Long-range snapshot spectral imaging radar system and its application

Abstract

The present invention discloses a long-distance snapshot spectral imaging radar system. The system comprises components such as a light source, a projection lens, a photographic lens, a random mask, a grating, and a SPAD. The light emitted by the light source is projected onto the target surface through the projection lens, and the reflected light is detected by the SPAD after being processed by various components in turn. It uses SPAD to realize single-photon detection, solving the problem of spectrum detection at long distances or in weak light or dark light. Through a specific optical path design, combined with a random mask and a grating, the light field is modulated and split. With the help of mathematical algorithms, such as obtaining distance information based on multiple detection statistical arrival times, and modulating, dispersing, and integrating the spectrum matrix, the simultaneous detection of the target spectrum and distance information is realized. Compared with the existing technology, more comprehensive and high-quality information can be obtained in complex environments.

Description

Technical Field

[0001] The present invention relates to the field of radar technology, and in particular to a long-distance snapshot spectral imaging radar system and application thereof. Background Art

[0002] In the field of photoelectric detection and imaging technology, traditional photoelectric image sensors have certain limitations. They can usually only sense intensity information and present two-dimensional (2D) image data, but cannot obtain the depth or distance information of the target. This makes them inadequate in many application scenarios that require comprehensive spatial perception of the target.

[0003] With the development of technology, in 2002, Lincoln Laboratory proposed that arrayed single-photon avalanche diodes (SPADs) have the advantages of high detection probability and low dark count rate. Based on this, in 2005, the Lausanne Polytechnic University successfully realized a 32×32 SPAD array lidar chip using a 0.8-micron CMOS process, which enabled the photoelectric image sensor to break through the traditional limitations and obtain distance information in addition to intensity information, achieving full three-dimensional perception capabilities and greatly expanding its application range.

[0004] Furthermore, combining hyperspectral technology with SPAD detectors has become a research hotspot. This combination attempts to integrate the advantages of SPAD in single-photon detection and the expertise of hyperspectral imaging technology in spectral analysis to achieve integrated information acquisition of long-distance three-dimensional-spectral information of the target space, providing richer and more accurate data support for many fields such as environmental monitoring, biomedical imaging, military reconnaissance, etc.

[0005] However, there are still severe challenges in the field of long-distance spectral detection. Although detectors based on waveform detection, such as avalanche photodiodes (APDs) and photodiodes (PINs), can realize full-waveform hyperspectral lidar from a technical theoretical level, in practical applications, when in low-light or dark-light environments, the problem of low signal-to-noise ratio becomes prominent. In this case, the weak signal received by the detector will be seriously interfered by noise, making it difficult to obtain valuable data through effective processing of waveform information, which limits the development and practical application of long-distance spectral detection technology.

[0006] In summary, the current spectral detection technology has shortcomings when dealing with long-distance, weak-light or dark-light environments. An innovative technical solution is urgently needed to solve these problems in order to meet the growing demand for high-precision, long-distance spectral detection. Summary of the invention

[0007] The embodiment of the present invention provides a long-distance snapshot spectral imaging radar system and its application, which aims to solve the problem that the existing waveform detection-based detectors (such as APD, PIN) in the current technology have extremely low signal-to-noise ratio at long distances and in weak light or dark light environments, making it difficult to obtain useful data through waveform information processing, thereby limiting the development and application effect of long-distance spectral detection technology.

[0008] The core technology of this invention mainly utilizes SPAD detectors based on the principle of photon technology, combined with random masks, gratings and other components, through specific optical path design and mathematical algorithms, to achieve simultaneous detection of target spectrum and distance information at long distances or under weak light or dark light conditions.

[0009] In a first aspect, the present invention provides a long-range snapshot spectral imaging radar system, comprising:

[0010] A light source for emitting continuous light in a wide spectral range;

[0011] A projection objective lens is disposed between the light source and the target surface and is used to project the light emitted by the light source onto the target surface;

[0012] A photographic lens is used to receive photons reflected from the target surface and form an image at its focal plane;

[0013] A random mask, located at the image plane of the photographic lens and the front focal plane of the first relay lens, for intensity modulating the imaging light field of the focal plane of the photographic lens;

[0014] The first relay lens is used to image the front focal plane light field modulated by the random mask to the back focal plane;

[0015] A grating, located at the rear focal plane of the first relay lens and the front focal plane of the second relay lens, is used to split the light field so that lights of different wavelengths are translated along the y direction;

[0016] A second relay lens is used to image the light field of the front focal plane after grating splitting to the back focal plane of the second relay lens;

[0017] SPAD, located at the rear focal plane of the second relay lens, is used to receive and detect the optical signal after grating splitting and imaging by the second relay lens;

[0018] The control unit is used to control the emission time of the light source and cooperate with the SPAD to perform data acquisition and processing.

