Measurement methods

Abstract

Multibeam sonar is used to measure changes in riverbed shape over time. [Solution] The solution includes a surveying method in which a floating body equipped with a multi-beam sonar that transmits multiple beams in a fan shape is carried along by the river current, and the riverbed shape is measured with the multi-beam sonar, wherein in the scanning step the swath direction of the multi-beam sonar is directed in the direction of the river current and the same point is measured multiple times from different positions, or a surveying method in which the riverbed shape is measured while the multi-beam sonar is continuously rotated or rotatable in the horizontal direction in the scanning step.

Description

Technical Field

[0001] The present invention relates to a surveying technique for riverbed shape.

Background Art

[0002] With the intensification of flood disasters due to global warming and the strengthening of legal systems related to disaster prevention, new flood control systems and river management methods that are not inferior to these are required. On the other hand, rivers, which are the targets of management, each have geographical and spatial characteristics and have the difficulty of prediction that their states change moment by moment due to floods. In order for rivers to continuously maintain the safety they should possess in the future, it is necessary to clarify the mechanisms of river channel changes such as riverbed erosion and deposition and to be able to quantitatively predict the hydraulic effects of rainfall and floods. As a technique for this, for example, Patent Document 1 below discloses a surveying system using a multicopter equipped with a multi-beam sonar and an ADCP (Acoustic Doppler Current Profiler).

[0003] Particularly, in rivers with quicksand, the "riverbed waves" generated by the interaction between the flow condition and quicksand are important factors that determine the flow resistance and the amount of scoured quicksand. However, many of the findings in river engineering to date have been obtained under controlled conditions in experimental flumes, and there have been scattered cases that do not match the previous findings in actual rivers where suspended sand is prominent or in places with rapid flow condition changes during floods. This gap appears as the uncertainty of the water level - discharge relationship (H - Q formula), the limit of the prediction accuracy of sediment movement amount, and furthermore, the looseness of risk assessment in the safety management of structures such as bridge piers.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The surveying system described in Patent Document 1 acquires river topographic data using a multibeam sonar mounted on a multicopter. This sonar transmits a fan-shaped beam along a direction perpendicular to the multicopter's direction of travel (along-track direction). This use, spreading the beam in the opposite direction, is the intended use of a multibeam sonar. In topographic surveying using a multibeam sonar, each point in the target area is scanned once, and the overall point cloud data is acquired.

[0006] Therefore, conventional river surveying using multibeam sonar had the following challenges: (1) It was not intended to scan the same location in the target area multiple times, and therefore it was not possible to obtain information on changes in topography over time during floods, etc. (2) Because the beam's orientation is fixed in the direction of the across plane, it is susceptible to disturbances in the attitude and position of the floating structure to which it is attached, and in some terrains, acoustic shadows (missing data) of the sonar occur. (3) With beams extending in the direction of the across, it is not possible to acquire terrain in the direction of the floating body's movement. Therefore, in order to prevent damage or loss of equipment due to collisions with the riverbed or obstacles, it was necessary to conduct thorough reconnaissance in advance.

[0007] The present invention aims to solve these problems by applying the characteristics of multibeam sonar. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides a surveying method that includes a scanning step in which a floating body equipped with a multi-beam sonar that transmits multiple beams in a fan shape is carried along by the river current, and the riverbed shape is measured with the multi-beam sonar. The scanning step involves orienting the swath direction of the multi-beam sonar in the direction of the river current and measuring the same point multiple times from different positions.

[0009] While multibeam sonar is typically used with its swath direction pointed in the opposite direction, deliberately pointing it in the direction of the river's water flow allows for scanning the riverbed shape both in front of and behind a floating object moving with the water current. By utilizing this, it is possible to obtain information on changes in the riverbed shape over time by measuring the same point on the riverbed multiple times from different positions.

[0010] In this case, during the scanning process, the riverbed shape may be measured while continuously directing the swath direction of the multibeam sonar in the direction of the river's water flow. This results in a measurement range that is almost linear, but allows for a more detailed observation of changes in the riverbed's irregularities (such as riverbed waves and erosion around bridges) within that range over a longer period of time.

