A rotatable ovular scanning airborne bathymetric laser radar system and positioning method

Abstract

The application discloses a rotatable oval scanning airborne depth measuring laser radar system, which comprises a pose positioning system, an airborne depth measuring laser radar and a rotatable laser radar mounting rack. The rotatable laser radar mounting rack is composed of a connecting mechanism 210, a hollow load rotating table 220 and a bolt assembly 230. The rotating angle of the hollow load rotating table motor is set to drive the oval scanning airborne depth measuring laser radar to rotate, so that the major and minor axis directions of the scanning track can be flexibly adjusted according to actual requirements. In addition, the application also discloses a positioning method based on the rotating angle of the hollow load rotating table motor, which can accurately calculate the spatial position of the target laser point. By realizing the variable major and minor axis directions of the scanning track of the oval scanning airborne depth measuring laser radar system, the flexibility of measurement is significantly improved, the oval scanning airborne depth measuring laser radar system is more suitable for various application scenarios, and the measurement quality and efficiency are effectively ensured.

Description

Technical Field

[0001] This invention belongs to the technical field of airborne depth sounding lidar systems, and specifically relates to a rotatable oval scanning airborne depth sounding lidar system and positioning method. Background Technology

[0002] Airborne lidar (ALB) systems are advanced technologies for underwater topographic mapping that actively emit 532nm wavelength blue-green laser pulses. They can simultaneously receive echo signals from both water and land areas, enabling joint land-sea observation. ALB offers high measurement efficiency, dense measurement points, and is not limited by terrain, making it suitable for inland rivers, mangrove forests, coastal zones, and other waters where traditional shipborne sonar sounding is difficult. In addition to basic depth measurement functions, ALB can also be used for shoreline detection. The mapping data it provides is crucial for the construction and operation of water-related projects such as water conservancy and transportation, and provides technical support for flood control and disaster reduction, water resource management, and coastal resource protection and development.

[0003] The oval-shaped scanning trajectory of an airborne depth sounding lidar (ALB) system is typically set with its major axis perpendicular to the flight direction to maximize the lateral scanning angle and improve lateral overlap. In measurement scenarios requiring only a single flight strip, such as waterline detection or depth measurement in narrow inland waterways, rotating the lidar to align the major axis of the scanning trajectory parallel to the waterline or river direction effectively reduces the measurement bandwidth and increases lateral overlap, improving measurement efficiency while maintaining the density of measurement points in the target area. Overall, the variable major and minor axes of the ALB system significantly enhance measurement flexibility, making it better suited for various application scenarios and ensuring both measurement quality and efficiency.

[0004] Currently, several laser depth sounding systems are publicly available, including spaceborne, airborne, and shipborne systems. Examples include a spaceborne laser near-shore terrain detection lidar and detection method patent (CN112526482A), a single-frequency water depth lidar (CN114167436A), a method for measuring water depth and a lidar system (CN106871990A), and a seamlessly integrated lidar and unmanned surface vessel water depth measurement system (CN114236556A). However, none of the existing publicly available laser depth sounding solutions involve designs with variable scanning trajectory major and minor axes. Summary of the Invention

[0005] The purpose of this invention is to provide a rotatable oval scanning airborne depth sounding lidar system and positioning method to solve the problem that the major and minor axes of the scanning trajectory of airborne depth sounding lidar systems cannot be changed, so that airborne depth sounding lidar systems can be better applied to various application scenarios and ensure measurement quality and efficiency.

[0006] To achieve the above objectives, according to one aspect of the present invention, a rotatable oval scanning airborne depth sounding lidar system is provided, comprising:

[0007] Airborne depth-sounding lidar uses an oval scanning method to emit laser pulses and receive echo information to obtain the slant range of the target point;

[0008] A rotatable lidar mounting bracket is used to fix the lidar to the flight vehicle;

[0009] An attitude determination and positioning system is used to acquire the spatial position and attitude information of the flight vehicle.

[0010] In the aforementioned rotatable oval scanning airborne depth sounding lidar system, the rotatable lidar mounting frame includes a connecting mechanism, a hollow load rotary table, and a bolt assembly.

[0011] In the rotatable lidar mounting frame, the connecting mechanism includes a cantilever buckle assembly and a connecting plate. The cantilever buckle assembly includes multiple cantilever buckles. The connecting plate is fixed to the top of the hollow load rotary table and is connected to a protrusion on the bottom of the flight vehicle that matches the cantilever buckle through the cantilever buckles.

