SAR (Synthetic Aperture Radar) incoherent superposition imaging method and device in terahertz frequency band bunching mode

Abstract

The invention relates to the technical field of radar signal processing, in particular to an SAR (Synthetic Aperture Radar) incoherent superposition imaging method and device in a terahertz frequency band bunching mode, which comprises the following steps of: acquiring a multi-frame SAR image in the terahertz frequency band bunching mode, preprocessing, selecting one frame as a reference frame and the rest as frames to be superposed, and combining a ground digital elevation model to obtain a multi-frame SAR image in the terahertz frequency band bunching mode; the method comprises the following steps: projecting two types of frames to a ground plane through interpolation to obtain corresponding projection images, determining central positions in the two types of projection images according to radar imaging centers and determining respective geometric centers according to a bunching imaging model, firstly translating and then rotating a projection image to be superposed, carrying out incoherent superposition on the projection image to be superposed and a reference projection image, and calculating the local structure similarity of the projection images to be superposed and the reference projection image. And adjusting the rotation angle to the maximum similarity, taking the superposed image as a next frame superposition reference, and repeating the process until all the to-be-superposed frames are superposed to obtain a final image. By adopting the method, the influence of speckles can be inhibited, and the geometric deformation of the target is corrected, so that a high-quality image is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radar signal processing, in particular to a SAR incoherent integration imaging method and device in a terahertz frequency band in a spotlight mode. BACKGROUND

[0002] In radar imaging, incoherent integration is a technology for improving signal-to-noise ratio (SNR) or suppressing clutter by accumulating the amplitudes or powers (rather than complex phase information) of multiple radar echo signals. The working frequency of a terahertz frequency band video synthetic aperture radar is high, and the imaging range is small. In order to improve the imaging resolution of the image and suppress the influence of the coherent speckle, incoherent integration needs to be performed on the images formed by the same radar. Unlike optical images, the images of the terahertz frequency band video synthetic aperture radar are easily affected by platform motion errors. Non-uniform motion of the platform, squint of the radar, and reflection of the ground target will cause the target position to deviate, and the image structure to be distorted. At the same time, due to the influence of the coherent speckle, the edges of the ground objects are not clear. After extracting feature points and purifying false feature point pairs by using the scale-invariant feature transform (SIFT), the speeded up robust features method (SURF) based on Hessian matrix detection, and the KAZE nonlinear diffusion filtering method, there are still false matching point pairs, which causes the image position to be incorrectly matched. For incoherent integration, the inaccuracy of the matching position will cause the image quality to deteriorate. Compared with the SAR image in a strip mode, the SAR image in a spotlight mode will be severely geometrically deformed. For the geometrically deformed spotlight mode SAR image, registration, splicing, fusion, and image integration will be a difficult problem by using the SAR-SIFT algorithm, the position scale orientation-scale invariant feature transform algorithm (PSO-SIFT), and other improved SIFT algorithms. SUMMARY

[0003] Therefore, it is necessary to provide a SAR incoherent integration imaging method and device in a terahertz frequency band in a spotlight mode, which can suppress the influence of the coherent speckle and correct the geometric deformation of the target, so as to obtain a high-quality image.

[0004] A SAR incoherent integration imaging method in a terahertz frequency band in a spotlight mode, the method comprising: After obtaining multiple SAR images in a terahertz frequency band in a spotlight mode and pre-processing each image, one of the images is selected as a reference frame image, and the other images are all taken as to-be-integrated frame images; Based on the digital elevation model of the SAR and the ground, the reference frame image and the to-be-integrated frame image are projected to the ground plane by an interpolation method, to obtain a reference projection image and a to-be-integrated projection image; Based on the imaging model of the spotlight mode SAR, the center positions of the reference projection image and the to-be-stacked projection image are determined according to the radar imaging center, and the geometric center positions of the two frames of projection images are determined at the same time; The center position of the to-be-stacked projection image is translated to the geometric center position, the to-be-stacked projection image is rotated by a preset initial rotation angle with the geometric center position as the center, the center of the to-be-stacked projection image after rotation is translated to the center position of the reference projection image, and then the non-coherent stacking of the reference projection image is performed to obtain a non-coherent stacked image, the local structure similarity function between the reference projection image and the non-coherent stacked image is calculated, the rotation angle of the to-be-stacked projection image is continuously adjusted until the local structure similarity function is maximum, and then the corresponding non-coherent stacked image is taken as the reference image for the next frame of non-coherent stacking. Until the non-coherent stacking of all to-be-stacked frames of images is completed, a final non-coherent stacked image is obtained, so as to complete the non-coherent stacking imaging of the SAR in the terahertz frequency band in the spotlight mode.

