Laser scanning device of unmanned aerial vehicle airborne LiDAR for water depth measurement, LiDAR and unmanned aerial vehicle

Abstract

The invention discloses a laser scanning device of an unmanned aerial vehicle airborne LiDAR for water depth measurement, the LiDAR and an unmanned aerial vehicle, and relates to the field of laser radar detection. In the laser scanning device, through synchronous driving of two motors, when an incident laser beam rotates in a light plane reflection rotating mirror to complete 360-degree light spot scanning once and a scanning light beam is in a position range of 0-X degrees and (360-X)-360 degrees, a light detector protection assembly also just rotates to an area with a light attenuation value of 0 or an unshielded area, so that the light attenuation value of the light detector protection assembly is reduced; light echoes (water surface and water bottom) generated by the scanning light beams in the range enter the optical detector without attenuation, the scanning light beams in the range of X-(360-X) degrees are shielded by the circular shielding cover with the notch, stray light generated by shielding is attenuated by the circular light attenuation sheet or shielded by the non-notch part of the circular shielding sheet and cannot enter the optical detector, and the scanning light beams in the range of X-(360-X) degrees cannot enter the optical detector. The method greatly improves the detection precision, and is especially suitable for water depth measurement. And the structural design of the light scanning assembly and the light receiving assembly reduces the overall complexity of the laser scanning device.

Description

Technical Field

[0001] The present application relates to the field of laser radar detection technology, and in particular to a laser scanning device of a drone-mounted LiDAR for water depth measurement, a LiDAR, and a drone. Background Art

[0002] The laser scanning device is one of the most important components of the laser radar (Light Laser Detection and Ranging, LiDAR). Its function is to use a pulsed laser to perform two-dimensional deflection scanning of light spots, or deflection scanning of light arrays, or deflection scanning of light surface arrays on the detection target area. At present, the LiDAR products on the market are usually used in the fields of autonomous driving, ground three-dimensional mapping, automated production, etc. The scanning methods of its laser scanning device include the following four: one is the two-dimensional scanning of light spots by a combination of galvanometers, prisms or optical wedges, the second is the 360° light spot scanning of light reflection rotating mirrors, the third is the large field of view scanning of light arrays, and the fourth is the large field of view scanning of light surface arrays. However, the laser scanning devices of these products are often not suitable for underwater measurement environments, because compared with the light diffuse reflectance of ground objects greater than 10%, the diffuse reflectance of underwater light is less than 0.1%, and the light absorption and light scattering of water bodies are large, resulting in the measurement accuracy cannot meet the work requirements. Therefore, this field is in urgent need of a LiDAR laser scanning product suitable for underwater measurement environments. Summary of the invention

[0003] In view of the problems existing in the above prior art, the purpose of this application is to provide a laser scanning device, LiDAR and drone for drone-mounted LiDAR for water depth measurement, so as to improve the accuracy of water depth measurement and reduce the complexity of the device.

[0004] To achieve the above objectives, this application provides the following solutions.

[0005] In a first aspect, the present application provides a laser scanning device of a drone-mounted LiDAR for water depth measurement, comprising: a laser, a light scanning component, a light receiving component and a light detector; the light scanning component comprises a light plane reflecting rotating mirror, a first motor and a ring-shaped shielding cover with a notch; the light receiving component comprises a light plane reflecting mirror with a central opening, a light receiving main mirror, a light detector protection component, a second motor, a light collimating mirror and a light converging mirror; the light detector protection component is a circular light attenuation sheet or a circular shielding sheet with a notch;

[0006] The laser is used to emit a laser beam, and the direction of the emitted laser beam is parallel to the flight direction of the drone; the light plane reflector with a central opening and the light plane reflective rotating mirror are sequentially located on the exit optical path of the laser and are placed at a preset angle with the optical axis of the incident laser beam; the laser beam emitted by the laser passes through the central opening of the light plane reflector with a central opening, directly incident on the light plane reflective rotating mirror, and is reflected downward by the light plane reflective rotating mirror to form a scanning beam; an XYZ coordinate system is established with the flight direction of the drone as the Y-axis direction and the horizontal plane as the XY plane, and the position where the scanning beam is parallel to the Z-axis is the rotation 0° position;

