Non-visual field detection method and device based on non-coaxial adaptive calibration

Abstract

The invention provides a non-visual field detection method and device based on non-coaxial adaptive calibration, and belongs to the technical field of optical non-visual field imaging. The method comprises the following steps: when a non-vision-field target is detected, transmitting low-power laser to an intermediate wall surface by using a transmitter unit of a non-coaxial transceiving system, and acquiring a primary echo signal through a receiver unit of the system; calculating absolute distance and angle information between the system and the intermediate wall surface based on the primary echo signal; based on the absolute distance and angle information, according to a preset non-vision field detection scanning strategy, the emitter unit is used for emitting high-power laser to the medium wall surface, and the receiver unit is used for obtaining three times of echo signals, so that reconstruction of the non-vision field target is achieved. The method has the characteristics of high detection speed, high calibration precision, accurate and controllable dislocation and high imaging speed.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical non-line-of-sight imaging, and in particular relates to a non-line-of-sight detection method and device based on non-coaxial adaptive calibration. Background Art

[0002] Non-line-of-sight imaging aims to visualize hidden objects outside the field of view through multiply scattered light. Typical non-line-of-sight imaging systems usually use pulsed light sources and time-domain resolved single-photon detection systems. By emitting pulsed lasers to the intermediate wall, weak echo signals after three scatterings are collected, and the signal histogram is accumulated in the time domain. Then, the spatial and temporal features in the signal histogram are fully extracted to reconstruct objects outside the field of view. This technology has great application potential in many fields such as autonomous driving and disaster relief.

[0003] Most existing non-line-of-sight imaging methods use a coaxial transceiver system for detection, that is, the transceiver is integrated and limited to a near-field laboratory environment. However, for practical applications, since the detection distance is usually far and is affected by saturation effects and echo crosstalk, the system needs to use a non-coaxial architecture for detection, that is, the transmitting optical path and the receiving optical path need to be separated. Recently, some scholars have proposed an adaptive calibration technology under a coaxial architecture. This method uses absolute distance information to achieve near-field wall parameter calibration. However, for a non-coaxial architecture, the lack of absolute distance information causes this method to fail. At present, there is no method that can quickly calibrate the intermediate wall in non-line-of-sight imaging under a non-coaxial architecture, which brings certain challenges to the practical application of non-line-of-sight imaging. In addition, in the field of non-line-of-sight imaging, in order to avoid the over-strength of the primary echo causing the submersion of the third echo, it is usually necessary to control the transmission and receiving optical paths to have a certain misalignment while using gating. The misalignment will greatly affect the quality of the third echo signal. However, there is currently no method that can accurately control the degree of misalignment. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and propose a non-line-of-sight detection method and device based on non-coaxial adaptive calibration. The present invention is based on the principle of single-photon detection, and makes full use of the echo information collected by the non-coaxial transceiver system to calibrate the wall parameters. There is no need to collect an additional echo as the translation reference of the three echoes, and automatically generates the primary echo information and its corresponding gated delay. It has the characteristics of fast detection speed, high calibration accuracy, precise and controllable dislocation, and fast imaging speed, which promotes the non-line-of-sight imaging technology towards practical application.

[0005] The first aspect of the present invention provides a non-line-of-sight detection method based on non-coaxial adaptive calibration, comprising:

[0006] When detecting a non-line-of-sight target, a low-power laser is emitted to the intermediate wall surface by using a transmitter unit of the non-coaxial transceiver system, and an echo signal is obtained by a receiver unit of the system;

[0007] Based on the primary echo signal, calculating the absolute distance and angle information between the system and the intermediate wall;

[0008] Based on the absolute distance and angle information, according to a preset non-line-of-sight detection scanning strategy, the transmitter unit is used to emit a high-power laser to the intermediate wall surface, and three echo signals are obtained through the receiver unit;

[0009] The non-viewing target is reconstructed based on the three echo signals.

[0010] In a specific embodiment of the present invention, the non-coaxial transceiver system comprises: a transmitter unit, a receiver unit, and an acquisition and control unit; wherein the transmitter unit comprises: a mode-locked pulse laser, a first galvanometer, and a first beam expander; wherein the output end face of the laser is placed perpendicular to the incident end face of the first galvanometer, and the first beam expander is placed perpendicular to and close to the output end face of the first galvanometer;

[0011] The receiver unit comprises: a single-photon detector, a filter, a second galvanometer and a second beam expander; wherein the second galvanometer is the same as the first galvanometer, and the second beam expander is the same as the first beam expander; the receiving end face of the detector is placed perpendicular to the incident end face of the second galvanometer, and the second beam expander is placed perpendicular to and close to the exit end face of the second galvanometer;

[0012] The acquisition and control unit includes: a time-correlated single-photon counter, a gate control board and a host computer; wherein the gate control board outputs an unmodulated signal to the counter as a synchronization signal, and the gate control board also outputs a pulse width and delay modulated signal to the gate control port of the detector for controlling the switch of the detector to isolate the photon single echo information; the detection signal output by the detector is connected to the counter, and the counter is used to record the timing information of the detected photons; the host computer is respectively connected to the laser, the detector, the counter, the first galvanometer, and the second galvanometer, and is used to control the signal acquisition of the system, process and display the imaging results of the non-field of view target.

[0013] In a specific embodiment of the present invention, the transmitter unit of the non-coaxial transceiver system transmits a low-power laser to the intermediate wall surface, and the receiver unit of the system obtains an echo signal, including:

[0014] A low-power laser pulse sequence is emitted to the intermediate wall surface by using a mode-locked pulse laser of the transmitter unit, wherein the low-power laser pulse sequence satisfies that when the laser irradiation point and the detection receiving point coincide, one echo cannot saturate the detector;

[0015] The receiver unit respectively hits the detection receiving point on the upper, lower, left, right and center areas of the intermediate wall, and uses the first galvanometer of the transmitter unit to perform laser scanning in each area to find the laser irradiation point that coincides with the detection receiving point in the corresponding area. The photon primary echo information captured by the receiver unit is used to obtain the signal histogram accumulated in the time domain of the photons corresponding to the area.

