A static scanning angle correction method for airborne bathymetric laser radar

Abstract

The invention discloses a static scanning angle correction method for an airborne bathymetric laser radar, which relates to the technical field of airborne bathymetric sounding, and comprises the following steps: a) laying out a site, and according to a design plan, setting up a stereoscopic measurement system and a bathymetric laser radar composed of two calibrated cameras; b) setting a motor speed D (D≤50r / min) of the airborne bathymetric laser radar for open-light scanning, and at the same time using the stereoscopic measurement system to completely photograph the scanning trajectory of a laser point corresponding to the rotation speed, and using the Hough method to detect the scanning trajectory of the corresponding laser points on two photos and perform fitting; c) using a scanning point positioning formula to obtain a direction vector Vs corresponding to each scanning point; the method can solve the problem of accurately obtaining the static scanning angle of the airborne bathymetric laser radar, and realize high-precision acquisition of the static scanning angle parameters of the bathymetric laser radar.

Description

Technical Field

[0001] The present invention relates to the technical field of airborne bathymetry, and in particular to a static scanning angle correction method for an airborne bathymetry laser radar. This research is funded by the National Natural Science Foundation of China (42106180). Background Art

[0002] With the rapid increase in my country's marine activities, the integrated measurement of land-sea transition zones in coastal areas, islands and reefs, nearshore underwater and water terrain, and intertidal zones with complex and varied terrain has always been a difficult problem in the field of marine surveying and mapping at home and abroad.

[0003] The airborne laser bathymetry system is a concentrated embodiment of advanced marine surveying and mapping technology. It has the advantages of high efficiency, speed, and seamless acquisition of land and sea data. It is the preferred method for integrated surveying and mapping of coastal areas, islands and reefs.

[0004] The airborne laser depth sounding system independently developed by my country has the ability to be applied in engineering, but there is a static angle correction of the optical path system. The angle α between the rotating axis and the optical axis of the emitted laser, the angle β between the rotating axis and the normal of the rotating mirror, and the zero angle θ of the rotating mirror are gradually calibrated during the integration of the scanning system using an autocollimator combined with an optical calibration solution. However, the correction amount of each angle will be affected by the residual error of the previous step, which will cause some angle correction amounts to deviate from the true correction value. Moreover, after system integration, the existing optical calibration method makes it difficult to decouple and precisely correct the angle of the optical path system, and the correction value cannot be verified.

[0005] In summary, it is particularly necessary to study the static scanning angle correction method of airborne bathymetric lidar. Summary of the invention

[0006] The purpose of the present invention is to provide a static scanning angle correction method for an airborne bathymetric laser radar to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for correcting the static scanning angle of an airborne depth-finding laser radar is proposed. The model is constructed using the dual-camera stereo measurement principle. The wall is scanned in the airborne depth-finding laser radar rotation speed D (D≤50r / min) mode. Two photos containing the scanning track of the egg-shaped curve and the waveform data of the corresponding time period are obtained through the stereo measurement camera. A stereo pair constraint is established with the two egg-shaped curves in the two photos. The scanning data track should satisfy the collinear relationship on the two photos and the egg-shaped curve equations on the corresponding photos respectively. The conditional adjustment with parameters is used as the adjustment model. The static scanning angle parameters α, β, and θ are iteratively solved according to the least squares criterion. The precise correction of the static scanning angle of the airborne depth-finding laser radar is completed. The following steps are specifically included:

[0009] Step a) setting up the site, according to the design plan, setting up a stereo measurement system composed of two calibrated cameras and a depth-measuring laser radar;

[0010] Step b) setting the motor speed D (D≤50r / min) of the airborne depth-sounding laser radar to perform open-beam scanning, and using the stereo measurement system to completely photograph the scanning trajectory of the laser point corresponding to the speed, and using the Hough method to detect the scanning trajectory of the corresponding laser points on the two photos and perform fitting;

