A multi-parameter monitoring atmospheric detection lidar and echo signal optimization method

Abstract

The present invention discloses a method for optimizing the echo signal of an atmospheric detection laser radar with multi-parameter monitoring. The method can optimize the divergence angle of the laser after passing through a laser beam expansion adjustment device by obtaining a photo of the end of the laser beam; use a photoelectric detector to monitor the laser energy passing through the reflector on a two-dimensional laser reflector; optimize the maximum detection altitude of the laser radar echo signal; determine the altitude position at which the laser beam completely enters the telescope field of view; and establish a prediction model for the maximum detection altitude. This prediction model can predict the maximum altitude detected by the laser radar in real time and make a decision on whether to optimize the echo signal. The present invention also discloses an atmospheric detection laser radar with multi-parameter monitoring. The present invention can greatly improve the quality and automation level of the laser radar echo signal reception.

Description

Technical Field

[0001] The present invention relates to the field of atmospheric detection, and in particular to an atmospheric detection laser radar for multi-parameter monitoring, and also to an echo signal optimization method of the atmospheric detection laser radar for multi-parameter monitoring, especially to high-precision detection of the laser radar echo signal. Background Art

[0002] LiDAR for detecting mid- and upper-level atmospheres actively detects atmospheric parameters such as temperature, density, and wind field by utilizing the interaction between lasers and the atmosphere. Its detection range can reach 110 kilometers or even over 200 kilometers. Because the intensity of background light noise is inversely proportional to the square of the receiving field of view, the field of view of the telescope receiver is typically controlled at around 0.5 mrad to effectively detect echo signals. To match the field of view of the laser emission with that of the telescope receiver and to improve the efficiency of echo signal acquisition, the far-field emission angle of the laser beam is generally smaller than the receiving field of view of the telescope, at approximately 0.2 mrad. Furthermore, to suppress photodetector saturation caused by strong echo signals generated in the low-altitude atmosphere, laser emission is typically conducted off-axis, and the distance between the laser transmitter and the telescope receiver is typically greater than 2 meters.

[0003] Due to the telescope's narrow field of view and the off-axis laser transmission method, lidar systems require extremely high stability in the field of view matching between laser emission and optical reception. During actual ground-based lidar detection, slight vibrations of the optical platform, foundation settlement, and deformation of the optical frame due to environmental influences can affect the field of view matching between laser emission and optical reception, thereby affecting the lidar's optical reception efficiency. This impact is particularly significant on vehicle-mounted radar platforms. Therefore, during lidar maintenance, to maximize the detection efficiency of echo signals and ensure that the lidar can continuously provide high-quality atmospheric detection data, professionals are often required to precisely adjust the laser energy, laser divergence angle, and the field of view matching between laser emission and telescope reception. This significantly restricts the operation and maintenance efficiency of mid- and high-level lidar equipment. Summary of the Invention

[0004] The purpose of the present invention is to address the above-mentioned problems existing in the prior art, provide an atmospheric detection lidar with multi-parameter monitoring, and also provide an echo signal optimization method of the atmospheric detection lidar with multi-parameter monitoring.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A multi-parameter monitoring atmospheric detection laser radar includes a laser. The laser generates a laser beam which is expanded by a laser beam expansion adjustment device and then emitted into the air through a reflector on a two-dimensional laser reflector. The laser light transmitted through the reflector on the two-dimensional laser reflector is detected by a photoelectric detector. The photoelectric detector is connected to a controller via a second data acquisition device. A first telescope receives an echo signal generated by the laser beam and transmits it to a signal detection device via an optical fiber. The signal detection device is connected to the controller via the first data acquisition device. An observation device consisting of a camera and a second telescope obtains an image of the end of the laser beam and transmits it to the controller. The controller is connected to a visibility meter.

[0007] A method for optimizing echo signals of an atmospheric detection lidar for multi-parameter monitoring comprises the following steps:

[0008] Step 1: Measure the visibility value through the visibility meter and feed it back to the controller in real time;

[0009] Step 2: The observation device consisting of a camera and a second telescope obtains an image of the end of the laser beam and transmits it to the controller to obtain the pixel length and average pixel width of the laser beam;

[0010] Step 3: Optimize the divergence angle of the laser after passing through the laser beam expansion adjustment device to obtain the position between the convex lens and the concave-convex mirror of the laser beam expansion adjustment device corresponding to the minimum average pixel width of the laser beam;

[0011] Step 4: Using a photoelectric detector to monitor the laser energy passing through the reflector on the two-dimensional laser reflector, the generated electrical signal is collected by a second data acquisition device and then transmitted to the controller;

[0012] Step 5: By adjusting the two-dimensional laser reflector, the actual field of view height at the highest detection height of the echo signal is consistent with the calculated field of view height h, thereby optimizing the laser radar echo signal;

[0013] Step 6: Establish a prediction model for the maximum detection height of echo signals under different visibility values ​​and different laser energies;

[0014] Step 7: Record the current visibility value and laser energy, and obtain the predicted maximum detection altitude based on the above prediction model, calculate the measured maximum detection altitude of the currently collected echo signal, and determine whether to repeat steps 3 and 5 based on the predicted maximum detection altitude and the measured maximum detection altitude.