[0011] Furthermore, in order to solve the above problems, the surveying method of the present invention includes a scanning step in which a floating body equipped with a multi-beam sonar that transmits multiple beams in a fan shape is carried along by the river current, and the riverbed shape is measured with the multi-beam sonar, and in the scanning step, the riverbed shape is measured while continuously rotating or rotating the multi-beam sonar in the horizontal direction.

[0012] By continuously rotating or turning a multi-beam sonar horizontally while it flows down a river, the same point on the riverbed can be measured multiple times from different positions. In particular, sonars fixed in the cross direction are prone to missing data, but according to the present invention, the same point can be scanned from various angles, thus reducing areas that are obscured by the sonar. Furthermore, by scanning the same point three-dimensionally from various angles, the quality of the 3D modeling of the riverbed shape can also be improved.

[0013] In this scanning process, it is desirable to determine, based on the multi-beam sonar's detection values, whether there are any downstream obstacles that the floating body or its equipment may collide with, in addition to measuring the riverbed shape. By scanning the area in front of (downstream of) the floating body with sonar, the height (water depth) of the riverbed at the floating body's destination and the presence or absence of structures can be detected in advance. This prevents damage to or loss of the floating body or equipment, and makes it possible to omit or simplify prior reconnaissance.

[0014] Furthermore, it is desirable that the multi-beam sonar be installed on the floating body in a orientation such that the bisector of the central angle of the fan-shaped beam is approximately a vertical line. This allows for wide-area measurement of the riverbed.

[0015] Furthermore, it is desirable that the surveying method of the present invention include an analysis step to identify changes in the riverbed shape over time from the riverbed shape data obtained in the scanning step. This analysis step may be performed after the completion of the scanning step, or it may be performed in parallel with the scanning step.

[0016] Furthermore, it is desirable that the floating body is further equipped with an ultrasonic Doppler flow meter, and that in the scanning step, the area below the floating body is measured using the ultrasonic Doppler flow meter. In this case, it is also desirable that the surveying method of the present invention further includes a sediment transport calculation step in which the amount of sediment transport in the river is calculated from the data of the ultrasonic Doppler flow meter obtained in the scanning step.

[0017] Furthermore, it is desirable that the floating body be an unmanned aerial vehicle (UAV). By using an UAV, the release and recovery of the floating body becomes easier, and it becomes possible to fly around and avoid or bypass floating objects, obstacles, and structures. [Effects of the Invention]

[0018] Thus, the above-mentioned problems can be solved by the surveying method of the present invention. [Brief explanation of the drawing]

[0019] [Figure 1] It is a perspective view of the multicopter 12. [Figure 2] It is a block diagram showing the functional configuration of the surveying system 10. [Figure 3] It is a block diagram showing a part of the autonomous control function provided by the FC / BC 20. [Figure 4] It is a schematic diagram showing the actual measurement ranges of the ADCP unit 70 and the sonar unit 80. [Figure 5] It is a schematic diagram showing an example of the scan range by the sonar unit 80. [Figure 6] It is a schematic diagram showing an overview of the collision avoidance function using the sonar unit 80. [Figure 7] It is a schematic diagram showing the state of scanning the same point on the riverbed from a plurality of different directions. [Figure 8] It is a schematic diagram showing the state of the multicopter 12 riding on the river flow and descending along the river. [Figure 9] It is a flowchart showing the flow of each step in the surveying method of this embodiment.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The surveying system 10 described below is a system that floats a multicopter 12, which is an unmanned aerial vehicle, on the river flow, actually measures the shape of the riverbed under the aircraft and the velocity distribution by layer, etc., and calculates the change over time of the riverbed shape and the amount of sediment movement based on these measured values. Hereinafter, the surveying system 10 will be described as an example of this feature and other features associated with it. Note that "surveying" in the present invention includes measuring the shape (topography) of the riverbed and river course, the amount of change thereof, the flow velocity, the amount of sediment movement, etc., and is not limited to the scope meant by "surveying" defined in the surveying method.

