A two-way laser scanning measurement system and method for beach topography in a water tank experiment.

Abstract

This invention relates to a bidirectional laser scanning measurement system and method for beach topography in a flume experiment. By using a platform equipped with a bidirectional laser ranging system that moves above the flume, a set of two-dimensional coordinate points determined by horizontal and vertical lasers is accurately acquired. An abnormal terrain response and remeasurement mechanism based on real-time slope judgment can automatically identify and correct data anomalies and outliers caused by transient interference. An innovative underwater laser autonomous refraction correction method under non-drainage conditions is proposed, enabling the direct acquisition of high-precision underwater topographic data without drainage or additional water level sensors. Finally, a bidirectional round-trip scanning data fusion mechanism based on interpolation alignment and averaging is introduced to reconstruct and track the evolution of the coastal profile over time. This invention features high precision, high versatility, automated data processing capabilities, and adaptability to amphibious scenarios, reducing the workload of experimental personnel while improving overall experimental efficiency.

Description

Technical Field

[0001] This invention relates to a two-way laser scanning measurement system and method for beach topography in a water tank experiment, belonging to the field of coastal engineering physical model testing technology. Background Technology

[0002] In coastal engineering physical model experiments, flume experiments are a core tool for studying wave-beach interactions to simulate natural beach topographic changes. The key lies in accurately measuring the evolution of beach topography along the course of wave action (i.e., from the waterline towards the shore to the wave uplift zone). Currently, observations of topographic changes in flume experiments typically rely on two methods: one is using single-point probes or fixed-position ultrasonic sensors. While this method can acquire elevation changes at specific points, it cannot quickly and synchronously acquire continuous topographic data for the entire beach profile, resulting in a significant loss of spatial information along the course and making it difficult to accurately depict the morphology and migration of micro-landforms such as sandbars and embankments. The other method relies on large, fixed two-dimensional or three-dimensional scanning equipment. Although these devices can acquire area data, their installation is complex, their scanning range is fixed, and they are usually expensive.

[0003] More importantly, traditional techniques often rely on manual measurement or single-direction laser scanning during experiments, which has significant limitations. For example, manual measurement is inefficient and makes it difficult to achieve continuous dynamic monitoring; single-direction laser scanning is prone to systematic errors due to equipment vibration and path deviation, resulting in insufficient data reliability.

[0004] Therefore, it is necessary to provide a measurement system and method that has high precision, high versatility, automated data processing capabilities, and can be adapted to beach topographic measurement systems for amphibious applications, in order to address many shortcomings in existing technologies and provide reliable data support for flume experiments. Summary of the Invention

[0005] This invention provides a two-way laser scanning measurement system and method for beach topography in a water tank experiment. It has high precision, high versatility, automated data processing capabilities, and can be adapted to amphibious scenarios, reducing the workload of test personnel and improving the overall efficiency of the experiment.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A two-way laser scanning measurement system for beach topography in a water tank experiment includes a water tank, in which sand is laid to simulate the surface of a beach. The center of the bottom of the water tank is defined as the origin, the direction parallel to the long side of the water tank is the X-axis, the direction parallel to the short side of the water tank is the Y-axis, and the direction perpendicular to the bottom of the water tank is the Z-axis, thus constructing a three-dimensional coordinate system.

[0008] A track is installed above the water tank, with the track directly above and flush with the X-axis.

[0009] An electric trolley is installed on a track. The electric trolley integrates two laser rangefinders. One is used to measure the horizontal distance to the end wall of the water tank or a fixed reference surface, and is defined as the horizontal laser rangefinder. The other is used to measure the vertical distance to the sandy terrain surface, and is defined as the vertical laser rangefinder.

[0010] It also includes a control system that is connected to the electric vehicle, the horizontal laser rangefinder, and the vertical laser rangefinder.