[0015] In step 2 above, the horizontal distance between the observation device consisting of the camera and the second telescope and the laser beam reflected to the sky by the two-dimensional laser reflector is greater than 15 m.

[0016] The pixel length and average pixel width of the laser beam in step 2 above are obtained based on the following steps:

[0017] Step 2.1: Fine-tune the observation angle of the observation device consisting of the camera and the second telescope so that the end of the captured laser beam is at the center of the camera's phase plane, and obtain an image of the laser beam end;

[0018] Step 2.2: Convert the image at the end of the laser beam into a grayscale image;

[0019] Step 2.3: Denoise the grayscale image;

[0020] Step 2.4: Binarize the denoised grayscale image to obtain a binary image;

[0021] Step 2.5: Filter out the contour containing the maximum number of pixels;

[0022] Step 2.6: Calculate the pixel length and average pixel width of the contour with the maximum number of pixels.

[0023] Optimizing the divergence angle of the laser after passing through the laser beam expansion adjustment device in step 3 above includes the following steps:

[0024] Step 3.1: Define the minimum average pixel width of the laser beam as d, and define the adjustment distance between the convex lens and the concave lens in the laser beam expansion adjustment device as S;

[0025] Step 3.2: Calculate the average pixel width of the laser beam obtained, and record it as the average pixel width d i , and let the adjustment distance S = D / K, D is the adjustment value, K is the adjustment ratio;

[0026] Step 3.3: Shorten the distance between the convex lens and the concave lens in the laser beam expansion adjustment device by the adjustment distance S, and calculate the average pixel width of the obtained laser beam, which is recorded as the average pixel width d i+1 ;

[0027] Step 3.4: If d i ≥d i+1 , then let d i =d i+1 , and return to step 3.3;

[0028] If d i <d i+1 , then let d=d i , K = K + 1, S = D / K, go to step 3.5;

[0029] Step 3.5: Let d i =d i+1 , increase the distance between the convex lens and the concave lens in the laser beam expansion adjustment device by the adjustment distance S, calculate the average pixel width of the laser beam, and record it as d i+1 ;

[0030] Step 3.6: If S ≤ 10 μm, proceed to step 3.7;

[0031] If S>10μm, further judgment:

[0032] If d i ≥d i+1 , then let d i =d i+1 , and return to step 3.5;

[0033] If d i <d i+1 , then let d=d i , K=K+1, S=D / K, if S>10μm, return to step 3.3;

[0034] Step 3.7: Record the distance between the convex lens and the concave lens of the laser beam expansion adjustment device corresponding to the minimum average pixel width of the laser beam, and record the average pixel width and pixel length of the laser beam as W and L respectively.

[0035] The optimization of the laser radar echo signal in step 5 above includes the following steps:

[0036] Step 5.1: Look up the field of view angle parameter of the first telescope, recorded as θ1;

[0037] Step 5.2: Measure the divergence angle of the laser beam after passing through the laser beam expansion and adjustment device, recorded as θ2, and measure the distance between the first telescope and the two-dimensional laser reflector, recorded as D;

[0038] Step 5.3: The height at which the laser beam completely enters the field of view of the first telescope is defined as the calculated field of view height h.

[0039] Step 5.4: using a first data acquisition device to acquire the echo signal;

[0040] Step 5.5: Set the angles of each adjustment of the pitch axis and azimuth axis of the two-dimensional laser reflector, recorded as the pitch axis adjustment angle θ3 and the azimuth axis adjustment angle θ4, and the number of adjustments is recorded as n;

[0041] Step 5.6: Let θ3 = θ / k, k = n, θ is the preset value of the adjustment angle, k is the multiple parameter,

[0042] Step 5.7: Obtain the highest detection height H of the echo signal i ;

[0043] Step 5.8: Adjust the pitch axis angle clockwise by θ3;

[0044] Step 5.9: Obtain the highest detection height value H of the echo signal i+1 ;

