Area array Gm-APD detection laser radar distance drift error correction method and system

Abstract

The invention discloses an area array Gm-APD detection laser radar distance drift error correction method and system, and belongs to the field of data processing. The method comprises the steps of building a single-photon laser ranging system, adjusting the width of a laser pulse, detecting a target distance by using an area array Gm-APD detection laser radar, carrying out repeated measurement on a certain plane for multiple times, obtaining arrival time distribution of a target single-photon event, carrying out weighted average after carrying out filtering and denoising on ranging signals, and obtaining a signal region ranging value. And estimating the average detection photon number of the received monopulse by using the statistical detection probability, and correcting the drift error. According to the method, the drift error caused by echo signal photon accumulation in the area array Gm-APD detection laser radar can be corrected, and the ranging error of the area array Gm-APD detection laser radar is reduced.

Description

Technical Field

[0001] The invention belongs to the field of data processing, and in particular relates to a method and system for correcting distance drift errors of a planar array Gm-APD detection laser radar. Background Art

[0002] The area array Gm-APD detection lidar has high detection sensitivity and high resolution, and can achieve high-precision distance accuracy under weak echo conditions. It is often used for high-precision three-dimensional imaging and plays an important role in terrain surveying and mapping, atmospheric environment monitoring, atmospheric science research, and forestry protection. The area array Gm-APD detection lidar system integrates a laser scanning output unit with a single-photon echo signal acquisition unit, a synchronous timing module, and an information system, and cooperates with the flight platform to acquire ground three-dimensional spatial information and achieve high-precision three-dimensional measurement of ground targets.

[0003] In the area array Gm-APD detection laser radar, photoelectric conversion is achieved through Geiger mode avalanche diodes. When the reverse bias voltage is higher than its avalanche breakdown voltage, the absorption of a single photon can trigger an avalanche multiplication effect, and the output current quickly reaches saturation. Therefore, the area array Gm-APD detection laser radar system has extremely high detection sensitivity and high distance resolution; combined with the timing module, it can achieve wide dynamic range, fast response, and long-distance detection.

[0004] In the ranging image, the horizontal axis and vertical axis are pixel position coordinates, and the value on the coordinate is the photon flight time, that is, the target ranging distance value; in multiple repeated measurements of a single target, the target single photon event arrival time distribution image has the photon arrival time on the horizontal axis and the photon count on the vertical axis. The time distribution image is related to the detection density function of the detector, and the time measurement accuracy of the laser echo signal directly determines the laser ranging accuracy. In order to achieve high-precision distance measurement, the ranging image and the time distribution image need to be processed to extract the coordinates of the center of mass of the echo signal flight time, and then obtain the spatial distance information of the target to be measured. However, since the echo signal pulse width has a certain width and the effective detection time range is large, as the number of echo signal photons increases, the ranging error also increases. Summary of the invention

[0005] The purpose of the present invention is to compensate for the drift error by obtaining the target detection probability, improve the measurement accuracy of the area array Gm-APD detection laser radar, and provide a method and system for correcting the distance drift error of the area array Gm-APD detection laser radar.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A method for compensating and correcting distance drift error of a planar array Gm-APD detection laser radar comprises:

[0008] To obtain the photon flight time, the laser emits a laser pulse, and the driving module generates a synchronization signal to provide a start signal for the timing module. The single-photon detector receives the echo signal after interacting with the target object. The single-photon event generated by the detector provides a stop signal for the timing module. After obtaining the start and stop signals, the timing module can obtain the single-photon flight time.