[0021] <Overview of the Surveying System> FIG. 1 is a perspective view of the multicopter 12, and FIG. 2 is a block diagram showing the functional configuration of the surveying system 10. Hereinafter, the overview of the surveying system 10 will be described with reference to FIGS. 1 and 2.

[0022] As shown in Figure 1, the multicopter 12 in this configuration is a so-called quadcopter, comprising four arms extending radially in a plan view and rotors 12, which are horizontal rotating blades, fixed to the ends of these arms. The multicopter 12 is equipped with a so-called trimaran-type float 50 that allows the aircraft to float on the water surface, and a pair of thrusters 42 for moving the multicopter 12 on the water surface are fixed to its outriggers (left and right floats). In addition, a sonar unit 80, which is a scanner device for measuring the riverbed shape beneath the aircraft, and an ADCP unit 70, which is an ultrasonic Doppler current meter for acquiring the flow velocity distribution of different layers directly beneath the aircraft, are embedded in the bottom of the main hull (central float) of the float 50. Furthermore, the multicopter 12 has a GPS receiver 31 (hereinafter simply referred to as "GPS31") and an RTK (Real Time Kinematic) receiver 32, which are GNSS (Global Navigation Satellite System) devices not shown in the diagram, located outside the aircraft.

[0023] As shown in Figure 2, the surveying system 10 in this embodiment mainly consists of an analysis device 11 and a multicopter 12. The analysis device 11 and the multicopter 12 are connected via the Internet. In this embodiment, the operator terminal 19 of the surveying system 10 is also connected to each device via the Internet. The operator terminal 19 may also be a so-called radio control type control device that directly controls the multicopter 12 via wireless communication.

[0024] (Multicopter) The multicopter 12 in this configuration consists of a control unit, a flight controller / boat controller 20 (hereinafter referred to as "FC / BC20"), a GPS 31 connected to the FC / BC20, an RTK receiver 32, a rotor 41, thrusters 42, and an omnidirectional camera 60 (hereinafter referred to as "camera 60"), as well as an ADCP unit 70, a sonar unit 80, and floats 50. The FC / BC20 in this configuration includes firmware for controlling the attitude of the multicopter 12 during flight, as well as an IMU (Inertial Measurement Unit), a barometric pressure sensor, a compass sensor (electronic compass), etc.

[0025] The FC / BC20 controls the rotational speed of the rotors 41 and thrusters 42 in accordance with the autopilot program described later and instructions from the operator terminal 19, thereby enabling the multicopter 12 to fly or navigate. Here, "navigation" means that the multicopter 12 moves on the water surface. The multicopter 12 in this configuration is equipped with six rotors 41, which are thrust sources for moving through the air, and two thrusters 42, which are dedicated thrust sources for moving on the water surface. The FC / BC20 can automatically switch between "flight mode," which moves through the air using the rotors 41, and "navigation mode," which moves on the water surface using the thrusters 42, or by instructions from the operator terminal 19. The operator can remotely control the multicopter 12 by visual observation if the multicopter 12 is within visual range, or by relying on images transmitted from the camera 60 if it is outside of visual range.

[0026] The RTK receiver 32 is a device that acquires correction information for signals received from GPS satellites. In this configuration, the RTK receiver 32 acquires correction information provided as an internet service via an LTE (Long Term Evolution) connection. Therefore, in this configuration of the surveying system 10, there is no need to install RTK base stations (fixed stations) around the survey points. Furthermore, the distance constraints between the RTK receiver 32 and the RTK base station are relaxed, allowing for faster, simpler, and more extensive surveying. In addition to the LTE connection, the RTK receiver 32 may also utilize other mobile communication networks such as 5G, 3G, or WiMAX (Worldwide Interoperability for Microwave Access). While this configuration uses GPS as the GNSS device, it may also use receivers such as GLONASS, Galileo BeiDou, Michibiki (Quasi-Zenith Satellite System), or COMPASS (system). Alternatively, instead of RTK, it is possible to use a GNSS device that can utilize Michibiki's CLAS (Centimeter-Level Augmentation Service). In that case, the signal correction using the RTK mechanism described below can be reinterpreted as correction using CLAS.