[0007] The optical plane reflection rotating mirror is driven by the first motor, and rotates 360° clockwise or counterclockwise around the optical axis of the incident laser beam with the 0° position as the reference, so that the incident laser beam forms a 360° light spot line scan in the XZ plane; an annular shielding cover with a gap is installed around the optical plane reflection rotating mirror, the gap of the annular shielding cover faces downward and the gap area ranges from 0° to X° and (360-X)° to 360°; the annular shielding cover with a gap is used to block the scanning light beam in the position range of X° to (360-X)°, and only the scanning light beam in the position range of 0° to X° and (360-X)° to 360° passes through the gap of the annular shielding cover to form a straight line scanning trajectory downward; wherein 5≤X≤25;

[0008] The scanning light beam emitted through the gap of the annular shield reaches the water surface downward, and part of it passes through the water body to the bottom of the water; the light echo reflected from the water surface and the bottom of the water is transmitted upward to the light plane reflection rotating mirror, reflected by the light plane reflection rotating mirror to the light plane reflection mirror with the central opening, and then reflected by the light plane reflection mirror with the central opening;

[0009] The light receiving main mirror, the light detector protection component, the light collimator, the light convergent mirror and the light detector are sequentially arranged on the reflection light path of the light plane reflector with the central opening; the light echo reflected by the light plane reflector with the central opening enters the light receiving main mirror, and then enters the light detector through the light collimator and the light convergent mirror after being attenuated or blocked by the light detector protection component; the light detector protection component is driven by a second motor, and the second motor is driven synchronously with the first motor, so that when the scanning light beam is in the position range of 0° to X° and (360-X)° to 360°, the light detector protection component also rotates to the area with the light attenuation value of 0 or the unblocked area, and the scanning light beam in the position range of X° to (360-X)° is blocked by the annular shielding cover with a notch, and the stray light generated by the blocking is attenuated or blocked by the light detector protection component and cannot enter the light detector.

[0010] Optionally, a preset angle between the light plane reflector with the central opening and the light plane reflective rotating mirror and the optical axis of the incident laser beam is 45°.

[0011] Optionally, the light plane reflecting mirror is configured to be circular.

[0012] Optionally, the first motor is coaxial with the incident laser beam.

[0013] Optionally, the second motor and the first motor drive the light detector protection assembly and the light plane reflecting rotating mirror to rotate in the same direction and synchronously.

[0014] Optionally, in the circular light attenuation sheet, the area corresponding to the scanning light beam position range of 0°~X° and (360-X)°~360° is a light attenuation zero value area, and the light attenuation value is 0; the area corresponding to the scanning light beam position range of X°~(360-X)° is a light attenuation high value area, and the light attenuation value is 60dB.

[0015] Optionally, in the circular shielding piece with a notch, the area corresponding to the scanning beam position range of 0°~X° and (360-X)°~360° is an unblocked area, and the area corresponding to the scanning beam position range of X°~(360-X)° is blocked by the circular shielding piece.

[0016] Optionally, the circular shielding sheet with a notch is a circular matte metal sheet with a notch.

[0017] In the second aspect, the present application provides a UAV-mounted LiDAR for water depth measurement, including: a controller and the laser scanning device; the controller is respectively connected to the laser, the first motor, the second motor and the light detector in the laser scanning device; the controller is used to control the optical power of the laser beam emitted by the laser and drive the synchronous movement of the first motor and the second motor; the controller is also used to record the reference time when the laser beam is emitted and the return time of the water surface and the bottom light echo, and calculate the depth of the water body based on the reference time and return time.

[0018] In a third aspect, the present application provides a drone equipped with the drone-mounted LiDAR for water depth measurement.