[0009] Acquisition of target single photon event arrival time distribution: Repeated measurement of a single planar target to obtain target single photon event arrival time distribution information;

[0010] Laser pulse ranging image denoising: by filtering and denoising the distance information image, the thermal noise and background light noise introduced in the distance information acquisition process are removed;

[0011] Laser pulse ranging image threshold segmentation: segment the filtered ranging information image by setting the trigger number threshold, obtain the laser pulse signal ranging area in the range image, and obtain the ranging rough value by the centroid method;

[0012] Acquisition of ranging error model: Based on the arrival time distribution information of single photon events, the effective detection time range of target events is defined to obtain the ranging error model;

[0013] Estimate the average number of detected photons. For a single-photon ranging system, repeated measurements of the same target can be used to obtain the statistical detection probability of the target and estimate the number of received single-pulse signal photons.

[0014] To correct the ranging error, substitute the number of photons of the single pulse signal into the ranging error model to obtain the ranging error correction value. The uncorrected ranging rough value plus the correction value is the corrected ranging value.

[0015] A range drift error correction system for a planar array Gm-APD detection laser radar, the system comprising a laser pulse control unit and a laser pulse ranging time distribution image centroid extraction unit;

[0016] The laser pulse control unit adjusts the spatial position and trigger time of the sub-nanosecond laser output pulse through a high-precision three-dimensional translation stage and a delay control unit, emits laser pulses to reach the detection target surface, and the host computer controls the operating voltage and operating temperature of the area array GM-APD;

[0017] The laser pulse ranging time distribution image centroid extraction unit converts the detected echo laser pulse signal into an arrival time distribution image after photoelectric conversion through the area array GM-APD, obtains the signal photon echo area in the time distribution image by filtering and reducing noise and performing threshold segmentation on the laser pulse ranging time distribution image, extracts the centroid coordinates of the signal photon echo area in the time distribution image, obtains the echo signal area centroid coordinate matrix as the ranging coarse value, and performs ranging correction.

[0018] The present invention controls the output pulse width of the laser, establishes an echo detectable probability model for single-photon ranging, obtains the arrival time distribution of the target single-photon event by repeatedly measuring a single target object, obtains the rough value of the detection distance by the centroid method after preliminary denoising, defines the effective detection time range of the target event, obtains the ranging error model, and estimates the number of received single-pulse signal photons based on the statistical detection probability of the target, obtains the error correction value, realizes drift error correction, and improves the measurement performance of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0020] Figure 1 A schematic diagram of a drift error correction process of a planar array Gm-APD detection laser radar according to an embodiment of the present invention;

[0021] Figure 2 It is a schematic diagram of the detection device of the area array Gm-APD detection laser radar;

[0022] Figure 3 The time-of-flight image imaging of the area array GM-APD laser radar according to an embodiment of the present invention;

[0023] Figure 4 The photon flight time distribution image detected by the area array GM-APD laser radar according to an embodiment of the present invention; DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The present invention provides a method for correcting drift errors of a planar array Gm-APD detection laser radar. The execution subject of the method for correcting drift errors of a planar array Gm-APD detection laser radar includes but is not limited to at least one of the electronic devices such as a server and a terminal that can be configured to execute the method provided in the embodiment of the present application. In other words, the image coordinate correction method of a streak tube imaging laser radar can be executed by software or hardware installed in a terminal device or a server device, and the server includes but is not limited to: a single server, a server cluster, a cloud server or a cloud server cluster, etc.

[0026] See also Figure 1 , is a schematic flow chart of a method for correcting drift errors of a surface array Gm-APD detection laser radar according to an embodiment of the present invention. In this embodiment, the method for correcting drift errors of a surface array Gm-APD detection laser radar includes:

[0027] S1. Obtain the photon flight time by building a single photon detection device

[0028] In the embodiment of the present invention, the photon flight time is the time from when the timing module receives the synchronous drive signal to generate the start signal, until the single photon event generated by the detector provides the stop signal to the timing module, and the intermediate time is the photon flight time. A single measurement of the detector can obtain a single frame of flight time image information, the horizontal axis and the vertical axis are the coordinates of a single pixel of the detector, and the color represents the photon flight time measured by the pixel at this position; repeated measurements are performed to obtain the laser pulse ranging time distribution image, the horizontal axis is the photon flight time, and the vertical axis is the photon count.