[0027] In this configuration, the FC / BC20 continues to operate the GPS31 and RTK receiver32 even after the rotor 41 has stopped, for example, after the multicopter 12 has landed on the water. Therefore, the position and speed of the multicopter 12 on the water surface can be calculated from the position information of the GPS31. This position information can also be used by the ADCP unit 70 and the sonar unit 80.

[0028] Camera 60 is a so-called 360° camera / spherical camera mounted on the body frame of the multicopter 12, capable of capturing images in any direction within a hemispherical range, including the sides and above the aircraft, including the water surface. Images captured by camera 60 are transmitted in real time to the analysis device 11 and the operator terminal 19.

[0029] The ADCP Unit 70 is a device that emits sound waves into water and measures the Doppler shift of scattering particles (such as suspended solids) that move with the water flow, thereby obtaining the flow velocity distribution for each layer according to the water depth. Due to this property, the ADCP Unit 70 can also determine the concentration of suspended solids in the water. The ADCP Unit 70 may also be equipped with its own electronic compass and IMU.

[0030] The ADCP unit 70 in this configuration is equipped with three or more probes with different orientation angles. The ADCP unit 70 converts the one-dimensional flow velocity measured by the probes into a three-dimensional flow velocity by applying trigonometry based on the arrangement angles of these probes. Furthermore, the ADCP unit 70 in this configuration can also be used as a DVL (Doppler Velocity Log). That is, by emitting sound waves from the multicopter 12 toward the bottom of the river, the relative velocity (bottom track) between the riverbed and the multicopter 12 can be measured from the amount of Doppler shift of the reflected waves from the bottom of the river.

[0031] The sonar unit 80 is a multi-beam acoustic depth sounder (a so-called multi-beam sonar) that transmits multiple sound wave beams into the water in a fan shape and acquires riverbed shape data by receiving the reflected waves.

[0032] The sonar unit 80 is a unit that includes a transmitter with multiple sonars arranged in a row, a receiver that receives reflected waves, a dedicated IMU, and a surface sound velocity meter, etc. Ultrasonic measurements are less affected by turbidity than optical cameras or green lasers, and can obtain highly accurate topographic data even under difficult conditions.

[0033] (Analysis equipment) The analysis device 11 in this configuration is a server computer, a PC, or a dedicated computer device. The analysis device 11 may be a single device or a combination of multiple devices. Alternatively, the operator terminal 19 may be equipped with the functions of the analysis device 11.

[0034] In this configuration, the analysis device 11 acquires the flow velocity distribution below the multicopter 12 from the ADCP unit 70, images of the area around the aircraft from the camera 60, and terrain data from the sonar unit 80. The analysis device 11 also acquires the latitude, longitude, and elevation values ​​of the GPS 31, which have been corrected using the correction information from the RTK receiver 32. For example, the velocity, such as the flow velocity, acquired by the ADCP unit 70 is calculated by taking into account the movement speed of the multicopter 12 itself, which is obtained from the GPS 31.

[0035] As will be explained in more detail later, the analysis device 11 identifies the temporal changes in the riverbed shape in the watershed where the multicopter 12 has moved, and calculates the amount of sediment movement, based on various measured values ​​received from the multicopter 12. In this configuration of the surveying system 10, the load and functions of the surveying system 10 are appropriately distributed throughout the system by having a configuration (analysis device 11) specifically for collecting, analyzing, and integrating data acquired by the multicopter 12 and its onboard equipment. Furthermore, the surveying results are stored in the analysis device 11, and the stored information is widely shared with river operators, researchers, etc. It should be noted that an independent analysis device 11 is not essential for the surveying system 10, and the functions of the analysis device 11 may be provided by the multicopter 12.

