Echo phase modulated array detector synthetic aperture laser imaging method and system

Abstract

The application provides an echo phase modulation array detector synthetic aperture laser imaging method and system, comprising: irradiating a target by using a laser emission signal to obtain an echo signal corresponding to the target; phase modulating the echo signal by using a spatial light modulator; collecting a spatial light path mixing signal of a local laser oscillator and the phase modulated echo signal by using a direct detection system array detector; constructing a laser complex image according to a two-step phase shift digital holography principle; repeating the above steps for a moving target at different time points to obtain multiple frames of laser complex images of the target; and processing the multiple frames of laser complex images by using an array detector synthetic aperture laser imaging algorithm to obtain a high resolution image corresponding to the target. The application applies the synchronous phase shift digital holography technology to the synthetic aperture laser imaging, realizes high resolution imaging of a moving target under the condition of a limited optical aperture, and has application value in the field of intersatellite imaging.

Description

Technical Field

[0001] This invention relates to the field of synthetic aperture laser imaging, and more specifically, to a method and system for synthetic aperture laser imaging using an array detector with echo phase modulation. Background Technology

[0002] To achieve high-resolution imaging at long distances, optical imaging systems need to increase their optical aperture. However, under practical conditions, the size of the system's optical aperture is limited by various factors such as platform load-bearing capacity and optical component manufacturing processes. To address this issue, current methods generally involve designing multi-mirror systems and processing laser echo signals to effectively increase the system's optical aperture. These solutions mainly include Optical Synthetic Aperture (OSA), Synthetic Aperture Laser (SAL), and Inverse Synthetic Aperture Laser (ISAL).

[0003] Thanks to the development of solid-state lasers with good coherence and laser coherent detection technology, SAL / ISAL combines synthetic aperture technology with laser coherent detection technology. Under the condition of limited optical aperture, it constructs a virtual large-aperture telescope through the relative motion of the target and the lidar to achieve high data rate and high resolution imaging of distant targets. However, it also has problems such as slow imaging speed, large amount of computation, large influence of noise and vibration phase error, and the need to use large bandwidth signals for high resolution imaging.

[0004] Synchronous phase-shift digital holography is a common method for acquiring phase information of laser complex images using a direct-detection array detector (hereinafter referred to as a direct array detector) and a laser local oscillator. Combining this method with SAL / ISAL, low-resolution images are acquired using an array detector positioned on the focal plane of a telescope. Computer processing then forms a laser complex image, which is then used for synthetic aperture laser imaging (SAR). This enables high-resolution elevation-azimuth imaging, and the imaging system does not require the transmission and processing of broadband signals, making it simple and easy to implement in engineering. Compared to SAR based array detectors, direct array detectors offer advantages such as higher technological maturity, smaller data volume, relatively lower cost, larger pixel size, larger imaging field of view, and higher instantaneous resolution.

[0005] Patent document (application number: CN202311851144.3) discloses a synthetic aperture laser imaging method using a spatial light modulator and a direct array detector. This patent performs phase modulation on the laser local oscillator in the row / column direction, and constructs a laser complex image by splitting the images of the laser local oscillator and laser echo, which affects the imaging resolution to some extent. At the same time, it is only applicable to targets with gradually changing row / column directions.

[0006] Patent document (application number: CN202411062413.2) discloses a sparse three-aperture optical synthetic aperture coherent imaging system and method. The patent sets up three small-aperture sub-mirrors, and performs computer processing on the laser complex images acquired by each sub-mirror to achieve high-resolution imaging of optical synthetic aperture. The method for imaging moving targets is not mentioned.

[0007] Patent document (application number: CN202411580096.3) discloses a method and system for forming infrared complex images of moving targets and synthetic aperture imaging with sub-mirror array. This patent sets up a multi-sub-mirror imaging system, constructs infrared complex images and completes high-resolution imaging with optical synthetic aperture by using laser local oscillator orthogonal phase modulation, but does not mention high-resolution synthetic aperture laser imaging of moving targets.

[0008] Patent document (application number: CN201710828948.X) discloses a multi-channel wide-amplitude synthetic aperture laser imaging radar transceiver system. This invention increases the optical toe and imaging strip amplitude of the target surface through multiple inputs and multiple outputs, but does not mention the formation of laser complex images through phase modulation of echo signals.

[0009] Patent document (application number: CN201610161607.7) discloses a local oscillator enhanced optical complexification receiving device for direct-view synthetic aperture laser imaging radar. This invention uses an optical method to interfere with the local oscillator light and the signal light and perform complexification, which avoids the spectral aliasing phenomenon caused by complexification in the digital signal processing process and improves the imaging quality of direct-view synthetic aperture laser imaging radar. However, it does not involve synthetic aperture laser imaging methods based on array detectors.