[0029] Specifically, the laser emits a laser pulse signal to the Geiger avalanche diode to detect the echo signal. Please refer to the calculation process of the photon flight time. Figure 2 , the photoelectric signal conversion process includes:

[0030] C1. The laser outputs a laser pulse signal to detect the surface of the target object, and synchronously triggers the timing module to start timing;

[0031] C2. The input laser pulse signal is focused by the optical lens, and the input laser light signal is converged to the area array GM-APD detector through the optical lens group;

[0032] C3. The single photon incident echo signal reaches the detector, triggering the avalanche effect, generating a current pulse, and converting the optical signal into an electrical signal;

[0033] C4. After the avalanche effect is triggered, the counting module stops timing, and the corresponding single-photon event flight time is obtained through the timing module;

[0034] C5. Collect statistics on photon flight time distribution and calculate the error model.

[0035] For more information, please refer to the GM-APD time-of-flight imaging Figure 3 , the time-of-flight image information includes:

[0036] Z1. Laser pulse echo signal area. The laser pulse echo signal spot area is the laser echo signal reflected from the target surface detected by the detector. Different colors represent different flight times detected by the detector. The shape of the laser pulse echo signal spot area is related to the input laser pulse beam quality and the detection performance of the array GM-APD. The actual collected echo spot shape is circular.

[0037] Z2. Background pixel area, the background pixel area is the non-laser pulse echo signal pixel area detected by the detector. Due to the influence of the collected environmental noise light signal and the detector dark count noise, there may be noise pixels in the background pixel area. The signal-to-noise ratio of the fringe image can be improved by adjusting the laser pulse and the array GM-APD parameters.

[0038] For more details, please refer to the GM-APD time-of-flight distribution image. Figure 4 , the flight time distribution image information includes:

[0039] K1. The laser pulse echo signal area is Gaussian distributed in the time domain, corresponding to Figure 3 Middle Z1.

[0040] K2. Background pixel area, evenly distributed in the entire time domain, corresponding to Figure 3 Middle Z2.

[0041] S2. Filter the collected fringe image through 3*3 Gaussian filtering

[0042] In the embodiment of the present invention, there is noise interference in the acquired time-of-flight image, and convolution filtering is performed on each pixel of the time-of-flight image using the Gaussian filtering formula to eliminate image noise introduced during the acquisition process;

[0043] In detail, the 3*3 Gaussian filter performs a convolution operation on the detected original image using the following preset matrix formula:

[0044]

[0045] G=I*T Gaussian

[0046] Where I is the original laser pulse echo time image collected by the GM-APD array, T Gaussian is a 3*3 Gaussian filter matrix, and G is the output image after filtering.

[0047] For more details, please refer to the time distribution image of GM-APD laser pulse ranging. Figure 4 The flight time distribution information includes: the horizontal axis is the echo signal flight time, and the vertical axis is the photon count.

[0048] S3. Perform echo signal threshold segmentation on the filtered laser pulse flight time image by threshold segmentation

[0049] In the embodiment of the present invention, the laser pulse signal echo area and the background noise area detected by the area array GM-APD in the laser pulse ranging time distribution image have different distributions on the time axis; the laser pulse signal is Gaussian distributed on the entire time axis, and the noise is uniformly distributed on the entire time axis; by setting a photon counting threshold, the pixel points in the filtered image that are greater than the photon counting threshold are retained as the echo signal area; the pixel points in the filtered image that are less than the counting threshold are taken as background pixels, and the flight time value of the background area pixel is set to 0;

[0050] S4. Extracting the centroid coordinates of the echo signal area in the laser pulse ranging time distribution image by weighted summation of flight time

[0051] In an embodiment of the present invention, the centroid of the echo signal area in the laser pulse ranging time distribution image represents the physical distance information and surface reflection information of the target detected by the laser pulse signal, and the calculation includes:

[0052] The following preset centroid formula is used to calculate the centroid of the echo signal area in the preprocessed laser pulse ranging time distribution image:

[0053]

[0054] Among them, t~ is the coordinate of the centroid feature point of the signal photon echo area flight time, t is the horizontal axis coordinate of the laser pulse ranging time distribution image flight time, N is the vertical axis coordinate of the laser pulse ranging time distribution image photon count, Ω is the signal photon echo area after preprocessing, and the centroid method is used to obtain As a coarse distance measurement value.