[0012] In the rotatable lidar mounting frame, the bottom end of the hollow load rotary table is connected to the top end of the lidar via the bolt assembly. The hollow load rotary table is driven by a stepper motor, and the lidar is rotated by controlling the rotation of the motor.

[0013] In the rotatable lidar mounting bracket, the bolt assembly comprises a plurality of bolts arranged in a circle around the periphery of the hollow load rotating platform, each bolt being threadedly connected to the hollow load rotating platform and the top of the lidar.

[0014] This invention also provides a positioning method for a rotatable oval-shaped scanning airborne depth sounding lidar system, comprising:

[0015] S1: Set the rotation angle of the hollow load rotary table motor;

[0016] S2: Obtain the propagation slant distance of the laser from the emission point to the target point in air and water, the rotation angle of the airborne depth sounding lidar reflector drive motor, the three-dimensional coordinates (WGS-84) of the attitude positioning system center, and the attitude angle of the flight vehicle;

[0017] S3: Calculate the three-dimensional coordinates of the target point in the laser scanning reference coordinate system based on the rotation angle of the hollow load rotary table motor, the propagation slant distance of the laser in air and water, and the rotation angle of the drive motor;

[0018] S4: Use a total station to measure the eccentricity correction from the center of the lidar reflector to the center of the attitude positioning system, and transform the three-dimensional coordinates of the target point in the laser scanning reference coordinate system to the carrier coordinate system;

[0019] S5: Based on the attitude angle of the flight vehicle, transform the three-dimensional coordinates of the target point in the vehicle coordinate system to the navigation coordinate system;

[0020] S6: Transform the three-dimensional coordinates of the center of the attitude positioning system in the geodetic coordinate system (WGS-84) to the geocentric coordinate system, and combine the three-dimensional coordinates of the target point in the navigation coordinate system to calculate the three-dimensional coordinates of the target point in the geocentric coordinate system;

[0021] S7: Transform the three-dimensional coordinates of the target point in the geocentric coordinate system to the geodetic coordinate system.

[0022] In the positioning method of the rotatable oval scanning airborne depth sounding lidar system, S3 includes:

[0023] Define the laser scanning coordinate system: with the center of the reflector as the origin O, establish the laser scanning coordinate system O-XYZ. The Z-axis is perpendicular to the flight vehicle and points upward. The X-axis is the opposite direction of the incident laser. The Y-axis and the X-axis form a right-handed rectangular coordinate system. The incident laser and the drive motor shaft are located in the same plane (XZ plane).

[0024] Define the laser scanning auxiliary coordinate system: Rotate the laser scanning coordinate system counterclockwise by 45° around the Y-axis with O as the center to establish the laser scanning auxiliary coordinate system OX. ′ Y ′ Z ′ ;

[0025] The direction vector of the mirror normal in the laser scanning auxiliary coordinate system :

[0026] ;

[0027] Based on the transformation relationship between the laser scanning coordinate system and the laser scanning auxiliary coordinate system, the direction vector of the mirror normal in the laser scanning coordinate system is obtained. :

[0028]

[0029] The angle φ between the projection of the normal of the reflector onto the XZ plane and the Z-axis. Fx :

[0030] ;

[0031] According to geometric relationships, the angle φ between the projection of the reflected ray onto the XZ plane and the Z-axis is... x :

[0032] ;

[0033] The angle φ between the projection of the normal of the reflector onto the YZ plane and the Z-axis. Fy :

[0034] ;

[0035] According to geometric relationships, the angle φ between the projection of the reflected ray onto the XY plane and the Z-axis is... y :

[0036] ;

[0037] According to φ x and φ y The scanning angle φ is obtained as follows:

[0038] ;

[0039] Based on the scanning angle φ, the perpendicular distance from the center of the reflector to the laser incident point on the water surface is calculated. Where d1 is the slant distance of the laser propagation in the air;

[0040] Based on geometric relationships, the three-dimensional coordinates of the laser incident point S on the water surface in the laser scanning coordinate system are obtained as follows:

[0041] ;

[0042] Then the azimuth angle is obtained. );

[0043] According to Snell's law, the laser refraction angle on the water surface is obtained. To determine the water depth Where d2 is the slant distance of the laser propagation underwater;

[0044] Based on geometric relationships, the three-dimensional coordinates of the laser incident point F at the underwater surface in the laser scanning coordinate system are obtained:

[0045] ;

[0046] Define the laser scanning reference coordinate system: establish the laser scanning reference coordinate system OX with the center of the reflector as the origin O. ′′ Y ′′ Z ′′ Y ′′ The axis is the direction of flight, Z. ′′ The axis is perpendicular to the flight vehicle and points upwards, X′′ axis and Y ′′ Z ′′ The axes form a right-handed rectangular coordinate system.