[0036] (Autopilot function) Figure 3 is a block diagram showing some of the control functions of the FC / BC20. The multicopter 12 in this embodiment has an autonomous flight program 21, an autonomous navigation program 22, and a collision avoidance program 23 as its autopilot functions.

[0037] The autonomous flight program 21 is a function that automatically flies the multicopter 12 according to a pre-prepared flight plan. The flight plan is data that includes parameters such as the takeoff (water takeoff) point, landing (water landing) point, one or more waypoints that make up the flight route, the flight altitude at each waypoint, and the flight speed between each waypoint, as specified on the map data.

[0038] The autonomous navigation program 22 is a function that automatically moves the multicopter 12 on the water surface according to a pre-prepared cruise plan. The cruise plan is data that includes a starting point, an ending point, and one or more waypoints that constitute the navigation route, as specified on map data. The autonomous navigation program 22 automatically operates the thrusters 42 so that the multicopter 12, riding the river current downstream, moves along the navigation route.

[0039] Here, the flow velocity of a river can vary depending on its position along its width. For example, even where a river flows in a straight line, in deeper areas, the flow velocity in the center of the river becomes faster than that on either bank due to the influence of two spiral flows aligned along the river's width. Also, when the water level of a river rises, the water level in the center of the river rises, creating a flow on the water surface from the center towards the banks. Conversely, when the water level of a river falls, the water level in the center of the river falls, creating a flow on the water surface from the banks towards the center. Furthermore, in areas where the river curves, the flow velocity on the outside of the curve is faster than that on the inside. And a floating object with water depth will naturally be guided towards the fastest current if it is facing the direction of the fastest current. Therefore, if the goal is to move the multicopter 12 along the fastest current course in the river, the cruise plan only needs to specify the starting and ending points, the heading at each position, and the detours around obstacles such as intake weirs, drops, and bridge piers.

[0040] The collision avoidance program 23 uses the sonar unit 80 to measure the distance between the aircraft and surrounding objects (structures, riverbeds, and other geological features). When a collision is predicted, it automatically changes the flight path to detour, remains stationary in place or in the air to await instructions from the operator, or cancels the cruise plan and returns. The mechanism by which the sonar unit 80 detects obstacles will be described later.

[0041] <Surveying method> (Method of surveying) Figure 4 is a schematic diagram showing the measurement range of the ADCP unit 70 and the sonar unit 80. As shown in Figure 4(a), the ADCP unit 70 measures the layered flow velocity distribution according to depth directly below the multicopter 12 (Figure A). As shown in Figure 4(b), the sonar unit 80 transmits a fan-shaped sound wave beam within the range of a set swath angle S to acquire point cloud data representing the topography of the riverbed and river channel. The swath angle S is generally adjustable within the range of 90 to 160 degrees. In this example, the sonar unit 80 is installed on the multicopter 12 in a orientation such that the bisector of the swath angle S (shown as a dashed line in Figure 4(b)) is approximately a vertical line.

[0042] (Examples of sonar unit applications) Figure 5 is a schematic diagram showing an example of the scan range (coverage) of the sonar unit 80. Figure 6 is a schematic diagram showing the same point on the riverbed being scanned from multiple different directions. In Figures 5 and 6, the black circles represent the sonar unit 80, the straight lines represent the swath width, and the shaded dots represent the coverage area. All examples in Figure 5 are characterized by the ability to scan the same point on the riverbed multiple times from different positions and directions. Note that, for the sake of explanation, each example in Figure 5 shows the coverage area when the sonar unit 80 is stationary; in actual surveying, the various parts will be stretched or compressed as the sonar unit 80 moves.