[0045] Step 5.10: If H i+1 ≥H i , then return to step 5.8 and let H i =H i+1 ;

[0046] Step 5.11: If H i+1 <H i , then rotate the pitch axis counterclockwise by θ3, and increase the multiplier parameter k by 1, θ3 = θ / k. If θ3 > 0.1 mrad, return to step 5.9; if θ3 ≤ 0.1 mrad, proceed to step 5.12;

[0047] Step 5.12: Let the azimuth axis adjustment angle θ4 = θ / k, k = n, and let H i =H i+1 ;

[0048] Step 5.13: Adjust the azimuth axis angle clockwise by θ4;

[0049] Step 5.14: Obtain the highest detection height H of the echo signal i+1 ;

[0050] Step 5.15: If H i+1 ≥H i , then return to step 5.13 and let H i =H i+1 ;

[0051] Step 5.16: If H i+1 <H i , then rotate the azimuth axis counterclockwise by θ4, and increase the multiple parameter k by 1. If θ4>0.1mrad, return to step 5.14; if θ4≤0.1mrad, jump to step 5.17;

[0052] Step 5.17: If |H i+1 -H i |>0.05km, increase the adjustment times n by 1 and return to step 5.6; |H i+1 -H i |≤0.05km, skip to step 5.18;

[0053] Step 5.18: Calculate the actual field of view height h based on the echo signal i , according to the actual field of view height h i The difference between the detected height and the calculated field of view height h is used to fine-tune the pitch axis and rotation axis of the two-dimensional laser reflector so that the highest detection height according to the echo signal is consistent with the calculated field of view height h.

[0054] Step 5.18 as described above includes the following steps:

[0055] Step 5.18.1: Use function fitting on the echo signal collected by the first data acquisition device to obtain a functional relationship between the number of echo photons and the maximum detection altitude;

[0056] Step 5.18.2: Take the derivative of the function relationship of the number of echo photons with respect to the highest detection altitude. Find the position where the derivative of the function relationship passes through zero or the highest detection altitude corresponding to the position where the positive value is infinitely close to 0. Record it as the actual field of view height h. i ;

[0057] Step 5.18.3: Calculate Δh i =|h i -h|;

[0058] Step 5.18.4: If Δh i ≤2, the adjustment is completed; if Δh i >2, then fine-tune the pitch axis and rotation axis of the two-dimensional laser reflector to make the calculated Δh i ≤2.

[0059] Step 7 as described above includes the following steps:

[0060] Step 7.1: Record the current visibility value and laser energy;

[0061] Step 7.2: Substitute the current visibility value and laser energy into the prediction model established in step 6 to obtain the predicted maximum detection altitude H p ;

[0062] Step 7.3: Calculate the maximum detection height H of the currently collected echo signal r ;

[0063] Step 7.4 If |H p -H r |>2km, repeat steps 3 and 5 to optimize the divergence angle and echo signal, and return to step 7.1. If |H p -H r |≤2km, then return directly to step 7.1.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] The present invention can determine whether the laser radar echo signal needs to be optimized based on atmospheric visibility, laser energy, divergence angle, and the characteristics of the collected laser radar Rayleigh echo signal. It can also quickly adjust the detection altitude of the collected laser radar Rayleigh echo signal and the position at which the laser beam completely enters the telescope's field of view. In addition, for the metal layer echo signal strength, the present invention can also use the detected laser radar Rayleigh echo signal strength as a reference to achieve optimization of the metal layer echo signal strength. The present invention can greatly improve the automation level of laser radar echo signal optimization and greatly improve the operation and maintenance efficiency of the long-term detection of the laser radar platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 This is a structural diagram of the atmospheric detection laser radar of the present invention.

[0067] Among them, 1-data acquisition device; 2-signal detection device; 3-optical fiber; 4-first telescope; 5-two-dimensional laser reflection frame; 6-laser beam expansion adjustment device; 7-laser; 8-controller; 9-camera; 10-second telescope; 11-visibility meter; 12-photoelectric detector; 13-second data acquisition device. DETAILED DESCRIPTION

[0068] In order to facilitate those skilled in the art to understand and implement the present invention, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0069] Example 1:

