Surveying system and river surveying method

Abstract

In order to improve the accuracy of observing the water area using SAR images, it is possible to store actual measurement data associated with the SAR images. [Solution] This problem is solved by a surveying system comprising a first floating body that is floated on the water surface and photographed by a synthetic aperture radar satellite, a GNSS receiver attached to the first floating body and that acquires position information from GNSS, and an RTK receiver that acquires correction information for position information by RTK, or an L6 receiver that receives correction information for position information from QZSS, and a river surveying method that uses the surveying system of the present invention and includes a step of photographing the first floating body with a synthetic aperture radar satellite while floating it on the water current of the river from upstream to downstream.

Description

[Technical Field]

[0001] The present invention relates to a surveying technique using a floating body. [Background technology]

[0002] Patent Document 1 below discloses a float that is equipped with a reflector that reflects radio waves from a synthetic aperture radar satellite and that is set afloat on salt fields. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2024-030909 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to diagnose the risk of rivers overflowing during floods, it is important to understand how the water level of a river and its shoreline change during floods. Water levels can be measured (observed) at points along the entire length of a river where water level observation stations have been installed, but water levels in other sections are substituted with estimated water levels (calculated water levels) calculated based on the actual measurements from the water level observation stations. However, there is currently no way to verify the accuracy of these estimated water levels.

[0005] Another potential method for observing rivers over a wide area is to use images from Synthetic Aperture Radar (SAR) satellites. Because SAR images are created using microwave reflection data, they offer the advantage of being less affected by observation accuracy at night or in bad weather. However, because the microwave reflection intensity varies depending on the state of the water surface, analyzing the location of a river's waterfront requires prior knowledge of the various water surface conditions and how the reflection intensity appears on the SAR image at each time. However, there is currently a lack of actual measurement data to clarify this relationship. Furthermore, trees sometimes grow on riverbanks and within the river, making it difficult to identify the waterfront. Furthermore, to obtain the elevation and horizontal position (latitude and longitude) of the earth's surface using SAR images, it is essential to capture multiple images of the same location at different times and obtain the phase difference between the images. To obtain detailed information about the earth's surface in a single shot, such as during a river flood, it is necessary to, for example, separate the images into the first and second halves of a continuous shot to ensure image quality and treat them as two separate shots, or to use a SAR satellite equipped with multiple antennas spaced apart, or a constellation of SAR satellites.

[0006] In view of these problems, the problem that the present invention aims to solve is to make it possible to accumulate actual measurement data associated with SAR images in order to improve the accuracy of observing the water area using SAR images. [Means for solving the problem]

[0007] In order to solve the above problem, the surveying system of the present invention comprises a first floating body that is floated on the water surface and photographed by a synthetic aperture radar satellite, a GNSS receiver that is attached to the first floating body and acquires position information from a GNSS (Global Navigation Satellite System), and an RTK receiver that acquires correction information for the position information using RTK (Real Time Kinematic), or an L6 receiver that receives correction information for the position information from a QZSS (Quasi-Zenith Satellite System).

[0008] In addition, in order to solve the above-mentioned problems, the river surveying method of the present invention is summarized as including a step of using the surveying system to carry out an image of the first floating body with the synthetic aperture radar satellite while floating the first floating body on the water current of the river from upstream to downstream of the river. [Effects of the Invention]

[0009] As described above, the surveying system and river surveying method of the present invention also make it possible to accumulate actual measurement data associated with SAR images. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing the configuration of a multicopter 10 used in a surveying system S. [Figure 2] 2A and 2B are perspective and plan views showing the structures of a reflector 70 and a reflector set 71. FIG. [Figure 3] FIG. 2 is a block diagram showing the functional configuration of the surveying system S. [Figure 4] FIG. 10 is a schematic diagram showing another example of installation of the LiDAR device 51 and the infrared camera 52. [Figure 5] FIG. 2 is a block diagram showing an automatic pilot function provided in the FC / BC 20. [Figure 6] FIG. 1 is a schematic diagram showing an overview of a river surveying method using a multicopter 10. [Figure 7] FIG. 1 is a schematic diagram showing a state in which Doppler shift or blur occurs in the position of the multicopter 10 captured in a SAR image. [Figure 8] 1 is a schematic diagram showing a river surveying method using a multicopter 10 and multiple sub-floats 11 equipped with reflectors 70. [Figure 9] FIG. 2 is a block diagram showing the functional configuration of the surveying system Sb. [Figure 10] FIG. 1 is a schematic cross-sectional view showing a multicopter 10b floating on the surface of a river. [Figure 11] This is a reference diagram to explain the cross section CS when calculating river flow rate. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Surveying system overview> Hereinafter, embodiments of the present invention will be described with reference to the drawings. The surveying system S and river surveying method described below are primarily characterized by: Equipping a multicopter floating on a river with a reflector that reflects microwaves from a SAR satellite, thereby clarifying the position of the multicopter in captured SAR images; and measuring the altitude of the multicopter at the time the SAR images were captured, i.e., the high-precision three-dimensional position of the multicopter, including the water level of the river on which the multicopter is floating, thereby improving the accuracy of SAR image analysis. This feature and other associated features will be described below through embodiments. Note that the term "surveying" in the following description is not limited to the meaning defined in the Surveying Act, but refers to measuring and observing the water level, waterfront line (water surface width), river channel shape (topography), flow velocity, flow rate, water surface conditions, etc., of a river, etc.

