A method and apparatus for laser radar detection imaging

Abstract

This invention relates to a lidar detection and imaging method and apparatus. The method includes emitting a laser pulse, preprocessing the returned signal and calculating approximate distance and time, continuously measuring to narrow down the target's range, and then iterating until the time interval between two measurements is approximately the same, at which point time-gated locking is achieved, and target detection begins. Compared with existing technologies, this invention has the advantages of providing high-quality time gating in a very short time, thereby increasing the accuracy of radar detection.

Description

Technical Field

[0001] This invention relates to the field of lidar, and in particular to a lidar detection and imaging method and apparatus. Background Technology

[0002] LiDAR (Light Detection and Ranging) is a device used for target distance detection. When a laser emits a laser pulse, it travels for a certain period before reaching the target. The laser pulse emitted by the target is then received by a detector. By recording the time interval between laser emission and reception, the distance to the target point can be directly detected. A three-dimensional image of the target can be obtained using a two-dimensional detector or a scanning one-dimensional detector. However, the detector is subject to ambient light interference during operation. After converting the background light or photons reflected from the target into electrical signals, noise from the detector itself is also added. Both background light and detector noise significantly degrade the quality of the LiDAR's three-dimensional imaging, severely limiting its application scenarios.

[0003] Selecting specific time gating can improve the effective detection time ratio of radar, thereby minimizing background noise interference, and is an effective method to improve the signal-to-noise ratio. Assume the time from photon emission to return is t. o , t o This reflects the distance from the target point to the lidar. Since the target is generally three-dimensional, the returned data usually consists of a group of points, i.e., a point cloud. The distance range of the target point cloud is assumed to be t. o to (t) o +Δt o ), where Δt o This reflects the target's depth in the distance dimension. The detection time of the lidar is t. d It needs to satisfy t d >(t o +Δt o ), during the entire detection time t d Within this timeframe, the effective detection window for the core target is Δt. o Aside from the target distance, the main interference received by lidar during the time frame is background light. This background light severely limits the signal-to-noise ratio (SNR) of the lidar, especially for Geiger avalanche photodetectors, where background interference can annihilate signal photons. If the detection time window of the lidar could be significantly compressed to t... w to t w +Δt w This makes the time-gated window of the detection (t) w ,t w +Δt w Slightly larger than the target return time window (t) o ,t o +Δt oIf this is the case, then background interference and detector noise will be reduced by Δt. w / t d .

[0004] There are two existing time gating schemes. One is to divide the entire detection time into N equal intervals, with each frame's detection time measured in t increments. d / N represents the step size, which changes the start time of the probe from 0 to t. d / N,2t d / N, sequentially step to i×t d / N, finally stepping to t d Each frame of acquired data undergoes image quality analysis. When the imaging quality is deemed to meet predetermined requirements, indicating that the detection start time is close to the target, the stepping of the start time is stopped. The drawback of this approach is that it requires an average of N / 2 frames to achieve time gating. Another approach is to start from t... d Using time / 2 as the starting time, determine whether the acquired data contains a target. If a target exists, adjust the gating start time to 3t. d / 4, If no target exists, then adjust the start time of the gating to t. d / 4, and then continue to refine the starting time of the gating until the image quality of the target meets the predetermined requirements. This scheme can complete the accurate locking of the gating in log2N times, but this scheme has a drawback: when the target is not detected, it may be because the target detection time window has been missed, or the target is still too far away. If the judgment is wrong, the target may not be detected at all. Summary of the Invention

[0005] The purpose of this invention is to provide a lidar detection and imaging method and apparatus.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A lidar detection and imaging method, comprising:

[0008] After emitting a laser pulse, the detector receives the light signal reflected by the laser pulse through the object under test and draws a point cloud of the object under test.

[0009] The time interval T is obtained by using a neural network model based on the point cloud of the object under test.

[0010] The laser pulse is emitted again, and the detector is controlled to receive the reflected light signal within the time interval obtained from the previous measurement, and a new point cloud is drawn. The time interval is then processed and calculated by the neural network model.

[0011] Compare the two most recent time intervals. If the difference is less than a set threshold, then determine the time gating based on the two time intervals.

[0012] Detection and imaging are performed based on the time gating.

[0013] The optical signal is processed by a preprocessing circuit, including digital-to-analog conversion, before entering the neural network model.

[0014] The neural network model maps the drawn point cloud onto a three-dimensional coordinate system.

[0015] The time interval is determined by the maximum and minimum values ​​of the coordinates representing the distance dimension in the three-dimensional coordinates of the object under test.

[0016] The time gating value is determined by the value of the last measured time interval.