[0016] In a specific embodiment of the present invention, the calculating the absolute distance and angle information between the system and the intermediate wall based on the primary echo signal includes:

[0017] 1) Using the signal histogram in the central area, calculate the absolute distance information between the non-coaxial transceiver system and the intermediate wall;

[0018] For the central area, note the angle θ of the second galvanometer in the receiver unit. SPAD is 0, and the deflection angle of the first galvanometer corresponding to the coincidence position of the laser irradiation point and the detection receiving point in this area is θ LASER , the relative distance between the transmitter unit and the receiver unit is Dsystem, then the absolute distance d0 between the intermediate wall and the non-coaxial transceiver system is:

[0019] d0=F(D S ystem,θ L aser,θ SPAD )

[0020] Where F represents the geometric operator related to non-planar lines;

[0021] 2) Using the signal histograms of other areas except the central area, calculate the angle information of the intermediate wall;

[0022] For any other area, the first galvanometer deflection angle corresponding to the coincidence position of the laser irradiation point and the detection receiving point in the area is recorded as θ other , according to the corresponding signal histogram, the absolute distance information dother between the other area and the non-coaxial transceiver system is obtained:

[0023]

[0024] Wherein, c represents the speed of light, Hother represents the signal histogram of the coincidence position of the laser irradiation point and the detection receiving point in the other regions, Hcenter represents the signal histogram of the coincidence position of the laser irradiation point and the detection receiving point in the central region, and peak(H) represents the product of the timestamp with the most accumulated photons in the signal histogram and the time resolution;

[0025] Based on the distance Δd between the central area on the intermediate wall and the other area, the angle component Θ of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system in the direction corresponding to the other area is obtained:

[0026]

[0027] In a specific embodiment of the present invention, the method further comprises:

[0028] The angles of the intermediate wall relative to the optical axis of the non-coaxial transceiver system in the left and right components are respectively denoted as θ left and θ right , for Θ left and θ right The calculated average value is the horizontal angle θ of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system. hor ; The angles of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system in the upper and lower components are recorded as Θ up and θ down , for Θ up and θ down The calculated average value is the vertical angle θ of the intermediate wall relative to the optical axis of the non-coaxial transceiver system. ver .

[0029] In a specific embodiment of the present invention, the method further comprises:

[0030] 1) Generate a non-line-of-sight detection scanning strategy according to the absolute distance between the non-coaxial transceiver system and the intermediate wall and the horizontal angle and vertical angle of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system, the strategy including: scanning area size, scanning matrix size and misalignment degree;

[0031] 2) According to the non-line-of-sight detection scanning strategy obtained in step 1), the relative distances between each point pair on the wall to be scanned are calculated, and the signal histogram of the overlapped position in the central area is used as a reference to calculate the real time position of the primary echo corresponding to all point pairs in the signal histogram, thereby obtaining the primary echo information and the corresponding gated delay under the strategy;

[0032] A high-power laser pulse sequence is emitted to the intermediate wall surface by a mode-locked pulse laser of the transmitter unit to generate a triple echo signal and perform measurement. According to the information of the first echo under this strategy, the triple echo signal is subjected to corresponding translation operation to obtain a signal histogram corresponding to the triple echo signal.

[0033] In a specific embodiment of the present invention, the reconstruction of the non-line-of-sight target adopts a phasor field algorithm.

[0034] A second aspect of the present invention provides a non-line-of-sight detection device based on non-coaxial adaptive calibration, comprising:

[0035] A low-power signal acquisition module is used to transmit a low-power laser to the intermediate wall surface by using the transmitter unit of the non-coaxial transceiver system when detecting a non-line-of-sight target, and obtain an echo signal through the receiver unit of the system;

[0036] A calibration module, used for calculating the absolute distance and angle information between the system and the intermediate wall based on the primary echo signal;

[0037] A high-power signal acquisition module, based on the absolute distance and angle information, uses the transmitter unit to emit a high-power laser to the intermediate wall surface according to a preset non-line-of-sight detection scanning strategy, and obtains three echo signals through the receiver unit;

[0038] An imaging module is used to reconstruct the non-viewing area target based on the three echo signals.

[0039] A third aspect of the present invention provides an electronic device, including:

[0040] at least one processor; and a memory communicatively coupled to the at least one processor;

[0041] The memory stores instructions executable by the at least one processor, and the instructions are configured to execute the above-mentioned non-line-of-sight detection method based on non-coaxial adaptive calibration.

[0042] A fourth aspect of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable the computer to execute the above-mentioned non-line-of-sight detection method based on non-coaxial adaptive calibration.

[0043] Features and beneficial effects of the present invention:

[0044] The present invention can realize the rapid calibration of distant walls without any auxiliary equipment. The present invention is based on a non-coaxial transceiver system, and searches for the position where the laser irradiation point and the detection receiving point coincide by scanning; then, by calculating the common perpendicular line of the eccentric light rays, the absolute distance information between the non-coaxial transceiver system and the intermediate wall is indirectly obtained, and then the relative distance information is extracted from the signal histogram information of the center and edge areas of the wall, and finally the angle information of the intermediate wall relative to the optical axis of the system is obtained. In addition, the present invention can realize the precise control of the degree of misalignment in non-field of view detection, fully analyze the noise source of the single-photon detector, and has good interpretability.