[0012] Fig. 1 is a schematic diagram showing the configuration of a multicopter 10 used in the surveying system S of this embodiment. The multicopter 10 is an example of the first floating body and unmanned aerial vehicle of the present invention. Fig. 1(a) is a plan view of the multicopter 10, and Fig. 1(b) is a plan view of a modified example thereof.

[0013] 1, the multicopter 10 of this embodiment is a so-called hexacopter, with rotors 41 fixed to the tips of six arms extending radially in a plan view. The multicopter 10 is equipped with a pair of pontoon-shaped floats 43 for floating the aircraft on the water surface, and each float 43 is equipped with a pair of thrusters 42 for adjusting the position of the multicopter 10 on the water surface.

[0014] The multicopter 10 in FIG. 1( a) is equipped with a reflector 70 on the upper surface of its fuselage that reflects microwaves from a SAR satellite. The reflector 70 in this embodiment is a so-called corner reflector. The specific structure and other options for the reflector 70 will be described later. The reflector 70 in FIG. 1( a) is supported by a stabilizer 79 that faces its reflective surface toward the SAR satellite. The stabilizer 79 is a three-axis stabilizer that automatically offsets the swinging of the reflector 70 in the pitch, roll, and yaw directions, keeping the reflector 70 always facing a single point (toward the SAR satellite). By providing such a reflector on the multicopter 10, the position of the multicopter 10 can be more clearly identified in SAR images.

[0015] FIG. 1(b) shows an example of a configuration in which the stabilizer 79 is omitted. In the example of FIG. 1(b), five reflector sets 71, each consisting of four reflectors 70, are distributed on the multicopter 10'. Each reflector set 71 is made up of four reflectors 70 combined with their openings facing outward. Each reflector set 71 has a different arrangement angle when viewed from above. This makes it possible to reflect microwaves from all directions on the celestial sphere even without the stabilizer 79.

[0016] (reflector) FIG. 2 is a perspective view and a plan view showing the structures of the reflector 70 and the reflector set 71. The reflector 70 of this embodiment is a hollow, approximately triangular pyramid-shaped reflector with an opening, and is composed of three right-angled isosceles triangular plates that are perpendicular to each other. The inner surface of the reflector 70 is a reflective surface that reflects microwaves from the SAR satellite. Microwaves that enter the opening (inner surface) of the reflector 70 are repeatedly reflected within the reflector 70 and are ultimately sent back in the direction of incidence (return). The reflector set 71 has a structure in which four reflectors 70 are arranged back to back, that is, the two side surfaces of each reflector 70 other than the bottom surface are combined so that they are in contact with the side surfaces of the other two reflectors 70. Theoretically, one reflector set 71 appears capable of retroreflecting microwaves from almost all directions on the celestial sphere. However, depending on the reflector 70, sufficient reflection strength may not be obtained unless the ideal incident angle is approximately ±10°. 1(b), five reflector sets 71 are arranged with their orientations shifted by 20° in plan view, thereby further increasing the strength and reliability of retroreflection. In this way, in the surveying system S of this embodiment, by supporting the reflectors 70 with a three-axis stabilizer 79 and using five or more reflectors 70, the position of the multicopter 10 in the SAR image can be clearly identified even when the multicopter 10, 10' is rocking on the water surface.

[0017] The reflector of the present invention may be any member capable of retroreflecting electromagnetic waves from a SAR satellite, and its form is not limited to reflector 70. For example, it may be a reflector 70b (a so-called corner cube reflector) shaped like one of eighths of a hollow cube, as shown in FIG. 2(c). If reflector 70 and reflector 70b have the same height, the reflecting surface area of ​​reflector 70b is approximately twice that of reflector 70, and therefore higher reflective performance can be expected. Therefore, reflector 70b may be used if there is sufficient installation space and payload. Other possible retroreflective materials include those with many embedded fine beads or prisms, or film-type or coating-type retroreflective materials.