[0047] When the rotation angle of the hollow load rotary table motor is 0°, the Y-axis of the laser scanning coordinate system points to the flight direction, i.e., O-XYZ and OX. ′′ Y ′′ Z ′ The three axes are in the same direction. When the no-load rotary table motor rotates clockwise, it drives the lidar to rotate clockwise around the reflection center as the origin. That is, the laser scanning coordinate system rotates clockwise around the Y-axis with O as the center.

[0048] The transformation relationship between the laser scanning reference coordinate system and the laser scanning coordinate system:

[0049] ;

[0050] in, The rotation angle of the hollow load rotary table motor;

[0051] Based on the aforementioned conversion relationship, the rotation angle of the hollow load rotary table motor is calculated as follows: At that time, the three-dimensional coordinates of the laser incident point S on the water surface in the laser scanning reference coordinate system are:

[0052] ;

[0053] The three-dimensional coordinates of the laser underwater incident point F in the laser scanning coordinate system are as follows:

[0054] .

[0055] Compared with existing technologies, this invention has the following advantages: First, this invention designs a rotatable lidar mounting frame. By setting the rotation angle of the hollow load rotary table motor, the oval-shaped scanning airborne depth sounding lidar is driven to rotate, thereby allowing the major and minor axes of the scanning trajectory to be flexibly adjusted according to actual needs. Second, this invention proposes a positioning method for a rotatable oval-shaped scanning airborne depth sounding lidar system, calculating the spatial position of the target laser point based on the rotation angle of the hollow load rotary table motor. By realizing the variable major and minor axes of the scanning trajectory of the oval-shaped scanning airborne depth sounding lidar system, the measurement flexibility can be significantly improved, making it more adaptable to various application scenarios, thereby effectively ensuring measurement quality and efficiency. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the device of the present invention;

[0057] Figure 2This is a schematic diagram of the device of the present invention from another perspective;

[0058] Figure 3 This is a flowchart of the method of the present invention;

[0059] Figure 4 A schematic diagram of the laser scanning reference coordinate system for an oval-shaped scanning airborne depth sounding lidar system;

[0060] Figure 5 A schematic diagram of a coastal zone operation scenario.

[0061] Figure 6 A schematic diagram of a waterline operation scenario.

[0062] Figure 7 This is a schematic diagram of a measurement operation scenario in an inland river channel. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0064] Example 1:

[0065] Combination Figure 1 This invention provides a rotatable oval-shaped scanning airborne depth sounding lidar system, comprising an attitude positioning system 100 for acquiring the spatial position and attitude information of a flight vehicle; a rotatable lidar mounting bracket 200 for fixing the lidar on the flight vehicle; and an airborne depth sounding lidar 300, which employs an oval scanning method to emit laser pulses and receive echo information to acquire the slant range of a target point.

[0066] Combination Figure 2 The description includes a rotatable lidar mounting bracket, comprising a connecting mechanism 210, a hollow load rotary table 220, and a bolt assembly 230.

[0067] The connecting mechanism includes a cantilever buckle assembly 211 and a connecting plate 212. The cantilever buckle assembly includes multiple cantilever buckles, and the connecting plate is fixed to the top of the hollow load rotary table and connected to a protrusion on the bottom of the flight vehicle that matches the cantilever buckle through the cantilever buckles.

[0068] The bottom of the hollow load rotary table is connected to the top of the lidar via bolt assembly. The hollow load rotary table is driven by a stepper motor, and the lidar is rotated by controlling the rotation of the motor.

[0069] The bolt assembly includes multiple bolts arranged in a circle around the periphery of the hollow load rotary table, each bolt being threaded to the top of the hollow load rotary table and the lidar.

