Non-contact liquid level measuring system and method

Abstract

The invention discloses a non-contact liquid level measuring system and method, an included angle is formed between a flat scanning surface position of a two-dimensional laser distance measuring sensor and an optical axis of a long-focus optical camera by adjusting a two-way degree-of-freedom adjusting mechanism, a calibration method is provided, and the included angle between the flat scanning surface position and the long-focus optical camera is adjusted through a calibration plate. The plane scanning surface of the two-dimensional laser distance measuring sensor is coplanar with the optical axis of the long-focus optical camera, so that the detection precision is improved, the two-way degree-of-freedom adjusting mechanism is simple in structure and flexible to use, the unmanned aerial vehicle measuring device can be adjusted according to actual conditions, and open type liquid pools with different scene complexity can be easily coped with. By adopting a mode of combining unsupervised clustering learning and median sampling, the influence of abnormal interference points on a liquid level calculation result can be avoided to the greatest extent, and the environmental adaptation robustness and the precision difference are improved. According to the invention, multi-frequency and high-precision detection can be carried out on the liquid level of the open type liquid pool, the early-stage investment is small, the later-stage maintenance is simple, and the production cost is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of automated detection, and particularly to a non-contact liquid level measurement system and method. Background Art

[0002] In many application scenarios of open liquid pools with a wide distribution range, the liquid level sometimes reflects the change in liquid concentration and sometimes the liquid volume. The liquid level height plays a crucial role in the technological process. Traditional monitoring methods require manual circuit measurement or automatically use contact-type liquid level measurement tools to read the liquid level. The former has a high labor cost, and it is difficult to ensure the timeliness of measurement, and the measurement accuracy is easily affected by human factors. The latter has the problem of corrosion resistance, resulting in high later maintenance costs, and even cannot work for a long time, making it difficult to be widely applied. In addition, the vast majority of open liquid pools are located in open areas, where wind causes waves, and it is difficult for traditional methods to accurately capture the accurate liquid level. The patent with the application number CN202410703541.4 discloses a drone liquid level measurement system for salt field environments. Its measurement part adopts a fixed structure, and after leaving the factory, the user cannot adjust the measurement angle according to the actual situation. Therefore, it is only limited to measuring the liquid level in salt field environments and cannot cope with open liquid pools with different measurement scene complexities. And due to the fixed angle, the user cannot calibrate the measurement part, that is, adjust the flat scan plane of the optical camera and the rangefinder. Therefore, it is impossible to ensure that the flat scan planes of the optical camera and the rangefinder are consistent, thus affecting the measurement accuracy. When measuring, the liquid surface calculation method adopted by this system is simple algebraic calculation. Once there are too many abnormal interference points in the data, it will directly affect the calculation accuracy and calculation results. Summary of the Invention

[0003] The present invention provides a non-contact liquid level measurement system and method to solve the technical problems raised in the background art.

[0004] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0005] A non-contact liquid level measurement system, characterized in that it includes a reference target system and a drone measurement device; the reference target system consists of a reference pile and a wave dissipation pool to form a basic measurement unit. Each wave dissipation pool is provided with a measurement unit, and multiple measurement units form the reference target system;

[0006] The drone measurement device includes: a drone;

[0007] A global positioning system, including a global positioning sensor installed above the drone and a positioning processor installed in the data processing unit box, and the data processing unit box is located inside the drone;

[0008] Ground reference observation and aiming optical subsystem, including a long-focus optical camera, a short-focus optical camera and an image data processor; the image data processor is installed in the data processing unit box, the long-focus optical camera and the short-focus optical camera are both installed on the measurement reference plane on the abdomen of the UAV body, the optical axes of both are parallel to the vertical axis of the UAV, and the line of sight is downward. The optical axis of the long-focus optical camera is located on the central axis of the UAV, and the optical axis of the short-focus optical camera is located on one side of the long-focus optical camera;