[0018] <Functional configuration> Fig. 3 is a block diagram showing the functional configuration of the surveying system S. As shown in Fig. 3, the surveying system S of this embodiment is mainly composed of a multicopter 10 and an analysis device 60. The multicopter 10 and the analysis device 60 are connected to each other so that they can communicate with each other via the Internet. In this embodiment, the operation terminal of an operator U of the surveying system S also communicates with each device via the Internet.

[0019] (multicopter) The multicopter 10 of this embodiment is composed of a flight controller / boat controller 20 (hereinafter referred to as "FC / BC 20"), which is a control device, a network RTK-compatible GNSS receiver 30 (hereinafter simply referred to as "GNSS receiver 30") connected to the FC / BC 20, a LiDAR (Light Detection and Ranging) device 51, a rotor 41, thrusters 42, an infrared camera 52, a reflector 70 supported by the above-mentioned three-axis stabilizer 79, and a float 43. The FC / BC 20 of this embodiment includes a dedicated IMU (Inertial Measurement Unit), a barometric pressure sensor, an electronic compass, etc.

[0020] (FC / BC) The FC / BC 20 drives the rotors 41 and thrusters 42 while checking the output values ​​of each sensor device in response to instructions from the operator U or an autopilot function (described later), thereby flying and navigating the multicopter 10. "Navigation" here refers to the multicopter 10 moving on the water surface, including the multicopter 10 drifting downstream on the current of a river. The multicopter 10 of this embodiment is equipped with six rotors 41 as thrust sources for movement through the air and two thrusters 42 as thrust sources for adjusting its position on the water surface. The FC / BC 20 can automatically switch between a "flight mode," in which the rotors 41 move through the air, and a "navigation mode," in which the thrusters 42 move on the water surface, either automatically or in response to instructions from the operator U. The operator U remotely controls the multicopter 10 visually when it is within line of sight, or by relying on data transmitted from the LiDAR device 51 and infrared camera 52 when it is out of line of sight. It is also possible to mount a separate visible light camera on the multicopter 10 for remote control by the operator U.

[0021] (GNSS receiver and RTK receiver) The GNSS receiver 30 of this embodiment has a built-in RTK receiver 31. The RTK receiver 31 acquires correction information for correcting positioning errors in GNSS signals via a network. The RTK receiver 31 may be a separate device from the GNSS receiver 30. The RTK receiver 31 of this embodiment acquires correction information provided as an internet service via an LTE (Long Term Evolution) line. This eliminates the need to install an RTK base station (fixed station) near the survey site, enabling surveying over a wider area more quickly and easily. The RTK receiver 31 may use other mobile communication networks, such as 5G, 3G, or WiMAX (Worldwide Interoperability for Microwave Access), in addition to an LTE line. The GNSS receiver 30 of this embodiment is compatible with signals from various GNSS satellites, including GPS, GLONASS, Galileo, BDS (BeiDou Navigation Satellite System), and QZSS.

[0022] Here, the FC / BC 20 of this embodiment can continue to acquire altitude from the GNSS receiver 30 and the RTK receiver 31 can continue to acquire correction information even after the rotor 41 has stopped. A typical unmanned aerial vehicle uses GNSS exclusively to acquire longitude and latitude, and acquires altitude during flight using a barometric pressure sensor built into the flight controller or a downward-facing ranging sensor. In other words, altitude values ​​obtained from GNSS are not generally used during flight, and even less so after landing. In contrast, in the surveying system S of this embodiment, the GNSS receiver 30 and RTK receiver 31 are also used to acquire water levels, so they continue to operate even after landing on water (when the rotor 41 has stopped).

[0023] (LiDAR device) The LiDAR device 51 is an example of a ranging device of the present invention. The LiDAR device 51 directs its laser from the multicopter 10 floating on a river toward at least both riverbanks to acquire point cloud data capable of identifying the position of the river's shoreline. The multicopter 10 includes a Simultaneous Localization and Mapping (SLAM) program 231 (described below), which maps the positional relationship between the multicopter 10 and its surrounding objects. By measuring the distance between the multicopter 10 and the shoreline of the body of water on which it is floating, the position of the shoreline in the SAR image, i.e., the water surface width, can be identified, and a reflection intensity threshold for distinguishing the water surface from land on the SAR image can be found. Note that the ranging device of the present invention is not limited to the LiDAR device 51, and any device capable of acquiring data capable of measuring the position of the shoreline of the body of water on which the multicopter 10 (first floating body) is floating can be used. For example, the sensor may be a laser distance measuring sensor other than the LiDAR device 51, a distance measuring sensor using other electromagnetic waves such as infrared rays or millimeter waves, a distance measuring sensor using ultrasonic waves, a stereo camera, or a depth camera.