[0019] Furthermore, the light source includes one of a deuterium lamp, a tungsten lamp, a xenon lamp, a mercury lamp, a white light LED, and a supercontinuum laser.

[0020] Furthermore, SPAD is a two-dimensional focal plane detector.

[0021] Furthermore, SPAD obtains the three-dimensional distance information of the target in the following ways:

[0022] Perform k detections on each pixel, count the arrival time of each detection, and obtain a statistical histogram repeated k times;

[0023] The time corresponding to the highest peak of the statistical histogram is the actual arrival time of the target. By calculating the distance measured by each pixel, the three-dimensional distance information of the target is obtained.

[0024] Furthermore, the light field information returned from the target surface is represented as a three-dimensional distance spectrum matrix X:

[0025]

[0026] Among them, n x Represents the number of pixels along the x-axis, n y Represents the number of pixels along the y-axis, n λ represents the number of bands in the spectrum, Represents dimension;

[0027] The three-dimensional distance spectrum matrix X is modulated by the two-dimensional mask M of the random mask plate. The ranging spectrum matrix X' is:

[0028]

[0029] in, , represents a three-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension , the length of the third dimension is n λ ; represents pixel-by-pixel multiplication, express The bth wavelength band in the , representing from Select a certain band from the spectral bands for processing; M is a two-dimensional mask, which is a two-dimensional matrix in the real number domain, and , the length of the first dimension , the length of the second dimension .

[0030] Furthermore, after the modulation, the ranging spectrum matrix X' is dispersed by the grating, and the images of different frequency bands are displaced in the dispersion direction, and the distance spectrum matrix X'' after the dislocation is obtained as follows:

[0031]

[0032] in, Represents the plane coordinate system of SPAD, represents the bth wavelength band, represents the central reference wavelength, Represents the translation distance of the bth wavelength band matrix relative to the central reference wavelength.

[0033] Furthermore, the signal is measured in the wavelength dimension by SPAD. Integrate to get the compressed measurement matrix :

[0034]

[0035] in, , represents a two-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension ; , represents a two-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension , represents the observation noise.

[0036] Furthermore, the compressed observation matrix The spectral distance data is obtained by using the least square method or the pseudo-inverse solution of the matrix.

[0037] In a second aspect, the present invention provides an application of a long-range snapshot spectral imaging radar system, and the long-range snapshot spectral imaging radar system is applied in the field of environmental monitoring.

[0038] The main contributions and innovations of the present invention are as follows:

[0039] 1. Improved detector performance: In the prior art, detectors based on waveform detection, such as APD and PIN, have extremely low signal-to-noise ratios when the number of photons is small, making it difficult to obtain valid data. The present invention uses a SPAD detector based on the principle of photon technology, which has single-photon detection capabilities. This enables the system to obtain high-quality echo information under conditions such as long distances, weak light, and dark light. For example, in weak light detection scenarios at night or at long distances, traditional detectors cannot work properly, while the SPAD detector of the present invention can accurately capture single-photon signals and provide reliable data support for subsequent analysis.

[0040] 2. Expansion of detection dimensions: Some existing technologies use one-dimensional detectors and can only perform one-dimensional spectral analysis, and cannot obtain grayscale image information of the target space; some technologies can only obtain spectral information and 2D grayscale information of the target space, but cannot obtain distance information. The present invention uses an array of detectors to not only realize two-dimensional spectral perception of the target space, but also combine the distance detection principle to realize three-dimensional space perception. It can simultaneously obtain the spectrum, grayscale and distance information of the target, construct complete three-dimensional space spectral data, provide users with more comprehensive and accurate target information, and meet the needs of multiple fields for precise detection of targets in complex environments.

[0041] 3. Enhanced adaptability to complex environments: The present invention effectively solves the problem of spectral detection at long distances or under weak or dark light conditions. In actual application scenarios, such as long-distance environmental monitoring and nighttime military reconnaissance, traditional spectral detection technology is greatly affected by ambient light intensity and is difficult to function. With its unique detector and system design, the present invention is able to work stably in complex environments, greatly expanding the scope of application of spectral imaging radar systems and providing more powerful technical support for the development of related fields.