[0070] The present invention proposes an atmospheric detection lidar for multi-parameter monitoring, such as Figure 1As shown, the system mainly includes a first data acquisition device 1, a signal detection device 2, an optical fiber 3, a first telescope 4, a two-dimensional laser reflector 5, a laser beam expansion and adjustment device 6, a laser 7, a controller 8, a camera 9, a second telescope 10, and a visibility meter 11. The laser 7 is used to generate a laser beam, which is then expanded by the laser beam expansion and adjustment device 6 and then emitted into the air through the reflector on the two-dimensional laser reflector 5. The laser light that partially transmits the reflector on the two-dimensional laser reflector 5 is detected by a photodetector 12. The photodetector 12 is connected to the controller 8 via the second data acquisition device 13 and transmits the collected relative energy value of the laser light to the controller. The first telescope 4 is used to receive the echo signal generated by the laser beam and transmit it to the signal detection device 2 via the optical fiber 3. The signal detection device 2 converts the optical signal into an electrical signal and collects it through the first data acquisition device 1. The first data acquisition device 1 transmits the collected echo signal to the controller 8. The photosensitive surface of the camera 9 is perpendicular to the central axis of the second telescope 10, and the extension line of the central axis of the second telescope 10 is basically parallel to the direction of the laser beam after being reflected by the two-dimensional laser reflection frame 5. The end picture of the laser beam taken by the camera 9 is transmitted to the controller 8. The controller 8 controls the laser beam expansion adjustment device 6 and the two-dimensional laser reflection frame 5 after analyzing and processing the data from the camera 9, the visibility meter 11 and the first data acquisition device 1.

[0071] Example 2:

[0072] A method for optimizing echo signals of an atmospheric detection laser radar for multi-parameter monitoring, using the atmospheric detection laser radar for multi-parameter monitoring described in Example 1, includes the following steps:

[0073] Step 1: The visibility value near the atmospheric detection laser radar is directly measured by the visibility meter 11, and the measured visibility value is fed back to the controller 8 in real time.

[0074] Step 2: Place the observation device consisting of the camera 9 and the second telescope 10 as far as possible from the horizontal distance of the laser beam reflected by the two-dimensional laser reflector 5 to the sky (the horizontal distance is greater than 15m), and take a picture of the end of the laser beam in the sky that can be observed. The obtained image of the end of the laser beam is transmitted to the controller 8. After analyzing and processing the image of the end of the laser beam, the controller 8 obtains the pixel length and average pixel width of the laser beam as a reference for the size of the laser beam divergence angle. The specific steps are as follows:

[0075] Step 2.1: Fine-tune the observation angle of the observation device composed of the camera 9 and the second telescope 10 so that the end of the captured laser beam is at the center of the phase plane of the camera 9, and fix the position of the observation device.

[0076] Step 2.2: The image of the end of the laser beam obtained by the camera 9 in step 2.1 is converted into a grayscale image.

[0077] Step 2.3: Use a 9×9 median filter to remove the salt and pepper noise in the grayscale image obtained in step 2.2.

[0078] Step 2.4: Calculate the maximum pixel value and the minimum pixel value of the grayscale image obtained in step 2.3, and binarize the grayscale image obtained in step 2.3 using the average value of the maximum pixel value and the minimum pixel value to obtain a binary image to highlight the bright spot area in the image.

[0079] Step 2.5: Find all contours of the binary image obtained in step 2.4 and select the contour containing the maximum number of pixels.

[0080] Step 2.6: Calculate the pixel length (expressed in number of pixels) and average pixel width of the contour obtained in step 2.5.

[0081] Step 3: Optimize the divergence angle of the laser after passing through the laser beam expander and adjuster 6. The main method is to gradually fine-tune the distance between the convex lens and the concave lens in the laser beam expander and adjuster 6, and record the average pixel width of the laser beam according to the method in step 2. Find the position between the convex lens and the concave lens of the laser beam expander and adjuster 6 corresponding to the minimum average pixel width of the recorded laser beam. The specific steps are as follows:

[0082] Step 3.1: Define the minimum average pixel width of the laser beam as d, and define the adjustment distance between the convex lens and the concave lens in the laser beam expansion adjustment device 6 as S.

[0083] Step 3.2: Calculate the average pixel width of the laser beam obtained using the method in step 2 and record it as the average pixel width d i , and set the adjustment distance S=D / K, the adjustment value D=1mm, and the adjustment ratio K=1.

[0084] Step 3.3: Shorten the distance between the convex lens and the concave lens in the laser beam expansion adjustment device 6 by the adjustment distance S, and calculate the average pixel width of the obtained laser beam using the method in step 2, and record it as the average pixel width d i+1 .

[0085] Step 3.4: If d i ≥d i+1 , then let d i =d i+1 , and return to step 3.3.

[0086] If d i <d i+1 , then let d=d i , K=K+1, S=D / K, go to step 3.5.