[0009] Two-dimensional laser scanning device, including a two-dimensional laser ranging sensor, a two-degree-of-freedom adjustment mechanism, a gravity tilt sensor and a laser data processor; the laser data processor is installed in the data processing unit box, floats are provided on both sides of the bottom of the UAV, the two-dimensional laser ranging sensor is installed on the abdomen of the UAV, and its horizontal scanning plane is located between the two floats through the two-degree-of-freedom adjustment mechanism, and the gravity tilt sensor is installed on the measurement reference plane;

[0010] The two-degree-of-freedom adjustment mechanism includes a base shaft, a cylindrical sleeve A, a cylindrical sleeve B, a Y-direction fastening screw, a Z-direction fastening screw and a Z-direction adjustment shaft; one end of the base shaft is connected to the measurement reference plane, and the connection position is on the center line on the measurement reference plane that is orthogonal to the optical axis of the long-focus optical camera. The cylindrical sleeve A is of a hollow structure, and the other end of the base shaft passes through the cylinder wall and is orthogonally connected to it, and the central axis of the cylindrical sleeve A is parallel to the center line on the measurement reference plane. The Y-direction fastening screw is located in the hollow hole of the cylindrical sleeve A and is threadedly connected to the cylindrical sleeve B at the lower end of the central axis; the cylindrical sleeve B is radially provided with a through hole, and the Z-direction adjustment shaft is movably connected to the cylindrical sleeve B through this through hole. The end of the Z-direction adjustment shaft is connected with a two-dimensional laser ranging sensor. A threaded hole is provided on the central axis of the cylindrical sleeve B, and the Z-direction fastening screw is threadedly connected to the cylindrical sleeve B through this threaded hole, and the head of the Z-direction fastening screw contacts the shaft body of the Z-direction adjustment shaft.

[0011] Furthermore, the UAV measurement device is calibrated through a calibration plate to minimize the angle between the optical axis of the long-focus optical camera and the horizontal scanning plane of the two-dimensional laser ranging sensor. The calibration method is as follows:

[0012] a. An L-shaped light-transmitting slit is opened at the center of the calibration plate, and an optical marking point P is set at the center position of the light-transmitting slit;

[0013] b. The calibration plate is vertically and fixedly placed at a position more than 5m away from the long-focus optical camera, and the two-degree-of-freedom adjustment mechanism is adjusted so that the Y-direction fastening screw and the Z-direction fastening screw are in a tightened state;

[0014] c. Observe the calibration board through the long - focal - length optical camera, and correspondingly adjust the attitude of the UAV measurement device so that the light observed by the long - focal - length optical camera can pass through all the light - transmissive slits within the field of view, and the center marking point P of the light - transmissive slit is located at the image center and the light - transmissive slit coincides with the image central axis. Then fix the UAV measurement device;

[0015] d. Loosen the Z - direction fastening screw of the two - degree - of - freedom adjustment mechanism, rotate the two - dimensional laser range finder around the Z - direction adjustment axis, observe the number of laser beams passing through the light - transmissive slit. When the number is the largest, tighten the Z - direction fastening screw. Then loosen the Y - direction fastening screw, observe the laser beam passing through the light - transmissive slit and make it located at the center of the observation range of the two - dimensional laser range finder, tighten the Y - direction fastening screw. Loosen the Z - direction fastening screw and repeat the above steps until the laser beam span range reaches L. Stop the adjustment and tighten the Y - direction fastening screw and the Z - direction fastening screw; At this time, the optical axis of the long - focal - length optical camera and the plane - scanning plane of the two - dimensional laser range finder are coplanar.

[0016] Further, the calibration board is square, and a typical value is 5 mm.

[0017] Further, the reference pile consists of a pile body cast with concrete and a reference coordinate point identification plate; The pile body is cylindrical, located at the inner center of the wave - dissipating pool, and the bottom is fixedly connected to the bottom of the liquid pool. There is a reference coordinate point identification plate at the top of the pile body. The diameter of the reference coordinate point identification plate is larger than the diameter of the pile body, and the overall height of the combination of the reference coordinate point identification plate and the pile body is greater than the height of the wave - dissipating pool wall.