[0045] The present invention has high practicality and a wide range of applications. It can automatically generate corresponding primary echo information and gated delay information according to the set wall size, and can perform signal translation without additional primary echo measurement. It can be applied to confocal detection mode or non-confocal detection mode, and can work in scenarios with a distance of 3 to 50 meters.

[0046] Compared with the traditional checkerboard calibration method, the calibration efficiency of the present invention is improved by about 20 times, and because there is no need to collect a primary echo, the acquisition time is shortened by 50%. The present invention directly uses the primary echo generated by calibration and the gating information for detection, and can obtain clear imaging results.

[0047] The present invention has a wide range of application scenarios and has potential application value in the fields of autonomous driving, disaster relief, landform detection, security and anti-terrorism, remote sensing imaging, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is an overall flow chart of a non-line-of-sight detection method based on non-coaxial adaptive calibration according to an embodiment of the present invention;

[0049] Figure 2 is a schematic diagram of a long-distance non-line-of-sight imaging scenario based on a non-coaxial transceiver system according to a specific embodiment of the present invention;

[0050] Figure 3 It is a structural schematic diagram of a non-coaxial transceiver system according to a specific embodiment of the present invention;

[0051] Figure 4 It is a schematic diagram of the principle of non-coaxial adaptive calibration according to a specific embodiment of the present invention;

[0052] Figure 5 is a schematic diagram of center count distribution in the center area of ​​the intermediate wall surface of a specific embodiment of the present invention;

[0053] Figure 6 It is a schematic diagram of the calibration steps and results of a specific embodiment of the present invention;

[0054] Figure 7It is a non-viewing area target and its reconstruction result diagram according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0055] The present invention proposes a non-line-of-sight detection method and device based on non-coaxial adaptive calibration, which is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] The first aspect of the present invention provides a non-line-of-sight detection method based on non-coaxial adaptive calibration, comprising:

[0057] When detecting a non-line-of-sight target, a low-power laser is emitted to the intermediate wall surface by using a transmitter unit of the non-coaxial transceiver system, and an echo signal is obtained by a receiver unit of the system;

[0058] Based on the primary echo signal, calculating the absolute distance and angle information between the system and the intermediate wall;

[0059] Based on the absolute distance and angle information, according to a preset non-line-of-sight detection scanning strategy, the transmitter unit is used to emit a high-power laser to the intermediate wall surface, and three echo signals are obtained through the receiver unit;

[0060] The non-viewing target is reconstructed based on the three echo signals.

[0061] In a specific embodiment of the present invention, the non-line-of-sight detection method based on non-coaxial adaptive calibration is divided into five stages, wherein the first stage is to build a non-coaxial transceiver system; the second stage is to use the transmitter unit of the non-coaxial transceiver system to transmit a low-power laser to the intermediate wall, and obtain a directly returned primary echo signal through the receiver unit; the third stage is to solve the absolute distance and angle information between the non-coaxial transceiver system and the unknown intermediate wall; the fourth stage is to analyze the long-distance non-line-of-sight imaging noise model, generate a non-line-of-sight scanning strategy, and automatically generate a primary echo and gated delay information, and use the transmitter unit to transmit a high-power laser to the intermediate wall, and obtain the weak signal generated by three diffuse reflections between the intermediate wall and the non-line-of-sight target through the receiver unit; the fifth stage is to use the classic non-line-of-sight imaging algorithm to reconstruct the non-line-of-sight target. The overall process of this method is as follows: Figure 1 As shown, the following steps are included:

[0062] 1) Build a non-coaxial transceiver system.

[0063] In this embodiment, the observer emits a laser to the intermediate wall surface, and the point on the intermediate wall surface that is irradiated is called the laser irradiation point. The photon enters the non-field of view area after the first diffuse reflection, and undergoes a second diffuse reflection on the target surface to be reconstructed and returns to the intermediate wall surface. At this time, a photon receiving device with time resolution capability is used to detect the photon echo information at a certain point on the intermediate wall surface, and this point is called the detection receiving point. The laser irradiation point and the detection receiving point form a measurement point pair. To image the non-field of view scene, it is necessary to obtain data at many measurement point pairs. If the laser irradiation point and the detection receiving point of all measurement point pairs are the same point, it is called the confocal detection mode, otherwise it is called the non-confocal detection mode.

[0064] In this embodiment, a non-coaxial transceiver system is used to avoid the crosstalk problem caused by long-distance detection and the saturation phenomenon caused by excessive mirror echo. Figure 2 The schematic diagram of a long-distance non-line-of-sight imaging scene based on a non-coaxial transceiver system in a specific embodiment of the present invention includes: a non-coaxial transceiver system, an intermediate wall, an obstruction, and a non-line-of-sight target. The intermediate wall is a flat wall for collecting non-line-of-sight triple echo information. The material is a common diffuse reflection material, such as a white foam board. The size of the wall can contain the scanning area. The distance between the non-coaxial transceiver system and the intermediate wall can be in the range of 3 to 50 meters. The obstruction is used to block the field of view between the non-line-of-sight target and the non-coaxial transceiver system, so that the non-line-of-sight target is outside the field of view of the non-coaxial transceiver system, but the obstruction cannot block the non-coaxial transceiver system and the intermediate wall. The obstruction can be selected arbitrarily, such as a screen; the hidden object is the target object to be detected. In this embodiment, there is no special requirement for the non-line-of-sight target. In a specific embodiment of the present invention, the target is a plane letter "Z" made of diffuse reflection material, and a three-dimensional object or an object of retroreflective material can also be selected. The distance between the non-coaxial transceiver system and the intermediate wall can be 0.8m to 1.2m.