[0087] Step 3.5: Let d i =d i+1 , increase the distance between the convex lens and the concave lens in the laser beam expansion adjustment device 6 by the adjustment distance S, and use the method in step 2 to calculate the average pixel width of the laser beam obtained, and record it as d i+1 .

[0088] Step 3.6: If S ≤ 10 μm, proceed to step 3.7;

[0089] If S>10μm, further judgment:

[0090] If d i ≥d i+1 , then let d i =d i+1 , and return to step 3.5;

[0091] If d i <d i+1 , then let d=d i , K=K+1, S=D / K, if S>10μm, return to step 3.3.

[0092] Step 3.7: Record the distance between the convex lens and the concave lens of the laser beam expansion adjustment device 6 corresponding to the minimum average pixel width of the laser beam, and record the average pixel width and pixel length of the laser beam as W and L respectively.

[0093] Step 4: Monitor the energy of the laser beam. The main method is to use a photoelectric detector 12 to monitor the laser energy passing through the reflector on the two-dimensional laser reflector frame 5. The generated electrical signal is collected by the second data acquisition device 13, and the collected laser energy value is transmitted to the controller 8. The reading of the photoelectric detector after being collected by the second data acquisition device 13 becomes the collected energy value (not measured by a calibrated energy meter). The stronger the laser beam, the stronger the output signal of the photoelectric detector, and the larger the collected value output by the second data acquisition device 13.

[0094] Step 5: Based on step 4, the two-dimensional laser reflector 5 is adjusted to ensure that the actual field of view height at the highest detection height of the echo signal is consistent with the calculated field of view height h. The specific steps are as follows:

[0095] Step 5.1: Look up the field angle parameter of the first telescope 4, recorded as θ1.

[0096] Step 5.2: Measure the divergence angle of the laser beam after passing through the laser beam expansion and adjustment device 6, recorded as θ2, and measure the distance between the first telescope 4 and the two-dimensional laser reflection frame 5, recorded as D.

[0097] Step 5.3: The height at which the laser beam completely enters the field of view of the first telescope 4 is defined as the calculated field of view height h.

[0098] Step 5.4: Use the first data acquisition device 1 to acquire the echo signal.

[0099] Step 5.5: Set the angles of each adjustment of the pitch axis and the azimuth axis of the two-dimensional laser reflector 5, which are recorded as the pitch axis adjustment angle θ3 and the azimuth axis adjustment angle θ4, and the number of adjustments is recorded as n.

[0100] Step 5.6: Let θ3 = θ / k, k = n, θ is the preset value of the adjustment angle, and k is the multiple parameter.

[0101] Step 5.7: Using the signal above 200 km in the echo data as the background signal, obtain the highest detection altitude value with a signal-to-noise ratio greater than 3 in the echo signal collected by the first data acquisition device 1, and record it as the highest detection altitude H i .

[0102] Step 5.8: Adjust the pitch axis angle clockwise by θ3.

[0103] Step 5.9: Using the signal above 200 km in the echo data as the background signal, obtain the highest detection altitude value with a signal-to-noise ratio greater than 3 in the echo signal collected by the first data acquisition device 1, and record it as the highest detection altitude H i+1 .

[0104] Step 5.10: If H i+1 ≥H i , then return to step 5.8 and let H i =H i+1 .

[0105] Step 5.11: If H i+1 <H i , then rotate the pitch axis counterclockwise by θ3, and increase the multiplier parameter k by 1, θ3 = θ / k. If θ3 > 0.1 mrad, return to step 5.9; if θ3 ≤ 0.1 mrad, proceed to step 5.12.

[0106] Step 5.12: Let the azimuth axis adjustment angle θ4 = θ / k, k = n.

[0107] Step 5.13: Adjust the azimuth axis angle clockwise by θ4.

[0108] Step 5.14: Using the signal above 200 km in the echo data as the background signal, obtain the highest detection altitude value with a signal-to-noise ratio greater than 3 in the echo signal collected by the first data acquisition device 1, and record it as the highest detection altitude H i+1 ;

[0109] Step 5.15: If H i+1 ≥H i , then return to step 5.13 and let H i =H i+1 .

[0110] Step 5.16: If H i+1 <H i , then rotate the azimuth axis counterclockwise by θ4, and increase the multiple parameter k by 1. If θ4>0.1mrad, return to step 5.14; if θ4≤0.1mrad, jump to step 5.17.

[0111] Step 5.17: If |H i+1 -H i |>0.05km, increase the adjustment times n by 1 and return to step 5.6; |H i+1 -H i |≤0.05km, skip to step 5.18.

