Real-time monitoring and 3d reconstruction of underwater terrain in experimental scale

Abstract

The present application relates to a kind of experimental scale underwater topography real-time monitoring and three-dimensional reconstruction method, belong to the technical field of pool and flume model test.It includes: track is laid on the flume and sets water walking platform;Underwater measuring device connects platform, including angle adjustable support, binocular industrial camera, bar laser emitter and lighting equipment;Mobile platform synchronous acquisition laser stripe deformation image sequence;After image enhancement, laser stripe extraction and stereo matching, profile point cloud is generated;Combined with platform displacement, complete underwater three-dimensional topographic map is reconstructed by splicing.The method avoids repeated drainage, realizes continuous monitoring in scouring process, can still efficiently obtain high-precision terrain data under low texture and turbid water body, and has reasonable structure and strong adaptability.

Description

Technical Field

[0001] This invention relates to the field of water tank and water tank model testing technology, and in particular to a method for real-time monitoring and three-dimensional reconstruction of underwater terrain at an experimental scale. Background Technology

[0002] With the development of pool and flume model testing technology, the research on local scour and erosion problems in marine engineering has been continuously deepened. Scour topography measurement technology has become one of the core technologies supporting experimental research in this field. Its measurement accuracy and efficiency directly determine the reliability of the test results and the test process, which in turn has led to the development of a variety of topography measurement methods and devices suitable for laboratory environments.

[0003] In related technologies, two main methods are used for measuring the scour topography of test objects such as bottom-mounted platforms and slender components near the bottom: one is the drainage topography measurement method, which involves completely draining the water in the pool after a single scour test, and then using a laser scanner to scan the exposed model bed point by point to complete the three-dimensional reconstruction of the scour topography; the other is the underwater real-time monitoring method, which involves directly acquiring image information of the underwater model bed by deploying binocular vision acquisition devices or structured light projection devices underwater, and then realizing real-time reconstruction of the underwater topography after feature matching and algorithm processing.

[0004] However, both the aforementioned drainage-type topographic surveying method and underwater real-time monitoring device have insurmountable technical flaws: Among them, the drainage topographic survey method requires repeated emptying and filling of the test water body, which not only wastes a lot of water resources, but also greatly prolongs the overall cycle of the model bed test, making it impossible to achieve continuous monitoring of the scouring process. However, underwater real-time monitoring devices based on binocular vision or structured light have inherent problems such as high equipment cost and complex system structure. Furthermore, in the clay and sand model beds commonly used in marine engineering laboratories (with single color and weak topographic features) and in low-visibility turbid water environments caused by sediment initiation, the image acquisition quality is poor and feature matching is difficult, making it hard to meet the needs of high-precision underwater topographic reconstruction. Summary of the Invention

[0005] To address the shortcomings of existing production technologies, the applicant provides a method for real-time underwater topography monitoring and 3D reconstruction at an experimental scale. This method is efficient, resource-saving, and adaptable to different aquatic environments, possessing significant engineering practical value and promising prospects for widespread application.

[0006] The technical solution adopted in this invention is as follows: This invention provides a method for real-time monitoring and three-dimensional reconstruction of underwater topography at an experimental scale, the method comprising the following steps: Step 1: Lay a track in advance above the test area of ​​the pool or tank, and set up a water-based stepping platform. The water-based stepping platform moves at a controlled, quantitative, and uniform speed along the track. Step 2: Provide an underwater measuring device and connect it to the above-water stepping platform to move synchronously with the platform; the underwater measuring device includes: an underwater support frame with an angle adjustment mechanism that can adjust its spatial attitude and viewing angle; two high-resolution industrial cameras, sealed in a waterproof housing and fixed to the underwater support frame at a preset angle; a narrow laser emitter fixed to the above-water stepping platform or the underwater support frame for projecting a narrow laser stripe onto the underwater terrain surface; and at least one underwater lighting device for providing auxiliary lighting in the underwater environment. Step 3: Control the movement of the waterborne stepping platform, and during the movement, use the two industrial cameras to synchronously and continuously acquire image sequences containing the deformation trajectory of the narrow laser stripe on the underwater terrain surface; Step 4: Process the acquired image sequence, including image enhancement, laser stripe extraction, and stereo matching based on binocular vision, to calculate the point cloud data of the underwater topographic profile corresponding to each frame of the image. Step 5: Combining the movement and displacement information of the waterborne stepping platform, the point cloud data corresponding to each frame of the image are stitched together to reconstruct and generate a complete and continuous underwater three-dimensional topographic map of the target area.