[0070] Example 2:

[0071] Combination Figure 4 This invention provides a positioning method for a rotatable oval-shaped scanning airborne depth sounding lidar system, comprising:

[0072] S1: Set the rotation angle of the hollow load rotary table motor;

[0073] S2: Obtain the propagation slant distance of the laser from the emission point to the target point in air and underwater, the rotation angle of the airborne depth sounding lidar reflector drive motor, the three-dimensional coordinates (WGS-84) of the attitude positioning system center, and the attitude angle of the flight vehicle;

[0074] S3: Calculate the three-dimensional coordinates of the target point in the laser scanning reference coordinate system based on the rotation angle of the hollow load rotary table motor, the propagation slant distance of the laser in air and underwater, and the rotation angle of the drive motor.

[0075] S4: Use a total station to measure the eccentricity correction from the center of the lidar reflector to the center of the attitude positioning system, and transform the three-dimensional coordinates of the target point in the laser scanning reference coordinate system to the carrier coordinate system;

[0076] S5: Based on the attitude angle of the flight vehicle, transform the three-dimensional coordinates of the target point in the vehicle coordinate system to the navigation coordinate system;

[0077] S6: Transform the three-dimensional coordinates of the center of the attitude determination and positioning system in the geodetic coordinate system (WGS-84) to the geocentric coordinate system, and combine the three-dimensional coordinates of the target point in the navigation coordinate system to calculate the three-dimensional coordinates of the target point in the geocentric coordinate system;

[0078] S7: Transform the three-dimensional coordinates of the target point in the Earth-centered Earth-fixed coordinate system to the geodetic coordinate system.

[0079] S1 includes:

[0080] Combination Figure 4 This describes an oval-shaped scanning airborne depth sounding lidar system. The incident light beam from the lidar and the drive motor shaft are in the same plane and form a 45° angle. The normal to the reflector is not aligned with the direction of the drive motor shaft, maintaining a 7.5° angle between them. When the reflector rotates at high speed under the drive motor's influence, the reflector normal forms a cone in space. The horizontally incident laser beam is reflected by the reflector and directed in different directions, forming an oval-shaped laser dot on the target plane.

[0081] In oval-shaped scanning airborne depth sounding lidar, the incident light beam is generally perpendicular to the flight direction; that is, the major axis of the scanning trajectory is set perpendicular to the flight direction to maximize the lateral scanning angle and improve lateral overlap. For example... Figure 5 As shown in the figure, the dashed line represents the flight direction. When the operation scenario involves large-area measurement (such as underwater topographic mapping of coastal zones), the rotation angle of the hollow load rotary table motor should be set to 0° so that the major axis of the scanning trajectory is perpendicular to the flight direction. Figure 6 and Figure 7 As shown, when the operation scenario is a small area measurement (such as waterline measurement and inland river underwater topography mapping), only one measurement strip is needed to cover the target area. By setting the rotation angle of the hollow load rotary table motor to drive the lidar to rotate, the long axis of the scanning trajectory is parallel to the waterline or river direction, thereby reducing the measurement bandwidth, increasing the heading overlap, and improving measurement efficiency while maintaining the density of measurement points in the target area.

[0082] S3 includes:

[0083] Define the laser scanning coordinate system: With the center of the reflector as the origin O, establish the laser scanning coordinate system O-XYZ. The Z-axis is perpendicular to the flight vehicle and points upwards. The X-axis is in the opposite direction to the incident laser. The Y-axis forms a right-handed rectangular coordinate system with the X-axis. The incident laser and the drive motor shaft are located in the same plane (XZ plane). Define the laser scanning auxiliary coordinate system: Rotate the laser scanning coordinate system counterclockwise by 45° around the Y-axis with O as the center to establish the laser scanning auxiliary coordinate system OX. ′ Y ′ Z ′ .

[0084] The direction vector of the mirror normal in the laser scanning auxiliary coordinate system :

[0085] .

[0086] Based on the transformation relationship between the laser scanning coordinate system and the laser scanning auxiliary coordinate system, the direction vector of the mirror normal in the laser scanning coordinate system is obtained. :

[0087]

[0088] The angle φ between the projection of the mirror normal onto the XZ plane and the Z-axis. Fx :

[0089] .

[0090] According to geometric relationships, the angle φ between the projection of the reflected ray onto the XZ plane and the Z-axis is... x :

[0091] .

[0092] The angle φ between the projection of the mirror normal onto the YZ plane and the Z-axis. Fy :

[0093] .