[0017] A lidar detection and imaging device includes a laser, a detector, a control circuit, a neural network processor, a memory, and a program, wherein the processor executes the program to implement the above-described method.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention differs from traditional fixed-determination methods for time gating. In unknown scenarios, combined with actual detection conditions, it obtains more precise time gating through multiple "detection-identification-iteration" loops, thereby achieving high-quality time gating in a very short time, reducing the impact of noise during detection, and improving the accuracy of radar laser imaging and the efficiency of detection. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the device structure of the present invention;

[0021] Figure 2 This is a schematic diagram of three-dimensional image processing according to an embodiment of the present invention;

[0022] Where: A1 is a target 3D view without interference / noise, A2 is a target planar view without interference / noise, A3 is a target 3D view with interference / noise throughout the detection time, A4 is a target planar view with interference / noise throughout the detection time, and A5 is a target 3D view with interference / noise in the gated area. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0024] This embodiment proposes a lidar detection and imaging method and apparatus, referencing... Figure 1 and Figure 2 The lidar detection and imaging device includes 1-laser, 2-photodetector, 3-control circuit, 4-preprocessing circuit, and 5-neural network processor. After the laser emits a laser pulse, it is reflected by the target (rabbit). The optical detector array receives the light signal after the laser pulse is reflected within the full detection time T1. Since there is a significant difference between the light of the target object and the background light, the point cloud of the target object can be drawn after processing by the preprocessing circuit.

[0025] The neural network processor maps the stereo view of the object under test onto a three-dimensional coordinate system based on the point cloud obtained from the drawing. Figure 2 (A4), where the z-coordinate in the three-dimensional coordinate system reflects the straight-line distance between the object to be measured and the laser. Based on the maximum and minimum z-coordinate values ​​of the object to be measured, and then divided by the speed of light, the time interval T between the laser pulse emitted by the laser and the near and far ends of the object to be measured can be calculated.

[0026] Then, a laser pulse is emitted again. The control circuit controls the photodetector array to receive the reflected light signal within the time interval calculated in the previous measurement, and draws a new point cloud. The new three-dimensional coordinate target view is obtained after processing by the neural network processor, and the time interval T2 of this time is calculated.

[0027] Compare the time intervals of the two most recent measurements and determine whether the difference is less than a set threshold. In this embodiment, the threshold is set to 10% of the time interval. If the previous time interval is 10s-11s, then the time interval value of the next measurement that is less than the set threshold should be (9.9s-10.1s)-(10.9s-11.1s). If the difference is less than the set threshold, the time interval of the next measurement is set as the determined time gate.

[0028] Finally, based on the obtained time gating, object detection and imaging are performed within the time gating interval, and the results are visible. Figure 2 (A6)

Claims

1. A lidar detection and imaging method, characterized in that, include: After emitting a laser pulse, the detector receives the light signal reflected by the laser pulse through the object under test and draws a point cloud of the object under test. The time interval T is obtained by using a neural network model based on the point cloud of the object under test. The laser pulse is emitted again, and the detector is controlled to receive the reflected light signal within the time interval obtained from the previous measurement, and a new point cloud is drawn. The time interval is then processed and calculated by the neural network model. Compare the two most recent time intervals. If the difference is less than a set threshold, then determine the time gating based on the two time intervals. Detection and imaging are performed based on the time-gated control; The time interval is determined by the maximum and minimum values ​​of the coordinates representing the distance dimension in the three-dimensional coordinates of the object under test; The time gating value is determined by the value of the last measured time interval.

2. The lidar detection and imaging method according to claim 1, characterized in that, The optical signal is processed by digital-to-analog conversion through a preprocessing circuit before entering the neural network model.

3. The lidar detection and imaging method according to claim 1, characterized in that, The neural network model maps the drawn point cloud onto a three-dimensional coordinate system.

4. A lidar detection and imaging device, comprising a laser, a detector, a control circuit, a neural network processor, a memory, and a program, characterized in that, When the processor executes the program, it performs the following steps: After emitting a laser pulse, the detector receives the light signal reflected by the laser pulse through the object under test and draws a point cloud of the object under test. The time interval T is obtained by using a neural network model based on the point cloud of the object under test. The laser pulse is emitted again, and the detector is controlled to receive the reflected light signal within the time interval obtained from the previous measurement, and a new point cloud is drawn. The time interval is then processed and calculated by the neural network model. Compare the two most recent time intervals. If the difference is less than a set threshold, then determine the time gating based on the two time intervals. Detection and imaging are performed based on the time-gated control; The time interval is determined by the maximum and minimum values ​​of the coordinates representing the distance dimension in the three-dimensional coordinates of the object under test; The time gating value is determined by the value of the last measured time interval.

5. The lidar detection and imaging device according to claim 4, characterized in that, The optical signal is processed by digital-to-analog conversion through a preprocessing circuit before entering the neural network model.

6. The lidar detection and imaging device according to claim 4, characterized in that, The neural network model maps the drawn point cloud onto a three-dimensional coordinate system.

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