[0065] Furthermore, the structure of the non-coaxial transceiver system described in this embodiment is as follows: Figure 3 As shown, it includes: a transmitter unit, a receiver unit, and an acquisition and control unit. The transmitter unit includes: a mode-locked pulse laser (hereinafter referred to as laser, and this embodiment uses a fiber laser VFLP-1550-M-50ps-FA, Connet Optics Fiber), a first galvanometer (GVS012 / M, Thorlabs) and a first beam expander; the laser is used as an active light source, and its output end face is placed perpendicular to the incident end face of the first galvanometer. The first galvanometer can realize the light field scanning function, and the first beam expander is placed perpendicular to and close to the output end face of the first galvanometer.

[0066] The receiver unit includes: a single photon detector (hereinafter referred to as the detector, and this embodiment uses a fiber-optic detector SPD_OEM_NIR, Aurea), a filter, a second galvanometer, and a second beam expander. The second galvanometer is the same as the first galvanometer, and the second beam expander is the same as the first beam expander. The detector is used as a receiving device, and its receiving end face is placed perpendicular to the incident end face of the second galvanometer. The second galvanometer can realize the light field scanning function, and the second beam expander is placed perpendicular to and close to the exit end face of the second galvanometer.

[0067] The acquisition and control unit includes: a time-correlated single photon counter (hereinafter referred to as the counter, this embodiment uses the Time Tagger Ultra, Swabian instruments), a gate control board and a host computer. The counter is used to record the timing information of the detected photons, the gate control board is used to control the high-speed switch of the detector in the time domain to fully isolate the photon primary echo information, and the host computer is used to control the signal acquisition, processing and display of the entire system.

[0068] In this system, the transmitter unit and the receiver unit are non-coaxial. In this embodiment, they are placed in two layers, the transmitter unit is located in the upper layer, and the receiver unit is located in the lower layer. The synchronization signal of the laser is connected to the input signal of the gate control board; the gate control board directly outputs the unmodulated signal 1 to the port 1 of the counter as a synchronization signal, and outputs the pulse width and delay modulated signal 2 to the gate port of the detector to control the switch of the detector; the detection signal output by the detector is connected to the port 2 of the counter. The upper computer is connected to the laser, detector, counter, first galvanometer, and second galvanometer at the same time to control the collection and recording of the timing signal histogram of photons.

[0069] In this embodiment, in the transmitter unit, the laser emitted by the laser has a central wavelength of 1550nm, a pulse width of less than 50ps, and a repetition frequency of 20MHz. After being collimated, the laser first passes through the first galvanometer to realize the light field scanning function, and then compresses the divergence angle through a 3x beam expander (i.e., the first beam expander), so that the light spot is minimized on the intermediate wall surface 18m away. In the receiver unit, an InGaAs / InP single-photon detector with a fast gating function is used, and its detection efficiency is set to 10%, the time jitter is about 250ps, and the dark count rate is about 2k per second. It is combined with multimode fiber coupling to realize the collection of one echo in the field of view and three echoes in the non-field of view. In the acquisition and control unit, a gate control board is used to control the switch of the single-photon detector, and a time-correlated single-photon counter is used to record the timestamp photon information. The gate control board receives the synchronization signal of the mode-locked pulse laser and divides the input signal into two paths. One path is directly output to the "1" port of the single-photon counter as a reference source, and the other path is output to the detector after shaping, pulse width modulation and delay modulation to control the timing switch of the detector. The detection signal collected by the single-photon detector is transmitted to the "2" port of the single-photon counter to calculate the timing information. The laser, detector, counter, first galvanometer, second galvanometer and gate control board are all controlled by the host computer. The signal is finally transmitted to the host computer, and the non-line-of-sight inversion image can be obtained after processing. The whole system works in the 1550nm band. The single pulse energy of the laser in the non-line-of-sight acquisition process is 50nJ, and the single pulse energy in the line-of-sight calibration process is 2nJ. In this embodiment, the distance between the laser and the intermediate wall is about 18m, the distance between the hidden target and the wall is set to 0.8m, the working mode is the confocal detection mode (the present invention can also use non-confocal detection), and the misalignment degree is set to 6cm through the non-coaxial adaptive calibration method. The scanning wall size is 0.8m×0.8m, the scanning matrix is ​​32×32, and the time resolution is 32ps.

[0070] 2) Use the transmitter unit of the non-coaxial transceiver system built in step 1) to emit a low-power laser to the set area of ​​the intermediate wall, and capture the photon echo information through the receiver unit of the system to obtain the signal histogram of the photons accumulated in the time domain corresponding to the area, that is, the accumulated number of photons at different time scales.

[0071] In this embodiment, since the non-coaxial architecture does not have a mirror echo as a starting reference point, and the wall distance is greater than the distance span that the system can measure, there is no direct absolute distance information. In this embodiment, a low-power laser pulse sequence with a single pulse energy of 2nJ is emitted to the intermediate wall by a mode-locked pulse laser of the transmitter unit (wherein, when the laser irradiation point and the detection receiving point coincide, a single echo cannot saturate the detector, and the laser is considered to be in a low-power state at this time), and the receiver unit respectively hits the detection receiving point to the upper, lower, left, right and center areas of the intermediate wall (there are 5 detection receiving points in this embodiment, and each area can be roughly divided according to the wall), and the first galvanometer of the transmitter unit is used to perform laser scanning in each area to find the point that best matches the area and the detection field of view.