[0007] Its beneficial effects are as follows: By combining an above-water walking platform with underwater binocular vision and laser beam cutting devices, a collaborative monitoring system is constructed, avoiding the drawbacks of repeatedly draining water in traditional drainage measurement methods, significantly saving water resources and shortening the experimental cycle; at the same time, by using laser narrow strip active projection to characterize topographic profiles, it overcomes the problem of feature matching difficulties in low-texture, turbid water bodies when relying solely on binocular vision. The system can achieve continuous, efficient, and high-precision monitoring and reconstruction of the erosion terrain evolution process, and has comprehensive advantages such as simple structure, flexible deployment, strong adaptability, and controllable cost.

[0008] As a further improvement, the underwater measuring device in step two also includes: a polarizing filter, which is disposed between the lens of the industrial camera and the waterproof housing; the angle adjustment mechanism is specifically an angle adjustment flange, which has a plurality of bolt holes distributed in a circular or arc shape, and the spatial angle of the industrial camera or the strip laser emitter is adjusted by the cooperation of the bolts with different bolt holes.

[0009] Its beneficial effects are as follows: the addition of a polarizing filter can effectively suppress the reflection and refraction of stray light generated by the laser beam and illumination light on the water medium and the surface of the waterproof shell, significantly improving the signal-to-noise ratio and the clarity of the laser stripes in underwater images; the use of an angle adjustment flange with bolt holes as an attitude adjustment mechanism provides a robust, reliable, and low-cost purely mechanical adjustment solution, which can maintain the long-term stability of the relative pose of the camera and laser under complex water flow disturbances, ensuring the repeatability of triangulation reconstruction accuracy.

[0010] Furthermore, the bolt holes on the angle adjustment flange are set at preset angle intervals, the preset angle interval being 5°.

[0011] Its beneficial effects are as follows: by specifying the angle adjustment interval to 5°, it meets the requirements for fine-tuning the viewing angle in laboratory erosion terrain monitoring, while also taking into account the convenience of adjustment operation and the manufacturability of structural processing. The quantified increment of 5° is sufficient to cover the optimization requirements for camera intersection angle and laser incident angle under most experimental conditions, providing a reliable physical benchmark for quickly determining the optimal optical configuration parameters through pre-experiments.

[0012] As a further improvement, different types of lighting equipment are selected according to the soil type of the test model bed. Specifically, when the model bed is clay, high-pressure sodium lamps are selected as the underwater lighting equipment; when the model bed is sandy, cool white LED strip lights are selected as the underwater lighting equipment.

[0013] Its beneficial effects are as follows: Differential lighting strategies are proposed for two common substrate materials (clay and sand) in marine engineering model tests; the longer wavelength of the high-pressure sodium lamp's yellow light enhances its ability to penetrate turbid water caused by sediment initiation, effectively ensuring image visibility of the trench evolution process on clay beds; the cool white LED strip lights offer good color rendering and uniform illumination, facilitating the presentation of subtle textures and laser line contrast on sandy beds. This adaptive lighting configuration method enables the monitoring system to maintain excellent image acquisition quality when facing different water environments and model bed materials, significantly expanding the applicability of the method.

[0014] As a further improvement, the "image enhancement and laser stripe extraction" in step four specifically includes: processing the image based on the dark channel dehazing algorithm; applying anisotropic diffusion filtering for noise suppression; and extracting continuous and complete laser stripe contours through image thresholding and morphological closing operations.

[0015] Its beneficial effects are as follows: This series of image processing operations constitutes a set of optimized processing links specifically for underwater laser scalpel images; the dark channel defogging algorithm can effectively overcome backscattering blur caused by suspended particles in the water; the anisotropic diffusion filter can sharply preserve the edge gradient of the laser stripes while smoothing the internal noise of the image, avoiding the edge blurring problem caused by conventional Gaussian filtering; combined with threshold segmentation and morphological closing operation, it can intelligently repair and form continuous terrain profile characterization lines when the laser line has a slight break due to steep changes in the bottom or local occlusion, thereby ensuring the integrity and accuracy of the subsequent three-dimensional inversion point cloud.

[0016] As a further improvement, the "stereo matching" in step four specifically includes: extracting a subpixel-level center point on the laser stripe of the first image frame in a pair of image frames acquired synchronously by the two industrial cameras; establishing a sliding window along the epipolar direction in the second image frame to find the maximum image gradient point corresponding to the subpixel-level center point; and calculating the three-dimensional spatial coordinates of the point based on the matching relationship using the principle of triangulation.