[0005] In one embodiment, the preprocessing of each frame of SAR image includes adjusting each frame of SAR image to the same geometric size, so that each frame of SAR image has the same geometric center.

[0006] In one embodiment, the number of the plurality of frames of SAR images is greater than or equal to 2.

[0007] In one embodiment, the non-coherent stacking is to average the amplitude intensity of the to-be-stacked projection image after rotation and the reference projection image.

[0008] In one embodiment, the non-coherent stacked image obtained after the non-coherent stacking of all to-be-stacked frames of images is completed is subjected to 3*3 Gaussian window smoothing processing to obtain the final non-coherent stacked image.

[0009] The application also provides a device for non-coherent stacking imaging of a SAR in a terahertz frequency band in a spotlight mode, the device comprising: A plurality of frames of SAR image acquisition modules are configured to acquire a plurality of frames of SAR images in a terahertz frequency band in a spotlight mode, and to select one frame as a reference frame image after preprocessing each frame of image, and the other frames are all to-be-stacked frames of images. An image projection module is configured to project the reference frame image and the to-be-stacked frame image to the ground plane by an interpolation method based on the SAR and the digital elevation model of the ground to obtain a reference projection image and a to-be-stacked projection image. an image center and geometric center determination module, configured to determine the center positions of the reference projection image and the to-be-stacked projection image according to a radar imaging center based on an imaging model of the spotlight SAR, and to determine the respective geometric center positions of the two frames of projection images; a non-coherent stacking module, configured to translate the center position of the to-be-stacked projection image to the geometric center position, to rotate the to-be-stacked projection image around the geometric center position at a preset initial rotation angle, to translate the center of the rotated to-be-stacked projection image to the center position of the reference projection image, and to perform non-coherent stacking of the reference projection image and the to-be-stacked projection image to obtain a non-coherently stacked image, to calculate a local structural similarity function between the reference projection image and the non-coherently stacked image, and to continuously adjust the rotation angle of the to-be-stacked projection image until the local structural similarity function is maximized, and to take the corresponding non-coherently stacked image as the reference image for the next frame of non-coherent stacking; a SAR non-coherent stacking imaging module, configured to complete the non-coherent stacking of all the to-be-stacked frames of images to obtain a final non-coherently stacked image, thereby completing the SAR non-coherent stacking imaging in the terahertz frequency band spotlight mode.