[0072] The principle of the non-coaxial adaptive calibration of this embodiment is as follows Figure 4 Taking the central area as an example, the second galvanometer angle of the receiver unit is set to zero, and the first galvanometer angle of the transmitter unit is traversed within the range of 0±0.08V. The traversal matrix size is 32×32, and the single-point acquisition time is set to 8ms. The signal is collected and recorded by the single-photon detector and the single-photon counter, and the total number of photons of each measurement point pair is counted. In a specific embodiment of the present invention, the count distribution of the center of the area is as follows Figure 5 As shown, when the laser irradiation point and the detection receiving point completely overlap, an obvious primary echo peak can be observed from the photon counting diagram. When the laser irradiation point and the detection receiving point are offset, no effective information can be observed under low-power laser irradiation. The measurement method of other areas (left, right, upper and lower areas) is the same as that of the central area. In this embodiment, the galvanometer angle of the lower receiving light path is first set to (0.2V, 0V), (-0.2V, 0V), (0V, 0.2V), (0V, -0.2V), corresponding to the left, right, upper and lower areas respectively, and then the first galvanometer angle of the transmitter unit is traversed in the corresponding area, and the traversal range is ±0.08V, and the measurement signal histogram is recorded. Among them, the setting of 0.2V and 0.08V in this embodiment is related to the actual scanning range of the system. It is only necessary to control the scanning point within the wall range according to the voltage-angle ratio coefficient. The size of the traversal matrix needs to be weighed in terms of accuracy and time. In this embodiment, 32×32 is selected, and 16×16 can also be selected. On the basis of ensuring that sufficient photon information can be collected, the lower the single-point collection time, the better, in order to accelerate the self-calibration process. According to actual experience, 8ms is selected in this embodiment. In this embodiment, the absolute distance information between the intermediate wall and the non-coaxial system is calculated through the matching of the central area, and the relative distance information in the signal histogram of the matching measurement point pair is extracted through other areas, thereby calculating the angle information of the intermediate wall relative to the optical axis of the system.

[0073] 3) Using the signal histogram obtained in step 2), calculate the absolute distance and angle information between the non-coaxial transceiver system and the intermediate wall; the specific steps are as follows:

[0074] 3-1) Using the signal histogram in the central area, calculate the absolute distance information between the non-coaxial transceiver system and the intermediate wall.

[0075] For the central area, note the angle θ of the second galvanometer in the receiver unit. SPAD =0, according to the echo signal size of the center count distribution, find the coincidence position of the laser irradiation point and the detection receiving point, and record the deflection angle of the first galvanometer of the transmitter unit as θ LASER , since the transmitter unit and the receiver unit are built vertically, the relative distance between them in the vertical direction is measured as Dsystem, such as Figure 4 As shown. Due to the scanning accuracy and detection accuracy, the transmitting light path and the receiving light path are often skewed, so the triangle method cannot be used directly. Since two skewed straight lines have only one common perpendicular line, according to the principle of geometry, let the origin of the transmitting light path of the transmitter unit and the origin of the receiving light path of the receiving unit be O1 and O2 respectively, let the common perpendicular line between the transmitting light path and the receiving light path and the intersection of the transmitting light path and the receiving light path be recorded as x t1 and x t2 , then point x t1 Taking O1 as the starting point, θ LASER On the ray with direction t2 Taking O2 as the starting point, θ SPAD On the ray with direction x t1 x t2 At the same time, it is perpendicular to the transmitting light path and the receiving light path, based on which the three-dimensional coordinates (x t1 +x t2 ) / 2, thus obtaining the absolute distance d0 between the intermediate wall and the non-coaxial transceiver system:

[0076] d0=F(D S ystem,θ L aser,θ SPAD )

[0077] Where F represents the geometric operator related to non-coplanar lines.

[0078] 3-2) Calculate the intermediate wall angle information using the signal histogram of other areas except the central area.

[0079] Specifically, for any other area, according to the echo signal size of the center count distribution, find the coincidence position of the laser irradiation point and the detection receiving point, and record the deflection angle of the first galvanometer of the transmitter unit at this time as θ other, and record the horizontal coordinate corresponding to the peak position from the corresponding signal histogram, that is, the time grid information. By extracting the relative distance information from the signal histogram (this content, as well as all the information that will be used in the signal histogram, needs to be introduced when the signal histogram is generated in the previous step), the absolute distance information dother between the other area and the non-coaxial transceiver system can be obtained:

[0080]

[0081] Where c is the speed of light, H other It represents the signal histogram of the overlapping positions of the laser irradiation points and the detection receiving points in the other areas, Hcenter represents the signal histogram of the overlapping positions of the laser irradiation points and the detection receiving points in the central area, and peak(H) represents the product of the timestamp with the most accumulated photons in the signal histogram and the time resolution.

[0082] By using the principle of triangle geometry, the distance Δd between the central area on the intermediate wall and the other area is calculated, so as to obtain the angle component Θ of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system in the corresponding direction of the other area:

[0083]

[0084] In this embodiment, in the left and right areas of the intermediate wall, the angles of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system in the left and right components can be obtained by calculation and are recorded as θ left and θ right , for Θ left and θ right The calculated average value is the horizontal angle θ of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system. hor In the upper and lower areas of the intermediate wall, the angles of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system in the upper and lower components are calculated and recorded as Θ up and θ down , for Θ up and θ down The calculated average value is the vertical angle θ of the intermediate wall relative to the optical axis of the non-coaxial transceiver system. ver .

[0085] In a specific embodiment of the present invention, the absolute distance between the non-coaxial transceiver system and the intermediate wall is calculated to be 18.69m, the horizontal angle is 49.34°, and the vertical angle is 1.14°, which are close to the true values ​​(18.53m, 48.9°, 0°). Figure 6 It is a schematic diagram of the calibration steps and results of a specific embodiment of the present invention. Figure 6 The actual scanning array on the wall is compared with the preset scanning array. The measurement steps are as follows: Figure 6As shown in (a), the laser irradiation point position of the laser emitted by the transmitter unit located on the upper layer of the system is found on the wall through the photosensitive card, and recorded with black tape, and measured with a ruler, and the upper and lower layer misalignment is set to zero through the computer. If the peak of the first echo corresponding to zero misalignment can be observed under low-power laser conditions, it is considered that the calibrated upper and lower layer optical paths are matched. The measurement results are shown in Figure 6 (b) and Table 1 show that when the side lengths of the preset scanning array are 0.8m, 0.6m, and 0.4m, the side lengths actually measured are matched. In addition, by keeping the laser working at low power and setting the misalignment value to zero, a significant primary peak can be obtained at each measurement point pair, proving that the non-coaxial adaptive calibration method achieves the consistency of the transceiver system. The overall acquisition time of the calibration is 40 seconds, and the calculation process only takes 0.32 seconds.