[0112] The highest detection altitude of the echo signal obtained by calculating in steps 5.1 to 5.17.

[0113] Step 5.18: Calculate the actual field of view height h based on the echo signal i , according to the actual field of view height h i The difference between the calculated field of view height h and the pitch axis and rotation axis of the two-dimensional laser reflector 5 are fine-tuned so that the highest detection height of the echo signal is consistent with the field of view height h calculated in step 5.3. Then, it is determined whether the height at which the laser beam completely enters the field of view of the first telescope 4 is consistent with the value calculated in step 3.3. The main steps are as follows:

[0114] Step 5.18.1: Use function fitting on the echo signal collected by the first data acquisition device 1 to obtain a functional relationship between the number of echo photons and the maximum detection height.

[0115] Step 5.18.2: Take the derivative of the function relationship of the echo photon number obtained in step 5.18.1 with respect to the highest detection altitude. Find the position where the derivative of the function relationship passes through zero or the position where the positive value is infinitely close to 0 corresponding to the highest detection altitude. Record this as the actual field of view height h. i .

[0116] Step 5.18.3: Calculate Δh i =|h i -h|, h is the calculated field of view height determined in step 5.3, in km,

[0117] Step 5.18.4: If Δh i ≤2, the adjustment is completed; if Δhi >2km, then fine-tune the pitch axis and rotation axis of the two-dimensional laser reflector 5 to make the calculated Δh i ≤2km,

[0118] Fine-tuning the pitch axis and rotation axis of the two-dimensional laser reflector 5 includes the following steps:

[0119] Step 5.18.4.1: Rotate the pitch axis by 0.01 mrad (generally speaking, the laser echo signal can be adjusted within a range of 2°). Since the divergence angle of the telescope is larger than the divergence angle of the laser beam, this is a fine adjustment. The laser beam should still be within the field of view of the telescope. Repeat steps 5.18.1, 5.18.2, and 5.18.3 to find Δh. i The minimum value of (at this time the laser beam completely enters the telescope field of view).

[0120] Step 5.18.4.2: Rotate the azimuth axis by 0.01 mrad (generally speaking, the laser echo signal can be adjusted within a range of 2°. Since the divergence angle of the telescope is larger than the divergence angle of the laser beam, this is a fine adjustment. The laser beam will still be within the field of view of the telescope.) Repeat steps 5.18.1, 5.18.2, and 5.18.3 to find Δh. i The minimum value of (at this time the laser beam completely enters the telescope field of view).

[0121] If Δh i ≤2, the adjustment is completed; if Δh i >2, return to step 5.18.4.1;

[0122] Step 6: Based on steps 1 to 5, the controller 8 accumulates and records the echo signals (LiDAR Rayleigh echo signals) and the highest detection altitude under different visibility values ​​and different laser energies (detected by the photoelectric detector 12), and establishes a prediction model for the highest detection altitude of the echo signals under different visibility values ​​and different laser energies. The main steps are as follows:

[0123] Step 6.1: Record the echo signal and the highest detection altitude under different visibility values ​​(≥10km) and laser energy.

[0124] Step 6.2 uses the support vector regression (SVR) prediction model to establish the relationship between the highest detection altitude of the echo signal, the visibility value, and the laser energy.

[0125] Step 7: Use the absolute value of the maximum detection height predicted by the prediction model established in step 6 and the absolute value of the actual maximum height value detected by the current echo signal to determine whether the lidar echo signal needs to be optimized. The main steps are as follows:

[0126] Step 7.1: Record the current visibility value (detected by the visibility meter 11) and the laser energy (detected by the photoelectric detector 12);

[0127] Step 7.2: Substitute the current visibility value and laser energy obtained in step 7.1 into the prediction model established in step 6 to predict the maximum detection height of the current echo signal and obtain the predicted maximum detection height, which is recorded as H. p .

[0128] Step 7.3: Repeat the method in step 5.7 to calculate the highest detected height of the echo signal currently collected, which is recorded as H. r .

[0129] Step 7.4 If |H p -H r |>2km, repeat steps 3 and 5 to optimize the divergence angle and echo signal, and return to step 7.1. If |H p -H r |≤2km, then return directly to step 7.1.