[0018] Further, the upper surface of the reference coordinate point identification plate is painted with a four - divided yellow - black alternating color disk using yellow and black paint for the UAV to identify and provide the coordinate reference.

[0019] Further, the wave - dissipating pool is a hollow cube, formed by concrete pouring. The hollow part runs through the three - dimensional structure, and the through - direction is called the hollow axis. A number of connecting holes are opened along the direction parallel to the hollow axis to connect the water bodies in the wave - dissipating pool and the liquid pool, so as to keep the water levels in the wave - dissipating pool and the liquid pool at the same height; The end of the wave - dissipating pool exposed above the liquid pool surface is called the exposed end, and its height is greater than the highest liquid level of the liquid pool, used to isolate the liquid surfaces in the wave - dissipating pool and the liquid pool. The other end is called the submerged end, which is fixedly installed at the bottom of the liquid pool.

[0020] The non - contact liquid - level measurement method includes the following steps:

[0021] 1) The global positioning sensor provides rough position information to guide the UAV to fly above the reference pile to achieve rough positioning;

[0022] 2) Capture the reference coordinate point identification plate at the top of the reference pile through the short - focal - length optical camera, and use this information to adjust the position of the UAV fuselage so that the identification center point on the reference coordinate point identification plate is located at the center of the field of view;

[0023] 3) Capture the reference coordinate point identification plate at the top of the reference pile through a long - focal - length optical camera, and further accurately calibrate the position of the UAV so that the identification points on the reference coordinate point identification plate are located at the center of the field of view;

[0024] 4) Measure the angle between the measurement reference plane and the gravity direction as 90° through a gravity inclination sensor, start the two - dimensional laser ranging sensor to scan and record distance data, and obtain a set of distance data ; 5) Intercept the set of distance data Intercept the distance data within the range of ±15° before and after the middle angle of the scanning plane, and set it as ; 6) Perform 3 - mean clustering on D to obtain 3 clustering sets , and the minimized objective function used is:

[0025] Among them, is the mean value of ;

[0026] 7) Respectively take the median points of the clustering sets, and set them as . Assume , then the distance between the two - dimensional laser ranging sensor (241) and the top surface of the reference pile (11) in the stilling basin (12) is , and the typical distance of the liquid level in the stilling basin (12) is . Let the altitude of the reference coordinate point of the reference pile (11) be z, and obtain the actual altitude of the liquid pool liquid level from the following formula:

[0027] .

[0028] Compared with the prior art, the present invention has the following advantages or beneficial effects:

[0029] By adjusting the two-degree-of-freedom adjustment mechanism, the plane sweep of the two-dimensional laser ranging sensor is located between the two pontoons at the bottom of the UAV, forming an angle with the optical axis of the long-focus optical camera, and a calibration method is provided. By using a calibration board to adjust the angle between the two, the angle is ensured to approach 0, so that the plane sweep of the two-dimensional laser ranging sensor is coplanar with the optical axis of the long-focus optical camera, thereby improving the detection accuracy. The two-degree-of-freedom adjustment mechanism has a simple structure and is flexible to use. It can adjust the UAV measurement device according to the actual situation and easily cope with open liquid pools with different levels of measurement scene complexity. By combining unsupervised clustering learning with median sampling, the influence of abnormal interference points on the liquid level calculation result can be avoided to the greatest extent, and the environmental adaptability robustness and accuracy are improved. The present invention can be used for multi-frequency and high-precision detection of the liquid level of open liquid pools, effectively improving the measurement density, the accuracy and reliability of measurement data, with low upfront investment and simple later maintenance, greatly reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions implemented in the present invention, the drawings required for describing the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 It is a block diagram of a non-contact liquid level measurement system;

[0032] Figure 2 It is a schematic structural diagram of a reference target;

[0033] Figure 3 It is a schematic structural diagram of a UAV;