[0017] Its advantages lie in the following: Unlike the computationally intensive global feature matching or region matching strategies in traditional binocular vision, this method utilizes the laser stripes themselves as strong feature constraints, simplifying the stereo matching problem into a local one-dimensional search problem along the laser line. Extracting sub-pixel-level center points greatly improves matching accuracy; finding the maximum gradient point as the corresponding matching point under epipolar constraints makes the algorithm efficient and robust. This lightweight stereo matching process significantly reduces computational complexity, enabling real-time or near-real-time 3D inversion of underwater terrain profiles on conventional computing devices.

[0018] As a further improvement, the water-based stepping platform in step one includes: a platform main frame, which is slidably connected to the track via a track slider; and a driving device, including a stepper motor, a fixed pulley, and a traction rope, wherein the stepper motor drives the platform main frame to move along the track via the fixed pulley and the traction rope.

[0019] Its advantages are as follows: the power transmission scheme of "stepper motor-fixed pulley-traction rope" has the advantages of smooth transmission, high positioning accuracy, simple structure, and easy deployment and maintenance in humid laboratory environments. Compared with lead screw or rack and pinion drives, the rope traction method has a higher tolerance for track straightness installation errors and can effectively isolate the transmission of motor vibration to the underwater measuring device, ensuring the stability of the image acquisition process and thus improving the spatial consistency of subsequent multi-frame point cloud stitching.

[0020] As a further improvement, a calibration step is included before step three. The calibration step includes: placing the checkerboard calibration plate underwater and calibrating the intrinsic and extrinsic parameter matrices of the two industrial cameras respectively; and correcting the refractive distortion caused by light passing through the multi-layer medium interface of water-air-waterproof shell based on Snell's law of refraction.

[0021] Its beneficial effects are as follows: Based on conventional camera calibration, an underwater refraction correction step based on Snell's law is specifically introduced. The waterproof shell, air gap, and water body constitute multiple refractive interfaces. If calibration parameters in the air are used directly for 3D reconstruction, severe systematic spatial distortion will be introduced. By reconstructing the real optical path through the refraction correction algorithm, a precise mapping relationship between pixels and actual underwater 3D coordinates can be obtained. This is a key technical guarantee for achieving millimeter-level or even sub-millimeter-level terrain reconstruction accuracy at the laboratory scale.

[0022] As a further improvement, a pre-experiment step is included before step three is performed. The pre-experiment step includes: operating the waterborne stepping platform and the underwater measuring device under still water conditions, and determining the optimal moving speed of the waterborne stepping platform by evaluating the quality of the acquired images, the disturbance of the water flow by the underwater measuring device, and the stability of the movement of the waterborne stepping platform.

[0023] Its beneficial effects are as follows: The addition of a pre-experiment stage allows for the calibration of the system's optimal operating parameters, especially the movement speed. Too slow a speed unnecessarily prolongs the test time and may exacerbate the thermal disturbance of the water body, while too fast a speed can lead to motion blur in the image or excessively large inter-frame spans of laser stripes, affecting image stitching. By comprehensively balancing image quality and measurement efficiency through pre-experiments, a standardized operating procedure and parameter table can be established for the formal scouring test, improving the method's engineering applicability and the comparability of test results.

[0024] As a further improvement, step five includes: smoothing, denoising, and meshing the point cloud data of the stitched underwater three-dimensional topographic map to obtain the final visualized three-dimensional topographic surface model.

[0025] Its beneficial effects are as follows: the original spliced ​​point cloud inevitably contains a small number of outliers or local holes; through smoothing and noise reduction processing, the point cloud quality can be optimized without losing the accuracy of terrain feature inflection points; further meshing processing converts the discrete point cloud into a continuous surface model, which facilitates the subsequent extraction of scour pit morphology parameters, volume calculation, and multi-temporal terrain comparison analysis in commercial software (such as Surfer and CloudCompare), directly serving the quantitative research on the scour mechanism of marine engineering. Attached Figure Description

[0026] Figure 1This is a schematic diagram of the underwater terrain monitoring component of the present invention.

[0027] Figure 2 This is a schematic diagram of the underwater terrain monitoring component of the present invention from another perspective.

[0028] Figure 3 This is a schematic diagram of the upper motion measurement platform component of the present invention.