[0019] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0020] The present application provides a laser scanning device, a LiDAR and a drone for a drone-mounted LiDAR for water depth measurement. Based on the structural arrangement of a light scanning component and a light receiving component in the laser scanning device, two motors are used to drive a light detector protection component to rotate synchronously with a light plane reflection rotating mirror, so that when the incident laser beam completes a 360° light spot scanning process during the rotation of the light plane reflection rotating mirror, when the scanning light beam is in the position range of 0° to X° and (360-X)° to 360°, the light detector protection component also rotates to an area with a light attenuation value of 0 or an unobstructed area, and the light echo (water surface, water bottom) generated by the scanning light beam in this range enters the light detector without attenuation, while the scanning light beam in the range of X° to (360-X)° is blocked by a circular annular shielding cover with a gap, and the stray light generated by the blocking is attenuated by the circular light attenuation plate or blocked by the unnotched part of the circular shielding plate and cannot enter the light detector. The laser scanning device of this application adopts a dual-motor synchronous optical scanning + optical attenuation (or light shielding) method, which eliminates the interference and damage of non-underwater light echoes such as shielded light and stray light to the optical detector as much as possible, greatly improving the detection accuracy, especially suitable for water depth measurement. In addition, the structural design of the optical scanning component and the optical receiving component reduces the overall weight, volume and complexity of the laser scanning device, which is conducive to the lightweight and miniaturization of the LiDAR machine, and facilitates the selection, use and operation of the drone platform it carries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 This is a schematic diagram of the overall structure of a laser scanning device of a drone-mounted LiDAR for water depth measurement in this application;

[0023] Figure 2 This is a schematic diagram of the structure of the optical scanning component of the present application;

[0024] Figure 3 This is a schematic diagram of the structure of the light detector protection component of this application. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0026] In response to the defects in the prior art, this application proposes a laser scanning device of a drone-mounted LiDAR for water depth measurement. The overall differences of feature descriptors of different images are learned by aggregating and classifying feature vectors of homologous images and different source images to improve the detection accuracy. At the same time, the complexity of the two-stage detection method is reduced by adjusting the similarity scores of feature descriptors.

[0027] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0028] In an exemplary embodiment, the present application provides a laser scanning device of a drone-mounted LiDAR for water depth measurement, such as Figure 1 As shown, the laser scanning device includes: a laser 1, a light scanning component, a light receiving component and a light detector 11. The light scanning component includes a light plane reflecting mirror 2, a first motor 3 and a ring-shaped shielding cover 4 with a gap. The light receiving component includes a light plane reflecting mirror 5 with a central opening, a light receiving main mirror 6, a light detector protection component 7, a second motor 8, a light collimating mirror 9 and a light converging mirror 10. The light detector protection component 7 can be a circular light attenuation sheet or a circular shielding sheet with a gap.

[0029] like Figure 1 As shown, the laser 1 is used to emit a pulsed laser beam (referred to as laser beam), and the direction of the emitted laser beam is parallel to the flight direction of the drone (Y-axis direction). The light plane reflector 5 with a central opening and the light plane reflective rotating mirror 2 are sequentially located on the outgoing light path of the laser 1 and are placed at a preset angle to the optical axis of the incident laser beam. Figure 1 In the embodiment shown, the preset angle is 45°, and the light plane reflective rotating mirror 2 is generally a circular light plane reflective rotating mirror. The laser beam emitted by the laser 1 passes through the central opening of the light plane reflective mirror 5 with the central opening, directly incident on the light plane reflective rotating mirror 2, and is reflected downward by the light plane reflective rotating mirror 2 to form a scanning beam. In the embodiment of the present application, an XYZ coordinate system is established with the flight direction of the drone (also the optical axis direction of the incident laser beam) as the Y-axis direction and the horizontal plane as the XY plane, and the position where the scanning beam is parallel to the Z axis is the rotation 0° position.