[0042] The details of one or more embodiments of the invention are set forth in the following drawings and description so that other features, objects, and advantages of the invention are more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0044] Figure 1 is a system block diagram of a long-range snapshot spectral imaging radar system according to an embodiment of the present invention;

[0045] Figure 2 is a schematic diagram of a SPAD distance detection principle according to an embodiment of the present invention;

[0046] Figure 3 is a schematic diagram of snapshot encoding according to an embodiment of the present invention.

[0047] In the figure, 1. projection objective lens; 2. light source; 3. control unit; 4. photographic lens; 5. random mask; 6. first relay lens; 7. grating; 8. second relay lens; 9. SPAD; 10. target surface. DETAILED DESCRIPTION

[0048] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with one or more embodiments of this specification. Instead, they are merely examples of devices and methods consistent with some aspects of one or more embodiments of this specification as detailed in the appended claims.

[0049] It should be noted that: in other embodiments, the steps of the corresponding method are not necessarily performed in the order shown and described in this specification. In some other embodiments, the steps included in the method may be more or less than those described in this specification. In addition, a single step described in this specification may be decomposed into multiple steps for description in other embodiments; and multiple steps described in this specification may be combined into a single step for description in other embodiments.

[0050] Embodiment 1

[0051] The present invention aims to propose a long-range snapshot spectral imaging radar system, which can, in particular, refer to Figure 1 , the system is specifically:

[0052] like Figure 1 As shown, the light source 2 can be a continuous light source in a wide spectral range, such as a deuterium lamp, a tungsten lamp, a xenon lamp, a mercury lamp, a white light LED, a supercontinuum laser, etc., which is projected onto a target surface 10 through a projection objective 1. The target reflects the incident photons, and the reflected photons are imaged on its focal plane through a photographic lens 4. A random mask 5 is located on the image plane of the photographic lens 4 and the front focal plane of a first relay lens 6. The photographic lens 4 continues to transmit the focal plane image backward after intensity modulation by the random mask 5. The first relay lens 6 images the light field of the front focal plane to the rear focal plane. A grating 7 is located on the rear focal plane of the first relay lens 6 and the front focal plane of a second relay lens 8. The grating 7 splits the light field, and each wavelength is translated along the y direction. The second relay lens 8 images the light field of the front focal plane to the rear focal plane. A single-photon detection device SPAD 9 is located on the rear focal plane of the second relay lens 8. The translation of each wavelength band caused by the grating 7 makes the final image on the SPAD The y direction of the plane 9 realizes a certain pixel translation, and the control unit 3 (such as a computer) is used to control the emission time of the light source 2 and cooperate with the SPAD 9 to perform data acquisition and processing.

[0053] In this embodiment, the specific implementation principle is as follows:

[0054] The pulse time of light source 2 is , SPAD 9 is a pixel The two-dimensional focal plane detector has the following principle for each pixel distance detection: Figure 2 As shown, k detections are performed and the arrival time of each detection is counted. , each pixel gets a statistical histogram repeated k times, and the highest peak of the histogram is the actual time of target arrival. , multiplied by the speed of light c, we get the distance measured by this pixel By performing such detection on each pixel, the three-dimensional distance information of the target is obtained.

[0055] like Figure 3 As shown, the n wavelengths in light source 2 ( ) overlap when returning from the target, each wavelength carries the same target distance information, and each wavelength is multiplied pixel by pixel with a fixed mask when passing through the random mask 5. At this time, all wavelengths have the same amplitude random code, and when the light field passes through the grating 7, the n wavelengths are split, and each wavelength is deflected at a certain angle. Due to the randomness of the random mask 5, when splitting occurs, the mask of each wavelength is shifted by a certain pixel due to the deflection, thereby changing the code corresponding to each wavelength, thereby realizing the encoding of different random masks for each wavelength.

[0056] The light field information returned from the target surface 10 is a three-dimensional range spectrum matrix. Indicates that ,express is a three-dimensional matrix in the real number field, with the length of the first dimension , the length of the second dimension , the length of the third dimension , is masked Modulation, where , mask is a two-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension .

[0057]

[0058] in, represents pixel-by-pixel multiplication, express The bth wavelength band in the , Represents selecting a band from the spectral bands for processing.

[0059] Then the modulated ranging spectrum matrix ,in , represents a three-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension , the length of the third dimension , through the dispersion effect of grating 7, the images of different frequency bands are in the dispersion direction (such as Figure 1 In the y direction shown, xyz satisfies the right-hand screw rule) and is misaligned. Assume is the reference wavelength, i.e. image No translation occurs, and the distance spectrum matrix after the grating 7 is displaced ,in , represents a three-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension , the length of the third dimension , which can be expressed as:

[0060]

[0061] in represents the sensor plane coordinate system, represents the bth wavelength band, represents the central (reference) wavelength, Represents the translation distance of the bth wavelength band matrix relative to the central wavelength.