[0010] Patent document (application number: CN200910045638.6) discloses a rectangular optical wedge array telescope antenna for synthetic aperture laser imaging radar. This invention is used as an optical receiving and transmitting antenna and can generate a wide scanning strip and high-resolution imaging in the azimuth direction, but does not mention the formation of laser complex images by phase modulation of the echo signal.

[0011] The papers “Optimization Research on Multi-channel Wide Amplitude Synthetic Aperture Laser Imaging Radar Transceiver” (Acta Optica Sinica, Vol. 38, No. 5, 2018) and “Analysis of Detection Capability of Large Field-of-View Receiver Synthetic Aperture Laser Imaging Radar” (Acta Optica Sinica, Vol. 33, No. 7, 2013) proposed an array detector composed of multi-heterodyne detector array elements, but still adopted the traditional range-azimuth imaging method of SAL, without mentioning the elevation-azimuth synthetic aperture imaging method based on laser complex images. Summary of the Invention

[0012] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for synthetic aperture laser imaging using an array detector with echo phase modulation.

[0013] The echo phase modulation array detector synthetic aperture laser imaging method provided by the present invention includes:

[0014] Step 1: Illuminate the target with a laser emission signal and obtain the echo signal corresponding to the target; Step 2: Use a spatial light modulator to perform phase modulation on the echo signal; Step 3: The phase-modulated echo signal is processed by a Fourier lens to form a laser complex image. The laser complex image is then spatially mixed with the laser local oscillator and acquired by an array detector. Step 4: Construct a laser composite image based on the two-step phase-shift digital holography principle; Step 5: Determine whether the target is within the imaging field of view. If the target is not outside the field of view, repeat steps 1 to 4 at different times to obtain multiple frames of laser complex images of the target; otherwise, proceed to step 6. Step 6: Use the array detector synthetic aperture laser imaging algorithm to process the multi-frame laser complex image to obtain a high-resolution image corresponding to the target.

[0015] Preferably, step 2 includes: Step 2.1: Set a point target at the center of the imaging scene, illuminate the point target with a laser emission signal, set the array detector at the spatial light modulator, and make it collect the corresponding echo signal. ; Step 2.2: Position the array detector at the focal point of the Fourier lens and acquire the laser complex image of the point target. ; Step 2.3: After the echo signal is phase-modulated by the spatial light modulator and processed by the Fourier lens, two frames with a 90° phase difference and the same amplitude are formed on the array detector. Taking the two frames arranged in the column direction as an example, its expression is:

[0016]

[0017]

[0018] in, This is the phase modulation matrix of the spatial light modulator. This is the echo signal matrix on the plane of the spatial light modulator after phase modulation. This represents the two-dimensional Fourier transform result of the echo signal matrix after phase modulation. This indicates that each element in the matrix is ​​multiplied in a one-to-one manner. and These are the number of rows and columns of the matrix, respectively. Step 2.4: Construct the phase modulation matrix of the spatial light modulator, expressed as:

[0019] in, This indicates the phase extraction process of the matrix. It is the inverse Fourier transform.

[0020] Preferably, step 4 includes: Step 4.1: Acquire the laser local oscillator intensity image using a spatial light modulator; Step 4.2: Use a spatial light modulator to perform phase modulation on the echo signal, so that after processing by a Fourier lens, two laser composite images with the same amplitude and orthogonal phase are formed on the array detector; Step 4.3: Use a spatial light modulator to acquire the light intensity image formed by mixing the laser local oscillator with the spatial optical path of the laser complex image; Step 4.4: Based on the spatial light modulator phase modulation matrix design, the light intensity image is split into light intensity images corresponding to the 0° and 90° laser composite images respectively; Step 4.5: Construct the laser composite image, expressed as:

[0021] in, For the laser composite image, and These are the light intensity images corresponding to the 0° and 90° laser composite images. This is the local oscillator light intensity image of the laser.

[0022] Preferably, step 6 includes: Step 6.1: Perform a two-dimensional Fourier transform on the multiple frames of the laser complex image to form corresponding multi-frame spatial sampling signals; Step 6.2: Based on the motion parameters of the target, perform first-order phase, second-order phase, and rotational phase compensation on the spatial sampling signal to achieve image registration and motion compensation; Step 6.3: Perform a two-dimensional inverse Fourier transform on the phase-compensated spatial sampling signals of multiple frames to form a phase-compensated laser complex image; Step 6.4: Based on the motion parameters of the target, multiply the phase-compensated laser complex image by a first-order phase to achieve translation of the corresponding spatial sampling signal; Step 6.5: Coherently accumulate the phase-compensated laser complex image to increase the range of the corresponding spatial sampling signal and achieve high-resolution imaging of the target's relative motion direction; The motion parameters of the target include: micro-rotation / lateral translation direction, micro-rotation angle, and lateral translation distance. The micro-rotation / lateral translation direction is obtained by interferometric phase estimation of the multi-frame laser complex image, and the micro-rotation angle and lateral translation distance are calculated based on the inter-frame phase change of the target with strong scattering points in the laser complex image.