[0029] Figure 4 This is a schematic diagram of the assembly and measurement process of the underwater terrain real-time monitoring system of the present invention.

[0030] Figure 5 This is a schematic diagram of the underwater topography monitoring process of the present invention.

[0031] Among them: 100, underwater topography monitoring component; 200, upper motion measurement platform component; 110. Industrial camera; 120. Polarizing filter; 130. Waterproof housing; 140. Positioning bolt; 150. Bracket base; 160. Vertical support rod; 170. Angle adjustment flange; 180. Camera sliding bracket; 190. Camera connector; 210. Support angle adjuster; 220. Platform main frame; 230. Track slider; 240. Steering slider; 250. High-energy laser generator; 260. Strip laser port; 270. Laser emitting device support; 280. Laser power supply; 290. Traction line; 2100. Fixed pulley; 2110. Stepper motor. Detailed Implementation

[0032] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the description of the present invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0034] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0035] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0036] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0037] This embodiment provides a method for real-time underwater terrain monitoring and 3D reconstruction at an experimental scale. This method is mainly based on a hardware system that coordinates the operation of an underwater terrain monitoring component 100 and an upper motion measurement platform component 200. The following describes the method in conjunction with... Figures 1 to 5 The system’s specific structure, connections, and workflow are described in detail.

[0038] like Figure 4As shown, the system of the present invention is composed of two main parts: an upper motion measurement platform component 200 located above the water surface and an underwater terrain monitoring component 100 located below the water surface. The two are rigidly connected by a vertical support rod 160 to ensure that the underwater terrain monitoring component 100 can move smoothly, uniformly, and quantitatively above the terrain area to be measured along with the upper motion measurement platform component 200.

[0039] Reference Figure 1 and Figure 2 The underwater topography monitoring component 100 is mainly used to actively sense and acquire structured light image data in the underwater environment. This component specifically includes the following parts: Industrial Camera 110: In this embodiment, two high-resolution industrial cameras 110 are used to form a binocular stereo vision acquisition system. The two industrial cameras 110 are fixed on the camera sliding bracket 180 at a preset angle. The angle is set to form a good triangulation angle so that the laser stripes can be spatially inverted for subsequent calculation.

[0040] Polarizing filter 120: A polarizer 120 is positioned at the front of the lens of the industrial camera 110, specifically between the lens of the industrial camera 110 and the transparent window of the waterproof housing 130. Its function is to perform physical filtering before the light enters the lens, effectively suppressing multiple reflections and scattered stray light generated by the laser beam and light emitted from underwater lighting equipment in turbid water and on the surface of the waterproof housing 130, thereby significantly improving the signal-to-noise ratio and edge sharpness of laser stripes in the acquired image.

[0041] Waterproof casing 130: The waterproof housing 130 is used to house and seal the industrial camera 110 and the polarizer 120. The waterproof housing 130 is preferably made of high-transmittance PC (polycarbonate) plastic or acrylic sheet. Its processing precision must ensure that the field of view of the internal lens is not significantly distorted by the curved surface of the housing, and that it can withstand the water pressure of a preset water depth without leakage.

[0042] Positioning bolt 140: The positioning bolt 140 is used to lock and fix the camera connector 190 on the camera sliding bracket 180, thereby achieving precise adjustment and locking of the axial position and pitch angle of the waterproof housing 130 and the industrial camera 110 inside.

[0043] Support base 150: The support base 150 is the basic load-bearing component of the entire underwater topography monitoring assembly 100, and it has multiple sets of connection through holes. The support base 150 is fixedly connected to the bottom flange of the vertical support rod 160 by bolts.

[0044] Vertical support rod 160: The vertical support rod 160 is a long, rigid stainless steel rod. Its bottom end is connected to the support base 150, and its top end extends upwards out of the water surface and is fixedly connected to the main frame 220 of the upper motion measurement platform assembly 200. The vertical support rod 160 is responsible for suspending the underwater topography monitoring assembly 100 at a specific depth underwater and transmitting the horizontal movement of the platform.

[0045] Angle Adjustment Flange 170: As a core component of the angle adjustment mechanism, the angle adjustment flange 170 is used to connect the vertical support rod 160 to the camera sliding bracket 180, or to connect support rods of different segments; such as Figure 1 and Figure 2 As shown, the disc or arc-shaped plate surface of the angle adjustment flange 170 is provided with multiple bolt holes distributed in a circular or arc shape. In this embodiment, these bolt holes are set at preset 5° angle intervals; during equipment assembly, by inserting the positioning bolts 140 into the bolt holes at different positions, the pitch or yaw angle of the camera sliding bracket 180 and its mounted industrial camera 110 in space can be precisely and quantitatively adjusted mechanically; this purely mechanical locking structure has extremely high vibration resistance and stability, ensuring that the relative posture of the industrial camera 110 will not shift during long-term water flow scouring measurement.