[0062] Finally, the signal is detected in the wavelength dimension by the single-photon detection device SPAD 9. Integrate to get the compressed measurement matrix ,in , represents a two-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension :

[0063]

[0064] in, , represents a two-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension , represents the observation noise.

[0065] Preferably, in order to facilitate numerical calculation, a vectorized form of the model is further given, using Represents a matrix vectorization operation, that is, concatenating each column of the matrix into a vector. Here we define ,express A two-dimensional matrix belonging to the real number field, with the first dimension length , the length of the second dimension ,and:

[0066]

[0067] in is a one-dimensional vector in the real number field, with dimension ,for ,have , is a one-dimensional vector in the real number field, with dimension .

[0068] The sensing matrix H of SPAD 9 can be defined as:

[0069]

[0070] in is a two-dimensional matrix in the real number field, consisting of multiple submatrices D b It is a matrix that expresses the optical process of the system and the response characteristics of the detector in the form of a matrix. It is the key matrix that connects the observation vector and the spectral distance data vector x to be solved. It plays an important role in the subsequent least squares method or matrix pseudo-inverse solution. The length of the first dimension of the matrix H is , the length of the second dimension Among them, the submatrix D b :

[0071]

[0072] in, , is a A diagonal matrix with diagonal elements, is a two-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension , is a one-dimensional vector in the real number field, with dimension , It is expressed as:

[0073]

[0074] It is expressed as:

[0075]

[0076] and is a zero matrix, when b=1, and ,Right now is a 0-dimensional matrix, is a two-dimensional matrix with the first dimension length , the length of the second dimension , when b=2, and ,Right now is a two-dimensional matrix with the first dimension length , the length of the second dimension , is a two-dimensional matrix with the first dimension length , the length of the second dimension , and so on.

[0077] The compressed observation of the three-dimensional range spectrum matrix can be written in vectorized form:

[0078]

[0079] This form is a typical linear system and can be solved by the least squares method. , or use the pseudo-inverse of the matrix to solve , That is, the spectral distance data obtained by solving the problem is used to realize the simultaneous detection of the target spectrum and distance information.

[0080] in, It is the transposed matrix of matrix H. The transposed matrix is ​​needed in the process of solving the pseudo-inverse matrix. is a matrix The inverse matrix of is used to solve the pseudo-inverse matrix , by performing a series of linear algebra operations on the matrix H, the best estimate of the original data is obtained.

[0081] Embodiment 2

[0082] Based on the same concept, the present invention also proposes an application of a long-distance snapshot spectral imaging radar system.

[0083] The long-distance snapshot spectral imaging radar system of the present invention has broad application prospects in many fields due to its unique advantages, such as:

[0084] Military reconnaissance and security: In complex environments with long distances, weak light or dark light, the system can use single-photon detection technology to accurately detect and identify targets. For example, at night or in bad weather conditions, it can quickly obtain spectral and distance information such as the location, shape and material of enemy targets, assist military decision-making, and improve battlefield situation awareness. In security monitoring, it can monitor suspicious targets at a distance in real time, determine target characteristics through spectral analysis, and achieve accurate positioning and tracking in combination with distance information, thereby enhancing the reliability and effectiveness of security monitoring.

[0085] Environmental monitoring: It can measure the spectrum and distance of the atmosphere, water bodies and vegetation at long distances. By analyzing the spectral characteristics of different components in the atmosphere and combining distance information to determine the distribution range and concentration gradient of pollutants, real-time monitoring and early warning of air pollution can be achieved. For water bodies, it can detect the depth, turbidity, and types and contents of pollutants in the water. For vegetation, it can obtain information such as its health status and growth trend, providing data support for ecological environment assessment and resource management.

[0086] Autonomous driving and intelligent transportation: In the autonomous driving scenario, the system can obtain the distance and spectral information of the target in front of the vehicle in real time. It can not only accurately identify the position, shape and distance of obstacles, but also determine the material of obstacles through spectral analysis, such as distinguishing metal, plastic, plants, etc., to assist the autonomous driving system to make more accurate decisions and improve driving safety. In terms of intelligent traffic management, it can be used to monitor traffic flow, vehicle speed, vehicle distance and other information, optimize traffic signal control, and improve traffic efficiency.