[0011] Step c) Using the scanning point positioning formula, the direction vector Vs corresponding to each scanning point is obtained. The direction vector Vs is calculated based on the conversion parameter ω, κ, Dx, Dy, and Dz are converted to the stereo camera coordinate system through coordinate transformation to obtain the corresponding direction vector Vc;

[0012] Step d) converting the vector Vc to the independent coordinate system of each camera according to the exterior orientation elements of the two cameras in the stereo camera coordinate system to obtain vectors Pa and Pb, and then intersecting the light vectors Pa and Pb with the image planes of their respective cameras to solve the corresponding image points Ca and Cb;

[0013] Step e) Substitute the two intersection points Ca and Cb into the corresponding egg-shaped curve equations on each photo to construct a curve including scanning angle parameters (angle α between the rotation axis and the emitting laser optical axis, angle β between the rotation axis and the normal line of the rotating mirror, zero angle θ of the rotating mirror) and coordinate transformation parameters The constraint equations of ω, κ, Dx, Dy, and Dz are used. The conditional adjustment with parameters is used as the adjustment model, and the static scanning angle parameters α, β, and θ are iteratively solved according to the least squares criterion. Thus, the precise correction of the static scanning angle of the airborne depth laser radar is completed.

[0014] As a further technical solution of the present invention: in the model construction, a flat wall surface is selected as the reference plane for scanning trajectory imaging, and the flatness variation within the scanning range is less than 1 mm. An airborne depth sounding radar is placed at a certain vertical distance from the flat wall surface and at a certain height from the ground to ensure that the scanning trajectory can be fully displayed on the wall surface after the equipment is placed.

[0015] As a further technical solution of the present invention: the layout position of the stereo measurement camera needs to ensure that the coordinate system of the stereo measurement camera is approximately parallel to the axis system of the depth measuring laser radar itself.

[0016] As a further technical solution of the present invention: In the construction of the model, a total station needs to be set up to establish an independent local coordinate system. The axial direction of the coordinate system is consistent with the coordinate system of the depth-finding lidar system. The total station is used to measure the initial conversion parameters of the stereo measurement camera coordinate system and the depth-finding lidar coordinate system.

[0017] As a further technical solution of the present invention: the data acquisition process is as follows:

[0018] Ⅰ. Turn on the airborne depth-sounding laser radar and start data recording. Set the speed D (D≤50r / min) so that the wall surface shows a scanning track. Wait for the camera to take a photo after each setting conversion.

[0019] Ⅱ. Adjust the exposure parameters and shutter of the stereo measurement camera. When the airborne depth-sounding lidar is in the rotation speed D (D≤50r / min) mode, use the camera to capture the complete scanning track image data and record the radar data at the corresponding time.

[0020] As a further technical solution of the present invention: the static scanning angle parameters include the angle α between the rotation axis and the optical axis of the emitted laser, the angle β between the rotation axis and the normal of the rotating mirror, and the zero angle θ of the rotating mirror.

[0021] As a further technical solution of the present invention: the scanning angle correction process is as follows:

[0022] ① Taking a certain set of data as an example, after the data collection is completed, the waveform file of the data is parsed to obtain the distance parsing file, and then two photos A and B are exported from the stereo measurement camera respectively;

[0023] ② Use the Hough transform ellipse detection method to extract the scanning point trajectories from photos A and B respectively and perform fitting to obtain two egg-shaped curve fitting equations F1 and F2.