[0011] Furthermore, the track is formed by splicing together several detachable I-shaped stainless steel concave-convex track units. Several fixed supports are sequentially arranged above the water tank along the X-axis direction. I-shaped stainless steel concave-convex track units are installed between two adjacent fixed supports, and the I-shaped stainless steel concave-convex track units are set perpendicular to the fixed supports.

[0012] Furthermore, the horizontal laser rangefinder has an accuracy of ±5mm; the vertical laser rangefinder has an accuracy of ±1mm, and the sampling frequency of both the horizontal and vertical laser rangefinders is 1000Hz.

[0013] The measurement method of the two-way laser scanning measurement system for beach topography used in the flume experiment specifically includes the following steps:

[0014] Step S1: Start the electric trolley, which slides along the X-axis on the track, and simultaneously start the horizontal laser rangefinder and the vertical laser rangefinder.

[0015] Step S2: Define one end along the X-axis of the water tank as point A and the other end as point B. The process of the electric trolley sliding from point A to point B to scan is called forward scanning, and the process of sliding from point B to point A to scan is called reverse scanning. One complete process includes one forward scanning and one reverse scanning.

[0016] Step S3: Obtain the raw data collected by the horizontal and vertical laser rangefinders during one forward and one backward measurement, and convert them into two-dimensional coordinate point sets in a unified coordinate system. The forward measurement data point set is defined as follows: The data point set for the backtest is ;

[0017] Step S4: Perform anomaly detection on the data point set obtained in step S3. If an anomaly is found, the electric trolley stops, and the horizontal and vertical laser rangefinders are turned off. Record the current location of the anomaly point, rescan the anomaly point, and obtain new data.

[0018] Step S5: For the data point set determined after eliminating anomalies in step S4, determine whether the beach in the tank is underwater. If the beach surface is exposed above the water, proceed to step S7; if the beach surface is underwater, proceed to step S6.

[0019] Step S6: Based on the signal characteristics of the vertical laser rangefinder, the elevation data of the measuring point is corrected using the multi-peak echo signal generated by the reflection and refraction of the laser at the air-water interface. The elevation coordinates of the measuring point are then obtained, and the coordinates of the data point sets detected by the horizontal and vertical laser rangefinders are updated. The forward-measured data point set... The updated coordinates of the measuring points are represented as follows: The set of data points for backtesting The updated coordinates of the measuring points are represented as follows: X represents the position coordinate along the X-axis, and Z represents the elevation coordinate, i.e., the position coordinate along the Z-axis.

[0020] Step S7: Set several alignment points in the X-axis direction. From the set of coordinate points respectively , In step S6, the elevation values ​​corresponding to the data points obtained are calculated using linear interpolation. as well as ;

[0021] Step S8, for each alignment point The elevation value obtained in step S7 as well as By merging, we obtain ;

[0022] Step S9, align all points Connect the data to generate a beach profile map after data fusion;

[0023] Furthermore, in step S4, the specific steps for anomaly detection and processing of the data point set obtained in step S3 are as follows:

[0024] Step S41: During the scanning process, monitor the elevation data detected by the vertical laser rangefinder in real time.

[0025] Step S42: If the detected elevation value exceeds the preset threshold, it is determined to be abnormal data; continue to calculate the elevation change rate of adjacent measuring points. If the change rate exceeds the threshold set by the beach sediment repose angle, it is determined to be abnormal data.

[0026] Step S43: After determining that the data is abnormal, stop the electric trolley, the horizontal laser rangefinder, and the vertical laser rangefinder, and record the location of the abnormal point where the abnormal data is located. ;

[0027] Step S44: Restart the electric trolley and control it to move backward to the preset safe distance, i.e., move backward 1m. At this point, the electric trolley will stop at the following position: , ;

[0028] Step S45, the electric car starts from position Restart and continue scanning beyond the specified location. And at least more than 0.5m, the segment obtained by rescanning is from arrive The data point set;

[0029] Furthermore, in step S6, the specific steps for correcting the elevation data at the location of the measuring point are as follows:

[0030] Step S61: When the laser pulse of the vertical laser rangefinder is emitted from the air to the air-water interface, two echo signals are generated, namely the water surface signal and the bottom signal.