[0010] The above-mentioned SAR non-coherent stacking imaging method and device in the terahertz frequency band spotlight mode, by acquiring multiple frames of SAR images in the terahertz frequency band spotlight mode, selecting one frame as a reference frame and the rest as to-be-stacked frames after preprocessing, combining the SAR and a digital elevation model of the ground, projecting the two types of frames onto the ground plane through interpolation to obtain corresponding projection images, determining the center positions in the two types of projection images according to a radar imaging center based on the spotlight SAR imaging model, determining the respective geometric centers, translating and then rotating the to-be-stacked frame projection images, non-coherently stacking the to-be-stacked frame projection images and the reference frame projection image, calculating the local structural similarity between the two, adjusting the rotation angle until the similarity is maximized, taking the stacked image at this time as the reference for the next frame of stacking, repeating the process until all the to-be-stacked frames are stacked to obtain a final image, thereby completing the SAR non-coherent stacking imaging in the terahertz frequency band spotlight mode. The method can suppress the influence of the speckle and correct the geometric deformation of the target, thereby obtaining a high-quality image. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 FIG. 1 is a flowchart of the SAR non-coherent stacking imaging method in the terahertz frequency band spotlight mode according to one embodiment; Figure 2 FIG. 2 is a detailed flowchart of the SAR non-coherent stacking imaging method in the terahertz frequency band spotlight mode according to one embodiment; Figure 3 FIG. 3 is a diagram of multiple frames of SAR images in a spotlight mode in one experiment; Figure 3 (a), Figure 3 (b), Figure 3(c) are respectively three images in the same terahertz video SAR image; Figure 4 For Figure 3 the projection images of the three SAR images in the middle after being projected to the ground plane, wherein, Figure 4 (a), Figure 4 (b), Figure 4 (c) are respectively Figure 3 (a), Figure 3 (b), Figure 3 the projection images of (c); Figure 5 is a projection image after non-coherent stacking by the method in an experiment; Figure 6 is a schematic diagram after non-coherent stacking by the SAR-SIFT algorithm in an experiment; Figure 7 is an optical image of the sundial of the imaging scene in an experiment; Figure 8 is a structural block diagram of a SAR non-coherent stacking imaging device in a terahertz frequency band beam mode in an embodiment; Figure 9 is an internal structure diagram of a computer device in an embodiment. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0013] In order to solve the problems of coherent speckle influence, feature point position offset and severe geometric deformation in the non-coherent stacking of terahertz frequency band video SAR images, as shown in Figure 1 In the present application, a SAR non-coherent stacking imaging method in a terahertz frequency band beam mode is proposed, which specifically includes the following steps: Step S100, a plurality of SAR images in a terahertz frequency band beam mode are obtained, and after pre-processing each image, one of the images is selected as a reference frame image, and the other images are all taken as to-be-stacked frame images.

[0014] Step S110, based on the digital elevation model of SAR and the ground, the reference frame image and the to-be-stacked frame image are projected to the ground plane by the interpolation method, to obtain the reference projection image and the to-be-stacked projection image.

[0015] Step S120, based on the imaging model of the beam mode SAR, the center positions of the reference projection image and the to-be-stacked projection image are determined according to the radar imaging center, and the geometric center positions of the two projection images are determined.

[0016] Step S130, the center position of the to-be-stacked projection image is moved to the geometric center position, rotated at a preset initial rotation angle with the geometric center position as the center, the center of the rotated to-be-stacked projection image is moved to the center position of the reference projection image, and then non-coherent stacking is performed with the reference projection image to obtain a non-coherent stacked image. The local structure similarity function between the reference projection image and the non-coherent stacked image is calculated, the rotation angle of the to-be-stacked projection image is continuously adjusted until the local structure similarity function is maximum, and then the corresponding non-coherent stacked image is taken as the reference image for the next frame of non-coherent stacking.

[0017] Step S140, until the non-coherent stacking of all to-be-stacked frame images is completed, the final non-coherent stacked image is obtained, and the SAR non-coherent stacking imaging under the terahertz band beamforming mode is completed.

[0018] The processing of the beamforming mode SAR image faces multiple technical challenges: on the one hand, the coherent speckle noise will significantly reduce the image signal-to-noise ratio, and the same ground object position between different frame images is prone to relative shift; on the other hand, the change of the imaging angle will cause the ground object to produce obvious geometric deformation, which puts extremely high requirements on the image registration accuracy. If there is an error in the registration process, even if a common feature point-based splicing method such as SAR-SIFT is used, it may also cause image quality deterioration (such as edge misplacement, detail blur, etc.). Due to the above technical difficulties, the existing technical solutions for the splicing, registration, fusion and image stacking of the beamforming mode SAR image are still relatively scarce. The present method addresses these problems by projecting the superimposed images onto the ground plane through interpolation to obtain projection images, determining the rotation center of the beamforming mode and the geometric center of the image in the projection images, moving the rotation center of the to-be-stacked projection image to the geometric center of the image, rotating by a certain angle, then moving the rotated image to the rotation center of the reference frame for stacking, calculating the local image structure similarity function (PSSIM) before and after stacking, taking the maximum function value, then taking other to-be-stacked images, repeating the above process until the stacking of all images is completed, to obtain the final imaging, to solve the problems of coherent speckle influence, feature point position shift and severe geometric deformation in the non-coherent stacking of terahertz band video SAR images.