[0024] ③Use the scanning point positioning formula to obtain the direction vector Vs corresponding to each scanning point;

[0025] ④Then the direction vector Vs is converted according to the conversion parameters between the laser radar and the stereo measurement system coordinate system ω, κ, Dx, Dy, and Dz are transformed into the stereo camera coordinate system by coordinate conversion to obtain the corresponding direction vector Vc;

[0026] ⑤ Convert the vector Vc to the independent coordinate system of each camera according to the exterior orientation elements of the two cameras in the stereo camera coordinate system to obtain vectors Pa and Pb;

[0027] ⑥ Then intersect the light vectors Pa and Pb with the image planes of their respective cameras to obtain the corresponding image points Ca and Cb;

[0028] ⑦ Substitute the two intersection points Ca and Cb into the corresponding egg-shaped curve equations F1 and F2 on each photo to construct a curve containing scanning angle parameters (angle α between the rotation axis and the optical axis of the emitted laser, angle β between the rotation axis and the normal line of the rotating mirror, zero angle θ of the rotating mirror) and coordinate transformation parameters Constraint equations for ω, κ, Dx, Dy, and Dz.

[0029] ⑧Use conditional adjustment with parameters as the adjustment model, and iteratively solve the static scanning angle parameters α, β, θ according to the least squares criterion;

[0030] As a further technical solution of the present invention: the scanning point positioning model determination method is specifically: using the law of light refraction and the ray tracing method, a scanning point positioning model is established based on the various angles in the scanning part as a theoretical basis.

[0031] As a further technical solution of the present invention: the automatic extraction method of the scanning trajectory is: capturing the blue-green laser depth sounding radar scanning trajectory by a camera, and extracting the scanning point rotation trajectory from the image by using the ellipse detection method of the automatic image recognition algorithm Hough transform.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] Based on the ray tracing model, the present invention utilizes the visible characteristics of blue-green lasers, the egg-shaped curve of the system scanning trajectory and a stereo measurement camera to construct a correction model for static scanning angle precision calibration, thereby solving the problem of precise correction of the angle decoupling of the optical path system after system integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the scanning trajectory diagram of the domestic airborne laser depth sounding system.

[0035] Figure 2 For the technology roadmap.

[0036] Figure 3 Create a plot for the static scan angle parameters and the radar coordinate system.

[0037] Figure 4 This is the actual scanning trajectory of the bathymetric lidar.

[0038] Figure 5 This is the actual detection result of the depth-measuring lidar.

[0039] Figure 6 This is a schematic diagram of a static scanning angle correction method for airborne bathymetric lidar.

[0040] Figure 7 This is the relationship diagram between incident light and reflected light. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of 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.

[0042] The present invention mainly includes:

[0043] ① Determination of the scanning point positioning model: According to the domestic airborne blue-green laser scanning structure, the law of light refraction and ray tracing method are used to establish a scanning point positioning model based on the various angles in the scanning part.

[0044] ②Automatic extraction of scanning trajectories: The blue-green laser depth sounding radar scanning trajectory is captured by a camera, and the rotation trajectory of the scanning point is extracted from the image using an automated image recognition algorithm, providing technical support for accurate trajectory fitting and automated processing of scanning angle correction.

[0045] ③A static scanning angle correction method for airborne depth-sounding laser radar. First, a scanning system is used to scan a certain facade, and a complete scanning trajectory curve is presented on the facade; secondly, two digital cameras in the stereo measurement system are used to set the camera exposure, shutter value and other parameters to shoot the scanning trajectory respectively to obtain the scanning pattern, and the scanning trajectory is extracted from the image using an automatic extraction algorithm; then, according to the egg-shaped scanning trajectory formed by the intersection of the scanning light and the plane, a static scanning angle correction method for airborne depth-sounding laser radar is constructed by using the relationship that the scanning trajectory should be collinear with the trajectory shot by the stereo measurement camera after coordinate transformation; finally, the precise parameters of each angle are calculated by the least squares method.

[0046] The purpose of this project is to develop a static scanning angle correction method for airborne depth-sounding laser radar, and to achieve decoupling and precise correction of static scanning angle after airborne depth-sounding radar integration. This method can solve the problem that the scanning angle cannot be decoupled and precisely corrected during the industrialization of domestic airborne blue-green laser depth-sounding radar, improve the ability to process details in the industrialization of this equipment, and break through and master the precision measurement and quality assessment methods.