[0031] Step S62: The optical path distance corresponding to the peak values ​​of the water surface signal and the bottom signal is calculated using a signal processing algorithm. The optical path distance from the vertical laser rangefinder to the water surface is... The total optical path from the vertical laser rangefinder to the bottom of the water tank is ;

[0032] Step S63: Obtain the apparent value of water depth without considering refraction. , , ;

[0033] Step S64: Obtain the true geometric depth in the water. , , is the refractive index of water;

[0034] Step S65: Obtain the actual elevation of the measuring point. or for , The vertical distance from the vertical laser rangefinder to the bottom of the water tank;

[0035] Furthermore, in step S8, the elevation value as well as The fusion method is to calculate the arithmetic mean, that is... .

[0036] By employing the above technical solutions, the present invention has the following beneficial effects compared to the prior art:

[0037] 1. The beach topography bidirectional laser scanning measurement system for water tank experiments provided by this invention, with dual laser rangefinders and high-precision configuration, can actively detect and compensate for platform position errors caused by height differences at track splicing points and trolley running bumps, ensuring the precision and completeness of topographic data collection and accurately capturing subtle undulations in the beach.

[0038] 2. The beach topography bidirectional laser scanning measurement system for water tank experiments provided by this invention can be flexibly assembled according to different water tank lengths, adapting to water tank experiments of various specifications, reducing the cost of equipment replacement, and expanding the scope of application.

[0039] 3. The measurement method of the beach topography bidirectional laser scanning measurement system for water tank experiments provided by the present invention adopts a forward-backward bidirectional scanning design combined with a data fusion algorithm. The system error of unidirectional scanning is offset by arithmetic averaging, which significantly improves the signal-to-noise ratio of the data. At the same time, the abnormal terrain response and retesting mechanism based on real-time slope judgment can automatically identify and correct data anomalies and outliers caused by instantaneous interference, ensuring the continuity, reliability and physical rationality of the output terrain.

[0040] 4. The measurement method of the beach topography bidirectional laser scanning measurement system for water tank experiments provided by this invention innovatively designs an underwater laser refraction correction method under non-drainage conditions for underwater topography scenarios. It can directly obtain high-precision underwater topography data without drainage or additional water level sensors, based solely on the dual-peak echo signal of the vertical laser rangefinder itself. This solves the elevation deviation caused by air-water interface refraction and enables accurate measurement in amphibious scenarios.

[0041] 5. The measurement method of the beach topography bidirectional laser scanning measurement system for water tank experiments provided by the present invention controls the electric trolley and dual laser rangefinder to realize full automation of bidirectional scanning. Data processing includes automatic rescanning of abnormal data, coordinate interpolation and alignment, elevation fusion and automatic generation of profile diagrams, which greatly improves measurement efficiency and reduces human operation errors. Attached Figure Description

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0043] Figure 1 This is a schematic diagram of the overall structure of the two-way laser scanning measurement system for beach topography used in a water tank experiment provided by the present invention;

[0044] Figure 2 This is a schematic diagram of track splitting in the two-way laser scanning measurement system for beach topography used in a water tank experiment provided by the present invention.

[0045] In the diagram: 1 is the track, 2 is the fixed support, 3 is the horizontal laser rangefinder, 4 is the vertical laser rangefinder, 5 is the electric trolley, 6 is the fixed reference surface, and 7 is the sandy terrain surface. Detailed Implementation

[0046] The present invention will now be described in further detail with reference to the accompanying drawings. In the description of this application, it should be understood that the terms "left side," "right side," "upper part," "lower part," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. "First," "second," etc., do not indicate the importance of the components, and therefore should not be construed as a limitation of the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution and do not limit the scope of protection of the present invention.