[0030] The structure of the optical scanning component is as follows Figure 2 As shown, Figure 2 Part (a) shows the scanning beam when rotated to 0°, which is a cross-sectional view of the optical scanning component structure. Figure 2Part (b) shows the scanning beam rotated to the position of X° and (360-X)°, which is a schematic diagram of the three-dimensional structure of the optical scanning component. 5≤X≤25. Figure 2 , the incident laser beam parallel to the Y-axis direction (flight direction) is reflected by the circular light plane reflection mirror 2, and forms a scanning beam vertically downward along the Z axis (assuming this position is 0°). The angle between the circular light plane reflection mirror 2 and the incident laser beam is 45°. The first motor 3 is coaxial with the incident laser beam. The light plane reflection mirror 2 is driven by the first motor 3, and rotates 360° clockwise or counterclockwise around the optical axis of the incident laser beam with the 0° position as the reference, so that the incident laser beam forms a 360° light point line scan in the XZ plane. A notched annular shielding cover 4 is installed around the optical plane reflective rotating mirror 2. The notch of the annular shielding cover 4 faces downward and the notch area ranges from 0° to X° and (360-X)° to 360°, so that the notched annular shielding cover 4 can block the scanning light beam in the position range of X° to (360-X)°. Only the scanning light beam in the position range of 0° to X° and (360-X)° to 360° passes through the notch of the annular shielding cover 4 to form a straight line scanning trajectory downward. When the LiDAR flies and moves along the Y-axis direction, the light spot line scanning trajectory on the XY plane will become a straight line scanning trajectory array tilted to the left rear and right front (relative to the flight direction), such as Figure 2 As shown in part (b).

[0031] See also Figure 1 and Figure 2 The scanning light beam emitted through the gap of the annular shielding cover 4 reaches the water surface downward, and partially passes through the water body to the bottom of the water. The light echo reflected from the water surface and the bottom of the water is transmitted upward to the light plane reflection mirror 2, and is reflected by the light plane reflection mirror 2 to the light plane reflection mirror 5 with a central opening, and then reflected by the light plane reflection mirror 5 with a central opening.

[0032] like Figure 2 As shown, the light receiving main mirror 6, the light detector protection assembly 7, the light collimator 9, the light converging mirror 10 and the light detector 11 are sequentially arranged on the reflection light path of the light plane reflector 5 with the central opening. The light echo reflected by the light plane reflector 5 with the central opening enters the light receiving main mirror 6, and then enters the light detector 11 after being attenuated or blocked by the light detector protection assembly 7 through the light collimator 9 and the light converging mirror 10. The light detector protection assembly 7 is driven by the second motor 8, and the second motor 8 can be set to rotate in the same direction and synchronously with the first motor 3, so that when the scanning light beam is in the position range of 0° to X° and (360-X)° to 360°, the light detector protection assembly 7 also rotates to the area with the light attenuation value of 0 or the unblocked area, and the scanning light beam in the position range of X° to (360-X)° is attenuated or blocked by the light detector protection assembly 7.

[0033] The structure of the photodetector protection component 7 is as follows: Figure 3 As shown, Figure 3 Part (a) shows a circular light attenuation sheet structure. In the circular light attenuation sheet, the area corresponding to the scanning light beam position range of 0° to X° and (360-X)° to 360° is the light attenuation zero value area, that is, the light attenuation value is 0; the area corresponding to the scanning light beam position range of X° to (360-X)° is the light attenuation high value area, and the light attenuation value is 60dB, that is, 10 6 In some embodiments, the circular light attenuation sheet can be realized by coating a lens.

[0034] Figure 3 Part (b) shows a circular shielding sheet structure with a notch, in which the area corresponding to the scanning light beam position range of 0° to X° and (360-X)° to 360° is an unshielded area (i.e., a notch area), and the area corresponding to the scanning light beam position range of X° to (360-X)° is shielded by the circular shielding sheet (i.e., a shielding area). In some embodiments, the circular shielding sheet with a notch can be a circular matte metal sheet with a notch.

[0035] like Figure 1 As shown, the present application adds a circular light attenuation sheet or a circular shielding sheet 7 with a notch in front of the photosensitive surface window of the light detector 11, and is driven by the second motor 8. The laser 1 emits a pulsed laser beam, and the incident laser beam passes through the light plane reflector 5 with a central opening, and forms a "one"-shaped light spot line scanning trajectory downward through the light plane reflector rotating mirror 2 (driven by the first motor 3 and rotated around the optical axis of the incident laser beam). The water surface and bottom light echoes upward through the light plane reflector rotating mirror 2, and then through the light plane reflector 5 with a central opening, enter the light receiving main mirror 6, and then enter the light detector 11 through the light detector protection component 7 (driven by the second motor 8), the light collimator 9, and the light converging mirror 10.