[0130] It should be noted that the embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A method for optimizing the echo signal of an atmospheric detection laser radar for multi-parameter monitoring, comprising a laser (7), wherein the laser (7) generates a laser beam which is expanded by a laser beam expansion adjustment device (6) and then emitted into the air through a reflector on a two-dimensional laser reflection frame (5), and the laser light transmitted through the reflector on the two-dimensional laser reflection frame (5) is detected by a photoelectric detector (12), the photoelectric detector (12) is connected to a controller (8) through a second data acquisition device (13), a first telescope (4) receives the echo signal generated by the laser beam and transmits it to a signal detection device (2) through an optical fiber (3), the signal detection device (2) is connected to a controller (8) through a first data acquisition device (1), an observation device composed of a camera (9) and a second telescope (10) obtains an image of the end of the laser beam and transmits it to the controller (8), and the controller (8) is connected to a visibility meter (11). It is characterized by: The above method comprises the following steps: Step 1: Measure the visibility value through the visibility meter (11) and feed it back to the controller (8) in real time; Step 2: The observation device composed of the camera (9) and the second telescope (10) obtains the image of the end of the laser beam and transmits it to the controller (8) to obtain the pixel length and average pixel width of the laser beam; Step 3: Optimizing the divergence angle of the laser after passing through the laser beam expansion adjustment device (6) to obtain the position between the convex lens and the concave-convex mirror of the laser beam expansion adjustment device (6) corresponding to the minimum average pixel width of the laser beam; Step 4: Using a photoelectric detector (12) to monitor the laser energy passing through the reflector on the two-dimensional laser reflector (5), the generated electrical signal is collected by a second data acquisition device (13) and then transmitted to the controller (8); Step 5: By adjusting the two-dimensional laser reflector (5), the actual field of view height under the highest detection height of the echo signal is made consistent with the calculated field of view height h, thereby optimizing the laser radar echo signal; Step 6: Establish a prediction model for the maximum detection height of echo signals under different visibility values ​​and different laser energies; Step 7: Record the current visibility value and laser energy, and obtain the predicted maximum detection altitude based on the above prediction model, calculate the measured maximum detection altitude of the currently collected echo signal, and determine whether to repeat steps 3 and 5 based on the predicted maximum detection altitude and the measured maximum detection altitude.

2. The method for optimizing the echo signal of the atmospheric detection lidar for multi-parameter monitoring according to claim 1, characterized in that: In step 2, the horizontal distance between the observation device composed of the camera (9) and the second telescope (10) and the laser beam reflected to the sky by the two-dimensional laser reflection frame (5) is greater than 15m.

3. The method for optimizing echo signals of an atmospheric detection lidar for multi-parameter monitoring according to claim 1, characterized in that: The pixel length and average pixel width of the laser beam in step 2 are obtained based on the following steps: Step 2.1: fine-tune the observation angle of the observation device composed of the camera (9) and the second telescope (10) so that the end of the captured laser beam is at the center of the phase plane of the camera (9), and obtain a picture of the end of the laser beam; Step 2.2: Convert the image at the end of the laser beam into a grayscale image; Step 2.3: Denoise the grayscale image; Step 2.4: Binarize the denoised grayscale image to obtain a binary image; Step 2.5: Filter out the contour containing the maximum number of pixels; Step 2.6: Calculate the pixel length and average pixel width of the contour with the maximum number of pixels.

4. The method for optimizing echo signals of an atmospheric detection laser radar for multi-parameter monitoring according to claim 1, characterized in that: Optimizing the divergence angle of the laser after passing through the laser beam expansion adjustment device (6) in step 3 includes the following steps: Step 3.1: Define the minimum average pixel width of the laser beam as d, and define the adjustment distance between the convex lens and the concave lens in the laser beam expansion adjustment device (6) as S; Step 3.2: Calculate the average pixel width of the laser beam obtained, and record it as the average pixel width d i , and let the adjustment distance S = D / K, D is the adjustment value, K is the adjustment ratio; Step 3.3: Shorten the distance between the convex lens and the concave lens in the laser beam expansion adjustment device (6) by the adjustment distance S, and calculate the average pixel width of the obtained laser beam, which is recorded as the average pixel width d i+1 ; Step 3.4: If d i ≥d i+1 , then let d i =d i+1 , and return to step 3.3; If d i <d i+1 , then let d=d i , K = K + 1, S = D / K, go to step 3.5; Step 3.5: Let d i =d i+1 , increase the distance between the convex lens and the concave lens in the laser beam expansion adjustment device (6) by the adjustment distance S, calculate the average pixel width of the laser beam, and record it as d i+1 ; Step 3.6: If S ≤ 10 μm, proceed to step 3.7; If S>10μm, further judgment: If d i ≥d i+1 , then let d i =d i+1 , and return to step 3.5; If d i <d i+1 , then let d=d i , K=K+1, S=D / K, if S>10μm, return to step 3.3; Step 3.7: Record the distance between the convex lens and the concave lens of the laser beam expansion adjustment device (6) corresponding to the minimum average pixel width of the laser beam, and record the average pixel width and pixel length of the laser beam as W and L respectively.