[0047] As described in the background section, traditional beach topographic measurement methods are prone to significant deviations in elevation data when applied to underwater beach scenarios. Existing measurement systems lack targeted correction mechanisms and cannot meet the requirements for accurate underwater topographic measurement. Furthermore, existing scanning equipment is mostly of a fixed structure, lacking versatility and unable to adapt to experiments with different flume sizes. The lack of real-time anomaly detection during data acquisition means that including anomalous data in the final results will affect the accuracy of experimental conclusions. Finally, the data processing capabilities are poor in the data processing process that relies on manual intervention, making it difficult to quickly generate intuitive topographic profile results.

[0048] To address the aforementioned issues, this application provides a two-way laser scanning measurement system for beach topography used in flume experiments, along with corresponding measurement methods. The core of the system lies in the integration of two-way laser ranging with a mobile platform, enabling real-time and precise calibration of the platform's position during measurement, thereby obtaining highly reliable topographic data.

[0049] The entire measurement system, such as Figure 1 As shown, the system includes a water tank, with sand laid inside to simulate a beach surface. For ease of explanation of the measurement method later, a three-dimensional coordinate system is constructed, with the center of the bottom of the water tank as the origin, the direction parallel to the long side of the water tank as the X-axis, the direction parallel to the short side of the water tank as the Y-axis, and the direction perpendicular to the bottom of the water tank as the Z-axis.

[0050] A track 1 is installed above the water tank, with the track directly above and flush with the X-axis. An electric trolley 5 is installed on the track, and two laser rangefinders are integrated on the electric trolley. One of them is used to measure the horizontal distance to the end wall of the water tank or the fixed reference surface 6, and is defined as the horizontal laser rangefinder 3. The other is used to measure the vertical distance to the beach surface 7, and is defined as the vertical laser rangefinder 4.

[0051] The electric trolley can move precisely along the track along the length of the water tank. Preferably, this application provides a programming control system based on the Arduino open-source platform for the drive and movement of the electric trolley. This system can realize the start and stop, movement speed, and travel distance of the electric trolley. Two laser rangefinders are integrated on the trolley. First, a direct measurement scheme of laser ranging is adopted, which directly obtains the distance value by calculating the laser flight time or phase difference. Each data point obtained by this design is the true coordinate of the target point. Compared with photogrammetric methods that reconstruct the terrain through indirect calculations such as image feature matching and stereo vision, this design avoids errors introduced by water turbidity, changes in lighting conditions, missing textures, or complex model calculations. Next, regarding the bidirectional laser ranging technology, the horizontal laser rangefinder accurately calibrates the horizontal position of the scanning trolley in real time, while the vertical laser rangefinder simultaneously measures the elevation, which can actively detect and compensate for platform position errors caused by height differences at track splicing points and trolley movement.

[0052] Another significant innovation in the system is the use of detachable, modular I-beam stainless steel concave-convex rails combined with an Arduino-based programmable control system. This eliminates the reliance on expensive and fixed high-rigidity guide rails for the entire scanning system. Furthermore, the detachable and modular rails ensure flatness and overall rigidity at the joints while providing high reconfigurability and adaptability, facilitating customized installation based on different tank lengths. The high strength and stability of the stainless steel material prevent the laser rangefinder from being affected by rail deformation during scanning, thus ensuring measurement accuracy. Specifically, the rails consist of several detachable I-beam stainless steel concave-convex rail units (… Figure 2 As shown, the system is formed by splicing together several fixed supports 2 arranged sequentially along the X-axis above the water tank. I-shaped stainless steel concave-convex track units are installed between two adjacent fixed supports, and the I-shaped stainless steel concave-convex track units are set perpendicular to the fixed supports.