[0086] Table 1 Non-coaxial adaptive calibration results of a specific embodiment of the present invention

[0087] Preset scanning area d1 d2 d3 d4 match 0.8m×0.8m 0.80m 0.80m 0.80m 0.80m √ 0.6m×0.6m 0.60m 0.60m 0.60m 0.60m √ 0.4m×0.4m 0.40m 0.40m 0.40m 0.40m √

[0088] 4) Using the calibration results of step 3), a non-line-of-sight detection scanning strategy is generated by emitting a high-power laser to the intermediate wall and capturing three echo signals through the receiver; the specific steps are as follows:

[0089] 4-1) Based on the calibration results of step 3), a non-line-of-sight detection scanning strategy is generated.

[0090] In this embodiment, the scanning area size is set to 0.8m×0.8m, the scanning matrix is ​​32×32, and the offset degree is set to 6cm in the vertical direction to reduce the background noise caused by an overly strong echo.

[0091] It should be noted that, in this embodiment, the scanning area is set to be no larger than the actual wall size according to the actual wall size, and the scanning wall size and the scanning matrix size can be freely set according to needs. According to actual experience, the misalignment degree is recommended to be set to 6cm to 30cm, and 6cm is selected in this embodiment.

[0092] The present invention can precisely control the degree of misalignment and for the first time analyzes the importance of misalignment in the field of non-line-of-sight detection:

[0093] For line-of-sight single-photon imaging, the noise sources usually include the dark counts of the single-photon detector and the environmental noise. The background noise can be effectively reduced by using gating technology and spatial filtering technology. However, for non-line-of-sight single-photon imaging, when the laser irradiation point and the detection receiving point completely overlap, the use of gating to isolate the first echo will fail to a certain extent. The increase in laser energy will inevitably increase the background noise, causing the effective information of the third echo to be submerged. The essence of this phenomenon is that the high-repetition-rate gating used in the detection process is electronic gating, not optical physical isolation gating, and there is charge persistence in the single-photon photoelectric avalanche diode. When the detector is in the dead time stage or the gate is in the closed state, the excessively strong first echo will form a hole accumulation that cannot be released in time during this period, triggering the photon avalanche effect at the moment the gate is opened, showing a strong background noise. Especially in long-distance non-line-of-sight imaging, since the laser energy decays with increasing distance, higher energy is usually required to ensure the signal-to-noise ratio of the third echo, and the background noise will be relatively higher. Therefore, in practical applications, for the confocal detection mode, the laser irradiation point and the detection receiving point need to be separated by a certain distance, that is, to ensure a certain misalignment, which is an approximate confocal mode. For the non-confocal detection mode, the fixed center is the detection receiving point, and the laser irradiation point needs to abandon the measurement point near the center, which is an approximate non-confocal mode. Similarly, in a long-distance non-line-of-sight imaging system, as the laser energy increases, the coaxial structure will have an overly strong mirror echo, and in non-line-of-sight imaging, in order to ensure enough triple echo signals, a high repetition rate laser is usually used. As the distance increases, the coaxial structure will show crosstalk. Taking a 20MHz laser repetition rate as an example, the measurable distance span is 7.5m, that is, when the detection distance is greater than 7.5m, the primary echo and the triple echo signals have the possibility of crosstalk with the mirror echo signal.

[0094] 4-2) According to the non-line-of-sight detection scanning strategy, the non-coaxial adaptive calibration algorithm can calculate the relative distance between each point pair on the wall to be scanned, and use the signal histogram of the overlapping position in the center area as a reference to calculate the real time position of the primary echo corresponding to all point pairs in the signal histogram. Therefore, the non-coaxial adaptive calibration algorithm can automatically generate the primary echo information corresponding to the scanned wall and the corresponding gated delay, without the need to measure the primary echo additionally and manually determine the gated delay, which greatly speeds up the non-line-of-sight detection speed.

[0095] In this embodiment, the measurement method adopts the serpentine scanning method to reduce the span of the galvanometer as much as possible to protect the galvanometer. A high-power laser pulse sequence with a single pulse energy of 50nJ is emitted to the intermediate wall by a mode-locked pulse laser (the ability to see a triple echo signal is used as the laser high power criterion), and the single-point acquisition time is set to 30ms (enough triple echo signals can be obtained), and the overall acquisition time is about 30s. According to the automatically generated single echo information, the measured triple echo signal is subjected to corresponding translation operations to obtain the signal histogram corresponding to the triple echo signal.

[0096] 5) Calculate the reflectivity information of non-viewing targets.

[0097] The signal histogram corresponding to the three echo signals obtained in step 4) is inverted using a classic non-line-of-sight imaging algorithm (such as a phasor field algorithm) to reconstruct the non-line-of-sight target and output the reflectivity information of the non-line-of-sight target.

[0098] Figure 7 is a non-viewing area target and its reconstruction result diagram according to a specific embodiment of the present invention, wherein: Figure 7 (a) is the real non-viewing target image, which is a plane letter “Z” with an overall width of 0.4m, a height of 0.55m, and a distance of 0.8m from the wall. Figure 7 (b) is the imaging result after the target is reconstructed. It can be seen from the imaging result that the target is clearly distinguishable after reconstruction and does not contain background noise.