[0036] In some preferred embodiments, X=20, then the second motor 8 is driven in the same direction and synchronously with the first motor 3, and when the incident laser beam completes a 360° light spot scanning process during the rotation of the light plane reflection mirror 2, when the scanning light beam is in the position range of 0°~20° and 340°~360°, the circular light attenuation plate also rotates to the position range where the light attenuation value is 0 (or the gap of the circular shielding plate is exactly in this position range), ensuring that the light echo (water surface, water bottom) generated by the scanning light beam in this range enters the light detector 11 without attenuation, while the scanning light beam in the range of 20°~340° is blocked by the circular annular shielding cover 4 with a gap, and the stray light generated by the blocking is attenuated by the circular light attenuation plate or blocked by the non-gap part of the circular shielding plate, and cannot enter the light detector 11.

[0037] The laser radar emits a pulsed laser through the laser 1, which passes through the optical scanning device of the present application and reaches the water surface downward. Part of the light passes through the water body and reaches the bottom of the water. When the pulsed laser light echo reflected from the water surface and the bottom of the water is received by the laser radar, its internal controller records three data, namely the reference time when the pulsed laser is emitted, the return time to the water surface and the bottom of the water. By measuring the round-trip time of the laser pulse, the depth of the water body (i.e., the water depth) can be calculated.

[0038] Compared with the existing optical scanning technology, the "I"-shaped light (reflection) scanning component and light receiving component protection combination method adopted by the laser scanning device of the present application has the following specific advantages:

[0039] (1) The circular light plane reflecting mirror 2 is relatively thin and light, and keeps rotating in the same direction during the operation of LiDAR (the first motor 3 can be set to rotate clockwise or counterclockwise). The first motor 3 can be a small motor. Therefore, the light scanning component is light in weight and small in size. The rotational inertia of the circular light plane reflecting mirror 2 (axisymmetrically installed) is small. Therefore, the first motor 3 drives the circular light plane reflecting mirror 2 to rotate faster, and the light scanning speed is faster.

[0040] (2) The circular light attenuation sheet or the circular shielding sheet with a notch in the light detector protection assembly 7 is relatively light and thin, and keeps rotating in the same direction during the operation of the LiDAR (the second motor 8 can be set to rotate in the same direction and synchronously with the first motor 3). The second motor 8 can be a small motor. Therefore, the light detector protection assembly 7 is light in weight and small in size. The rotational inertia of the circular light attenuation sheet or the circular shielding sheet with a notch (axisymmetrically installed) is small, and its rotation speed is fast, and the light scanning speed is fast.

[0041] (3) The mechanical structure design and processing of the optical scanning component are simple, and the process of installing and debugging the optical scanning component together with other optical components is not difficult.

[0042] (4) The optical route for optical scanning and optical echo reception is simple, and there are relatively few error factors that may affect the measurement results that need to be compensated. Later data processing can avoid more complex algorithms, the relevant program software is streamlined, and data processing runs relatively quickly.

[0043] (5) The underwater echo signal is 3 to 4 orders of magnitude weaker than the surface echo signal. In order to receive as many underwater echoes as possible to improve the water depth measurement range, LiDAR usually uses a laser 1 with a higher output light peak power to emit pulsed lasers to compensate for the light absorption and light scattering of the water body, and selects a high-sensitivity light detector 11 to enhance the detection of weak underwater light echoes. The laser scanning device of the present application adopts a dual-motor synchronous light scanning + light attenuation (or light shielding) method to eliminate the interference and damage of non-underwater light echoes such as shielding light and stray light caused by the increase in laser power to the light detector as much as possible, greatly improving the detection accuracy, especially suitable for measuring water depth.