[0019] In step S100, first, in order to solve the size mismatch problem of multiple frames of images caused by differences in imaging parameters (such as observation angle, distance, etc.), provide a unified spatial reference for subsequent projection to the ground plane, translation and rotation geometric operations, avoid edge misalignment or information loss when directly superimposed due to size differences, and ensure pixel-level correspondence in the non-coherent superposition process, so that the pixels in the same ground object area in different frames of images can be correctly aligned for operation, laying the foundation for accurate calculation of local structural similarity, thereby improving registration accuracy and reducing superposition quality deterioration caused by inconsistent sizes. The pre-processing of each frame of SAR image includes adjusting each frame of SAR image to the same geometric size.

[0020] In this embodiment, the number of multiple frames of SAR images is greater than or equal to 2.

[0021] In step S110, according to the SAR imaging principle, the actual ground position corresponding to each pixel in the SAR image is found, and then combined with the elevation data of the position in the digital elevation model of the ground, the gaps in the position information are filled by interpolation, and finally the SAR image pixels of the reference frame and the frame to be superimposed are mapped to the horizontal ground plane coordinate system according to this correspondence, to obtain two projection images that fit the actual terrain of the ground.

[0022] In step S120, when the to-be-superimposed projection image is processed by translation and rotation, the center position of the to-be-superimposed projection image is first translated to the geometric center position of the image, and then rotated according to the preset initial rotation angle with the geometric center position of the image as the center.

[0023] In step S130, when the rotated to-be-superimposed projection image and the reference projection image are non-coherently superimposed, the center positions of the rotated to-be-superimposed projection image and the reference projection image are aligned, and then non-coherent superposition is performed.

[0024] In this embodiment, non-coherent superposition refers to averaging the amplitude intensity of the rotated to-be-superimposed projection image and the reference projection image.

[0025] In this embodiment, by continuously rotating the to-be-superimposed projection image and non-coherently superimposing it with the reference projection image, until the local structural similarity function between the non-coherent superimposed image and the reference projection image is maximum when rotated to a certain angle, the current non-coherent superposition is completed, and the obtained non-coherent superimposed image is taken as the reference frame image, and is non-coherently superimposed with the SAR image of the next frame to be superimposed. Repeat steps S110 to S130, until all to-be-superimposed frame images are completed, and the final non-coherent superimposed image is obtained.

[0026] Specifically, the rotation angle is adjusted to maximize the local structural similarity, which can accurately align the reference frame and the frame to be superimposed, reduce the influence of speckle, and avoid image quality deterioration such as misalignment and blur during non-coherent superposition.

[0027] In step S140, the non-coherent superimposed image obtained after completing the non-coherent superposition of all frames to be superimposed is subjected to 3*3 Gaussian window smoothing processing to obtain the final non-coherent superimposed image.

[0028] As shown in Figure 2 , it is a complete flowchart of the method.

[0029] In this paper, the effectiveness of the method is also proved by experimental results. In the experiment, the spotlight SAR images come from terahertz video SAR imaging, and the parameters of the imaging scene are shown in Table 1. At the same time, the flowchart in the experiment is shown in Figure 2 .

[0030] Table 1 Parameters of measured data imaging

[0031] Figure 3 The selected three terahertz spotlight SAR images are shown in

[0032] Figure 4 The projection image after the image is projected onto the ground plane is shown in

[0033] Figure 5 The projection image after non-coherent superposition by the method proposed in this paper is shown in

[0034] Figure 6 The image after non-coherent superposition by the SAR-SIFT algorithm is shown in