[0099] To implement the above embodiment, a second aspect of the present invention provides a non-line-of-sight detection device based on non-coaxial adaptive calibration, comprising:

[0100] A low-power signal acquisition module is used to transmit a low-power laser to the intermediate wall surface by using the transmitter unit of the non-coaxial transceiver system when detecting a non-line-of-sight target, and obtain an echo signal through the receiver unit of the system;

[0101] A calibration module, used for calculating the absolute distance and angle information between the system and the intermediate wall based on the primary echo signal;

[0102] A high-power signal acquisition module, based on the absolute distance and angle information, uses the transmitter unit to emit a high-power laser to the intermediate wall surface according to a preset non-line-of-sight detection scanning strategy, and obtains three echo signals through the receiver unit;

[0103] An imaging module is used to reconstruct the non-viewing area target based on the three echo signals.

[0104] It should be noted that the aforementioned explanation of the embodiment of a non-line-of-sight detection method based on non-coaxial adaptive calibration is also applicable to a non-line-of-sight detection device based on non-coaxial adaptive calibration in the present embodiment, and will not be repeated here. According to a non-line-of-sight detection device based on non-coaxial adaptive calibration proposed in an embodiment of the present invention, when detecting a non-line-of-sight target, a transmitter unit of a non-coaxial transceiver system is used to emit a low-power laser to an intermediate wall surface, and a primary echo signal is obtained through a receiver unit of the system; based on the primary echo signal, the absolute distance and angle information between the system and the intermediate wall surface is calculated; based on the absolute distance and angle information, according to a preset non-line-of-sight detection scanning strategy, a high-power laser is emitted to the intermediate wall surface by using the transmitter unit, and three echo signals are obtained through the receiver unit; based on the three echo signals, the non-line-of-sight target is reconstructed. This allows The echo information collected based on the non-coaxial transceiver system is fully utilized to calibrate the wall parameters. There is no need to collect an additional echo as the translation reference of the three echoes. The echo information and its corresponding gated delay are automatically generated. It has the characteristics of fast detection speed, high calibration accuracy, precise and controllable misalignment, and fast imaging speed.

[0105] To implement the above embodiment, a third aspect of the present invention provides an electronic device, including:

[0106] at least one processor; and a memory communicatively coupled to the at least one processor;

[0107] The memory stores instructions executable by the at least one processor, and the instructions are configured to execute the above-mentioned non-line-of-sight detection method based on non-coaxial adaptive calibration.

[0108] To implement the above-mentioned embodiment, the fourth aspect of the present invention proposes a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable the computer to execute the above-mentioned non-line-of-sight detection method based on non-coaxial adaptive calibration.

[0109] It should be noted that the computer-readable medium disclosed above may be a computer-readable signal medium or a computer-readable storage medium or any combination of the above two. The computer-readable storage medium may be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device or device, or any combination of the above. More specific examples of computer-readable storage media may include, but are not limited to: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In the present disclosure, a computer-readable storage medium may be any tangible medium containing or storing a program that may be used by or in combination with an instruction execution system, device or device. In the present disclosure, a computer-readable signal medium may include a data signal propagated in a baseband or as part of a carrier wave, in which a computer-readable program code is carried. This propagated data signal may take a variety of forms, including but not limited to an electromagnetic signal, an optical signal, or any suitable combination of the above. The computer readable signal medium may also be any computer readable medium other than a computer readable storage medium, which may send, propagate or transmit a program for use by or in conjunction with an instruction execution system, apparatus or device. The program code contained on the computer readable medium may be transmitted using any suitable medium, including but not limited to: wires, optical cables, RF (radio frequency), etc., or any suitable combination of the above.

[0110] The computer-readable medium may be included in the electronic device, or may exist independently without being installed in the electronic device. The computer-readable medium carries one or more programs, and when the one or more programs are executed by the electronic device, the electronic device performs a non-line-of-sight detection based on non-coaxial adaptive calibration according to the above embodiment.

[0111] Computer program code for performing the operations of the present disclosure may be written in one or more programming languages, or a combination thereof, including object-oriented programming languages, such as Java, Smalltalk, C++, and conventional procedural programming languages, such as "C" or similar programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., through the Internet using an Internet service provider).

[0112] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0113] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0114] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present application belong.

[0115] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute the instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purpose of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or otherwise processing in a suitable manner if necessary, and then stored in a computer memory.

[0116] It should be understood that the various parts of the present application can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0117] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0118] In addition, each functional unit in each embodiment of the present application may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0119] The storage medium mentioned above may be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A non-line-of-sight detection method based on non-coaxial adaptive calibration, characterized in that: include: When detecting a non-line-of-sight target, a low-power laser is emitted to the intermediate wall surface by using a transmitter unit of the non-coaxial transceiver system, and an echo signal is obtained by a receiver unit of the system; Based on the primary echo signal, calculating the absolute distance and angle information between the system and the intermediate wall; Based on the absolute distance and angle information, according to a preset non-line-of-sight detection scanning strategy, the transmitter unit is used to emit a high-power laser to the intermediate wall surface, and three echo signals are obtained through the receiver unit; The non-viewing target is reconstructed based on the three echo signals.