[0055] S5. Establish a ranging error model based on the estimated number of echo photons

[0056] In the embodiment of the present invention, the spatial angular distribution and delay information of each pulse in the input laser pulse matrix are known, the centroid of each echo signal area is extracted, and the number of echo photons is estimated by the detector detection probability distribution function, and a ranging error model is established according to the number of echo photons to obtain a ranging correction value, including:

[0057] The following pulse waveform echo function is used to describe N s The photon flight time distribution of each echo photon is:

[0058]

[0059] Among them, N s is the number of echo photons, C is a constant, is the coarse value of ranging, σ is the laser pulse width;

[0060] The following formula is used to describe N s The timing error corresponding to the echo photon is:

[0061]

[0062] Among them, t1, They correspond to the echo photon number of 1 and N respectively. s The measured value of the pulse arrival time at ;

[0063] The corrected flight time error is described by the following formula:

[0064]

[0065] in, is the coarse value of ranging.

[0066] In this embodiment, the echo photons reflected from the target surface are collected by the area array GM-APD, and the photon flight time is calculated by the counting module to measure the distance of the target object. The laser echo photon time distribution is preprocessed by Gaussian filtering and threshold segmentation to obtain the spot area in the distribution image of the echo photon time, and the background noise and dark count noise are removed. The center of mass position is obtained by weighted summation of the signal echo photon area, and the center of mass position is used as the coarse value detection time of the ranging. The ranging error detection model is constructed by estimating the number of echo photons according to the detector detection probability function. The correction matrix is ​​used for the coordinate correction of the collected stripe image to ensure the accuracy of the stripe image coordinates. Therefore, the area array GM-APD detection distance correction method proposed in the present invention can correct the distance drift error caused by the photon accumulation effect.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for correcting the range drift error of a surface array Gm-APD detection laser radar, characterized in that: The method comprises: Step 1: Photon flight time acquisition. The laser pulse is output by the laser. When the laser pulse is emitted, the driving module generates a synchronization signal to generate a start signal for the timing module. The timing module starts timing. The single-photon detector receives the echo signal after interacting with the target object. The single-photon time generated by the detector provides a stop signal for the timing module. The flight time of the corresponding single-photon event is obtained through the timing module. Step 2: Obtain the arrival time distribution of the target photon event. By repeatedly measuring the fixed plane target and continuously collecting the flight time, the time distribution of the flight time of different photons on the time axis can be obtained. The horizontal axis is the photon flight time and the vertical axis is the photon count. Step 3: Processing of laser pulse ranging time distribution image. After filtering and noise reduction and threshold segmentation preprocessing for the thermal noise and background light noise introduced during laser ranging, the flight time is extracted as the ranging rough value through the centroid method, the effective detection time range of the target event is defined, and the ranging error model is obtained. Step 4: Estimate the average number of detected photons, correct the ranging error, repeat the measurement multiple times to obtain the statistical detection probability of the target, estimate the number of received single pulse signal photons, substitute it into the ranging error model, and obtain the ranging error correction value. The ranging rough value plus the error correction value is the corrected ranging value.

