1303 is used to correct the phase error of the compensation image by using a self-focusing algorithm based on weighted minimum entropy to obtain a corrected image; The output module 1304 is used to use the current image as the output image when the image entropy of the rectified image meets a preset condition.

[0058] For the specific definition of an imaging device based on a calm water surface, please refer to the definition of an imaging method based on a calm water surface in the above text, which will not be repeated here. Each module in the above device can be implemented in whole or in part by software, hardware and a combination thereof. Each of the above modules can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute the operations corresponding to each of the above modules.

[0059] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0060] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. An imaging method based on a calm water surface, characterized in that: include: Obtain the observation scene of the calm water environment and construct the observation model of the calm water environment; According to the observation model of calm water environment, the ray tracing method is used to calculate the propagation distance difference between the direct wave and the multipath signal to obtain the compensation phase; according to the compensation phase, the multipath target is moved to the real target position to obtain the compensation image; The phase error of the compensation image is corrected by using the self-focusing algorithm based on weighted minimum entropy to obtain the corrected image. When the image entropy of the rectified image meets the preset conditions, the current image is used as the output image.

2. The imaging method based on calm water surface according to claim 1, characterized in that: When the image entropy of the corrected image does not meet the preset conditions, a self-focusing algorithm based on weighted minimum entropy is used to perform phase error correction on the corrected image to obtain the next corrected image until the image entropy of the next corrected image meets the preset conditions.

3. The imaging method based on calm water surface according to claim 2, characterized in that: According to the observation model of calm water environment, the ray tracing method is used to calculate the propagation distance difference between the direct wave and the multipath signal to obtain the compensation phase, including: Determine the reflection path based on the observation model of the calm water environment; According to the reflection path, the direct wave and multipath signal are obtained, and the propagation distance difference between the direct wave and the multipath signal is calculated; According to the difference in propagation distance, the compensation phase is obtained.

4. The imaging method based on calm water surface according to claim 3, characterized in that: Determine the reflection path based on the observation model of the calm water environment, including: According to the observation model of the calm water environment, the mirror image radio equipment of the radio equipment about the reflecting surface is obtained by the mirror symmetry; The first straight line defined by the radio device and the target point is the direct wave propagation distance, the second straight line defined by the mirror image radio device and the target point is the multipath signal propagation distance, and the intersection of the second straight line and the reflection surface is the reflection point; According to the length of the reflection point, when the reflection point is verified to be within the range of the reflection surface, the effective reflection point is obtained; While verifying that there are no obstructions between the radio device and the target and between the mirror radio device and the target, determine the reflection path based on the target point, the effective reflection point, the radio device, and the mirror radio device.

5. The imaging method based on calm water surface according to claim 4, characterized in that: When verifying that there is an obstruction between the radio device and the target or between the mirror radio device and the target, the mirror radio device of the radio device with respect to the reflecting surface is obtained again by mirror symmetry, and the effective reflection point is obtained again until it is verified that there is no obstruction between the radio device and the target or between the mirror radio device and the target.

6. The imaging method based on calm water surface according to any one of claims 1 to 5, characterized in that: The phase error of the compensation image is corrected by using the self-focusing algorithm based on weighted minimum entropy to obtain the corrected image, including: Perform azimuth Fourier transform on the compensated image to construct a phase error model; According to the phase error model, the least square estimation criterion is adopted to define the weighted entropy of the compensation image and obtain the phase error cost function; According to the phase error cost function, the compensated image is subjected to phase error correction and inverse Fourier transform to obtain a corrected image.

7. The imaging method based on calm water surface according to claim 6, characterized in that: The phase error model is: In the formula, is the phase error model, For the The distance unit signal, For the The phase variance of the signal of the range unit is For the The distance unit signal, For the The phase variance of the signal of the range unit is For the The signal phase of the distance unit, For the The weighting coefficient of a distance unit is inversely proportional to the phase variance of the distance unit.

8. The imaging method based on calm water surface according to claim 7, characterized in that: The weighted entropy of the compensated image is: In the formula, To compensate for the weighted entropy of the image, For the A azimuth unit signal, is the pixel image density, is the pixel energy, is the total energy of the image.

9. The imaging method based on calm water surface according to claim 8, characterized in that: The phase error cost function is: In the formula, is the error phase estimate, is the error phase.

10. An imaging device based on a calm water surface, characterized in that: include: An acquisition module is used to acquire the observation scene of the calm water surface environment and construct an observation model of the calm water surface environment; A compensation module is used to calculate the propagation distance difference between the direct wave and the multipath signal by using a ray tracing method according to an observation model of a calm water surface environment to obtain a compensation phase; According to the compensation phase, the multipath target is moved to the real target position to obtain a compensated image; A correction module, used for correcting the phase error of the compensation image by using a self-focusing algorithm based on weighted minimum entropy to obtain a corrected image; The output module is used to use the current image as the output image when the image entropy of the rectified image meets a preset condition.

Images