[0024] (infrared camera) The infrared camera 52 is an example of the water surface observation means of the present invention, and is a camera that captures the state of the water surface on which the multicopter 10 is floating. By observing the state of the water surface when the SAR image is captured, i.e., the state of the waves, it is possible to correlate the roughness of the water surface with the way its reflection intensity appears in the SAR image. In this embodiment, the infrared camera 52 is used as the water surface observation means rather than a visible light camera, so that the water surface state can be observed with stable quality even at night or in bad weather. Note that the water surface observation means of the present invention is not limited to the infrared camera 52 as long as it is capable of identifying the water surface state with the naked eye or mechanically. For example, it could be a visible light camera, or microwave radar.

[0025] Here, in the surveying system S of this embodiment, the LiDAR device 51 and the infrared camera 52 are mounted on the multicopter 10 itself, but they can also be installed in a location away from the multicopter 10. FIG. 4 is a schematic diagram showing another installation example of the LiDAR device 51 and the infrared camera 52. As shown in FIG. 4, the infrared camera 52 may be installed in advance as a fixed camera 54 along the water area to be surveyed, and the state of the water surface of the surveyed area may be observed from the image of this fixed camera 54. Furthermore, the water surface width w and the state of the water surface of the water area to be surveyed may be separately obtained from the sky using a so-called aerial photography drone 53 equipped with the LiDAR device 51 and the infrared camera 52.

[0026] (Analysis equipment) Returning to FIG. 3, the explanation will continue. The analysis device 60 is a dedicated computer device such as a server computer or PC, which analyzes and integrates the data collected by the multicopter 10 and arranges it in a form useful for interpreting SAR images. The analysis device 60 may be a single device or a combination of multiple devices. Furthermore, the function of the analysis device 60 may be provided in the control terminal of the operator U.

[0027] The analysis device 60 of this embodiment acquires from the multicopter 10 not only the longitude and latitude information corrected using the correction information from the RTK receiver 31, but also a corrected altitude value, which is the altitude value corrected using the same correction information. The analysis device 60 calculates the water surface elevation, which is the value obtained by subtracting the geoid height from the corrected altitude value, and sets this as the water level at that position of the multicopter 10. For example, the geoid height may be obtained using gravity geoid model data provided by the Geospatial Information Authority of Japan. The water surface elevation may also be calculated within the multicopter 10 and transmitted to the analysis device 60. Furthermore, in the surveying system S of this embodiment, the water surface elevation is set as the water level at each position in the river, but it is also possible to treat the corrected altitude value as the water level. Here, interferometry technology (InSAR: Interferometric Synthetic Aperture Radar) is generally used to obtain the water surface elevation from SAR images, but it is difficult to obtain the water surface elevation from SAR images taken at a single time. According to the surveying system S of this embodiment, highly accurate water levels can be obtained even from SAR images taken at a single time.

[0028] The analysis device 60 also collects images captured by the infrared camera 52 from the multicopter 10 and point cloud data from the LiDAR device 51. The analysis device 60 of this embodiment identifies the position of the river's shoreline from the water level at the location where the multicopter 10 is floating and 3D topographical data periodically surveyed by the river office of that river, and also identifies the position of the shoreline from the point cloud data from the LiDAR device 51. Then, by comparing and integrating these, a more accurate position of the shoreline can be calculated.

[0029] The surveying system S of this embodiment is equipped with a specialized configuration (analysis device 60) for collecting and integrating data acquired by each sensor device on the multicopter 10, thereby appropriately distributing the load and functions of each device throughout the system. Furthermore, the analysis device 60 acts as a hub for storing surveying results and sharing them with other stakeholders and researchers. Note that an independent analysis device 60 is not essential for the surveying system S; for example, the multicopter 10 could be equipped with processing functions equivalent to the analysis device 60, and the results of various calculations performed within the multicopter 10 could be transmitted to the operator U, who would then store and share them separately.

[0030] As described above, the surveying system S of this embodiment employs a multicopter 10 as the first floating body, thereby increasing the flexibility of the water area and location where the survey is performed. This allows the operator U to easily survey the river from a safe, remote location. The first floating body of the present invention does not necessarily have to be a multicopter 10; it can simply be anything that can float on the water surface and has a reflector capable of retroreflecting electromagnetic waves from a SAR satellite. For example, it may be something like a ring float 19 equipped with multiple reflector sets 71, as shown in FIG. 8(a) (described later). The data collected by the multicopter 10 is optimized for SAR image interpretation and stored in the analysis device 60. This is expected to improve the accuracy of SAR image analysis as the surveying system S is used more frequently. For example, if the surveying system S accumulates actual measurement data and comparison data, and the accuracy of SAR image analysis is sufficiently improved, it may be possible to accurately identify the waterfront and water level of a river from SAR images and their orthoimages.