[0046] Camera sliding bracket 180: The camera sliding bracket 180 is a profile bracket with a sliding groove. One end of it is connected to the angle adjustment flange 170, and the other end is connected to the camera connector 190 through the sliding groove and the positioning bolt 140. After loosening the positioning bolt 140, the camera connector 190 can slide along the sliding groove of the camera sliding bracket 180 to adjust the baseline distance, i.e., the binocular distance, between the two industrial cameras 110, to adapt to the observation needs of scour trenches of different widths.

[0047] Camera connector 190: The camera connector 190 is an L-shaped or U-shaped metal connecting plate. One end is clamped or bolted to fix the waterproof housing 130, and the other end has a through hole for the positioning bolt 140 to pass through and fix to the camera sliding bracket 180.

[0048] Reference Figure 3 The upper motion measurement platform assembly 200 is used to provide precise quantitative horizontal driving force and carries some opto-mechanical equipment. The specific structure of the platform is as follows: Bracket angle adjuster 210: The bracket angle adjuster 210 is similar to a flange with bolt holes spaced at 5° intervals and is fixed to the main frame 220 of the platform. The top of the vertical support rod 160 passes through the device and can be locked with bolts. By rotating the vertical support rod 160 and then locking it, the angle of the underwater topography monitoring component 100 relative to the direction of water flow can be macroscopically adjusted.

[0049] Platform main framework 220: The main frame 220 of the platform is constructed from welded or bolted stainless steel profiles, providing sufficient rigidity and load-bearing capacity. The bracket angle adjuster 210 is fixed in its central position via profile support members.

[0050] Track slider 230: The track slider 230 is fixed to the bottom or side of the platform main frame 220, and its shape matches the track pre-laid on the bank of the water tank or pool; the track slider 230 is preferably made of polytetrafluoroethylene or oil-impregnated nylon to reduce the coefficient of sliding friction.

[0051] Steering slider 240: The steering slider 240 is used in conjunction with the fixed pulley 2100 to guide the traction rope 290 in changing direction at curved sections or ends of the track. The upper and lower contact surfaces of the steering slider 240 are coated with lubricating oil to reduce frictional resistance.

[0052] High-energy laser generator 250: It is installed inside the laser emitting device bracket 270 to generate a high-power, high-brightness laser beam, preferably a green laser with a wavelength of 520nm to 550nm, because its transmission attenuation in turbid water near the bottom is relatively small.

[0053] 260mm strip laser port: Located at the front end of the high-energy laser generator 250, it contains cylindrical lenses or Powell prism optical elements to shape the point laser beam into a narrow, straight line laser stripe and project it onto the underwater terrain surface.

[0054] Laser emitter bracket 270: The bracket 270 is fixed to the front end of the platform's main frame 220 and has been structurally reinforced, with a heat dissipation mesh also installed. This bracket 270 is used to mount the high-energy laser generator 250 and the laser power supply 280 that powers it.

[0055] Laser power supply 280: In this embodiment, three 80W laser power supplies 280 can be installed, which are connected to the high-energy laser generator 250 via cables to provide a stable driving current to ensure that the strip laser has sufficient irradiation brightness on the substrate.

[0056] Traction line 290: The traction line 290 is preferably a stainless steel wire rope or a high-strength nylon rope. One end of the rope is fixed to the front traction ring of the platform main frame 220, passes around the fixed pulley 2100 at the end of the track, and the other end is wound around the output shaft reel of the stepper motor 2110.

[0057] Fixed pulley 2100: The fixed pulley 2100 is fixed to the end crossbeam of the track in the water tank or pool via a bearing seat, and is used to change the direction of force applied by the traction line 290.

[0058] Stepper motor 2110: The stepper motor 2110 is equipped with a high-resolution driver and a motion controller. After receiving instructions from the host computer, the controller drives the stepper motor 2110 to precisely rotate through a specific angle according to the set number of pulses, thereby dragging the entire upper motion measurement platform assembly 200 and the underwater terrain monitoring assembly 100 along the track for quantitative and uniform movement via the traction cable 290.