[0023] Preferably, the target is repeatedly observed, and the high-resolution imaging results are processed using a phase gradient autofocus algorithm to suppress the sidelobe effect of the imaging results. The motion of the moving target includes micro-rotation and lateral translation, wherein the lateral translation refers to the motion direction being in a plane perpendicular to the normal direction of the imaging system; for a target performing lateral translation, as the target passes through the laser emission signal spot, a multi-frame array detector synthetic aperture laser imaging result is formed, and the multi-frame imaging result is incoherently superimposed to achieve large field of view imaging.

[0024] The echo phase modulation array detector synthetic aperture laser imaging system provided by the present invention includes: Module M1: Illuminates the target with a laser emission signal and obtains the echo signal corresponding to the target; Module M2: Uses a spatial light modulator to perform phase modulation on the echo signal; Module M3: The phase-modulated echo signal is processed by a Fourier lens to form a laser complex image, the laser complex image is mixed with the laser local oscillator in a spatial optical path, and then acquired by an array detector; Module M4: Constructs a laser composite image based on the principle of two-step phase-shift digital holography; Module M5: Determines whether the target is within the imaging field of view. If the target is within the field of view, modules M1 to M4 are repeatedly triggered at different times to acquire multiple frames of laser complex images of the target; otherwise, module M6 is triggered. Module M6: Uses an array detector synthetic aperture laser imaging algorithm to process the multi-frame laser complex image to obtain a high-resolution image corresponding to the target.

[0025] Preferably, the module M2 includes: Module M2.1: Set a point target at the center of the imaging scene, illuminate the point target with a laser emission signal, place the array detector at the spatial light modulator, and enable it to collect the corresponding echo signal. ; Module M2.2: Positions the array detector at the focal point of the Fourier lens to acquire the laser complex image of the point target. ; Module M2.3: After the echo signal is phase-modulated by the spatial light modulator and processed by the Fourier lens, two frames of images with a 90° phase difference and the same amplitude are formed on the array detector. Taking the two frames of images arranged in the column direction as an example, its expression is:

[0026]

[0027]

[0028] in, This is the phase modulation matrix of the spatial light modulator. This is the echo signal matrix on the plane of the spatial light modulator after phase modulation. This represents the two-dimensional Fourier transform result of the echo signal matrix after phase modulation. This indicates that each element in the matrix is ​​multiplied in a one-to-one manner. and These are the number of rows and columns of the matrix, respectively. Module M2.4: Constructs the phase modulation matrix of the spatial light modulator, with the following expression:

[0029] in, This indicates the phase extraction process of the matrix. It is the inverse Fourier transform.

[0030] Preferably, the module M4 includes: Module M4.1: Acquires laser local oscillator intensity images using a spatial light modulator; Module M4.2: Uses a spatial light modulator to phase modulate the echo signal, so that after being processed by a Fourier lens, it forms two laser composite images with the same amplitude and orthogonal phase on the array detector; Module M4.3: Uses a spatial light modulator to acquire a light intensity image formed by mixing the laser local oscillator with the spatial optical path of the laser complex image; Module M4.4: Based on the spatial light modulator phase modulation matrix design, the light intensity image is split and light intensity images corresponding to the 0° and 90° laser composite images are formed respectively; Module M4.5: Constructs a laser complex image, expressed as:

[0031] in, For the laser composite image, and These are the light intensity images corresponding to the 0° and 90° laser composite images. This is the local oscillator light intensity image of the laser.

[0032] Preferably, the module M6 includes: Module M6.1: Performs a two-dimensional Fourier transform on the multiple frames of the laser complex image to form corresponding multi-frame spatial sampling signals; Module M6.2: Based on the motion parameters of the target, performs first-order phase, second-order phase, and rotational phase compensation on the spatial sampling signal to achieve image registration and motion compensation; Module M6.3: Performs a two-dimensional inverse Fourier transform on the phase-compensated spatial sampling signals of multiple frames to form a phase-compensated laser complex image; Module M6.4: Based on the motion parameters of the target, multiply the phase-compensated laser complex image by a first-order phase to achieve translation of the corresponding spatial sampling signal; Module M6.5: Coherently accumulates the phase-compensated laser complex image to increase the range of the corresponding spatial sampling signal and achieve high-resolution imaging of the target's relative motion direction; The motion parameters of the target include: micro-rotation / lateral translation direction, micro-rotation angle, and lateral translation distance. The micro-rotation / lateral translation direction is obtained by interferometric phase estimation of the multi-frame laser complex image, and the micro-rotation angle and lateral translation distance are calculated based on the inter-frame phase change of the target with strong scattering points in the laser complex image.