[0031] <Autopilot function> 5 is a block diagram showing the autopilot functions of the FC / BC 20. The multicopter 10 of this embodiment is equipped with the following autopilot functions: an autonomous flight program 21, an autonomous navigation program 22, a collision avoidance program 23, a SLAM program 231, a heading control program 24, and a flight detouring program 25. Each of the autopilot functions of the FC / BC 20 will be described below.

[0032] The autonomous flight program 21 is a function that automatically flies the multicopter 10 according to a flight plan prepared in advance. The flight plan is data that includes parameters such as a takeoff point (takeoff) and landing point (landing) specified on map data of a GCS (Ground Control Station), a plurality of waypoints that constitute the flight route between these points, flight altitude at each waypoint, flight speed between each waypoint, etc.

[0033] The autonomous navigation program 22 is a function that automatically moves the multicopter 10 on the water surface according to a pre-prepared cruise plan (navigation plan). The cruise plan is data including parameters for the start point, end point, and multiple waypoints that constitute the navigation route specified on map data in the GCS. The multicopter 10 may travel to the start point of the cruise plan by flying or by navigating. When the multicopter 10 floats on the water surface, the FC / BC 20 switches the multicopter 10 from flight mode to navigation mode. As described above, the FC / BC 20 continues to operate the GNSS receiver 30 and the RTK receiver 31 even after switching the multicopter 10 to navigation mode (stopping the rotors 41). The autonomous navigation program 22 automatically controls the thrusters 42 so that the multicopter 10, riding the river current and traveling downstream, moves along the navigation route.

[0034] The collision avoidance program 23 and the SLAM program 231 are functions that prevent the multicopter 10 from colliding with floating objects on the water surface or surrounding objects in the navigation mode. The SLAM program 231 identifies the positional relationship between the multicopter 10 and its surrounding objects based on the output data of the LiDAR device 51. The collision avoidance program 23 automatically controls the thrusters 42 based on the analysis results of the SLAM program 231 so that the distance between the multicopter 10 and its surrounding objects does not fall below a predetermined distance and so that the multicopter 10 does not deviate from its navigation route as much as possible. The collision avoidance program 23 and the SLAM program 231 can also be used in the flight mode.

[0035] The heading control program 24 is a function that controls the heading direction of the aircraft (nose) in a specified direction using the electronic compass provided in the FC / BC 20.

[0036] The flight detour program 25 is a function that allows the multicopter 10, which rides the river current down the river, to fly around structures that it cannot pass through, such as water intake weirs and dams. When the multicopter 10 reaches a predetermined position down the river, the flight detour program 25 automatically causes the multicopter 10 to take off and fly, and land at another position further downstream. In this embodiment, the takeoff and landing points of the flight detour program 25, as well as the flight altitude between these two points, are specified as waypoints in the cruise plan.

[0037] In this way, the multicopter 10 of this embodiment is equipped with various automatic piloting functions, and even an inexperienced operator U or surveying outside of visual line of sight can perform surveying with a certain level of quality or above.

[0038] <River surveying method> Figure 6 is a schematic diagram showing an overview of a river surveying method using a multicopter 10. In the example of Figure 6, the surveying is carried out at night or during bad weather (flooding). The multicopter 10 is placed on the water surface in accordance with the scheduled SAR satellite imaging time, and is carried by the river current from upstream to downstream.

[0039] As shown in FIG. 6, a multicopter 10 deployed in a river rides the current and descends the river. The autonomous navigation program 22 automatically controls the thrusters 42 so that the multicopter 10 descends the river along the navigation route R1 of the cruise plan. If the multicopter 10 deviates from the navigation route R1, it gradually returns to the navigation route R1 while descending the river (R3). When the multicopter 10 reaches a predetermined position on the navigation route R1, the flight detouring program 25 flies around the intake weir B1, an impassable structure, and detours it (R2). Note that the altitude of the multicopter 10 while the flight detouring program 25 is operating does not reflect the water level of the river, so the analysis device 60 excludes the water level during this period from the analysis target. The SLAM program 231 detects a bridge pier B2 located along the navigation route R1, and the collision avoidance program 23 passes through it with the minimum deviation required (R4).

[0040] The flow speed of a river may vary depending on the position along the river width. For example, even in areas where the river flows in a straight line, two spiral currents aligned along the river width cause the flow speed in the center of the river to be faster than the flow speed on either side of the river. Furthermore, as the river volume increases, the water level in the center rises, creating a flow on the surface from the center toward both banks. Conversely, as the river volume decreases, the water level in the center drops, creating a flow on the surface from both banks toward the center. Furthermore, in areas where the river curves, the flow speed on the outside of the curve is faster than the flow speed on the inside. If a floating object in deep water faces the direction of the fastest flow, it will naturally be guided toward the faster flow. Therefore, if the multicopter 10 is to be guided along the course of the river with the fastest flow speed, the longitude and latitude values ​​specified in the automatic navigation program 22 may be given some leeway (width).