[0059] The workflow and measurement principle of this invention are as follows: Combination Figure 5 The diagram illustrates the underwater topography monitoring process. The detailed implementation steps of the method of this invention are as follows: Platform setup and system connection pre-testing: First, based on FLOW3D hydrodynamic calculations and empirical formulas for sediment transport mechanics, the maximum scour range and depth of the test model bed are estimated. Then, guide rails are laid and leveled above the water tank or pool, and the assembled upper motion measurement platform component 200 is mounted on the guide rails via track sliders 230. Next, the underwater topography monitoring assembly 100 is assembled underwater: the polarizer 120 is placed inside the waterproof housing 130, the industrial camera 110 is installed, and sealed. The camera connector 190 is fixed to the waterproof housing 130 and mounted on the camera sliding bracket 180. Based on the estimated erosion range, the relative angle and top-view angle of the two industrial cameras 110 are adjusted by loosening and tightening the positioning bolts 140 and changing the corresponding bolt holes on the angle adjustment flange 170 (in 5° intervals), and then all bolts are tightened. Finally, the entire underwater topography monitoring assembly 100 is connected and locked to the bracket angle adjuster 210 of the upper motion measurement platform assembly 200 via the vertical support rod 160.

[0060] Calibration steps: Before formally measuring and acquiring the image sequence, a high-precision calibration operation must be performed; Intrinsic and extrinsic parameter calibration: A specially made waterproof checkerboard calibration plate is submerged in water and leveled; two industrial cameras 110 are controlled by the host computer software to simultaneously capture multiple checkerboard images in different poses; the intrinsic parameter matrix (including focal length, principal point coordinates, radial and tangential distortion coefficients) of each industrial camera 110 and the extrinsic parameter matrix (rotation matrix and translation vector, i.e., relative pose relationship) between the two industrial cameras 110 are calculated using the Zhang Zhengyou calibration method. Underwater refraction correction: As light passes through water, the 130mm waterproof PC sheet, and the air layer inside the shell before entering the lens, the light path is refracted at the interfaces of different media. Directly using the parameters calibrated in air will cause spatial distortion in the 3D reconstructed point cloud. This step is based on Snell's law of refraction to establish a multi-layer medium refraction light path tracing model and correct the above calibration parameters, thereby obtaining the equivalent focal length and coordinate mapping relationship that can reflect the real underwater light propagation path, laying the foundation for subsequent sub-millimeter-level triangulation.

[0061] Preliminary experimental steps: Before the formal flushing test, the entire system was operated under still water conditions.

[0062] Start the stepper motor 2110 to drive the platform to move at different speeds, and at the same time turn on the high-energy laser generator 250 and the underwater lighting equipment; By observing the real-time images acquired by the host computer, the motion blur of the images, the continuity of the laser stripes, and the micro-vibration of the vertical support rod 160 due to water flow resistance during movement are evaluated. By comprehensively balancing measurement efficiency and data quality, the optimal moving speed that is most suitable for the current water depth and model bed material was determined and recorded as a fixed parameter for subsequent formal experiments.

[0063] In addition, during the pre-experimental stage or the formal test preparation stage, the underwater lighting equipment is configured according to the soil type of the model bed: if the model bed is clay, high-pressure sodium lamps are selected as underwater lighting equipment to enhance their penetration ability in turbid water caused by scouring and ensure the visualization of the evolution process of the clay bed surface grooves; if the model bed is sandy, cool white LED strip lights are selected as underwater lighting equipment to provide uniform, high color rendering illumination and highlight the contrast between the faint texture of the sandy bed surface and the laser stripes.

[0064] Image sequence acquisition: After the formal test begins, the stepper motor 2110 drives the upper motion measurement platform component 200 to move the underwater terrain monitoring component 100 along the track at a constant speed. During the movement, the narrow stripe laser stripe projected by the stripe laser port 260 illuminates the uneven terrain surface at the bottom of the water, forming a bright line that deforms with the undulation of the terrain. The two industrial cameras 110 continuously capture image sequences containing the deformation trajectory of the laser stripe by means of hardware triggering or software synchronization.