2. The method for correcting the range drift error of a planar array Gm-APD detection laser radar according to claim 1, characterized in that: In step three, the laser pulse ranging time distribution image processing includes: Step 31: Process the laser pulse ranging time distribution image, use median filtering to filter the ranging image, filter out thermal noise and background noise, and reduce the interference of noise on the extraction of ranging coarse value; Step 32: Threshold segmentation of laser pulse ranging time distribution image, threshold segmentation is performed by setting the photon count threshold, dark counts and photon counts are distinguished, and the signal photon echo area in the time distribution image is extracted to perform flight time centroid extraction; Step 3: Define the effective detection time range and use the centroid method to extract the flight time centroid as the rough value T of the ranging struggle , define the effective detection time range as [T struggle -2s,T struggle +2s], estimate the average number of detected photons received in a single pulse, and establish a ranging error model.

3. The method for correcting the range drift error of a planar array Gm-APD detection laser radar according to claim 2, characterized in that: Centroid extraction is performed on the laser pulse ranging time distribution image, including: The following preset centroid formula is used to calculate the centroid coordinates of the echo signal area in the preprocessed fringe image: in, is the coordinate of the centroid feature point of the signal photon echo area flight time, t is the flight time on the horizontal axis of the laser pulse ranging time distribution image, N is the photon count on the vertical axis of the laser pulse ranging time distribution image, Ω is the signal photon echo area after preprocessing, and x~ obtained by the centroid method is used as the rough value of ranging.

4. The method for correcting the range drift error of a planar array Gm-APD detection laser radar according to claim 1, characterized in that: In step 4, an error correction model is constructed based on the detection density function of the area array Gm-APD detector and the average number of received single pulse detection photons estimated based on the statistical detection probability, including: The following preset matrix formula is used to describe the centroid matrix of the preprocessed laser pulse ranging time distribution image: Among them, N s is the average number of single pulse detection photons received, C is the centroid matrix of the time distribution image, is the centroid time of the first pixel position, is the centroid time of the nth pixel position; The error correction model is constructed using the single-photon detection probability model and the estimated average number of detected photons per pulse. Among them, N s is the average number of detected photons received in a single pulse, σ is the pulse width of the emitted laser, and t s is the corrected ranging flight time, t1 is the flight time measured at one photon, N s The flight time detected when the echo photon N s The timing error corresponding to the echo photon is To detect N s f1 is the pulse waveform echo function when a photon is detected, and f2 is the pulse waveform echo function when 1 photon is detected, which can correct the ranging error caused by photon accumulation.

5. A range drift error correction system for a surface array Gm-APD detection laser radar, characterized in that: The system includes a laser pulse control unit and a laser pulse ranging time distribution image centroid extraction unit; The laser pulse control unit adjusts the spatial position and trigger time of the sub-nanosecond laser output pulse through a high-precision three-dimensional translation stage and a delay control unit, emits laser pulses to reach the detection target surface, and the host computer controls the operating voltage and operating temperature of the area array GM-APD; The laser pulse ranging time distribution image centroid extraction unit converts the detected echo laser pulse signal into an arrival time distribution image after photoelectric conversion through the area array GM-APD, obtains the signal photon echo area in the time distribution image by filtering and reducing noise and performing threshold segmentation on the laser pulse ranging time distribution image, extracts the centroid coordinates of the signal photon echo area in the time distribution image, obtains the echo signal area centroid coordinate matrix as the ranging coarse value, and performs ranging correction.

6. The range drift error correction system of the area array Gm-APD detection laser radar according to claim 5 is characterized in that: The laser pulse control unit is used to control and adjust the input laser pulse energy, spatial angular position and delay information, including: The sub-nanosecond laser outputs ns-level pulse width laser pulses, the pulse frequency matches the acquisition frequency of the area array GM-APD, and the pulse energy is adjusted according to the distribution of photon events; The high-precision three-dimensional translation stage is a sub-nanosecond laser working platform. The spatial angle adjustment of the output laser pulse is achieved by adjusting the position of the translation stage. The delay control unit provides trigger signals for the laser light source and the various components of the area array GM-APD acquisition system, and the output laser pulse is set by adjusting the delay of the laser trigger signal; The host computer control module sets the optimal operating voltage and operating temperature of the area array GM-APD acquisition system to enable it to work under optimal conditions.

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