[0041] Because the multicopter 10 of this embodiment is equipped with a reflector 70, it is relatively easy to identify the position of the multicopter 10 in the SAR image. By combining the corrected three-dimensional position of the multicopter 10 with the point cloud data from the LiDAR device 51, the water level and waterfront of the river can be identified with high accuracy in the SAR image. Furthermore, by comparing the water surface conditions at each position photographed by the infrared camera 52, it is possible to associate the water surface conditions with the way their reflection intensity appears in the SAR image.

[0042] 7 is a schematic diagram showing Doppler shift or blurring of the position of the multicopter 10 captured in a SAR image. In the river surveying method of this embodiment, the multicopter 10 is floated down the river while capturing images using a SAR satellite. As the multicopter 10 moves while capturing SAR images, Doppler shift or blurring may occur in the position of the multicopter 10 captured in the captured SAR image.

[0043] As shown in Figure 7(a), if the SAR satellite and the multicopter 10 were moving in orthogonal directions, the position of the multicopter 10 on the SAR image may be shifted due to Doppler shift. The amount of Doppler shift is calculated using the following formula. x=H×tanθ×V D H:Satellite altitude θ: Incident angle V D : Relative speed (moving speed of the multicopter 10 / moving speed of the SAR satellite) And the moving speed of the multicopter 10 and the relative speed V D are in the following relationship: V R =V D ×V S V R : Multicopter 10 movement speed V D : Relative speed (moving speed of the multicopter 10 / moving speed of the SAR satellite) V S :SAR satellite movement speed

[0044] 7(b), if the SAR satellite and the multicopter 10 were moving in parallel directions, the position of the multicopter 10 on the SAR image would be displayed with a blur in the azimuth direction Az of the SAR image. The amount of this blur is calculated using the following formula: V=x / T V: Multicopter 10 movement speed x: length of blur T: SAR image acquisition time

[0045] As described above, in this embodiment, the corrected three-dimensional position of the multicopter 10 is acquired, and therefore the movement path (movement direction) and movement speed (flow velocity) of the multicopter 10 at the time of capturing the SAR image are known. Therefore, by applying known values ​​to the above equations, the original position of the multicopter 10 on the SAR image can be identified.

[0046] FIG. 8 is a schematic diagram showing a river surveying method using a multicopter 10 and multiple sub-floats 11 equipped with reflectors 70. The sub-floats 11 are an example of the second float of the present invention. As shown in FIG. 8(a), the sub-float 11 is a simple float with five reflector sets 71 installed on a general float ring 19. The five reflector sets 71 are arranged so that their orientations are offset by 20°, similar to the example in FIG. 1(b). The sub-float 11 does not have a driving source such as a thruster, nor is it equipped with a sensor such as a GNSS receiver. The sub-float 11 simply floats downstream with the river current.

[0047] In the example of Figure 8, a SAR satellite equipped with multiple antennas spaced apart, or a formation of SAR satellites, is used for imaging. In other words, position information including the phase difference between each point can be obtained through a single imaging session. The multicopter 10 and sub-floats 11 are placed on the water surface in accordance with the scheduled SAR satellite imaging time, and are carried by the river current from upstream to downstream. The multicopter 10 and each sub-float 11 start from a different position on the river and float downstream. The sub-floats 11 are thrown into the river by workers.

[0048] The sub-float 11 is equipped with a reflector 70 (reflector set 71), making it relatively easy to identify its position in the SAR image. However, since the sub-float 11 is not equipped with a sensor device such as a GNSS receiver, its three-dimensional position cannot be directly acquired. However, since the multicopter 10 of this embodiment is also included in the SAR image, the water level at the position of each sub-float 11 can be calculated from the phase difference Δ (see Figure 8(b)) between the position of the multicopter 10 in the SAR image and the position of each sub-float 11. This increases the amount of information obtained from a single SAR image capture. Note that if the above-mentioned Doppler shift and blur are a concern, the sub-float 11 may be moored and fixed, or a separate GNSS receiver or the like may be mounted on the sub-float 11. Furthermore, even when using a single-antenna SAR satellite, i.e., when using a SAR satellite that cannot obtain phase information of the earth's surface (water surface) in a single capture, a separate GNSS receiver or the like may be mounted on the sub-float 11 to acquire its three-dimensional position.

[0049] Although water levels can be measured (observed) at points along the entire length of the river where water level observation stations are installed, water levels in other sections are substituted with estimated water levels calculated based on the actual measurements from the water level observation stations. Currently, the accuracy of these estimated water levels cannot be guaranteed. Whether surveying using only the multicopter 10 or including the sub-float 11, the accuracy of the measurements can be verified by having the multicopter pass the locations where water level observation stations are installed. Once the accuracy of the measurements has been verified, the accuracy of the estimated water levels can also be verified by comparing the measurements with the estimated water levels.