[0047] See also Figure 1-Figure 6 The present invention discloses a static scanning angle correction method for an airborne depth-sounding laser radar.

[0048] First, set up the venue:

[0049] a1. Select a flat wall as the reference plane for scanning trajectory imaging, and the flatness variation within the scanning range should be less than 1mm;

[0050] a2. Figure 6 As shown, the airborne depth sounding radar is placed at a certain vertical distance from the flat wall and at a certain height from the ground to ensure that the scanning track can be fully displayed on the wall after the device is placed.

[0051] a3. Deploy the stereo camera. The placement of the stereo measurement camera should ensure that the coordinate system of the stereo measurement camera is approximately parallel to the axis system of the depth-measuring laser radar. This can ensure that the conversion angle parameters of the two coordinate systems are small, which can reduce the requirements for the accuracy of the initial value to a certain extent.

[0052] a4. Set up a total station and establish an independent local coordinate system. The axial direction of the coordinate system is basically consistent with the coordinate system of the depth-finding lidar system. Use the total station to measure the initial conversion parameters of the stereo measurement camera coordinate system and the depth-finding lidar coordinate system.

[0053] Among them, data acquisition is performed:

[0054] b1. Turn on the airborne depth-measuring laser radar and start data recording. Set the speed D (D≤50r / min) so that the wall (such as Figure 4 ) presents a scanning trajectory;

[0055] b2. Adjust the exposure parameters and shutter of the stereo measurement camera, and use the camera to capture the complete scanning trajectory and record the corresponding lidar data in the airborne depth-sounding lidar rotation speed D mode.

[0056] b3. Extract the scanning point trajectory from the image through the ellipse detection method based on Hough transform, such as Figure 5 .

[0057] b4. Based on the Hough transform method, the trajectory formed by the scanning points taken on the photo is detected, and the fitting equations F1 and F2 formed by the scanning trajectory points taken on the two photos are fitted using the least squares method and the egg-shaped curve formula;

[0058] Finally, perform static correction of the scanning angle:

[0059] ① Taking a certain set of data as an example, after the data collection is completed, the waveform file of the data is parsed to obtain the distance parsing file, and then two photos A and B are exported from the stereo measurement camera respectively;

[0060] ② Use the Hough transform ellipse detection method to extract the scanning point trajectories from photos A and B respectively and perform fitting to obtain two egg-shaped curve fitting equations F1 and F2.

[0061] ③Use the scanning point positioning formula to obtain the direction vector Vs corresponding to each scanning point;

[0062] ④Then the direction vector Vs is converted according to the conversion parameters between the laser radar and the stereo measurement system coordinate system ω, κ, Dx, Dy, and Dz are transformed into the stereo camera coordinate system by coordinate conversion to obtain the corresponding direction vector Vc;

[0063] ⑤ Convert the vector Vc to the independent coordinate system of each camera according to the exterior orientation elements of the two cameras in the stereo camera coordinate system to obtain vectors Pa and Pb;

[0064] ⑥ Then intersect the light vectors Pa and Pb with the image planes of their respective cameras to obtain the corresponding image points Ca and Cb;

[0065] ⑦ Substitute the two intersection points Ca and Cb into the corresponding egg-shaped curve equations F1 and F2 on each photo to construct a curve containing scanning angle parameters (angle α between the rotation axis and the optical axis of the emitted laser, angle β between the rotation axis and the normal line of the rotating mirror, zero angle θ of the rotating mirror) and coordinate transformation parameters Constraint equations for ω, κ, Dx, Dy, and Dz.