[0043] Figure 5(a) shows an example of a multicopter 12 being moved downstream while the swath direction of the sonar unit 80 is continuously pointed in the direction of the river's water flow. While multibeam sonar is normally used with its swath direction pointed in the direction of the ship's across-flow, deliberately pointing it in the direction of the river's water flow allows for scanning of the riverbed shape both in front of and behind the multicopter 12 as it moves with the water current. In this case, the coverage area of ​​the sonar unit 80 becomes almost linear, and this can be used to continuously scan each point within the coverage area along the entire length of its swath width. This allows for detailed observation of changes in the riverbed's irregularities (such as riverbed waves and erosion around bridge piers) over a long period (tens of seconds). The sonar unit 80 may always keep its swath direction pointed in the direction of the water flow, but it may also be appropriately pointed in the across-flow direction to acquire the cross-sectional shape of the river channel as well.

[0044] Figure 5(b) shows an example in which the sonar unit 80 is continuously rotated horizontally while the multicopter 12 flows down a river. Similarly, Figures 5(c) and (d) show an example in which the sonar unit 80 is rotated horizontally back and forth within a predetermined angular range. While sonar fixed in the cross direction is prone to missing data, the examples in Figures 5(b) to (d) allow the same point to be scanned from various angles, thus reducing areas that are obscured by the sonar. Furthermore, scanning the same point three-dimensionally from multiple directions can improve the quality of the 3D modeling of the riverbed shape. More specifically, for example, when scanning the riverbed shape using the method in Figure 5(b), the point represented as a black triangle in Figure 6 can be scanned first when it is in front of the sonar unit 80, then when it is to the side, and finally when it is behind it. The speed at which the sonar unit 80 rotates can be adjusted as appropriate according to the ping rate, resolution, swath width, flow velocity of the multicopter 12, and required accuracy of the sonar unit 80.

[0045] Here, the shape of the riverbed wave is dynamically determined by the correlation between the riverbed shear force and the riverbed material (grain size distribution, etc.), and the shape itself is a major factor in changing the water resistance. This fluctuation in resistance affects the construction of the water level-flow rate relationship, which is fundamental to river management. Total resistance in a river can be understood as the sum of the "sand grain roughness" due to individual riverbed materials (sand and gravel) and the "shape roughness (shape resistance)" due to the irregularities of the riverbed wave. During floods, riverbed waves develop rapidly as the water depth increases and the flow velocity changes, and shape resistance increases as the wave height and wavelength change. According to academic observations, in areas where dunes (sand dunes) are formed, the flow velocity accelerates at the top of the crest (top) of the riverbed wave, and energy loss occurs in the trough (valley) due to the decrease in flow velocity or the generation of separation vortices. This energy dissipation leads to an increase in Manning's roughness coefficient, which in turn causes a hysteresis phenomenon (a phenomenon in which the water level-to-flow rate relationship forms a loop between the rising and falling phases of a flood) where the water level differs depending on the development of the riverbed waves, even if the flow rate is the same.

[0046] In current river management practices, conversion from surface velocity (application of a velocity correction coefficient) is widely used to estimate flow rates during floods. However, the presence of riverbed waves introduces uncertainty into the value of this correction coefficient. As relative roughness (ratio of riverbed wave height to water depth) increases, the ratio of surface velocity to average velocity tends to decrease. Measured data suggests that in sandy rivers where riverbed waves are dominant, a lower value (around 0.80) than the generally recommended value (0.85) should be adopted. Obtaining "temporal changes" in riverbed waveforms means tracking these dynamic roughness changes in real time. This allows for accurate evaluation of changes in flow capacity during floods and improves the accuracy of water level predictions, which form the basis for issuing evacuation advisories.

[0047] Furthermore, in conventional observations, the velocity distribution obtained by ADCP and the riverbed shape obtained by sonar were often measured separately, making it difficult to accurately grasp the dynamic causal relationship between flow conditions and topographic changes. In this configuration, by mounting both on the same floating device (multicopter 12), the spatiotemporal measurement gap is eliminated, and it becomes possible to directly correlate what kind of velocity distribution occurs at which phase (crest or trough) of the riverbed wave.