[0053] The horizontal laser rangefinder is used to measure the horizontal distance to the end wall of the water tank or another fixed reference surface, and the vertical laser rangefinder is used to measure the vertical distance to the surface of the beach. Therefore, in order to better obtain the horizontal displacement and vertical elevation movement measurement requirements in the future, this application preferably sets the accuracy of the horizontal laser rangefinder to ±5mm, the accuracy of the vertical laser rangefinder to ±1mm, and the sampling frequency of both the horizontal and vertical laser rangefinders to 1000Hz.

[0054] It also includes a control system that is connected to the electric cart, the horizontal laser rangefinder, and the vertical laser rangefinder. The Arduino control system drives the electric cart to move at a constant speed along the I-shaped stainless steel track above the water tank. During the movement, the horizontal and vertical laser rangefinders simultaneously collect vertical and horizontal distance data.

[0055] Having determined the high-specification system hardware configuration, in order to achieve real-time and accurate calibration of the beach topography surface during the measurement process and obtain highly reliable topographic data, this application further provides a measurement method for the aforementioned two-way laser scanning measurement system for beach topography used in the flume experiment, specifically including the following steps:

[0056] Step S1: Start the electric trolley, which slides along the X-axis on the track, and simultaneously start the horizontal laser rangefinder and the vertical laser rangefinder.

[0057] Step S2: Define one end along the X-axis of the water tank as point A and the other end as point B. The process of the electric trolley sliding from point A to point B to perform scanning is called forward scanning, and the process of sliding from point B to point A to perform scanning is called reverse scanning. One complete process includes one forward scanning and one reverse scanning.

[0058] A single full-process measurement includes forward and backward measurements. Bidirectional data comparison provides a foundation for subsequent fusion and reduces systematic errors that may arise from unidirectional scanning. Step S3 involves acquiring the raw data collected by the horizontal and vertical laser rangefinders during both forward and backward measurements, and converting them into two-dimensional coordinate point sets in a unified coordinate system. The forward measurement data point set is defined as follows: The data point set for the backtest is .

[0059] After completing the preprocessing and coordinate unification of the forward and reverse measurement data, it is necessary to further improve the reliability of the data. Therefore, in step S4, anomaly detection is performed on the data point set obtained in step S3. If an anomaly is found, the electric trolley stops, and the horizontal and vertical laser rangefinders are turned off. The current location of the anomaly point is recorded, and the anomaly point is scanned again to obtain new data. The specific steps are as follows:

[0060] Step S41: During the scanning process, monitor the elevation data detected by the vertical laser rangefinder in real time.

[0061] Step S42: If the detected elevation value exceeds the preset threshold, it is determined to be abnormal data. In addition to monitoring whether the absolute elevation value of a single point exceeds the preset threshold, the elevation change rate (slope) of adjacent measuring points is calculated. If the change rate exceeds the reasonable physical threshold set by the beach sediment repose angle, it is determined that the area has a "sudden maximum or minimum value", which may be caused by instantaneous jitter, laser ranging misalignment or foreign object obstruction, resulting in abnormal data.

[0062] Step S43: After determining that the data is abnormal, stop the electric trolley, the horizontal laser rangefinder, and the vertical laser rangefinder, and record the location of the abnormal point where the abnormal data is located. .

[0063] In step S44, the electric trolley is restarted and controlled to move backward to a preset safe distance, which is set to 1m (safe distance) in this application. At this time, the electric trolley stops at the following position: , .

[0064] Step S45 performs local retesting and data overlay, and the electric car starts from the position Restart and continue scanning at normal speed until you reach a location beyond the original anomaly point. If it exceeds 0.5m, the segment obtained by rescanning will be from... arrive The new data point set. The segment obtained from this rescan (from arrive The new data point set will directly overwrite and replace the data at the corresponding positions in the original scan data. To ensure a smooth transition between the retested data and the preceding and following data, a short-distance weighted average transition processing can be performed between the two ends of the retested section and the original data before overwriting. This mechanism gives the system the ability to self-correct in complex experimental environments, effectively identifying and eliminating outliers caused by transient interference, and avoiding the impact of local errors on the continuity and accuracy of the entire profile reconstruction.