[0033] Preferably, the target is repeatedly observed, and the high-resolution imaging results are processed using a phase gradient autofocus algorithm to suppress the sidelobe effect of the imaging results. The motion of the moving target includes micro-rotation and lateral translation, wherein the lateral translation refers to the motion direction being in a plane perpendicular to the normal direction of the imaging system; for a target performing lateral translation, as the target passes through the laser emission signal spot, a multi-frame array detector synthetic aperture laser imaging result is formed, and the multi-frame imaging result is incoherently superimposed to achieve large field of view imaging.

[0034] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses a direct array detector to collect light intensity images and combines the synchronous phase-shift digital holography principle to construct laser complex images. Compared with array detector synthetic aperture laser imaging based on coherent detection system, the equipment used in the present invention has advantages such as high technical maturity, small data volume, relatively low cost, large pixel scale, large imaging field of view and high instantaneous resolution, and the formation of complex images has high timeliness. (2) The method of the present invention achieves high-resolution imaging of moving targets under the condition of limited optical aperture through computer processing. Compared with the optical synthetic aperture method, it has the characteristics of lightweight system. Compared with SAL / ISAL, it has the advantages of fast imaging speed and large influence of noise and vibration phase error. (3) The method of the present invention modulates the phase of the laser local oscillator through a spatial light modulator, so that after two-dimensional Fourier transform processing, two frames of images with the same amplitude and orthogonal phase are formed on the direct array detector. Although the system imaging field of view is sacrificed to a certain extent, the resolution of the laser complex image and the timeliness of imaging are ensured. Furthermore, through the incoherent superposition processing of multiple synthetic aperture laser imaging results, the imaging field of view can be effectively increased, thereby reducing the influence of the limited field of view. Attached Figure Description

[0035] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the array detector synthetic aperture laser imaging system with echo phase modulation according to the method of the present invention; Figure 3a The echo signal involved in the SLM phase modulation matrix of the method of the present invention; Figure 3b The Fourier transform amplitude diagram of the echo signal before SLM phase modulation involved in the SLM phase modulation matrix of the present invention is shown. Figure 3c The Fourier transform amplitude diagram of the echo signal after SLM phase modulation involved in the SLM phase modulation matrix of the present invention is shown. Figure 3d The Fourier transform phase diagram of the laser echo signal after SLM phase modulation, which is involved in the SLM phase modulation matrix of the present invention. Figure 3e This is an example of an SLM phase modulation matrix for the method of the present invention; Figure 4a The amplitude diagram of the laser complex image based on echo phase modulation is shown in the method of the present invention. Figure 4b The present invention provides a laser complex image phase map based on echo phase modulation. Figure 5a Imaging results of the array detector before synthetic aperture processing according to the method of the present invention; Figure 5b The imaging results after the array detector synthetic aperture processing is obtained by the method of the present invention. Detailed Implementation

[0036] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0037] Example 1 See Figure 1 This is a flowchart of a synthetic aperture laser imaging method using an array detector with echo phase modulation provided in this embodiment. The method steps are as follows: Step S1: Illuminate the target with a laser emission signal to obtain the echo signal corresponding to the target; Step S2: Use SLM to perform phase modulation on the echo signal; Step S3: The echo signal is processed by a Fourier lens to form a laser complex image. The laser complex image is mixed with the laser local oscillator in a spatial optical path and acquired by a direct array detector. Step S4: Construct a laser composite image based on the two-step phase-shifting digital holography principle; Step S5: Repeat steps S1 to S4 for the moving target at different times to obtain multiple frames of laser composite images of the target; Step S6: Use the array detector synthetic aperture laser imaging algorithm to process the multi-frame laser complex image to obtain a high-resolution image corresponding to the target.

[0038] Furthermore, the echo signal phase modulation array detector synthetic aperture laser imaging system of the present invention consists of a laser, a polarization-maintaining fiber beam splitter, a collimator, a beam expander, a non-polarizing beam splitter (NPBS), a direct array detector, and an SLM, etc. The laser-generated signal is split by the polarization-maintaining fiber beam splitter to form a laser emission signal and a laser local oscillator. The laser emission signal illuminates the target after passing through the collimator and beam expander. The generated echo signal is phase-modulated by the SLM and then mixed with the laser local oscillator via the NPBS to achieve spatial optical path mixing. The direct array detector acquires the spatial optical path mixing result. See the schematic diagram of the echo signal phase modulation array detector synthetic aperture laser imaging system. Figure 2 .