[0034] Figure 4 It is a partial enlarged view of the ground reference observation optical subsystem and the two-dimensional laser scanning device;

[0035] Figure 5 It is a calibration configuration diagram;

[0036] Figure 6 It is a schematic diagram of liquid level calculation;

[0037] In the figure, 1 is the reference target system, 11 is the reference pile, 111 is the reference coordinate point identification plate, 112 is the pile body, 12 is the wave dissipation pool, 2 is the unmanned aerial vehicle (UAV) measurement device, 21 is the UAV, 22 is the global positioning system (GPS), 221 is the GPS sensor, 23 is the ground reference sighting optical subsystem, 231 is the short-focus optical camera, 232 is the long-focus optical camera, 24 is the two-dimensional laser scanning device, 241 is the two-dimensional laser range finder sensor, 2421 is the base axis, 2422 is the cylindrical sleeve A, 2423 is the Y-direction fastening screw, 2424 is the Z-direction adjustment axis, 2425 is the Z-direction fastening screw, 2426 is the cylindrical sleeve B, 243 is the gravity inclination sensor, 4 is the liquid pool, 41 is the data processing unit box, 51 is the buoy, 52 is the measurement reference plane, and 61 is the calibration plate. Detailed implementation manners

[0038] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] As Figures 1 - 4 shown, the present invention provides a non-contact liquid level measurement system, which includes a reference target system 1 and a UAV measurement device 2; the reference target system 1 consists of a reference pile 11 and a wave dissipation pool 12 to form a basic measurement unit, and one measurement unit is arranged in each wave dissipation pool 12, and multiple measurement units form the reference target system 1.

[0040] The UAV measurement device 2 includes: a UAV 21, a GPS 22, a ground reference sighting optical subsystem 23, and a two-dimensional laser scanning device 24. The GPS 22 includes a GPS sensor 221 installed above the UAV 21 and a positioning processor installed in the data processing unit box 41, and the data processing unit box 41 is located inside the UAV 21. The rough positioning information provided by the GPS 22 guides the UAV 21 to fly above the reference pile 11.

[0041] The ground reference observation optical subsystem 23 includes a long-focus optical camera 232, a short-focus optical camera 231, and an image data processor. The image data processor is installed in the data processing unit box 41. The long-focus optical camera 232 and the short-focus optical camera 231 are both installed on the measurement reference plane 52 on the abdomen of the UAV 21. The optical axes of both are parallel to the vertical axis of the UAV 21, and the line of sight is downward. The optical axis of the long-focus optical camera 232 is located on the central axis of the UAV 21, and the optical axis of the short-focus optical camera 231 is located on one side of the long-focus optical camera 232. Set the longitudinal installation height so that the buoy 51 does not block the field of view. Both are used to find the reference coordinate point identification plate 111 of the reference pile 11 and further guide the UAV 21 to fine-position on the horizontal plane and align with the measurement position.

[0042] The two-dimensional laser scanning device 24 includes a two-dimensional laser ranging sensor 241, a two-way degree-of-freedom adjustment mechanism, a gravity inclination sensor 243, and a laser data processor. The laser data processor is installed in the data processing unit box 41. Buoys 51 are provided on both sides of the bottom of the UAV 21. The two-dimensional laser ranging sensor 241 is installed on the abdomen of the UAV 21. Through the two-way degree-of-freedom adjustment mechanism, its plane scan surface is located between the two buoys 51 and the included angle with the optical axis of the long-focus optical camera 232 is β. Through the UAV measurement device calibration method, the β angle is made as small as possible. The gravity inclination sensor 243 is installed on the measurement reference plane 52.