[0066] ⑧Use conditional adjustment with parameters as the adjustment model, and iteratively solve the static scanning angle parameters α, β, θ according to the least squares criterion;

[0067] Here’s how it works:

[0068] (1) Derivation of scanning point formula

[0069] In the auxiliary coordinate system, we can get Figure 3 Results shown;

[0070] Incident light A i :

[0071]

[0072] α is the angle between the rotation axis and the optical axis of the emitted laser;

[0073] Normal N:

[0074]

[0075] β is the angle between the rotation axis and the normal of the rotating mirror, θ is the zero angle of the rotating mirror;

[0076] First, the incident light A i Reverse, and then the reverse incident light -A i The line rotates 180 degrees around the normal N, and the reflected light A is obtained. r The position and direction of Figure 7 As shown:

[0077] Rotation matrix R a for:

[0078]

[0079] in They correspond to the three directional components of the normal line respectively.

[0080] The reflected light is:

[0081] A r =R a *(-A i ) (4)

[0082] At this time, the direction vector of the reflected light in the auxiliary coordinate system is obtained, and then it is rotated around the Y axis by an angle α and transferred to the scanning coordinate system to obtain the direction vector of the reflected light in the scanning coordinate system.

[0083]

[0084] After obtaining the distance S from the laser to the target point, scan point P S Positioning formula:

[0085] P S =S*R b *(R a *(-A i )) (6)

[0086] Incident light A i is the rotation matrix R corresponding to the reflected light a ;

[0087] A i Reverse direction for incident light;

[0088] R b The rotation matrix corresponding to the direction vector of the reflected light in the auxiliary coordinate system is converted to the scanning coordinate system;

[0089] (2) Egg-shaped curve formula:

[0090] Depend on Figure 4 It can be seen that the scanning trajectory presents an egg-shaped curve structure on the image, showing an egg-shaped curve with "one end big" and "one end small". An egg-shaped curve function is constructed as:

[0091]

[0092] Where a e , b e 、c e d e 、e e 、f e are the egg-shaped curve parameters.

[0093] (3) Hough transform detection scanning trajectory: From the scanning trajectory, we can see that the scanning pattern of the domestic airborne depth sounding radar is an egg-shaped curve, but it is also close to an ellipse. The actual scanning trajectory is as follows Figure 5As shown in the figure, it can be seen that by controlling the camera exposure and shutter parameters, the scanning trajectory is clearly visible in the photo and can be distinguished from the background very well. Therefore, the scanning point trajectory can be extracted from the image through the ellipse detection method based on Hough transform.

[0094] Random Hough transform uses a many-to-one mapping. This random sampling will bring a lot of invalid calculations. When the number of points is large, the performance of the algorithm drops sharply. The geometric characteristics of the ellipse can be used to reduce the dimension of the parameters to improve the efficiency and accuracy of the algorithm. On this basis, improvements need to be made to Hough, and the improved dependency theorem is as follows:

[0095] Suppose there is an ellipse on the plane, point c is the center of the ellipse, and for any point p on the plane (different from point c), the maximum distance between point p and the point on the ellipse must be greater than the maximum distance between point c and the point on the ellipse.

[0096] Based on the above theorem, first perform edge detection on the image to obtain a binary edge contour map, and store the point coordinates on the edge map into array A. Secondly, for each point on the image, calculate the distance from the midpoint of array A obtained in the previous step, and obtain the maximum distance of each point from the midpoint of array A. The point with the largest distance among all points corresponds to the smallest point, which is the center of the ellipse (P, Q). The maximum distance is the length of the major axis of the ellipse a. Then substitute the value of each point in array A and the three ellipse parameters P, Q, and a just obtained into the ellipse equation (8).

[0097]

[0098] Where: a, b are the major axis and minor axis of the ellipse, P, Q are the coordinates of the center of the ellipse, and θ is the rotation angle of the ellipse.

[0099] Finally, after taking statistics on the parameters b and θ, a set of parameters with a peak value exceeding a certain threshold is obtained, which is an ellipse, thus realizing automatic detection of the scanning trajectory. Figure 5 :

[0100] (4) Scanning angle static correction method Figure 6 As shown:

[0101] The laser radar positioning equation contains both angle information and distance information. In order to reduce the influence of distance error on angle, the dual-camera stereo measurement principle is used to build the model. The wall is scanned in the low speed mode (D < 50rmp) of the airborne depth-sounding laser radar. After obtaining two photos containing the scanning track of the egg-shaped curve and the waveform data of the corresponding time period through the stereo camera, the two egg-shaped curves in the two photos are used to establish a stereo pair constraint. The scanning data track should satisfy the collinear relationship on the two photos and the egg-shaped curve equation on the corresponding photos respectively.