[0048] In addition, the multicopter 12 in this configuration is also equipped with a camera 60 capable of photographing the water surface. When dunes are formed in an open channel under sub-current conditions, the water surface shape appears in "opposite phase" to the riverbed shape. That is, the flow velocity increases where the riverbed is raised (shallow water), and the water level drops according to Bernoulli's theorem. By accumulating measured values ​​of this physical interaction in the surveying system 10, it becomes theoretically possible to estimate the scale and movement velocity of riverbed waves below the water surface by analyzing the spatiotemporal distribution of fine irregularities (water surface disturbances) acquired by, for example, the camera 60. Furthermore, there is a correlation between the movement velocity of water surface waves and the movement velocity of riverbed waves, and by measuring the movement velocity of ripples on the water surface using image velocity measurement techniques such as STIV (Space-time image velocityimetry), it becomes possible to identify the peak position of riverbed waves from fluctuations in the surface flow velocity distribution.

[0049] It is known that the maximum scour depth around bridge piers can reach approximately twice the width of the pier, but the application of this knowledge in the field has been limited. The difficulty in conducting scour depth surveys lies in the fact that deep scour holes generated during the flood peak are "backfilled" by sediment deposition during the flood subsidence. Even if there appears to be no abnormality on the surface, the backfilled sediment is weaker than the original ground and may cause fatal damage in the next flood. This method allows for the identification of the true maximum scour depth by continuously monitoring the scour process during floods, and enables accurate assessment of the soundness of the foundation piles of structures. This has the advantage of contributing to rapid flood control activities and the optimization of the scope of repairs in disaster recovery.

[0050] Figure 6 is a schematic diagram illustrating the collision avoidance function using the sonar unit 80. As shown in Figure 6, the sonar unit 80 continuously or periodically scans the area in front of the multicopter 12, allowing for the detection of obstacles downstream of the multicopter 12 in advance. Here, "obstacles" refer to, for example, the riverbed in shallow sections, underwater structures, and other geological or floating objects that could potentially collide with the multicopter 12 itself or equipment such as the sonar unit 80. As mentioned above, the FC / BC20 in this configuration has a collision avoidance program 23, which automatically avoids collisions using one of the methods described above when a collision is predicted. Alternatively, an operator may visually monitor the values ​​detected by the sonar unit 80 to determine the presence or absence of obstacles.

[0051] (Surveying process) Figure 8 is a schematic diagram showing how the multicopter 12 travels downstream on the river current. Figure 9 is a flowchart showing the flow of each step in this surveying method.

[0052] When starting a survey using the surveying system 10, first, the multicopter 12 is launched onto the upstream water surface of the river, as shown in Figure 8 (release process S10). The multicopter may either fly or sail to the starting point of the cruise plan. Once the multicopter 12 is launched onto the water surface, the FC / BC20 switches the multicopter 12 from flight mode to navigation mode. As mentioned above, the FC / BC20 continues to operate the GPS 31 and RTK receiver 32 even after switching the multicopter 12 to navigation mode.

[0053] The multicopter 12, switched to navigation mode, travels downstream along the river current, scanning the flow velocity and riverbed shape with the ADCP unit 70 and sonar unit 80 (scanning process S21). Upon reaching the end of the survey area, the multicopter 12 automatically takes off and returns to a predetermined location (retrieval process S30).

[0054] In this configuration, the multicopter 12 continuously transmits the flow velocity and riverbed shape data acquired in the scanning process S21 to the analysis device 11. The analysis device 11 analyzes the data received from the multicopter 12 and identifies the riverbed shape and its changes over time (analysis process S22). Note that this analysis process S22 may be performed after the completion of the scanning process S21.

[0055] After the scanning process S21 is completed, the analysis device 11 calculates the amount of sediment transport in the river from the data acquired by the ADCP unit 70 in the scanning process S21 (sediment transport calculation process S23). The calculation of sediment transport is performed separately for two components: suspended sediment and bed sediment.