[0065] Next is step S5, the most innovative part of this application. For the data point set determined after eliminating anomalies in step S4, it is determined whether the beach in the tank is underwater. If the beach surface is exposed above the water, then proceed to step S7; if the beach surface is underwater, then proceed to step S6.

[0066] In existing technologies, when conducting experimental measurements of underwater topography, it is necessary to frequently drain the water tank to avoid interfering with the experimental process and potentially disturbing the topography. This approach is cumbersome, costly, and inefficient. Therefore, step S5 first categorizes whether the object is underwater. When the beach topography surface is underwater, this application designs an underwater refraction autonomous correction method based on the signal characteristics of the vertical laser rangefinder itself. The core of this method lies in utilizing the multi-peak echo signal generated by the reflection and refraction of laser light at the air-water interface, thereby achieving accurate correction without the need for an external water level sensor.

[0067] That is, in step S6, based on the signal characteristics of the vertical laser rangefinder itself, the elevation data of the measuring point is corrected using the multi-peak echo signal generated by the reflection and refraction of the laser at the air-water interface, the elevation coordinates of the measuring point are obtained, and the coordinates of the data point set detected by the horizontal and vertical laser rangefinders are updated. The data point set measured in the past... The updated coordinates of the measuring points are represented as follows: The set of data points for backtesting The updated coordinates of the measuring points are represented as follows: X represents the position coordinate along the X-axis, and Z represents the elevation coordinate, i.e., the position coordinate along the Z-axis; the specific steps are as follows:

[0068] In step S61, when the laser pulse from the vertical laser rangefinder is emitted from the air towards the air-water interface, a portion of the laser energy (approximately 2%) undergoes Fresnel reflection at the water surface, forming the first echo signal (water surface signal). The majority of the energy (approximately 98%) is refracted into the water, reflects off the bottom, and passes through the water-air interface again, ultimately being received by the detector to form the second echo signal (bottom signal). The vertical laser rangefinder distinguishes and records these two continuous, time-separated echo signals.

[0069] In step S62, the vertical laser rangefinder measures the complete echo waveform or time series. Using signal processing algorithms (such as peak detection), the optical path distances corresponding to the first peak (corresponding to water surface reflection) and the second peak (corresponding to bottom reflection) can be accurately identified. The optical path distance from the vertical laser rangefinder to the water surface is... The total optical path from the vertical laser rangefinder to the bottom of the water tank is ;

[0070] Step S63: Obtain the apparent value of water depth without considering refraction. , The optical path length of a vertical laser rangefinder from the water surface to the bottom and back to the surface is... Optical path length is This is the actual physical distance from the vertical laser rangefinder to the water surface. (Because this section of the path is entirely in the air).

[0071] Step S64, because the speed of light in water decreases (refractive index) Laser rangefinders measure optical path distance, not actual geometric distance. The true geometric depth in water... With the measured apparent water depth The following relationship exists: , Let be the refractive index of water. By introducing this method, the system can seamlessly switch between two measurement modes—drained (exposed terrain) and undrained (underwater terrain)—using the signal from a single vertical laser rangefinder without any hardware modifications. This enables uninterrupted, high-precision continuous observation of the entire process of beach topography evolution from above water to underwater.

[0072] Step S65: Obtain the actual elevation of the measuring point. or for , This is the vertical distance from the vertical laser rangefinder to the bottom of the water tank.

[0073] After correcting the elevation value in step S7, several alignment points are set in the X-axis direction. From the set of coordinate points respectively , In step S6, the elevation values ​​corresponding to the data points obtained are calculated using linear interpolation. as well as .