[0043] The two-way degree-of-freedom adjustment mechanism includes a base shaft 2421, a cylindrical sleeve A 2422, a cylindrical sleeve B 2426, a Y-direction fastening screw 2423, a Z-direction fastening screw 2425, and a Z-direction adjustment shaft 2424. One end of the base shaft 2421 is connected to the measurement reference plane 52, and the connection position is on the center line on the measurement reference plane 52 that is orthogonal to the optical axis of the long-focus optical camera 232. The cylindrical sleeve A 2422 has a hollow structure. The other end of the base shaft 2421 passes through the cylinder wall and is orthogonally connected to it, and the central axis of the cylindrical sleeve A 2422 is parallel to the center line on the measurement reference plane 52. The Y-direction fastening screw 2423 is located in the hollow hole of the cylindrical sleeve A 2422 and is threadedly connected to the cylindrical sleeve B 2426 at the lower end of the central axis. The cylindrical sleeve B 2426 is radially provided with a smooth through hole, and the Z-direction adjustment shaft 2424 is movably connected to the cylindrical sleeve B 2426 through this through hole. The end of the Z-direction adjustment shaft 2424 is connected with the two-dimensional laser ranging sensor 241. A threaded hole is provided on the central axis of the cylindrical sleeve B 2426, and the Z-direction fastening screw 2425 is threadedly connected to the cylindrical sleeve B 2426 through this threaded hole. The head of the Z-direction fastening screw 2425 contacts the shaft body of the Z-direction adjustment shaft 2424 to play a role of loosening and tightening. Under the adjustment of the two-way degree-of-freedom adjustment mechanism, the two-dimensional laser ranging sensor 241 can rotate around the y-axis and the z-axis and be locked in an appropriate position.

[0044] As Figure 5 shown, in this embodiment, the calibration plate 61 is used to calibrate the UAV measuring device, so that the included angle between the optical axis of the long-focus optical camera 232 and the plane scanning surface of the two-dimensional laser ranging sensor 241 is minimized. The calibration method is as follows:

[0045] a. An L-shaped light-transmitting slit is opened at the center of the calibration plate 61, and an obvious optical marking point P is set at the center position of the light-transmitting slit, which can be marked with yellow pigment.

[0046] b. The calibration plate 61 is vertically and fixedly placed at a position more than 5 m away from the long-focus optical camera 232, and the two-degree-of-freedom adjustment mechanism is adjusted so that the Y-direction fastening screw 2423 and the Z-direction fastening screw 2425 are in a fastened state.

[0047] c. Observe the calibration plate 61 through the long-focus optical camera 232, and correspondingly adjust the attitude of the UAV measuring device so that the light observed by the long-focus optical camera 232 can pass through all the light-transmitting slits within the field of view, and the central marking point P of the light-transmitting slit is located at the center of the image and the light-transmitting slit coincides with the central axis of the image. Then fix the UAV measuring device.

[0048] d. Loosen the Z-direction fastening screw 2425 of the two-degree-of-freedom adjustment mechanism, rotate the two-dimensional laser ranging sensor 241 around the Z-direction adjustment axis 2424, observe the number of laser beams passing through the light-transmitting slit. When the number is the largest, tighten the Z-direction fastening screw 2425. Then loosen the Y-direction fastening screw 2423, observe the laser beam passing through the light-transmitting slit, and make it located at the center of the observation range of the two-dimensional laser ranging sensor 241. Tighten the Y-direction fastening screw 2423, loosen the Z-direction fastening screw 2425 and repeat the above steps until the laser beam span range reaches L, stop the adjustment and tighten the Y-direction fastening screw 2423 and the Z-direction fastening screw 2425. At this time, the included angle β between the optical axis of the long-focus optical camera 232 and the plane scanning surface of the two-dimensional laser ranging sensor 241 is very small and can be approximately considered coplanar. Preferably, the calibration plate 61 is square and has a certain thickness, and the typical value is 5 mm.