[0039] Further, in step S2, the present invention constructs the phase modulation matrix of the spatial light modulator based on the two-step phase-shift digital holography principle, the main steps of which include: Step S2.1: Set a point target at the center of the imaging scene, illuminate the point target with the laser emission signal, set the direct array detector at the SLM, and make it collect the corresponding echo signal. ; Step S2.2: Set the direct array detector at the focal point of the Fourier lens and acquire the laser complex image of the point target. ; Step S2.3: Assuming that the echo signal, after being modulated by the SLM phase and processed by the Fourier lens, can form two frames of images with a 90° phase difference and the same amplitude on the direct array detector, taking the two frames of images arranged in the column direction as an example, its expression is:

[0040]

[0041]

[0042] in, The phase modulation matrix of the SLM is... This is the echo signal matrix on the SLM plane after phase modulation. This represents the two-dimensional Fourier transform result of the echo signal matrix after phase modulation. This indicates that each element in the matrix is ​​multiplied in a one-to-one manner. and , where are the number of rows and columns of the matrix, respectively, and j is the imaginary unit.

[0043] Step S2.4: The phase modulation matrix of the SLM can be constructed according to the formula:

[0044] in, This indicates the phase extraction process of the matrix. It is the inverse Fourier transform.

[0045] At a target distance of 1.05m, the direct array detector has a pixel size of 20. m, pixel size 128×128, Fourier lens aperture 8.3mm, focal length 35mm, laser wavelength 1.55 For an example of the phase modulation matrix of a spatial light modulator under condition m, see [example]. Figures 3a-3e .

[0046] Furthermore, in step S4, the two-step phase-shift digital holography requires that the intensity of the laser local oscillator be much greater than the intensity of the laser complex image corresponding to the echo signal, and that the direct array detector has a large dynamic range.

[0047] Further, in step S4, the present invention constructs a laser composite image based on the principle of two-step phase-shifting digital holography, the main steps of which include: Step S4.1: Use SLM to acquire the local oscillator light intensity image of the laser; Step S4.2: Use SLM to perform phase modulation on the echo signal, so that after processing by Fourier lens, two laser complex images with the same amplitude and orthogonal phase are formed on the direct array detector; Step S4.3: Use SLM to acquire the light intensity image formed by mixing the laser local oscillator with the spatial optical path of the laser complex image; Step S4.4: Based on the SLM phase modulation matrix design, the light intensity image is split into light intensity images corresponding to the 0° and 90° laser composite images respectively; Step S4.5: Construct the laser composite image according to the formula:

[0048] in, For the laser composite image, and These are the light intensity images corresponding to the 0° and 90° laser composite images. This is the local oscillator light intensity image of the laser.

[0049] At a target distance of 1.05m, the direct array detector has a pixel size of 20. m, pixel size 128×128, Fourier lens aperture 8.3mm, focal length 35mm, laser wavelength 1.55 Under the condition of m, the laser complex image formation result based on echo phase modulation of the present invention is shown in [reference]. Figure 4a and Figure 4b .

[0050] Further, in step S5, the present invention needs to determine whether the target is within the system's imaging field of view. If the target is not outside the field of view, then steps S1 to S4 are repeated; otherwise, proceed to step S6. The motion form of the moving target includes micro-rotation and lateral translation, wherein the lateral translation refers to the motion direction being in a plane perpendicular to the normal direction of the imaging system.

[0051] Further, in step S6, the present invention achieves high-resolution imaging in the direction of relative target motion through array detector synthetic aperture laser imaging processing, the main steps of which include: Step S6.1: Perform a two-dimensional Fourier transform on the multiple frames of the laser complex image to form corresponding multi-frame spatial sampling signals; Step S6.2: Based on the motion parameters of the target, perform first-order phase, second-order phase, and rotational phase compensation on the spatial sampling signal to achieve image registration and motion compensation; Step S6.3: Perform a two-dimensional inverse Fourier transform on the phase-compensated spatial sampling signals of multiple frames to form a phase-compensated laser complex image; Step S6.4: Based on the motion parameters of the target, multiply the phase-compensated laser complex image by a first-order phase to achieve translation of the corresponding spatial sampling signal; Step S6.5: Coherently accumulate the phase-compensated laser complex image to increase the range of the corresponding spatial sampling signal and achieve high-resolution imaging of the target's relative motion direction.

[0052] At a target distance of 1.05m, the direct array detector has a pixel size of 20. m, pixel size 128×128, Fourier lens aperture 8.3mm, focal length 35mm, laser wavelength 1.55 For the target's lateral translation in the X and Y directions, the results of the echo phase-modulated array detector synthetic aperture laser imaging are shown below. Figure 5a and Figure 5b The synthetic aperture processing of the array detector effectively improves the two-dimensional resolution of the imaging results.

[0053] Further, in step S6, the motion parameters of the target include: micro-rotation / lateral translation direction, micro-rotation angle, and lateral translation distance. The micro-rotation / lateral translation direction can be obtained by interferometric phase estimation of the multi-frame laser complex image, and the micro-rotation angle and lateral translation distance can be calculated based on the inter-frame phase change of the target at the strong scattering point in the laser complex image.

[0054] Furthermore, this invention uses an imaging system to conduct repeated observations of the target, combined with the PGA algorithm, to suppress the sidelobe effect of high-resolution imaging results.