[0035] From the parameters of the affine matrix, there is image scaling and image clipping between images, which indicates that the target image has geometric deformation or mis-matching of feature point pairs. After removing mis-matching by fast sample consistency (FSC), there are 16 feature point pairs. After matching the superimposed image of the 3rd frame with the superimposed images of the 1st and 2nd frames and removing mis-matching by fast sample consistency (FSC), there are 2 feature point pairs, which is less than the minimum number of point pairs for solving the affine matrix, and the matching is unsuccessful. The superimposed image of the 1st and 2nd frames is still retained, and the superimposed image of the 3rd frame is matched with the superimposed image of the 1st and 2nd frames. After removing mis-matching by fast sample consistency (FSC), there are 2 feature point pairs, which is less than the minimum number of point pairs for solving the affine matrix, and the matching is unsuccessful. Figure 5 Compared with the method proposed in the present application, the Arabic characters around the sundial and the rows of green forests on the sundial steps can be clearly seen. Figure 5 The image entropy of the image of the 3rd frame is 12.360673, Figure 6 The image entropy of the image of the 3rd frame is 12.892146, which indicates Figure 5 The image quality of the image of the 3rd frame is better than that of the image of the 2nd frame. Figure 6 The imaging quality of the image of the 3rd frame is better than that of the image of the 2nd frame.

[0036] Figure 7 The optical image of the imaging scene sundial. Compared with the image formed by the method, the steps around the sundial have more stereoscopic effect.

[0037] In the SAR non-coherent superimposed imaging method in the above-mentioned terahertz band beamforming mode, according to the imaging scene of the beamforming mode SAR, the image is projected to the ground imaging plane, the geometric deformation of the SAR image is corrected, at the same time, the position of the imaging center in the projected image and the position of the image geometric center are determined, two times of translation and one time of rotation are performed, the local structural similarity is taken as the measurement standard, the best image alignment angle is selected, and accurate images can still be obtained in the case that there is speckle noise and the position of the feature point is offset. Compared with the SAR-SIFT and PSO-SIFT algorithms, better superimposed image quality can be obtained. According to the characteristics of the beamforming mode SAR image, the present application can realize non-coherent superimposition between images without feature point extraction, feature point pair matching and affine matrix calculation, and the method is more operable based on the characteristics of such SAR images.

[0038] It should be understood that, although Figure 1 the steps in the flowchart of the method of the present application are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise explicitly stated herein, the execution of these steps is not strictly limited in sequence, and these steps can be executed in other orders. Moreover, Figure 1At least one of the steps in the method can comprise a plurality of sub-steps or stages which are not necessarily performed at the same time but can be performed at different times, and the order of the sub-steps or stages is not necessarily sequential but can be performed in rotation or alternation with other steps or sub-steps or stages of other steps.

[0039] In one embodiment, as shown in Figure 8 In one embodiment, as shown in The multi-frame SAR image acquisition module 200 is configured to acquire a plurality of frames of SAR images in a terahertz frequency range in a spotlight mode, and to pre-process each frame of image, and to select one frame as a reference frame image, and to select the other frames as to-be-stacked frame images. The image projection module 210 is configured to project the reference frame image and the to-be-stacked frame images to a ground plane by an interpolation method based on a digital elevation model of the SAR and the ground, to obtain a reference projection image and a to-be-stacked projection image. The image center and geometric center determination module 220 is configured to determine the center positions of the reference projection image and the to-be-stacked projection image according to a radar imaging center based on an imaging model of the spotlight mode SAR, and to determine the geometric center positions of the two frames of projection images. The non-coherent stacking module 230 is configured to translate the center position of the to-be-stacked projection image to the geometric center position, to rotate the to-be-stacked projection image according to a preset initial rotation angle with the geometric center position as the center, to translate the center of the rotated to-be-stacked projection image to the center position of the reference projection image, and to perform non-coherent stacking of the reference projection image to obtain a non-coherent stacked image, to calculate a local structure similarity function between the reference projection image and the non-coherent stacked image, to continuously adjust the rotation angle of the to-be-stacked projection image until the local structure similarity function is maximum, and to select the corresponding non-coherent stacked image as a reference image for the next frame of non-coherent stacking. The SAR non-coherent stacking imaging module 240 is configured to perform non-coherent stacking of all to-be-stacked frame images until a final non-coherent stacked image is obtained, to complete the SAR non-coherent stacking imaging in the terahertz frequency range in the spotlight mode.

[0040] The specific limitations of the SAR non-coherent stacking imaging device in the terahertz frequency band in the spotlight mode can be seen from the limitations of the SAR non-coherent stacking imaging method in the terahertz frequency band in the spotlight mode, which will not be repeated here. Each module in the above-mentioned SAR non-coherent stacking imaging device in the terahertz frequency band in the spotlight mode can be realized by software, hardware and their combination. The above-mentioned modules can be embedded in or independent of the processor in the computer device in hardware form, or can be stored in the memory in the computer device in the form of software, so that the processor calls and executes the operations corresponding to each of the above-mentioned modules.