5. The method for optimizing echo signals of an atmospheric detection lidar for multi-parameter monitoring according to claim 1, characterized in that: The optimization of the laser radar echo signal in step 5 includes the following steps: Step 5.1: Look up the field angle parameter of the first telescope (4), denoted as θ1; Step 5.2: Measure the divergence angle of the laser beam after passing through the laser beam expansion and adjustment device (6), which is recorded as θ2, and measure the distance between the first telescope (4) and the two-dimensional laser reflector (5), which is recorded as D; Step 5.3: The height at which the laser beam completely enters the field of view of the first telescope (4) is defined as the calculated field of view height h, Step 5.4: using the first data acquisition device (1) to acquire the echo signal; Step 5.5: Set the angles of each adjustment of the pitch axis and the azimuth axis of the two-dimensional laser reflector (5), which are recorded as the pitch axis adjustment angle θ3 and the azimuth axis adjustment angle θ4, and the number of adjustments is recorded as n; Step 5.6: Let θ3 = θ / k, k = n, θ is the preset value of the adjustment angle, k is the multiple parameter, Step 5.7: Obtain the highest detection height H of the echo signal i ; Step 5.8: Adjust the pitch axis angle clockwise by θ3; Step 5.9: Obtain the highest detection height value H of the echo signal i+1 ; Step 5.10: If H i+1 ≥H i , then return to step 5.8 and let H i =H i+1 ; Step 5.11: If H i+1 <H i , then rotate the pitch axis counterclockwise by θ3, and increase the multiplier parameter k by 1, θ3 = θ / k. If θ3 > 0.1 mrad, return to step 5.9; if θ3 ≤ 0.1 mrad, proceed to step 5.12; Step 5.12: Let the azimuth axis adjustment angle θ4 = θ / k, k = n, and let H i =H i+1 ; Step 5.13: Adjust the azimuth axis angle clockwise by θ4; Step 5.14: Obtain the highest detection height H of the echo signal i+1 ; Step 5.15: If H i+1 ≥H i , then return to step 5.13 and let H i =H i+1 ; Step 5.16: If H i+1 <H i , then rotate the azimuth axis counterclockwise by θ4, and increase the multiple parameter k by 1. If θ4>0.1mrad, return to step 5.14; if θ4≤0.1mrad, jump to step 5.17; Step 5.17: If |H i+1 -H i |>0.05km, increase the adjustment times n by 1 and return to step 5.6; |H i+1 -H i |≤0.05km, skip to step 5.18; Step 5.18: Calculate the actual field of view height h based on the echo signal i , according to the actual field of view height h i The difference between the height h of the calculated field of view is used to fine-tune the pitch axis and the rotation axis of the two-dimensional laser reflector (5) so that the highest detection height according to the echo signal is consistent with the calculated field of view height h.

6. The method for optimizing echo signals of an atmospheric detection laser radar for multi-parameter monitoring according to claim 5, characterized in that: The step 5.18 includes the following steps: Step 5.18.1: Using function fitting on the echo signal collected by the first data acquisition device (1), obtain a functional relationship between the number of echo photons and the maximum detection height; Step 5.18.2: Take the derivative of the function relationship of the number of echo photons with respect to the highest detection altitude. Find the position where the derivative of the function relationship passes through zero or the highest detection altitude corresponding to the position where the positive value is infinitely close to 0. Record it as the actual field of view height h. i ; Step 5.18.3: Calculate Δh i =|h i -h|; Step 5.18.4: If Δh i ≤2, the adjustment is completed; if Δh i >2, then fine-tune the pitch axis and rotation axis of the two-dimensional laser reflector (5) so that the calculated Δh i ≤2.

7. The method for optimizing echo signals of an atmospheric detection lidar for multi-parameter monitoring according to claim 5, characterized in that: The step 7 comprises the following steps: Step 7.1: Record the current visibility value and laser energy; Step 7.2: Substitute the current visibility value and laser energy into the prediction model established in step 6 to obtain the predicted maximum detection altitude H p ; Step 7.3: Calculate the maximum detection height H of the currently collected echo signal r ; Step 7.4 If |H p -H r |>2km, repeat steps 3 and 5 to optimize the divergence angle and echo signal, and return to step 7.

1. If |H p -H r |≤2km, then return directly to step 7.1.

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