[0044] (6) The structural design of the optical scanning component and the optical receiving component reduces the overall weight and volume of the laser scanning device, which is conducive to the lightweight and miniaturization of the LiDAR machine, and facilitates customers to select, use and operate various commercial suspended wing UAV platforms on the market. Of course, the LiDAR and laser scanning device of the present application can also be used on other manned or unmanned platforms.

[0045] In an exemplary embodiment, the present application also provides a drone-mounted LiDAR for water depth measurement, including: a controller and the laser scanning device. The laser scanning device includes a light scanning component (a light plane reflective rotating mirror 2 + a first motor 3 + a notched annular shielding cover 4) and a light receiving component (a light plane reflective mirror with a central opening 5 + a light receiving main mirror 6 + a light detector protection component 7 + a second motor 8 + a light collimating mirror 9 + a light converging mirror 10). Figure 1 As shown, the laser 1 outputs a laser beam, which passes through the light plane reflection rotating mirror 5 with a central opening, and forms an "I"-shaped light (reflection) scanning beam downward (from the bottom window of the product downward) through the light scanning component, completing the optical scanning of the water surface and the bottom below. The light echo returned from the water surface and the bottom below passes through the light plane reflection rotating mirror 2 and the light plane reflection mirror 5 with a central opening, and successively enters the light receiving main mirror 6 of the light receiving component, the light detector protection component 7, the light collimating mirror 9, the light converging mirror 10, and finally enters the light detector 11. The light detector protection component 7 is placed at the focal position of the light receiving main mirror 6 and the light collimating mirror 9. The light detector protection component 7 can use a circular light attenuation plate, or a circular extinction metal plate with a notch. As shown in FIG. Figure 3 In the preferred embodiment shown, the circular light attenuation sheet is arranged as follows: in the position range of 0° to 20° and 340° to 360°, the light attenuation value is 0; in the range of 20° to 340°, the light attenuation value is 60dB (i.e., 10 6The circular matte metal sheet with notches is set as follows: there are notches in the position range of 0° to 20° and 340° to 360°; there is no notch in the range of 20° to 340°. The second motor 8 is driven in the same direction and synchronously with the first motor 3 to ensure that only the light echo (water surface, water bottom) of the scanning light beam in the range of 0° to 20° and 340° to 360° enters the light detector 11 without attenuation.

[0046] The controller is respectively connected to the laser 1, the first motor 3, the second motor 8 and the light detector 11 in the laser scanning device. The controller is used to control the optical power of the laser beam emitted by the laser 1 and to control the synchronous and co-directional rotation of the first motor 3 and the second motor 8. The controller is also used to record the reference time when the laser beam is emitted and the return time of the light echo on the water surface and the bottom of the water, and calculate the depth of the water body according to the reference time and the return time.

[0047] In an exemplary embodiment, the present application also provides a drone equipped with the drone-mounted LiDAR for water depth measurement. The LiDAR includes a laser scanning device, and the structural design of its light scanning component and light receiving component reduces the overall weight and volume of the laser scanning device, which is conducive to the lightweight and miniaturization of the LiDAR machine, thereby facilitating customers' selection, use and operation of various commercial cantilevered wing drone platforms on the market.