[0041] In one embodiment, a computer device, which can be a terminal, has an internal structure diagram as shown in Figure 9 The computer device includes a processor, a memory, a network interface, a display screen and an input device connected by a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The network interface of the computer device is used to communicate with external terminals through network connection. The computer program is executed by the processor to implement a SAR non-coherent stacking imaging method in the terahertz frequency band in the spotlight mode. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen. The input device of the computer device can be a touch layer overlaid on the display screen, or a key, trackball or touchpad arranged on the shell of the computer device, or an external keyboard, touchpad or mouse, etc.

[0042] Those skilled in the art can understand that Figure 9 The structure shown in the above-mentioned figure is only a block diagram of part of the structure related to the scheme of the present application, and does not constitute a limitation on the computer device to which the scheme of the present application is applied. The specific computer device can include more or fewer components than those shown in the figure, or combine certain components, or have a different component arrangement.

[0043] In one embodiment, a computer device is provided, which includes a memory and a processor, the memory stores a computer program, and the processor implements the following steps when executing the computer program: After obtaining multiple frames of SAR images in the terahertz frequency band in the spotlight mode and pre-processing each frame of image, one frame is selected as a reference frame image, and the other frames are all taken as to-be-stacked frame images; Based on the SAR and the digital elevation model of the ground, the reference frame image and the to-be-stacked frame image are projected to the ground plane by the interpolation method to obtain a reference projection image and a to-be-stacked projection image; According to a center of radar imaging, center positions of the reference projection image and the to-be-stacked projection image are determined respectively based on an imaging model of the spotlight mode SAR, and geometric center positions of the two projection images are determined simultaneously; The center position of the to-be-stacked projection image is translated to the geometric center position, the to-be-stacked projection image is rotated at the geometric center position according to a preset initial rotation angle, the center of the rotated to-be-stacked projection image is translated to the center position of the reference projection image, and then the non-coherent stacking is performed on the reference projection image to obtain a non-coherent stacked image; a local structure similarity function between the reference projection image and the non-coherent stacked image is calculated; the rotation angle of the to-be-stacked projection image is continuously adjusted until the local structure similarity function is maximum, and then the corresponding non-coherent stacked image is taken as a reference image for the next frame of non-coherent stacking. Until the non-coherent stacking of all to-be-stacked frames of images is completed, a final non-coherent stacked image is obtained, and the non-coherent stacking imaging of the SAR in the terahertz frequency band spotlight mode is completed.

[0044] In one embodiment, a computer readable storage medium is provided, and a computer program is stored on the computer readable storage medium. When the computer program is executed by a processor, the following steps are implemented: After a plurality of frames of SAR images in the terahertz frequency band spotlight mode are acquired and preprocessed, one frame is selected as a reference frame image, and the other frames are taken as to-be-stacked frame images; Based on a digital elevation model of the SAR and the ground, the reference frame image and the to-be-stacked frame image are projected to a ground plane by an interpolation method to obtain a reference projection image and a to-be-stacked projection image; According to a center of radar imaging, center positions of the reference projection image and the to-be-stacked projection image are determined respectively based on an imaging model of the spotlight mode SAR, and geometric center positions of the two projection images are determined simultaneously; The center position of the to-be-stacked projection image is translated to the geometric center position, the to-be-stacked projection image is rotated at the geometric center position according to a preset initial rotation angle, the center of the rotated to-be-stacked projection image is translated to the center position of the reference projection image, and then the non-coherent stacking is performed on the reference projection image to obtain a non-coherent stacked image; a local structure similarity function between the reference projection image and the non-coherent stacked image is calculated; the rotation angle of the to-be-stacked projection image is continuously adjusted until the local structure similarity function is maximum, and then the corresponding non-coherent stacked image is taken as a reference image for the next frame of non-coherent stacking. Until the non-coherent stacking of all to-be-stacked frames of images is completed, a final non-coherent stacked image is obtained, and the non-coherent stacking imaging of the SAR in the terahertz frequency band spotlight mode is completed.