[0050] <Other embodiments> Figure 9 is a block diagram showing the functional configuration of a surveying system Sb, which is another embodiment of the surveying system of the present invention. In the following explanation, the same components as those in the above embodiment are assigned the same reference numerals, and their explanation will be omitted. Note that although the infrared camera 52 is omitted in Figure 9, it may also be included.

[0051] The main feature of the surveying system Sb is that the multicopter 10b, which is floated on a river and carried downstream by the water current, is equipped with a GNSS receiver 30b compatible with the CLAS (Centimeter Level Augmentation Service) and MADOCA-PPP (Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis - Precise Point Positioning) services provided by QZSS. The GNSS receiver 30b receives correction information transmitted from QZSS to correct positioning errors in the GNSS signal, and uses the resulting altitude value to calculate the three-dimensional position and water level of the multicopter 10b. The surveying system Sb of this embodiment does not require a reflector 70. This feature and other associated features will be described below using the CLAS as an example. Note that the configuration, other than the differences described below, can be considered to be the same or similar to the above-described embodiment. For example, the multicopter 10b is equipped with an autopilot function similar to that of the multicopter 10.

[0052] (L6 receiver) As shown in FIG. 9 , the GNSS receiver 30b of the multicopter 10b includes an L6 receiver 31b that receives the L6D signal of the CLAS. The L6 receiver 31b receives correction information from the QZSS to correct positioning errors in the GNSS signal. The L6 receiver 31b may be a separate device from the GNSS receiver 30b. This allows the surveying system Sb of this embodiment to perform relatively high-precision surveying anywhere within the QZSS coverage area without installing an RTK base station (fixed station) near the survey site or subscribing to a network RTK service such as VRS-RTK (Virtual Reference Station Real-Time Kinematic). As mentioned above, the L6 receiver 31b can also receive the L6E signal of the MADOCA-PPP. Similar to the above embodiment, the GNSS receiver 30b of this embodiment also supports signals from various GNSS satellites, including GPS, GLONASS, Galileo, BDS, and QZSS.

[0053] The analysis device 60b of this embodiment receives the longitude and latitude information corrected by the CLAS correction information, as well as the corrected altitude value, which is the altitude value corrected by the same correction information, and calculates the water surface elevation, which is the value obtained by subtracting the geoid height from the corrected altitude value. The surveying system Sb also treats this water surface elevation as the water level at each point in the river.

[0054] (multi-beam sonar) The multicopter 10b of this embodiment is equipped with a sonar unit 55 for acquiring underwater topographical data (cross-sectional shape of the river channel) after landing on water. The sonar unit 55 is an example of a scanner device of the present invention. The sonar unit 55 is a multi-beam echo sounding device that transmits sound beams of different frequencies in a fan-shaped pattern into the water and acquires river topographical data by receiving the reflected waves.

[0055] The sonar unit 55 is a unit equipped with a transmitter with an array of multiple sonars, a receiver for receiving reflected waves, a dedicated IMU, a surface sound velocity meter, and the like. Ultrasonic measurements are less affected by turbidity than optical cameras or green lasers, making it possible to obtain more accurate terrain data even under difficult conditions. The scanner device installed on the multicopter 10b need only be capable of acquiring underwater terrain data after the multicopter 10b lands on the water, and is not limited to the sonar unit 55. For example, if only highly transparent, still water areas are to be surveyed, it is believed that terrain data can also be acquired using a scanner device using an optical camera or laser.

[0056] FIG. 10 is a cross-sectional schematic diagram showing a multicopter 10b floating on the surface of a river. As shown in FIG. 10, the multicopter 10b lands on the river, switches to navigation mode, and begins scanning the water with the sonar unit 55. The sonar unit 55 transmits a fan-shaped sound beam over a set swath width θ to acquire point cloud data representing the topography of the river channel RC. Setting the swath width θ of the sonar unit 55 to 180° or greater makes it possible to acquire the cross-sectional shape of the entire current water area. The heading control program 24 (see FIG. 5) of the FC / BC 20 automatically controls the thrusters 42 to maintain, as much as possible, a state in which the sonar array direction of the sonar unit 55 intersects with the direction of travel of the navigation route R1 (see FIG. 6).