[0048] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0049] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A laser scanning device of UAV-mounted LiDAR for water depth measurement, characterized in that: include: A laser, a light scanning component, a light receiving component and a light detector; the light scanning component includes a light plane reflecting mirror, a first motor and a ring-shaped shielding cover with a gap; the light receiving component includes a light plane reflecting mirror with a central opening, a light receiving main mirror, a light detector protection component, a second motor, a light collimating mirror and a light converging mirror; the light detector protection component is a circular light attenuation sheet or a circular shielding sheet with a gap; The laser is used to emit a laser beam, and the direction of the emitted laser beam is parallel to the flight direction of the drone; the light plane reflector with a central opening and the light plane reflective rotating mirror are sequentially located on the exit optical path of the laser and are placed at a preset angle with the optical axis of the incident laser beam; the laser beam emitted by the laser passes through the central opening of the light plane reflector with a central opening, directly incident on the light plane reflective rotating mirror, and is reflected downward by the light plane reflective rotating mirror to form a scanning beam; an XYZ coordinate system is established with the flight direction of the drone as the Y-axis direction and the horizontal plane as the XY plane, and the position where the scanning beam is parallel to the Z-axis is the rotation 0° position; The optical plane reflection rotating mirror is driven by the first motor, and rotates 360° clockwise or counterclockwise around the optical axis of the incident laser beam with the 0° position as the reference, so that the incident laser beam forms a 360° light spot line scan in the XZ plane; an annular shielding cover with a gap is installed around the optical plane reflection rotating mirror, the gap of the annular shielding cover faces downward and the gap area ranges from 0° to X° and (360-X)° to 360°; the annular shielding cover with a gap is used to block the scanning light beam in the position range of X° to (360-X)°, and only the scanning light beam in the position range of 0° to X° and forms a straight line scanning trajectory downward through the gap of the annular shielding cover; wherein 5≤X≤25; The scanning light beam emitted through the gap of the annular shield reaches the water surface downward, and part of it passes through the water body to the bottom of the water; the light echo reflected from the water surface and the bottom of the water is transmitted upward to the light plane reflection rotating mirror, reflected by the light plane reflection rotating mirror to the light plane reflection mirror with the central opening, and then reflected by the light plane reflection mirror with the central opening; The light receiving main mirror, the light detector protection component, the light collimator, the light convergent mirror and the light detector are sequentially arranged on the reflection light path of the light plane reflector with the central opening; the light echo reflected by the light plane reflector with the central opening enters the light receiving main mirror, and then enters the light detector through the light collimator and the light convergent mirror after being attenuated or blocked by the light detector protection component; the light detector protection component is driven by a second motor, and the second motor is driven synchronously with the first motor, so that when the scanning light beam is in the position range of 0° to X° and (360-X)° to 360°, the light detector protection component also rotates to the area with the light attenuation value of 0 or the unblocked area, and the scanning light beam in the position range of X° to (360-X)° is blocked by the annular shielding cover with a notch, and the stray light generated by the blocking is attenuated or blocked by the light detector protection component and cannot enter the light detector.

2. The laser scanning device according to claim 1, characterized in that: The preset angle between the light plane reflector with the central opening and the light plane reflective rotating mirror and the optical axis of the incident laser beam is 45°.

3. The laser scanning device according to claim 1, characterized in that: The light plane reflecting mirror is arranged in a circular shape.

4. The laser scanning device according to claim 1, characterized in that: The first motor is coaxial with the incident laser beam.

5. The laser scanning device according to claim 1, characterized in that: The second motor and the first motor drive the light detector protection component and the light plane reflection rotating mirror to rotate in the same direction and synchronously.

6. The laser scanning device according to claim 1, characterized in that: In the circular light attenuation sheet, the area corresponding to the scanning light beam position range of 0° to X° and (360-X)° to 360° is the light attenuation zero value area, and the light attenuation value is 0; the area corresponding to the scanning light beam position range of X° to (360-X)° is the light attenuation high value area, and the light attenuation value is 60dB.

7. The laser scanning device according to claim 1, characterized in that: In the circular shielding piece with a notch, the area corresponding to the scanning beam position range of 0°~X° and (360-X)°~360° is an unshielded area, and the area corresponding to the scanning beam position range of X°~(360-X)° is shielded by the circular shielding piece.

8. The laser scanning device according to claim 7, characterized in that: The circular shielding sheet with a notch is a circular matte metal sheet with a notch.

9. A drone-mounted LiDAR for water depth measurement, characterized in that: include: A controller and a laser scanning device as claimed in any one of claims 1 to 8; The controller is respectively connected to the laser, the first motor, the second motor and the light detector in the laser scanning device; the controller is used to control the optical power of the laser beam emitted by the laser and drive the synchronous movement of the first motor and the second motor; the controller is also used to record the reference time when the laser beam is emitted and the return time of the light echo on the water surface and the bottom of the water, and calculate the depth of the water body based on the reference time and return time.

10. An unmanned aerial vehicle equipped with the unmanned aerial vehicle airborne LiDAR for water depth measurement according to claim 9.

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