[0055] Furthermore, for targets that move laterally, the present invention generates a multi-frame array detector synthetic aperture laser imaging result as the target passes through the laser emission signal spot, and achieves large field-of-view imaging through incoherent processing.

[0056] Example 2 The present invention also provides an echo phase-modulated array detector synthetic aperture laser imaging system, comprising: Module M1: Illuminates the target with a laser emission signal and obtains the echo signal corresponding to the target; Module M2: Uses a spatial light modulator to perform phase modulation on the echo signal; Module M3: The phase-modulated echo signal is processed by a Fourier lens to form a laser complex image, the laser complex image is mixed with the laser local oscillator in a spatial optical path, and then acquired by an array detector; Module M4: Constructs a laser composite image based on the principle of two-step phase-shift digital holography; Module M5: Determines whether the target is within the imaging field of view. If the target is within the field of view, modules M1 to M4 are repeatedly triggered at different times to acquire multiple frames of laser complex images of the target; otherwise, module M6 is triggered. Module M6: Uses an array detector synthetic aperture laser imaging algorithm to process the multi-frame laser complex image to obtain a high-resolution image corresponding to the target.

[0057] The module M2 includes: Module M2.1: Set a point target at the center of the imaging scene, illuminate the point target with a laser emission signal, place the array detector at the spatial light modulator, and enable it to collect the corresponding echo signal. ; Module M2.2: Positions the array detector at the focal point of the Fourier lens to acquire the laser complex image of the point target. ; Module M2.3: After the echo signal is phase-modulated by the spatial light modulator and processed by the Fourier lens, two frames of images with a 90° phase difference and the same amplitude are formed on the array detector. Taking the two frames of images arranged in the column direction as an example, its expression is:

[0058]

[0059]

[0060] in, This is the phase modulation matrix of the spatial light modulator. This is the echo signal matrix on the plane of the spatial light modulator after phase modulation. This represents the two-dimensional Fourier transform result of the echo signal matrix after phase modulation. This indicates that each element in the matrix is ​​multiplied in a one-to-one manner. and These are the number of rows and columns of the matrix, respectively. Module M2.4: Constructs the phase modulation matrix of the spatial light modulator, with the following expression:

[0061] in, This indicates the phase extraction process of the matrix. It is the inverse Fourier transform.

[0062] The module M4 includes: Module M4.1: Acquires laser local oscillator intensity images using a spatial light modulator; Module M4.2: Uses a spatial light modulator to phase modulate the echo signal, so that after being processed by a Fourier lens, it forms two laser composite images with the same amplitude and orthogonal phase on the array detector; Module M4.3: Uses a spatial light modulator to acquire a light intensity image formed by mixing the laser local oscillator with the spatial optical path of the laser complex image; Module M4.4: Based on the spatial light modulator phase modulation matrix design, the light intensity image is split and light intensity images corresponding to the 0° and 90° laser composite images are formed respectively; Module M4.5: Constructs a laser complex image, expressed as:

[0063] in, For the laser composite image, and These are the light intensity images corresponding to the 0° and 90° laser composite images. This is the local oscillator light intensity image of the laser.

[0064] The module M6 includes: Module M6.1: Performs a two-dimensional Fourier transform on the multiple frames of the laser complex image to form corresponding multi-frame spatial sampling signals; Module M6.2: Based on the motion parameters of the target, performs first-order phase, second-order phase, and rotational phase compensation on the spatial sampling signal to achieve image registration and motion compensation; Module M6.3: Performs a two-dimensional inverse Fourier transform on the phase-compensated spatial sampling signals of multiple frames to form a phase-compensated laser complex image; Module M6.4: Based on the motion parameters of the target, multiply the phase-compensated laser complex image by a first-order phase to achieve translation of the corresponding spatial sampling signal; Module M6.5: Coherently accumulates the phase-compensated laser complex image to increase the range of the corresponding spatial sampling signal and achieve high-resolution imaging of the target's relative motion direction; The motion parameters of the target include: micro-rotation / lateral translation direction, micro-rotation angle, and lateral translation distance. The micro-rotation / lateral translation direction is obtained by interferometric phase estimation of the multi-frame laser complex image, and the micro-rotation angle and lateral translation distance are calculated based on the inter-frame phase change of the target with strong scattering points in the laser complex image.

[0065] The target is repeatedly observed, and the high-resolution imaging results are processed using a phase gradient autofocus algorithm to suppress the sidelobe effect of the imaging results. The motion of the moving target includes micro-rotation and lateral translation, wherein the lateral translation refers to the motion direction being in a plane perpendicular to the normal direction of the imaging system; for a target performing lateral translation, as the target passes through the laser emission signal spot, a multi-frame array detector synthetic aperture laser imaging result is formed, and the multi-frame imaging result is incoherently superimposed to achieve large field of view imaging.