2. The method according to claim 1, characterized in that The non-coaxial transceiver system comprises: a transmitter unit, a receiver unit, and an acquisition and control unit; wherein the transmitter unit comprises: a mode-locked pulse laser, a first galvanometer, and a first beam expander; wherein the output end face of the laser is placed perpendicular to the incident end face of the first galvanometer, and the first beam expander is placed perpendicular to and close to the output end face of the first galvanometer; The receiver unit comprises: a single-photon detector, a filter, a second galvanometer and a second beam expander; wherein the second galvanometer is the same as the first galvanometer, and the second beam expander is the same as the first beam expander; the receiving end face of the detector is placed perpendicular to the incident end face of the second galvanometer, and the second beam expander is placed perpendicular to and close to the exit end face of the second galvanometer; The acquisition and control unit includes: a time-correlated single-photon counter, a gate control board and a host computer; wherein the gate control board outputs an unmodulated signal to the counter as a synchronization signal, and the gate control board also outputs a pulse width and delay modulated signal to the gate control port of the detector for controlling the switch of the detector to isolate the photon single echo information; the detection signal output by the detector is connected to the counter, and the counter is used to record the timing information of the detected photons; the host computer is respectively connected to the laser, the detector, the counter, the first galvanometer, and the second galvanometer, and is used to control the signal acquisition of the system, process and display the imaging results of the non-field of view target.

3. The method according to claim 2, characterized in that The method of using a transmitter unit of the non-coaxial transceiver system to transmit a low-power laser to the intermediate wall surface and obtaining an echo signal through a receiver unit of the system includes: A low-power laser pulse sequence is emitted to the intermediate wall surface by using a mode-locked pulse laser of the transmitter unit, wherein the low-power laser pulse sequence satisfies that when the laser irradiation point and the detection receiving point coincide, one echo cannot saturate the detector; The receiver unit respectively hits the detection receiving point on the upper, lower, left, right and center areas of the intermediate wall, and uses the first galvanometer of the transmitter unit to perform laser scanning in each area to find the laser irradiation point that coincides with the detection receiving point in the corresponding area. The photon primary echo information captured by the receiver unit is used to obtain the signal histogram accumulated in the time domain of the photons corresponding to the area.

4. The method according to claim 3, characterized in that The calculating the absolute distance and angle information between the system and the intermediate wall based on the primary echo signal includes: 1) Using the signal histogram in the central area, calculate the absolute distance information between the non-coaxial transceiver system and the intermediate wall; For the central area, note the angle θ of the second galvanometer in the receiver unit. SPAD is 0, and the deflection angle of the first galvanometer corresponding to the coincidence position of the laser irradiation point and the detection receiving point in this area is θ LASER , the relative distance between the transmitter unit and the receiver unit is Dsystem, then the absolute distance d0 between the intermediate wall and the non-coaxial transceiver system is: d0=F(D S system,θ L aser,θ SPAD ) Where F represents the geometric operator related to non-planar lines; 2) Using the signal histograms of other areas except the central area, calculate the angle information of the intermediate wall; For any other area, the first galvanometer deflection angle corresponding to the coincidence position of the laser irradiation point and the detection receiving point in the area is recorded as θ other , according to the corresponding signal histogram, the absolute distance information dother between the other area and the non-coaxial transceiver system is obtained: Where c is the speed of light, H other represents the signal histogram of the coincidence position of the laser irradiation point and the detection receiving point in the other area, Hcenter represents the signal histogram of the coincidence position of the laser irradiation point and the detection receiving point in the central area, and peak(H) represents the product of the timestamp with the most accumulated photons in the signal histogram and the time resolution; Based on the distance Δd between the central area on the intermediate wall and the other area, the angle component Θ of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system in the direction corresponding to the other area is obtained:

5. The method according to claim 4, characterized in that The method further comprises: The angles of the intermediate wall relative to the optical axis of the non-coaxial transceiver system in the left and right components are respectively denoted as θ left and θ right , for Θ left and θ right The calculated average value is the horizontal angle θ of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system. hor ; The angles of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system in the upper and lower components are recorded as Θ up and θ down , for Θ up and θ down The calculated average value is the vertical angle θ of the intermediate wall relative to the optical axis of the non-coaxial transceiver system. ver .

6. The method according to claim 5, characterized in that The method further comprises: 1) Generate a non-line-of-sight detection scanning strategy according to the absolute distance between the non-coaxial transceiver system and the intermediate wall and the horizontal angle and vertical angle of the intermediate wall relative to the optical axis direction of the non-coaxial transceiver system, the strategy including: scanning area size, scanning matrix size and misalignment degree; 2) According to the non-line-of-sight detection scanning strategy obtained in step 1), the relative distances between each point pair on the wall to be scanned are calculated, and the signal histogram of the overlapped position in the central area is used as a reference to calculate the real time position of the primary echo corresponding to all point pairs in the signal histogram, thereby obtaining the primary echo information and the corresponding gated delay under the strategy; A high-power laser pulse sequence is emitted to the intermediate wall surface by a mode-locked pulse laser of the transmitter unit to generate a triple echo signal and perform measurement. According to the information of the first echo under this strategy, the triple echo signal is subjected to corresponding translation operation to obtain a signal histogram corresponding to the triple echo signal.

7. The method according to claim 6, characterized in that The reconstructing of the non-viewing target adopts a phasor field algorithm.

8. A non-line-of-sight detection device based on non-coaxial adaptive calibration, characterized in that: include: A low-power signal acquisition module is used to transmit a low-power laser to the intermediate wall surface by using the transmitter unit of the non-coaxial transceiver system when detecting a non-line-of-sight target, and obtain an echo signal through the receiver unit of the system; A calibration module, used for calculating the absolute distance and angle information between the system and the intermediate wall based on the primary echo signal; A high-power signal acquisition module, based on the absolute distance and angle information, uses the transmitter unit to emit a high-power laser to the intermediate wall surface according to a preset non-line-of-sight detection scanning strategy, and obtains three echo signals through the receiver unit; An imaging module is used to reconstruct the non-viewing area target based on the three echo signals.

9. An electronic device, characterized in that: include: at least one processor; and, a memory communicatively coupled to the at least one processor; The memory stores instructions executable by the at least one processor, and the instructions are configured to execute the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable the computer to execute the method according to any one of claims 1 to 7.

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