[0102] The processing process is divided into the following steps:

[0103] ① Taking a certain set of data as an example, after the data collection is completed, the waveform file of the data is parsed to obtain the distance parsing file, and then two photos A and B are exported from the stereo measurement camera respectively;

[0104] ② Use the Hough transform ellipse detection method to extract the scanning point trajectories from photos A and B respectively and perform fitting to obtain two egg-shaped curve fitting equations F1 and F2.

[0105] ③Use the scanning point positioning formula to obtain the direction vector Vs corresponding to each scanning point;

[0106] ④Then the direction vector Vs is converted according to the conversion parameters between the laser radar and the stereo measurement system coordinate system ω, κ, Dx, Dy, and Dz are transformed into the stereo camera coordinate system by coordinate conversion to obtain the corresponding direction vector Vc;

[0107] All coordinate transformation matrices use the rotation matrix of the Euler angle model, which is given by The three Euler angles ω and κ represent:

[0108]

[0109] in, is the rotation matrix around the x-axis, is the rotation angle around the X axis, R y (ω) is the rotation matrix around the y-axis, ω is the rotation angle around the Y-axis, R z (κ) is the rotation matrix around the z-axis, κ is the rotation angle around the Z-axis, and the three independent rotation matrices are shown as follows:

[0110]

[0111]

[0112]

[0113] The coordinate transformation model is as follows:

[0114]

[0115] Dx, Dy, Dz are translation parameters, X i ', Y i ', Z i ' is the transformed coordinate, X i , Y i , Z i Coordinates before transformation;

[0116] ⑤ Convert the vector Vc to the independent coordinate system of each camera according to the exterior orientation elements of the two cameras in the stereo camera coordinate system to obtain vectors Pa and Pb;

[0117] ⑥ Then intersect the light vectors Pa and Pb with the image planes of their respective cameras to obtain the corresponding image points Ca and Cb;

[0118] ⑦ Substitute the two intersection points Ca and Cb into the corresponding egg-shaped curve equations F1 and F2 on each photo to construct a curve containing scanning angle parameters (angle α between the rotation axis and the optical axis of the emitted laser, angle β between the rotation axis and the normal line of the rotating mirror, zero angle θ of the rotating mirror) and coordinate transformation parameters Constraint equations for ω, κ, Dx, Dy, and Dz.

[0119] ⑧Use conditional adjustment with parameters as the adjustment model, and iteratively solve the static scanning angle parameters α, β, and θ according to the least squares criterion.

[0120] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0121] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A static scanning angle correction method for an airborne depth-sounding laser radar, characterized in that: The specific steps include: a) Lay out the site and set up a stereo measurement system consisting of two calibrated cameras and a depth-measuring laser radar according to the design plan; b) Set the motor speed D of the airborne depth-sounding laser radar for open-beam scanning, D≤50r / min, and use the stereo measurement system to completely capture the scanning trajectory of the laser point at the corresponding speed, and use the Hough method to detect the scanning trajectory of the corresponding laser points on the two photos and fit them to obtain the scanning trajectory fitting equations F1 and F2; c) Use the scanning point positioning formula to obtain the direction vector Vs corresponding to each scanning point. The direction vector is based on the conversion parameters , , , Obtain the corresponding direction vector Vc by coordinate conversion to the stereo camera coordinate system; d) Convert the vector Vc to the independent coordinate system of each camera according to the exterior orientation elements of the two cameras in the stereo camera coordinate system to obtain the vectors Pa and Pb, and then intersect the light vectors Pa and Pb with the image planes of their respective cameras to solve for the corresponding image points Ca and Cb; e) Substitute the two intersection points Ca and Cb into the corresponding egg-shaped curve equations on each photo to construct a curve containing scanning angle parameters and coordinate transformation parameters , , , The constraint equation is used, and the conditional adjustment with parameters is used as the adjustment model. The static scanning angle parameters are iteratively solved according to the least squares criterion. , , ; The scanning angle parameters include the angle between the rotation axis and the emitting laser optical axis , Angle between the axis of rotation and the normal of the rotating mirror , Rotating mirror zero angle .