[0066] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0067] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for synthetic aperture laser imaging using an array detector with echo phase modulation, characterized in that, include: Step 1: Illuminate the target with a laser emission signal and obtain the echo signal corresponding to the target; Step 2: Use a spatial light modulator to perform phase modulation on the echo signal; Step 3: The phase-modulated echo signal is processed by a Fourier lens to form a laser complex image. The laser complex image is then spatially mixed with the laser local oscillator and acquired by an array detector. Step 4: Construct a laser composite image based on the two-step phase-shift digital holography principle; Step 5: Determine whether the target is within the imaging field of view. If the target is not outside the field of view, repeat steps 1 to 4 at different times to obtain multiple frames of laser complex images of the target; otherwise, proceed to step 6. Step 6: Use the array detector synthetic aperture laser imaging algorithm to process the multi-frame laser complex image to obtain a high-resolution image corresponding to the target.

2. The echo-phase modulated array detector synthetic aperture laser imaging method according to claim 1, characterized in that, Step 2 includes: Step 2.1: Set a point target at the center of the imaging scene, illuminate the point target with a laser emission signal, set the array detector at the spatial light modulator, and make it collect the corresponding echo signal. ; Step 2.2: Position the array detector at the focal point of the Fourier lens and acquire the laser complex image of the point target. ; Step 2.3: After the echo signal is phase-modulated by the spatial light modulator and processed by the Fourier lens, two frames with a 90° phase difference and the same amplitude are formed on the array detector. Taking the two frames arranged in the column direction as an example, its expression is: in, This is the phase modulation matrix of the spatial light modulator. This is the echo signal matrix on the plane of the spatial light modulator after phase modulation. This represents the two-dimensional Fourier transform result of the echo signal matrix after phase modulation. This indicates that each element in the matrix is ​​multiplied in a one-to-one manner. and These are the number of rows and columns of the matrix, respectively. Step 2.4: Construct the phase modulation matrix of the spatial light modulator, expressed as: in, This indicates the phase extraction process of the matrix. It is the inverse Fourier transform.

3. The echo-phase modulated array detector synthetic aperture laser imaging method according to claim 1, characterized in that, Step 4 includes: Step 4.1: Acquire the laser local oscillator intensity image using a spatial light modulator; Step 4.2: Use a spatial light modulator to perform phase modulation on the echo signal, so that after processing by a Fourier lens, two laser composite images with the same amplitude and orthogonal phase are formed on the array detector; Step 4.3: Use a spatial light modulator to acquire the light intensity image formed by mixing the laser local oscillator with the spatial optical path of the laser complex image; Step 4.4: Based on the spatial light modulator phase modulation matrix design, the light intensity image is split into light intensity images corresponding to the 0° and 90° laser composite images respectively; Step 4.5: Construct the laser composite image, expressed as: in, For the laser composite image, and These are the light intensity images corresponding to the 0° and 90° laser composite images. This is the local oscillator light intensity image of the laser.

4. The echo-phase modulated array detector synthetic aperture laser imaging method according to claim 1, characterized in that, Step 6 includes: Step 6.1: Perform a two-dimensional Fourier transform on the multiple frames of the laser complex image to form corresponding multi-frame spatial sampling signals; Step 6.2: Based on the motion parameters of the target, perform first-order phase, second-order phase, and rotational phase compensation on the spatial sampling signal to achieve image registration and motion compensation; Step 6.3: Perform a two-dimensional inverse Fourier transform on the phase-compensated spatial sampling signals of multiple frames to form a phase-compensated laser complex image; Step 6.4: Based on the motion parameters of the target, multiply the phase-compensated laser complex image by a first-order phase to achieve translation of the corresponding spatial sampling signal; Step 6.5: Coherently accumulate the phase-compensated laser complex image to increase the range of the corresponding spatial sampling signal and achieve high-resolution imaging of the target's relative motion direction; The motion parameters of the target include: micro-rotation / lateral translation direction, micro-rotation angle, and lateral translation distance. The micro-rotation / lateral translation direction is obtained by interferometric phase estimation of the multi-frame laser complex image, and the micro-rotation angle and lateral translation distance are calculated based on the inter-frame phase change of the target with strong scattering points in the laser complex image.

5. The echo-phase modulated array detector synthetic aperture laser imaging method according to claim 1, characterized in that, The target is repeatedly observed, and the high-resolution imaging results are processed using a phase gradient autofocus algorithm to suppress the sidelobe effect of the imaging results. The motion of the moving target includes micro-rotation and lateral translation, wherein the lateral translation refers to the motion direction being in a plane perpendicular to the normal direction of the imaging system; for a target performing lateral translation, as the target passes through the laser emission signal spot, a multi-frame array detector synthetic aperture laser imaging result is formed, and the multi-frame imaging result is incoherently superimposed to achieve large field of view imaging.