[0049] Further explanation: The reference pile 11 is composed of a pile body 112 cast with concrete and a reference coordinate point identification plate 111. The pile body 112 is cylindrical and is located at the inner center of the wave dissipating pool 12. The bottom is fixedly connected to the bottom of the liquid pool 4. The reference coordinate point identification plate 111 is fixedly provided at the top of the pile body 112. The diameter of the reference coordinate point identification plate 111 is larger than that of the pile body 112. The overall height of the combination of the reference coordinate point identification plate 111 and the pile body 112 is greater than the height of the pool wall of the wave dissipating pool 12. Preferably, the upper surface of the reference coordinate point identification plate 111 is painted with a four-part yellow and black alternating color plate using yellow and black paint for the drone to identify and provide the reference coordinate. Let the absolute position of the reference coordinate point identification plate be (x, y, z), where x and y are the longitude and latitude respectively, and z is the altitude, which can be obtained by civil survey methods.

[0050] Further explanation: The wave dissipating pool 12 is a hollow cube, formed by concrete casting. The hollow part runs through the three-dimensional structure, and the running-through direction is called the hollow axis. A number of connecting holes are opened along the direction parallel to the hollow axis for connecting the water body in the wave dissipating pool 12 and the water body in the liquid pool 4, so as to keep the water level in the wave dissipating pool 12 consistent with the water level in the liquid pool 4 and not affected by external waves. The end of the wave dissipating pool 12 exposed above the liquid pool water surface is called the exposed end, and its height is greater than the highest liquid level of the liquid pool 4, which is used to isolate the liquid surface in the wave dissipating pool 12 and the liquid surface in the liquid pool 4. The other end is called the submerged end, which is fixedly installed on the bottom of the liquid pool 4.

[0051] The present invention provides a non-contact liquid level measurement method, and the specific steps are as follows:

[0052] 1) The global positioning sensor 221 provides rough position information to guide the drone (21) to fly to about 5 - 7 m above the reference pile 11 to achieve rough positioning.

[0053] 2) First, the short-focus optical camera 231 captures the reference coordinate point identification plate 111 at the top of the reference pile 11, and uses this information to adjust the position of the drone 21 fuselage so that the identification center point on the reference coordinate point identification plate 111 is located at the center of the field of view.

[0054] 3) The long-focus optical camera 232 captures the reference coordinate point identification plate 111 at the top of the reference pile 11 to further accurately calibrate the position of the drone 21 so that the identification point on the reference coordinate point identification plate 111 is located at the center of the field of view.

[0055] 4) The gravity inclination sensor 243 measures that the angle between the measurement reference plane 52 and the gravity direction is α≈90°, and starts the two-dimensional laser ranging sensor 241 to scan and record distance data to obtain a distance data set ; 5) Intercept the distance data set to intercept the distance data set within the range of ±15° before and after the middle angle of the scanning plane, and set it as ; 6) Perform 3 - means clustering on D to obtain 3 clustering sets , and the minimized objective function used is: , where is the mean value of

[0056] 7) Respectively take the median points of the clustering sets, denoted as , assume , then the distance between the two - dimensional laser ranging sensor (241) and the top surface of the reference pile (11) in the wave - dissipating pool (12) is , the typical distance of the liquid level in the wave - dissipating pool (12) is , assume the altitude of the reference coordinate point of the reference pile (11) is z, and the actual altitude of the liquid level in the liquid pool is obtained by the following formula: , Enlightened by the ideal embodiments of the present invention as described above, through the above - described description content, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification.