[0094] According to geometric relationships, the angle φ between the projection of the reflected ray onto the XY plane and the Z-axis is... y :

[0095] .

[0096] According to φ x and φ y The scanning angle φ is obtained as follows:

[0097] .

[0098] Based on the scanning angle φ, the perpendicular distance from the center of the reflector to the laser incident point on the water surface is calculated. , where d1 is the slant distance of the laser propagation in the air.

[0099] Based on geometric relationships, the three-dimensional coordinates of the laser incident point S on the water surface in the laser scanning coordinate system are obtained as follows:

[0100]

[0101] Then the azimuth angle is obtained. ).

[0102] According to Snell's law, the laser refraction angle on the water surface is obtained. To determine the water depth , where d2 is the slant distance of the laser propagation underwater.

[0103] Based on geometric relationships, the three-dimensional coordinates of the laser incident point F underwater in the laser scanning coordinate system are obtained as follows:

[0104] .

[0105] Define the laser scanning reference coordinate system: Establish the laser scanning reference coordinate system OX with the center of the reflector as the origin O. ′′ Y ′′ Z ′′ Y ′′ The axis is the direction of flight, Z. ′′ The axis is vertical, and the flight vehicle is pointing upwards. ′′ axis and Y ′′ Z ′′ The axes form a right-handed Cartesian coordinate system. When the rotation angle of the hollow load rotary table motor is 0°, the Y-axis of the laser scanning coordinate system points in the flight direction, i.e., O-XYZ and OX.′′ Y ′′ Z ′ The three axes are in the same direction. When the no-load rotary table motor rotates clockwise, it drives the lidar to rotate clockwise with the reflection center as the origin. That is, the laser scanning coordinate system rotates clockwise around the Y-axis with O as the center.

[0106] Transformation relationship between laser scanning reference coordinate system and laser scanning coordinate system:

[0107]

[0108] in, This refers to the rotation angle of the hollow load rotary table motor.

[0109] Based on the conversion relationship, the rotation angle of the hollow load rotary table motor is obtained as follows: At that time, the three-dimensional coordinates of the laser incident point S on the water surface in the laser scanning reference coordinate system are:

[0110] .

[0111] The three-dimensional coordinates of the laser incident point F underwater in the laser scanning coordinate system:

[0112] .

[0113] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of the present invention.