[0056] The suspended sediment concentration is calculated based on the acoustic reflection intensity (backscatter) received by the ADCP unit 70. Specifically, the suspended sediment concentration in each cell is estimated by comparing the amount of sound wave diffusion and attenuation due to water and sediment with the measured values ​​(SSC: Suspended Sediment Concentration) of water samples collected on-site. This is then multiplied by the flow velocity and the cross-sectional area of ​​the river, and integrated over the entire cross-section to obtain the suspended sediment flow rate (Q). s Derive ).

[0057] For the bed sand, the bottom track function of the ADCP unit 70 is used. Specifically, the movement speed of the riverbed particles is estimated from the difference between the movement speed of the multicopter 12 based on RTK-corrected position information and the relative velocity of the bottom surface determined by the bottom track, and the friction speed and bottom surface shear force are applied to hydraulic formulas such as the "Ashida-Michigami formula" to determine the bed sand flow rate per unit width (Q b Calculate ).

[0058] And finally, these are added together to get the total amount of soil displacement across the entire cross-section (Q total =Q s +Q bThe sediment transport amount is calculated. Here, the use of a multi-frequency instrument and calibration by Bayesian estimation are effective in reducing uncertainty. By performing corrections that take particle size changes into account, it becomes possible to perform highly accurate estimations that can respond to rapid changes in flow conditions such as during floods. By optimizing these tools and correction methods according to the flow conditions at the site, sediment characteristics, and required accuracy, the accuracy of calculating sediment transport amount can be improved. Note that the cross-sectional shape of the river channel may be obtained using cross-sectional shape data acquired by the sonar unit 80, or data acquired by other methods may be used. If the cross-sectional shape data acquired by the sonar unit 80 is not used, the sediment transport amount calculation process S23 may be performed in parallel with the scanning process S21.

[0059] The dynamic riverbed wave data acquired using this method is considered highly valuable as calibration data for flood flow simulations. It can clarify the basis for practical river design, such as identifying areas of strong water impact within the river channel, providing design rationale for accurately aligning bridge pier orientation with the flow direction, and predicting the formation of dead zones due to river channel widening.

[0060] Although embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and various modifications can be made without departing from the spirit of the invention. For example, in the above embodiments, a multicopter 12 was used as the floating body, but the floating body is not limited to an unmanned aerial vehicle, and may also be a radio-controlled boat or a manned boat, for example. [Explanation of Symbols]

[0061] 10: Surveying system, 11: Analysis device, 12: Multicopter (unmanned aerial vehicle, floating vehicle), 19: Operator, 20: Flight controller / boat controller, 21: Autonomous flight program, 22: Autonomous navigation program, 23: Collision avoidance program, 31: GPS receiver, 32: RTK receiver, 41: Rotor, 42: Thruster, 60: Omnidirectional camera, 50: Float, 70: ADCP unit (ultrasonic Doppler flow meter), 80: Sonar unit (multibeam sonar)

Claims

1. A scanning process is performed in which a floating body equipped with a multi-beam sonar that transmits multiple beams in a fan shape and an ultrasonic Doppler current meter is carried along by the river current, and the riverbed shape is measured with the multi-beam sonar. The process includes a sediment transport calculation step that calculates the amount of sediment transport in a river from the data of the ultrasonic Doppler flowmeter obtained in the scanning step, In the scanning process, the swath direction of the multibeam sonar is directed in the direction of the river's water flow, and the same point is measured multiple times from different positions, while the area below the floating object is measured using the ultrasonic Doppler current meter. Surveying method.

2. A scanning process is performed in which a floating body equipped with a multi-beam sonar that transmits multiple beams in a fan shape and an ultrasonic Doppler current meter is carried along by the river current, and the riverbed shape is measured with the multi-beam sonar. The process includes a sediment transport calculation step that calculates the amount of sediment transport in a river from the data of the ultrasonic Doppler flowmeter obtained in the scanning step, In the scanning process, the riverbed shape is measured while the multibeam sonar is continuously rotated or turned horizontally, and the area below the floating body is measured using the ultrasonic Doppler current meter. Surveying method.

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