Claims

1. A non-contact liquid level measurement system, characterized in that, It includes a reference target system (1) and an unmanned aerial vehicle (UAV) measurement device (2); the reference target system (1) consists of reference piles (11) and wave dissipating basins (12) to form a basic measurement unit. One measurement unit is arranged in each wave dissipating basin (12), and multiple measurement units form the reference target system (1); The UAV measurement device (2) includes: a UAV (21); A global positioning system (GPS) (22), which includes a global positioning sensor (221) installed above the UAV (21) and a positioning processor installed in a data processing unit box (41). The data processing unit box (41) is located inside the UAV (21); A ground reference viewing optical subsystem (23), which includes a long - focal - length optical camera (232), a short - focal - length optical camera (231) and an image data processor; the image data processor is installed in the data processing unit box (41). The long - focal - length optical camera (232) and the short - focal - length optical camera (231) are both installed on a measurement reference plane (52) on the abdomen of the UAV (21). The optical axes of both are parallel to the vertical axis of the UAV (21), and the line - of - sight direction is downward. The optical axis of the long - focal - length optical camera (232) is located on the central axis of the UAV (21), and the optical axis of the short - focal - length optical camera (231) is located on one side of the long - focal - length optical camera (232); Two-dimensional laser scanning device (24), comprising a two-dimensional laser ranging sensor (241), a two-degree-of-freedom adjustment mechanism, a gravity inclination sensor (243) and a laser data processor; the laser data processor is installed in the data processing unit box (41), floaters (51) are provided on both sides of the bottom of the unmanned aerial vehicle (21), the two-dimensional laser ranging sensor (241) is installed on the abdomen of the unmanned aerial vehicle (21), and its horizontal scanning plane is located between the two floaters (51) through the two-degree-of-freedom adjustment mechanism, and the gravity inclination sensor (243) is installed on the measurement reference plane (52); the two-degree-of-freedom adjustment mechanism includes a base shaft (2421), a cylindrical sleeve A (2422), a cylindrical sleeve B (2426), a Y-direction fastening screw (2423), a Z-direction fastening screw (2425) and a Z-direction adjustment shaft (2424); one end of the base shaft (2421) is connected to the measurement reference plane (52), and the connection position is on the center line of the measurement reference plane (52) that is orthogonal to the optical axis of the long-focus optical camera (232). The cylindrical sleeve A (2422) has a hollow structure, and the other end of the base shaft (2421) passes through the cylinder wall and is orthogonally connected thereto, and the central axis of the cylindrical sleeve A (2422) is parallel to the center line on the measurement reference plane (52). The Y-direction fastening screw (2423) is located in the hollow hole of the cylindrical sleeve A (2422) and is threadedly connected to the cylindrical sleeve B (2426) at the lower end of the central axis. The cylindrical sleeve B (2426) is radially provided with a through hole, and the Z-direction adjustment shaft (2424) is movably connected to the cylindrical sleeve B (2426) through this through hole. The end of the Z-direction adjustment shaft (2424) is connected with the two-dimensional laser ranging sensor (241). A threaded hole is provided on the central axis of the cylindrical sleeve B (2426), and the Z-direction fastening screw (2425) is threadedly connected to the cylindrical sleeve B (2426) through this threaded hole, and the head of the Z-direction fastening screw (2425) contacts the shaft body of the Z-direction adjustment shaft (2424).

2. The non-contact liquid level measurement system according to claim 1, wherein Calibrate the unmanned aerial vehicle measurement device through a calibration plate (61) to minimize the angle between the optical axis of the long-focus optical camera (232) and the horizontal scanning plane of the two-dimensional laser ranging sensor (241). The calibration method is as follows: a. An L-shaped light-transmitting slit is opened at the center of the calibration plate (61), and an optical marking point P is set at the center position of the light-transmitting slit. b. The calibration plate (61) is vertically and fixedly placed at a position more than 5 m away from the long-focus optical camera (232), and the two-degree-of-freedom adjustment mechanism is adjusted so that the Y-direction fastening screw (2423) and the Z-direction fastening screw (2425) are in a tightened state. c. Observe the calibration plate (61) through the long-focus optical camera (232), and correspondingly adjust the attitude of the unmanned aerial vehicle measurement device so that the light observed by the long-focus optical camera (232) can pass through all the light-transmitting slits within the field of view, and the center marking point P of the light-transmitting slit is located at the center of the image and the light-transmitting slit coincides with the central axis of the image, and then fix the unmanned aerial vehicle measurement device. d. Loosen the Z-direction fastening screw (2425) of the two-degree-of-freedom adjustment mechanism, rotate the two-dimensional laser range finder (241) around the Z-direction adjustment shaft (2424), observe the number of laser beams passing through the light-transmitting slit. When the number is the largest, tighten the Z-direction fastening screw (2425). Then loosen the Y-direction fastening screw (2423), observe the laser beam passing through the light-transmitting slit, and make it located at the center of the observation range of the two-dimensional laser range finder (241). Tighten the Y-direction fastening screw (2423), loosen the Z-direction fastening screw (2425) and repeat the above steps until the laser beam span range reaches L. Stop the adjustment and tighten the Y-direction fastening screw (2423) and the Z-direction fastening screw (2425). At this time, the optical axis of the long-focus optical camera (232) is coplanar with the scanning plane of the two-dimensional laser range finder (241).