[0087] Astronomical observation: Astronomical observation often faces challenges in long distances and weak light conditions, and the system's single-photon detection and spectral imaging capabilities can play an important role. It can detect the faint light of distant celestial bodies, obtain their spectral information, analyze the chemical composition, temperature, motion state and other characteristics of celestial bodies, and combine distance measurement to provide richer data for astronomical research, help explore the mysteries of the universe, and promote the development of astronomy.

[0088] Those skilled in the art should understand that the technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0089] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A long-range snapshot spectral imaging radar system, characterized in that: include: A light source (2) for emitting continuous light in a wide spectral range; A projection objective lens (1) is disposed between the light source (2) and the target surface (10) and is used to project light emitted by the light source (2) onto the target surface (10); A photographic lens (4) for receiving photons reflected from a target surface (10) and forming an image on its focal plane; A random mask (5) is located at the image plane of the photographic lens (4) and the front focal plane of the first relay lens (6), and is used to modulate the intensity of the imaging light field on the focal plane of the photographic lens (4); A first relay lens (6) is used to image the front focal plane light field modulated by the random mask (5) onto the rear focal plane; The grating (7) is located at the rear focal plane of the first relay lens (6) and the front focal plane of the second relay lens (8), and is used to split the light field so that light of different wavelengths is translated along the y direction; A second relay lens (8) is used to image the light field on the front focal plane after being split by the grating (7) onto the rear focal plane of the second relay lens (8); The SPAD (9) is located at the rear focal plane of the second relay lens (8) and is used to receive and detect the optical signal after being split by the grating (7) and imaged by the second relay lens (8); A control unit (3) is used to control the emission time of the light source (2) and to cooperate with the SPAD (9) to perform data collection and processing.

2. A long-distance snapshot spectral imaging radar system as claimed in claim 1, characterized in that: The light source (2) comprises one of a deuterium lamp, a tungsten lamp, a xenon lamp, a mercury lamp, a white light LED, and a supercontinuum laser.

3. The long-distance snapshot spectral imaging radar system according to claim 1, characterized in that: The SPAD (9) is a two-dimensional focal plane detector.

4. A long-distance snapshot spectral imaging radar system as claimed in claim 3, characterized in that: The SPAD (9) obtains the three-dimensional distance information of the target by: Perform k detections on each pixel, count the arrival time of each detection, and obtain a statistical histogram repeated k times; The time corresponding to the highest peak of the statistical histogram is the actual arrival time of the target. By calculating the distance measured by each pixel, the three-dimensional distance information of the target is obtained.

5. The long-distance snapshot spectral imaging radar system according to claim 1, characterized in that: The light field information returned from the target surface (10) is represented as a three-dimensional range-spectrum matrix X: Among them, n x Represents the number of pixels along the x-axis, n y Represents the number of pixels along the y-axis, n λ represents the number of bands in the spectrum, Represents dimension; The three-dimensional distance spectrum matrix X is modulated by the two-dimensional mask M of the random mask (5) to obtain the ranging spectrum matrix X': in, , represents a three-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension , the length of the third dimension is n λ ; represents pixel-by-pixel multiplication, express The bth wavelength band in the , representing from Select a certain band from the spectral bands for processing; M is a two-dimensional mask, which is a two-dimensional matrix in the real number domain, and , the length of the first dimension , the length of the second dimension .

6. The long-distance snapshot spectral imaging radar system according to claim 5, characterized in that: After the modulation, the distance spectrum matrix X' is dispersed by the grating (7), and the images of different frequency bands are displaced in the dispersion direction. The distance spectrum matrix X'' after the dislocation is obtained as follows: in, represents the plane coordinate system of SPAD (9), represents the bth wavelength band, represents the central reference wavelength, Represents the translation distance of the bth wavelength band matrix relative to the central reference wavelength.

7. The long-distance snapshot spectral imaging radar system according to claim 6, characterized in that: The signal is measured in the wavelength dimension by SPAD (9) Integrate to get the compressed measurement matrix : in, , represents a two-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension ; , represents a two-dimensional matrix in the real number field, with the first dimension length , the length of the second dimension , represents the observation noise.

8. The long-distance snapshot spectral imaging radar system according to claim 7, characterized in that: Compress the observation matrix The spectral distance data is obtained by using the least square method or the pseudo-inverse solution of the matrix.

9. The application of a long-distance snapshot spectral imaging radar system according to any one of claims 1 to 8, characterized in that: Long-range snapshot spectral imaging radar system is used in the field of astronomical observation.

10. The application of a long-distance snapshot spectral imaging radar system according to any one of claims 1 to 8, characterized in that: Long-range snapshot spectral imaging radar system is used in the field of environmental monitoring.

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