[0045] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer readable storage medium, and when the computer program is executed, the processes of the above-mentioned embodiments of the methods can be included. Any reference to memory, storage, databases, or other media in the embodiments provided by the present application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration but not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct RAMbus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0046] Any combination of the technical features of the above embodiments can be made. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combination of the technical features does not exist, it should be considered as the scope of the present application.

[0047] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A SAR incoherent superposition imaging method in terahertz band spotting mode, characterized in that, The method includes: Acquire multiple frames of SAR images in terahertz band spotting mode, and after preprocessing each frame, select one frame as the reference frame image, and then use the other frames as the frames to be superimposed. Based on the SAR and ground digital elevation model, the reference frame image and the frame image to be superimposed are projected onto the ground plane by interpolation to obtain the reference projected image and the projected image to be superimposed. Based on the beamforming SAR imaging model, the center positions of the reference projection image and the projection image to be superimposed are determined according to the radar imaging center, and the geometric center positions of the two projection images are determined respectively. The center position of the image to be superimposed is translated to the geometric center position. The image is then rotated around the geometric center position according to a preset initial rotation angle. The center of the rotated image to be superimposed is translated to the center position of the reference image. The image is then incoherently superimposed with the reference image to obtain an incoherently superimposed image. The local structural similarity function between the reference image and the incoherently superimposed image is calculated. The rotation angle of the image to be superimposed is continuously adjusted until the local structural similarity function is maximized. The corresponding incoherently superimposed image is then used as the reference image for the next frame of incoherent superimposition. The process continues until all frames to be superimposed are incoherently superimposed, resulting in the final incoherent superimposed image, thus completing SAR incoherent superimposed imaging in terahertz band spotting mode.

2. The SAR incoherent superposition imaging method in terahertz band spotting mode according to claim 1, characterized in that, Preprocessing each frame of SAR image involves adjusting each frame of SAR image to the same geometric size so that each frame of SAR image has the same geometric center.

3. The SAR incoherent superposition imaging method in terahertz band spotting mode according to claim 2, characterized in that, The number of multi-frame SAR images is greater than or equal to 2.

4. The SAR incoherent superposition imaging method in terahertz band spotting mode according to claim 3, characterized in that, The incoherent superposition is to average the amplitude intensity of the rotated projection image to be superimposed and the reference projection image.

5. The SAR incoherent superposition imaging method in terahertz band spotting mode according to claim 4, characterized in that, After completing the incoherent overlay of all frames to be overlaid, the resulting incoherent overlay image is smoothed using a 3×3 Gaussian window to obtain the final incoherent overlay image.

6. A SAR incoherent superposition imaging device in terahertz band spotting mode, characterized in that, The device includes: The multi-frame SAR image acquisition module is used to acquire multi-frame SAR images in terahertz band spotting mode. After preprocessing each frame image, one frame is selected as the reference frame image, and the other frames are used as the frames to be superimposed. The image projection module is used to project the reference frame image and the frame image to be superimposed onto the ground plane through interpolation to obtain the reference projected image and the projected image to be superimposed. The image center and geometric center determination module is used to determine the center positions of the reference projection image and the projection image to be superimposed based on the radar imaging center of the SAR imaging model, and at the same time, determine the geometric center positions of the two projection images respectively. The incoherent overlay module is used to translate the center position of the projection image to be overlaid to the geometric center position, rotate it around the geometric center position according to a preset initial rotation angle, translate the center of the rotated projection image to the center position of the reference projection image, and then incoherently overlay it with the reference projection image to obtain the incoherently overlaid image. The local structural similarity function between the reference projection image and the incoherently overlaid image is calculated. By continuously adjusting the rotation angle of the projection image to be overlaid until the local structural similarity function is maximized, the corresponding incoherently overlaid image is used as the reference image for the next frame of incoherent overlay. The SAR incoherent stacking imaging module is used to incoherently stack all frames to be stacked until the final incoherent stacked image is obtained, so as to complete SAR incoherent stacking imaging in terahertz band spotting mode.

Images