3. The non-contact liquid level measurement system according to claim 2, wherein The calibration plate (61) is square, and the typical value is 5 mm.

4. The non-contact liquid level measurement system according to claim 1, wherein The reference pile (11) consists of a pile body (112) cast by concrete and a reference coordinate point identification plate (111). The pile body (112) is cylindrical, located at the inner center of the wave-dissipating pool (12), and its bottom is fixedly connected to the bottom of the liquid pool (4). The top of the pile body (112) is provided with a reference coordinate point identification plate (111). The diameter of the reference coordinate point identification plate (111) is larger than that of the pile body (112), and the overall height of the combination of the reference coordinate point identification plate (111) and the pile body (112) is greater than the height of the pool wall of the wave-dissipating pool (12).

5. The non-contact liquid level measurement system according to claim 4, characterized in that, The upper surface of the reference coordinate point identification plate (111) is painted with a four-part yellow and black alternating color disk using yellow and black paint, for the drone to identify and provide the coordinate reference coordinate.

6. The non-contact liquid level measurement system according to claim 1, wherein The wave-dissipating pool (12) is a hollow cube, formed by concrete casting. The hollow part penetrates the three-dimensional structure, and the penetration direction is called the hollow axis. A number of connecting holes are opened along the parallel direction of the hollow axis, for connecting the water body in the wave-dissipating pool (12) and the water body in the liquid pool (4), so as to keep the water level in the wave-dissipating pool (12) consistent with the water level in the liquid pool (4). The end of the wave-dissipating pool (12) exposed above the liquid pool water surface is called the exposed end, and its height is greater than the highest liquid level of the liquid pool (4), for isolating the liquid surface in the wave-dissipating pool (12) and the liquid surface in the liquid pool (4). The other end is called the submerged end, and is fixedly installed at the bottom of the liquid pool (4).

7. A non-contact liquid level measurement method, based on any one of the non-contact liquid level measurement systems described in claims 1-6, characterized in that, It includes the following steps: 1) The global positioning sensor (221) provides rough position information to guide the drone (21) to fly above the reference pile (11) to achieve rough positioning; 2) Capture the reference coordinate point identification plate (111) at the top of the reference pile (11) through the short-focus optical camera (231), and use this information to adjust the position of the drone (21) fuselage so that the identification center point on the reference coordinate point identification plate (111) is located at the center of the field of view; 3) Capture the reference coordinate point identification plate (111) at the top of the reference pile (11) through the long-focus optical camera (232), and further accurately calibrate the position of the drone (21) so that the identification point on the reference coordinate point identification plate (111) is located at the center of the field of view; 4) When the angle between the measurement reference plane (52) and the gravity direction measured by the gravity inclination sensor (243) is 90°, the two-dimensional laser ranging sensor (241) is activated to scan and record distance data, obtaining a set of distance data ; 5) Intercept the distance data set to obtain the distance data set within the range of ±15° before and after the middle angle of the scanning plane, denoted as ; 6) Perform 3-means clustering on D to obtain 3 clustering sets , and the minimized objective function used is: ， Among them, is the mean value of 7) Take the median points of the clustering sets respectively and set them as , assuming , then the distance between the two-dimensional laser distance sensor (241) and the top surface of the reference pile (11) in the wave dissipating pool (12) is , the typical distance of the liquid level in the wave dissipating pool (12) is , set the altitude of the reference coordinate point of the reference pile (11) as z, and obtain the actual altitude of the liquid level of the liquid pool from the following formula: 。

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