6. A synthetic aperture laser imaging system for an array detector with echo phase modulation, characterized in that, include: Module M1: Illuminates the target with a laser emission signal and obtains the echo signal corresponding to the target; Module M2: Uses a spatial light modulator to perform phase modulation on the echo signal; Module M3: The phase-modulated echo signal is processed by a Fourier lens to form a laser complex image, the laser complex image is mixed with the laser local oscillator in a spatial optical path, and then acquired by an array detector; Module M4: Constructs a laser composite image based on the principle of two-step phase-shift digital holography; Module M5: Determines whether the target is within the imaging field of view. If the target is within the field of view, modules M1 to M4 are repeatedly triggered at different times to acquire multiple frames of laser complex images of the target; otherwise, module M6 is triggered. Module M6: Uses an array detector synthetic aperture laser imaging algorithm to process the multi-frame laser complex image to obtain a high-resolution image corresponding to the target.

7. The echo phase modulation array detector synthetic aperture laser imaging system according to claim 6, characterized in that, The module M2 includes: Module M2.1: Set a point target at the center of the imaging scene, illuminate the point target with a laser emission signal, place the array detector at the spatial light modulator, and enable it to collect the corresponding echo signal. ; Module M2.2: Positions the array detector at the focal point of the Fourier lens to acquire the laser complex image of the point target. ; Module M2.3: After the echo signal is phase-modulated by the spatial light modulator and processed by the Fourier lens, two frames of images with a 90° phase difference and the same amplitude are formed on the array detector. Taking the two frames of images arranged in the column direction as an example, its expression is: in, This is the phase modulation matrix of the spatial light modulator. This is the echo signal matrix on the plane of the spatial light modulator after phase modulation. This represents the two-dimensional Fourier transform result of the echo signal matrix after phase modulation. This indicates that each element in the matrix is ​​multiplied in a one-to-one manner. and These are the number of rows and columns of the matrix, respectively. Module M2.4: Constructs the phase modulation matrix of the spatial light modulator, with the following expression: in, This indicates the phase extraction process of the matrix. It is the inverse Fourier transform.

8. The echo phase-modulated array detector synthetic aperture laser imaging system according to claim 6, characterized in that, The module M4 includes: Module M4.1: Acquires laser local oscillator intensity images using a spatial light modulator; Module M4.2: Uses a spatial light modulator to phase modulate the echo signal, so that after being processed by a Fourier lens, it forms two laser composite images with the same amplitude and orthogonal phase on the array detector; Module M4.3: Uses a spatial light modulator to acquire a light intensity image formed by mixing the laser local oscillator with the spatial optical path of the laser complex image; Module M4.4: Based on the spatial light modulator phase modulation matrix design, the light intensity image is split and light intensity images corresponding to the 0° and 90° laser composite images are formed respectively; Module M4.5: Constructs a laser complex image, expressed as: in, For the laser composite image, and These are the light intensity images corresponding to the 0° and 90° laser composite images. This is the local oscillator light intensity image of the laser.

9. The echo-phase modulated array detector synthetic aperture laser imaging system according to claim 6, characterized in that, The module M6 includes: Module M6.1: Performs a two-dimensional Fourier transform on the multiple frames of the laser complex image to form corresponding multi-frame spatial sampling signals; Module M6.2: Based on the motion parameters of the target, performs first-order phase, second-order phase, and rotational phase compensation on the spatial sampling signal to achieve image registration and motion compensation; Module M6.3: Performs a two-dimensional inverse Fourier transform on the phase-compensated spatial sampling signals of multiple frames to form a phase-compensated laser complex image; Module M6.4: Based on the motion parameters of the target, multiply the phase-compensated laser complex image by a first-order phase to achieve translation of the corresponding spatial sampling signal; Module M6.5: Coherently accumulates the phase-compensated laser complex image to increase the range of the corresponding spatial sampling signal and achieve high-resolution imaging of the target's relative motion direction; The motion parameters of the target include: micro-rotation / lateral translation direction, micro-rotation angle, and lateral translation distance. The micro-rotation / lateral translation direction is obtained by interferometric phase estimation of the multi-frame laser complex image, and the micro-rotation angle and lateral translation distance are calculated based on the inter-frame phase change of the target with strong scattering points in the laser complex image.

10. The echo phase-modulated array detector synthetic aperture laser imaging system according to claim 6, characterized in that, The target is repeatedly observed, and the high-resolution imaging results are processed using a phase gradient autofocus algorithm to suppress the sidelobe effect of the imaging results. The motion of the moving target includes micro-rotation and lateral translation, wherein the lateral translation refers to the motion direction being in a plane perpendicular to the normal direction of the imaging system; for a target performing lateral translation, as the target passes through the laser emission signal spot, a multi-frame array detector synthetic aperture laser imaging result is formed, and the multi-frame imaging result is incoherently superimposed to achieve large field of view imaging.

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