2. The static scanning angle correction method of an airborne depth-sounding laser radar according to claim 1, characterized in that: Step a includes the following sub-steps: a1. Select a flat wall as the reference plane for scanning trajectory imaging, and the flatness variation within the scanning range should be less than 1mm; a2. Place the airborne depth sounding radar at a certain vertical distance from the flat wall and at a certain height from the ground to ensure that the scanning track can be fully displayed on the wall after the device is placed; a3. Deploy stereo cameras. The placement of the stereo measurement cameras should ensure that the coordinate system of the stereo measurement cameras is approximately parallel to the axis system of the depth-measuring laser radar itself. This ensures that the conversion angle parameters of the two coordinate systems are small and reduces the requirements for the accuracy of the initial value. a4. Set up a total station and establish an independent local coordinate system. The axial direction of the coordinate system is consistent with the coordinate system of the depth-sounding laser radar system. Use the total station to measure the initial conversion parameters between the stereo measurement camera coordinate system and the depth-sounding laser radar coordinate system.

3. The static scanning angle correction method of an airborne depth-sounding laser radar according to claim 1, characterized in that: Step b includes the following sub-steps: b1. Turn on the airborne depth-sounding laser radar and start data recording. Set the rotation speed D, D≤50r / min, so that the wall surface shows a scanning track; b2. Adjust the exposure parameters and shutter of the stereo measurement camera, and use the camera to capture the complete scanning track and record the corresponding laser radar data in the airborne depth laser radar speed D mode; b3. Extract the scanning point trajectory from the image through the ellipse detection method based on Hough transform; b4. The trajectory formed by the scanning points taken on the photo is detected based on the Hough transform method, and the fitting equations F1 and F2 formed by the scanning trajectory points taken on the two photos are fitted using the least square method and the egg-shaped curve formula.

4. The static scanning angle correction method of an airborne depth-sounding laser radar according to claim 1, characterized in that: Step c includes the following sub-steps: c1. Using the scanning point positioning formula, obtain the direction vector Vs corresponding to each scanning point; c2. Then the direction vector Vs is converted according to the conversion parameters between the laser radar and the stereo measurement system coordinate system , , , Vs is converted to the stereo camera coordinate system through coordinate conversion to obtain the corresponding direction vector Vc.

5. The static scanning angle correction method of an airborne depth-sounding laser radar according to claim 1, characterized in that: The step d comprises the following sub-steps: d1. Convert the vector Vc to the independent coordinate systems of each camera according to the exterior orientation elements of the two cameras in the stereo camera coordinate system to obtain vectors Pa and Pb; d2. Then intersect the light vectors Pa and Pb with the image planes of their respective cameras to obtain the corresponding image points Ca and Cb.

6. The static scanning angle correction method of an airborne depth-sounding laser radar according to claim 1, characterized in that: Step e includes the following sub-steps: e1. Substitute the two intersection points Ca and Cb into the corresponding egg-shaped curve equations F1 and F2 on each photo to construct a curve containing scanning angle parameters and coordinate transformation parameters. , , , The constraint equations of the scanning angle include the angle between the rotation axis and the optical axis of the emitted laser. , Angle between the axis of rotation and the normal of the rotating mirror , Rotating mirror zero angle ; e2. Use conditional adjustment with parameters as the adjustment model and iteratively solve the static scanning angle parameters according to the least squares criterion , , .

Images