Claims

1. A positioning method for a rotatable oval-shaped scanning airborne depth sounding lidar system, characterized in that, The system includes: Airborne depth-sounding lidar uses an oval scanning method to emit laser pulses and receive echo information to obtain the slant range of the target point; A rotatable lidar mounting bracket is used to fix the airborne depth sounding lidar on the flight vehicle; the incident light of the oval-shaped scanning airborne depth sounding lidar is perpendicular to the flight direction to maximize the lateral scanning angle and improve the lateral overlap; when the operation scenario is a large-area measurement, the rotation angle of the hollow load rotary table motor is set to 0°, so that the long axis of the scanning trajectory is perpendicular to the flight direction; when the operation scenario is a small-area measurement, only one measurement strip is needed to cover the target area. By setting the rotation angle of the hollow load rotary table motor to drive the lidar to rotate, the long axis of the scanning trajectory is parallel to the waterline or river direction, thereby reducing the measurement bandwidth and improving the lateral overlap; An attitude determination and positioning system is used to acquire spatial position and attitude information of the flight vehicle; The rotatable lidar mounting frame includes a connecting mechanism, a hollow load-bearing rotary table, and a bolt assembly; The connecting mechanism includes a cantilever buckle assembly and a connecting plate. The cantilever buckle assembly includes multiple cantilever buckles. The connecting plate is fixed to the top of the hollow load rotary table and is connected to a protrusion on the bottom of the flight vehicle that matches the cantilever buckle through the cantilever buckles. The bottom end of the hollow load rotary table is connected to the top end of the lidar via the bolt assembly. The hollow load rotary table is driven by a stepper motor, and the lidar is rotated by controlling the rotation of the motor. The bolt assembly includes a plurality of bolts arranged in a circle around the periphery of the hollow load rotary table, each bolt being threadedly connected to the hollow load rotary table and the top of the lidar. The method includes: S1: Set the rotation angle of the hollow load rotary table motor; S2: Obtain the propagation slant distance of the laser from the emission point to the target point in air and water, the rotation angle of the airborne depth sounding lidar reflector drive motor, the three-dimensional coordinates of the center of the attitude positioning system (WGS-84), and the attitude angle of the flight vehicle. S3: Calculate the three-dimensional coordinates of the target point in the laser scanning reference coordinate system based on the rotation angle of the hollow load rotary table motor, the propagation slant distance of the laser in air and water, and the rotation angle of the drive motor; S4: Use a total station to measure the eccentricity correction from the center of the lidar reflector to the center of the attitude positioning system, and transform the three-dimensional coordinates of the target point in the laser scanning reference coordinate system to the carrier coordinate system; S5: Based on the attitude angle of the flight vehicle, transform the three-dimensional coordinates of the target point in the vehicle coordinate system to the navigation coordinate system; S6: Transform the three-dimensional coordinates of the center of the attitude determination and positioning system in the geodetic coordinate system WGS-84 to the geocentric coordinate system, and combine the three-dimensional coordinates of the target point in the navigation coordinate system to calculate the three-dimensional coordinates of the target point in the geocentric coordinate system. S7: Transform the three-dimensional coordinates of the target point in the geocentric coordinate system to the geodetic coordinate system; S3 includes: Define the laser scanning coordinate system: With the center of the reflector as the origin O, establish the laser scanning coordinate system O-XYZ. The Z-axis is perpendicular to the flight vehicle and points upward. The X-axis is the opposite direction of the incident laser. The Y-axis and the X-axis form a right-handed rectangular coordinate system. The incident laser and the drive motor shaft are located in the same plane, which is the XZ plane. Define the laser scanning auxiliary coordinate system: Rotate the laser scanning coordinate system counterclockwise by 45° around the Y-axis with O as the center to establish the laser scanning auxiliary coordinate system OX. ′ Y ′ Z ′ ; The direction vector of the mirror normal in the laser scanning auxiliary coordinate system : ； Based on the transformation relationship between the laser scanning coordinate system and the laser scanning auxiliary coordinate system, the direction vector of the mirror normal in the laser scanning coordinate system is obtained. : ； The angle φ between the projection of the normal of the reflector onto the XZ plane and the Z-axis. Fx : ； According to geometric relationships, the angle φ between the projection of the reflected ray onto the XZ plane and the Z-axis is... x : ； The angle φ between the projection of the normal of the reflector onto the YZ plane and the Z-axis. Fy : ； According to geometric relationships, the angle φ between the projection of the reflected ray onto the XY plane and the Z-axis is... y : ； According to φ x and φ y The scanning angle φ is obtained as follows: ； Based on the scanning angle φ, the perpendicular distance from the center of the reflector to the laser incident point on the water surface is calculated. Where d1 is the slant distance of the laser propagation in the air; Based on geometric relationships, the three-dimensional coordinates of the laser incident point S on the water surface in the laser scanning coordinate system are obtained as follows: ； Then the azimuth angle is obtained. ); According to Snell's law, the laser refraction angle on the water surface is obtained. To determine the water depth Where d2 is the slant distance of the laser propagation underwater; Based on geometric relationships, the three-dimensional coordinates of the laser incident point F at the underwater surface in the laser scanning coordinate system are obtained: ； Define the laser scanning reference coordinate system: establish the laser scanning reference coordinate system OX with the center of the reflector as the origin O. ′′ Y ′′ Z ′′ Y ′′ The axis is the direction of flight, Z. ′′ The axis is perpendicular to the flight vehicle and points upwards, X ′′ axis and Y ′′ Z ′′ The axes form a right-handed rectangular coordinate system. When the rotation angle of the hollow load rotary table motor is 0°, the Y-axis of the laser scanning coordinate system points to the flight direction, i.e., O-XYZ and OX. ′′ Y ′′ Z ′ The three axes are in the same direction. When the no-load rotary table motor rotates clockwise, it drives the lidar to rotate clockwise around the reflection center as the origin. That is, the laser scanning coordinate system rotates clockwise around the Y-axis with O as the center. The transformation relationship between the laser scanning reference coordinate system and the laser scanning coordinate system: ； in, The rotation angle of the hollow load rotary table motor; Based on the aforementioned conversion relationship, the rotation angle of the hollow load rotary table motor is calculated as follows: At that time, the three-dimensional coordinates of the laser incident point S on the water surface in the laser scanning reference coordinate system are: ； The three-dimensional coordinates of the laser incident point F underwater in the laser scanning coordinate system are as follows: 。

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