[0074] Step S8, for each alignment point The elevation value obtained in step S7 as well as By merging, we obtain Elevation value as well as The fusion method is to calculate the arithmetic mean, that is... By using interpolation alignment and arithmetic averaging, random errors caused by minor track unevenness, slight shaking of the scanning vehicle, or random environmental interference are effectively suppressed, further reducing random errors and improving data consistency.

[0075] Step S9, align all points By connecting the data, a beach profile map after data fusion is generated, which intuitively presents the beach topography, simplifies the subsequent data processing and analysis process, and improves experimental efficiency.

[0076] In summary, the two-way laser scanning measurement system and method for beach topography used in flume experiments provided in this application, based on a real-time slope judgment-based abnormal topography response and remeasurement mechanism, can automatically identify and correct data anomalies and outliers caused by transient interference, ensuring the continuity, reliability, and physical rationality of the output topography. By innovatively proposing an underwater laser autonomous refraction correction method under undrained conditions, the system can directly acquire high-precision underwater topography data without dredging or additional water level sensors, relying solely on the bi-peak echo signal of the vertical laser rangefinder itself. This method, by identifying surface and bottom echoes, separating optical paths, and utilizing the refractive index of water for real-time geometric correction, extends the system's application range from exposed beach surfaces to underwater areas, achieving undisturbed and continuous observation of the entire wave-beach interaction process, greatly improving experimental efficiency and data integrity. Finally, by introducing a two-way round-trip scanning data fusion mechanism based on interpolation alignment and averaging, the system can effectively smooth random errors and significantly improve the signal-to-noise ratio of the data.

[0077] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0078] The meaning of "and / or" as used in this application includes both situations where each exists alone or both exist simultaneously.

[0079] The term "connection" as used in this application can mean a direct connection between components or an indirect connection between components through other components.

[0080] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A measurement method for a two-way laser scanning measurement system for beach topography used in a water tank experiment, characterized in that: The beach topography bidirectional laser scanning measurement system includes a water tank, in which sand is laid to simulate the beach topography surface. Its features include: defining the center of the bottom of the water tank as the origin, the direction parallel to the long side of the water tank as the X-axis, the direction parallel to the short side of the water tank as the Y-axis, and the direction perpendicular to the bottom surface of the water tank as the Z-axis, thus constructing a three-dimensional coordinate system; erecting a track above the water tank, with the track directly above and flush with the X-axis; mounting an electric trolley on the track, which integrates two laser rangefinders, one for measuring the horizontal distance to the end wall of the water tank or a fixed reference surface (defined as the horizontal laser rangefinder), and the other for measuring the vertical distance to the beach topography surface (defined as the vertical laser rangefinder); and including a control system that is simultaneously connected to the electric trolley, the horizontal laser rangefinder, and the vertical laser rangefinder. Specifically, the following steps are included: Step S1: Start the electric trolley, which slides along the X-axis on the track, and simultaneously start the horizontal laser rangefinder and the vertical laser rangefinder. Step S2: Define one end along the X-axis of the water tank as point A and the other end as point B. The process of the electric trolley sliding from point A to point B to scan is called forward scanning, and the process of sliding from point B to point A to scan is called reverse scanning. One complete process includes one forward scanning and one reverse scanning. Step S3: Obtain the raw data collected by the horizontal and vertical laser rangefinders during one forward and one backward measurement, and convert them into two-dimensional coordinate point sets in a unified coordinate system. The forward measurement data point set is defined as follows: The data point set for the backtest is ; Step S4: Perform anomaly detection on the data point set obtained in step S3. If an anomaly is found, the electric trolley stops, and the horizontal and vertical laser rangefinders are turned off. Record the current location of the anomaly point, rescan the anomaly point, and obtain new data. Step S5: For the data point set determined after eliminating anomalies in step S4, determine whether the beach in the tank is underwater. If the beach surface is exposed above the water, proceed to step S7; if the beach surface is underwater, proceed to step S6. Step S6: Based on the signal characteristics of the vertical laser rangefinder, the elevation data of the measuring point is corrected using the multi-peak echo signal generated by the reflection and refraction of the laser at the air-water interface. The elevation coordinates of the measuring point are then obtained, and the coordinates of the data point sets detected by the horizontal and vertical laser rangefinders are updated. The forward-measured data point set... The updated coordinates of the measuring points are represented as follows: The set of data points for backtesting The updated coordinates of the measuring points are represented as follows: X represents the position coordinate along the X-axis, and Z represents the elevation coordinate, i.e., the position coordinate along the Z-axis. Step S7: Set several alignment points in the X-axis direction. From the set of coordinate points respectively , In step S6, the elevation values ​​corresponding to the data points obtained are calculated using linear interpolation. as well as ; Step S8, for each alignment point The elevation value obtained in step S7 as well as By merging, we obtain ; Step S9, align all points Connect the data to generate a beach profile map after data fusion.