[0065] Image enhancement and laser stripe extraction: To address image degradation caused by underwater turbidity, the following processing steps are performed: Dark channel dehazing: Apply the dark channel prior dehazing algorithm to the original image to eliminate backscattering blur caused by suspended particles in the water and restore the clear outline of the laser stripes; Anisotropic diffusion filtering: While preserving the sharp edges of laser stripes, it smooths out random noise inside the water body; Threshold segmentation and morphological operations: The laser stripes are separated from the background using the Otsu method or adaptive thresholding; for the tiny breaks in the laser lines caused by local accumulation of sediment in the bed, morphological closing operations (dilation followed by erosion) are used to connect them into a complete continuous curve.

[0066] Stereo matching and 3D coordinate calculation: Reconstruction based on the principle of binocular vision: Subpixel center extraction: In the image frame acquired by the first industrial camera 110, the subpixel-level center point coordinates of the laser stripe are extracted using the gray-scale centroid method or the Hessian matrix method. Epipolar constraint matching: In the corresponding image frames acquired by the second industrial camera 110, the epipolar equation is calculated based on the extrinsic parameter matrix obtained from the aforementioned calibration. A one-dimensional sliding window is established along the epipolar direction, and the point with the largest gray-level gradient on the laser stripe is searched as the matching corresponding point; Triangulation Reconstruction: After obtaining the matching point pairs, the camera's intrinsic and extrinsic parameters, after refraction correction, are combined with the simultaneous equations obtained using the principle of triangulation to calculate the true three-dimensional coordinates of the laser point on the profile in the underwater spatial coordinate system, thus forming the point cloud data of a single frame profile.

[0067] Point cloud stitching and post-processing: Spatial stitching: The stepper motor 2110 controller provides real-time feedback on the displacement increment of the platform. Combined with the frame rate of image acquisition, the single-section point cloud data corresponding to each frame of image is translated, superimposed, and stitched according to its spatial acquisition position, thereby reconstructing a complete and continuous underwater three-dimensional terrain point cloud covering the entire target scour area; Smoothing and Meshing: Statistical filtering is applied to the original stitched point cloud to remove outliers. Subsequently, the discrete point cloud is converted into a continuous 3D mesh model using Delaunay triangulation or Poisson surface reconstruction algorithms.

[0068] Output results: Rendering, contour drawing, and scour pit volume calculation are performed using professional software such as Surfer or CloudCompare to obtain an intuitive and visualized three-dimensional terrain surface model, enabling high-precision quantitative monitoring of the dynamic evolution of the model bed scour process.

[0069] In summary, this application provides a method for real-time underwater topographic monitoring and 3D reconstruction suitable for experimental scales. By using a stepping platform and track system positioned above a water tank or pool, the monitoring equipment can move stably and at a constant speed above the area to be measured, ensuring spatial consistency and repeatability of topographic data acquisition. The proposed underwater measuring device integrates laser projection, an industrial camera, and lighting equipment, enabling simultaneous acquisition of underwater topographic contour images and efficient data processing and 3D reconstruction. This method is particularly suitable for high-precision measurement of the topographic evolution process of model beds in marine engineering experiments, offering advantages such as simple structure, flexible deployment, and low cost. Compared with traditional methods, this invention avoids frequent drainage scanning, significantly saving water resources, shortening the experimental cycle, and simplifying experimental procedures. Furthermore, this method exhibits good adaptability to different soil conditions (such as clay and sand beds) and various water turbidity environments. The use of laser narrow-strip projection and profile stitching eliminates the complex spatial matching process of traditional binocular vision algorithms, reducing computational complexity, improving reconstruction efficiency, and enabling rapid acquisition of representative 3D point cloud data. Therefore, this invention has significant engineering practical value and promotion prospects in the field of laboratory underwater topographic monitoring.

[0070] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0071] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for real-time monitoring and three-dimensional reconstruction of underwater topography at an experimental scale, characterized in that, Includes the following steps: Step 1: Lay a track in advance above the test area of ​​the pool or tank, and set up a water-based stepping platform. The water-based stepping platform moves at a controlled, quantitative, and uniform speed along the track. Step 2: Provide an underwater measuring device and connect it to the above-water stepping platform to move synchronously with the above-water stepping platform; the underwater measuring device includes: The underwater support frame has an angle adjustment mechanism that can adjust its spatial attitude and viewing angle. Two industrial cameras are sealed in a waterproof housing and fixed to the underwater support frame at a preset angle; A strip laser emitter, fixed to the above-water stepping platform or the underwater support frame, is used to project narrow strip laser stripes onto the underwater terrain surface. At least one underwater lighting device for providing auxiliary lighting in an underwater environment; Step 3: Control the movement of the waterborne stepping platform, and during the movement, use the two industrial cameras to synchronously and continuously acquire image sequences containing the deformation trajectory of the narrow laser stripe on the underwater terrain surface; Step 4: Process the acquired image sequence, including image enhancement, laser stripe extraction, and stereo matching based on binocular vision, to calculate the point cloud data of the underwater topographic profile corresponding to each frame of the image. Step 5: Combining the movement and displacement information of the waterborne stepping platform, the point cloud data corresponding to each frame of the image are stitched together to reconstruct and generate a complete and continuous underwater three-dimensional topographic map of the target area.

2. The method for real-time monitoring and three-dimensional reconstruction of underwater topography at the experimental scale according to claim 1, characterized in that, The underwater measuring device in step two also includes: A polarizing filter is placed between the lens of the industrial camera and the waterproof housing to reduce the interference of reflection and refraction of laser and illumination light in water; The angle adjustment mechanism is specifically an angle adjustment flange, which has multiple bolt holes arranged in a circular or arc shape. The spatial angle of the industrial camera or the bar laser emitter can be adjusted by the cooperation of the bolts with different bolt holes.

3. The method for real-time monitoring and three-dimensional reconstruction of underwater topography at the experimental scale according to claim 2, characterized in that: The bolt holes on the angle adjustment flange are set at preset angle intervals, and the preset angle interval is 5°.

4. The method for real-time monitoring and three-dimensional reconstruction of underwater topography at the experimental scale according to claim 1, characterized in that, Step two further includes: Different types of lighting equipment are selected based on the soil type of the test model bed, including: When the model bed is made of clay, the underwater lighting equipment uses high-pressure sodium lamps to enhance their penetration ability in turbid water. When the model bed is made of sandy soil, the underwater lighting equipment is a cool white LED strip light.

5. The method for real-time monitoring and three-dimensional reconstruction of underwater topography at the experimental scale according to claim 1, characterized in that, The image enhancement and laser stripe extraction in step four specifically include: The image is processed based on the dark channel dehazing algorithm to reduce the influence of light scattering in water and enhance the clarity of laser stripes; Anisotropic diffusion filtering is applied to suppress noise in order to preserve the edge information of the laser stripes; By using image thresholding and morphological closing operations, continuous and complete laser stripe contours are extracted.

6. The method for real-time monitoring and three-dimensional reconstruction of underwater topography at the experimental scale according to claim 1, characterized in that, The stereo matching in step four specifically includes: In a pair of image frames acquired synchronously by the two industrial cameras, a subpixel-level center point is extracted from the laser stripes of the first image frame. In the second image frame, a sliding window is established along the epipolar direction to find the maximum image gradient point corresponding to the sub-pixel center point. Based on the matching relationship between the sub-pixel level center point and the maximum image gradient point, the three-dimensional spatial coordinates of the point are calculated using the principle of triangulation.

7. The method for real-time monitoring and three-dimensional reconstruction of underwater topography at the experimental scale according to claim 1, characterized in that, The water-based walking platform in step one includes: The main frame of the platform is slidably connected to the track via a track slider; The driving device includes a stepper motor, a fixed pulley, and a traction rope. The stepper motor drives the main frame of the platform to move along the track through the fixed pulley and the traction rope.

8. The method for real-time monitoring and three-dimensional reconstruction of underwater topography at the experimental scale according to claim 1, characterized in that, Before step three is performed, a calibration step is also included, which includes: The checkerboard calibration plate was placed underwater, and the intrinsic and extrinsic parameter matrices of the two industrial cameras were calibrated to obtain the focal length, principal point coordinates, distortion coefficients, and relative pose relationship between the two cameras. Based on Snell's law of refraction, the refractive distortion caused by light passing through the multi-layer medium interface of water-air-waterproof shell is corrected to obtain the true underwater point coordinates.

9. The method for real-time monitoring and three-dimensional reconstruction of underwater topography at the experimental scale according to claim 1, characterized in that, Before step three is performed, a pre-experimental step is also included, which includes: The optimal moving speed of the water-based stepping platform is determined by evaluating the quality of the acquired images, the disturbance of the water flow by the underwater measuring device, and the stability of the water-based stepping platform's movement under still water conditions.

10. The method for real-time monitoring and three-dimensional reconstruction of underwater topography at the experimental scale according to claim 1, characterized in that, Step five is followed by: The point cloud data of the stitched underwater 3D topographic map is smoothed, denoised, and meshed to obtain the final visualized 3D topographic surface model.

Images