2. The measurement method of the two-way laser scanning measurement system for beach topography used in a water tank experiment according to claim 1, characterized in that: In step S4, the specific steps for anomaly detection and processing of the data point set obtained in step S3 are as follows: Step S41: During the scanning process, monitor the elevation data detected by the vertical laser rangefinder in real time; Step S42: If the detected elevation value exceeds the preset threshold, it is determined to be abnormal data; continue to calculate the elevation change rate of adjacent measuring points. If the change rate exceeds the threshold set by the beach sediment repose angle, it is determined to be abnormal data. Step S43: After determining that the data is abnormal, stop the electric trolley, the horizontal laser rangefinder, and the vertical laser rangefinder, and record the location of the abnormal point where the abnormal data is located. ; Step S44: Restart the electric trolley and control it to move backward to the preset safe distance, i.e., move backward 1m. At this point, the electric trolley will stop at the following position: , ; Step S45, the electric car starts from position Restart and continue scanning beyond the specified location. And at least more than 0.5m, the segment obtained by rescanning is from arrive The data point set.

3. The measurement method of the two-way laser scanning measurement system for beach topography used in a water tank experiment according to claim 1, characterized in that: In step S6, the specific steps for correcting the elevation data at the location of the measuring point are as follows: Step S61: When the laser pulse of the vertical laser rangefinder is emitted from the air to the air-water interface, two echo signals are generated, namely the water surface signal and the bottom signal. Step S62: The optical path distance corresponding to the peak values ​​of the water surface signal and the bottom signal is calculated using a signal processing algorithm. The optical path distance from the vertical laser rangefinder to the water surface is... The total optical path from the vertical laser rangefinder to the bottom of the water tank is ; Step S63: Obtain the apparent value of water depth without considering refraction. , , ; Step S64: Obtain the true geometric depth in the water. , , is the refractive index of water; Step S65: Obtain the actual elevation of the measuring point. or for , This is the vertical distance from the vertical laser rangefinder to the bottom of the water tank.

4. The measurement method of the two-way laser scanning measurement system for beach topography used in a water tank experiment according to claim 1, characterized in that: In step S8, the elevation value as well as The fusion method is to calculate the arithmetic mean, that is... .

5. The measurement method of the two-way laser scanning measurement system for beach topography used in a water tank experiment according to claim 1, characterized in that: The track is formed by splicing together several detachable I-shaped stainless steel concave-convex track units. Several fixed supports are arranged sequentially above the water tank along the X-axis direction. I-shaped stainless steel concave-convex track units are installed between two adjacent fixed supports, and the I-shaped stainless steel concave-convex track units are set perpendicular to the fixed supports.

6. The measurement method of the two-way laser scanning measurement system for beach topography used in a water tank experiment according to claim 1, characterized in that: The horizontal laser rangefinder has an accuracy of ±5mm; the vertical laser rangefinder has an accuracy of ±1mm. The sampling frequency of both the horizontal and vertical laser rangefinders is 1000Hz.

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