[0057] (Calculation of flow rate) Figure 11 is a reference diagram for explaining the cross-section CS when calculating the flow rate of a river. In this embodiment, "flow rate" refers to the volume of water flowing through a certain cross-section of a river in a predetermined unit of time. For example, it is the volume of water passing through the cross-section CS of the river shown in Figure 11 in one second. The flow rate of a river is calculated by multiplying the flow velocity by the cross-sectional area of ​​the cross-section CS. The unit of measurement is cubic meters per second (m 3 / s). More specifically, although there are many calculation formulas, the flow rate is calculated using the following formula, etc. The flow velocity can be calculated using the latitude and longitude acquired by the GNSS receiver 30b, their correction values, and the time of acquisition. Flow rate Q(m 3 / s) = flow velocity V (m / s) × cross-sectional area A (m 2 ) Manning formula

number

[0058] As described above, the surveying system Sb of this embodiment can easily acquire the water level and flow velocity of rivers in the QZSS coverage area. Furthermore, by providing a sonar unit 55, it is possible to measure the actual topographical data and flow rate of the river channel RC. Furthermore, by providing a reflector 70 on the multicopter 10b of the surveying system Sb, various data collected by the multicopter 10b can be used to improve the accuracy of SAR image analysis.

[0059] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and various modifications can be made without departing from the spirit of the invention. For example, in the above embodiments, only rivers are given as examples of water bodies to be surveyed, but water bodies to be surveyed are not limited to rivers and may be other water bodies such as the sea, dams, lakes, and marshes. [Explanation of symbols]

[0060] S,Sb: Surveying system, U: Operator, RC: River channel, CS: Cross section, GS: Water level observation station, R1-4: Navigation route, B1: Water intake weir, B2: Pier, 10,10b: Multicopter (first floating body, unmanned aerial vehicle), 11: Sub-float (second floating body), 19: Float, 20: Flight controller / boat controller, 21: Autonomous flight program, 22: Autonomous navigation program, 23: Collision avoidance program, 231: SLAM program, 24: Heading control program, 25: Flight detouring program, 30: Network Work RTK-compatible GNSS receiver (GNSS receiver, RTK receiver), 30b: CLAS-compatible GNSS receiver (GNSS receiver, L6 receiver), 31: RTK receiver, 31b: L6 receiver, 41: rotor, 42: thruster, 43: float, 51: LiDAR device, 52: infrared camera, 53: aerial photography drone, 54: fixed camera, 55: sonar unit (scanner device), 60: analyzer (data analysis unit), 70, 70b: corner reflector (reflector), 71: reflector set, 79: stabilizer

Claims

1. a first floating body that is floated on the water surface and photographed by a synthetic aperture radar satellite; a GNSS (Global Navigation Satellite System) receiving unit attached to the first floating body and configured to acquire position information from a GNSS; an RTK (Real Time Kinematic) receiver that acquires correction information for the position information, or an L6 receiver that receives correction information for the position information from a QZSS (Quasi-Zenith Satellite System); and a distance measuring means for acquiring data capable of measuring the position of the waterfront of the water body in which the first floating body is floated. Surveying system.

2. a first floating body that is floated on the water surface and photographed by a synthetic aperture radar satellite; a GNSS (Global Navigation Satellite System) receiving unit attached to the first floating body and configured to acquire position information from a GNSS; An RTK (Real Time Kinematic) receiver that acquires correction information for the position information, or an L6 receiver that receives correction information for the position information from a QZSS (Quasi-Zenith Satellite System), The first floating body is an unmanned aerial vehicle capable of landing on the water surface. Surveying system.

3. Further, a scanner device is attached to the first floating body and acquires underwater topographical data. The surveying system according to claim 1 or 2.

4. The water surface observation means further includes a water surface observation means for acquiring the state of the water surface of the water area in which the first floating body is floated. The surveying system according to claim 1 or 2.

5. The apparatus further includes a second floating body that floats on the water surface together with the first floating body and is photographed by the synthetic aperture radar satellite. The surveying system according to claim 1 or 2.

6. Further comprising a data analysis unit, The data analysis unit determines the water level at the position of the first floating body to be a corrected altitude value, which is a value obtained by correcting the altitude value included in the position information with any of the correction information, or a water surface elevation, which is a value obtained by subtracting the geoid height from the corrected altitude value. The surveying system according to claim 1 or 2.

7. The first floating body further includes a distance measuring means for acquiring data that can measure the position of the waterfront of the water body where the first floating body is floated, The data analysis unit (1) the water level of the first floating body and the position of the water's shoreline identified from three-dimensional topographical data of the water area prepared in advance; (2) the position of the waterfront of the water area identified by the distance measuring means, estimating the probable location of the waterfront of said body of water; The surveying system according to claim 6.

8. a first floating body that is floated on the water surface and photographed by a synthetic aperture radar satellite; a GNSS (Global Navigation Satellite System) receiving unit attached to the first floating body and configured to acquire position information from a GNSS; A surveying system is used that includes an RTK (Real Time Kinematic) receiver that acquires correction information for the position information, or an L6 receiver that receives correction information for the position information from a QZSS (Quasi-Zenith Satellite System), a step of photographing the first floating body with the synthetic aperture radar satellite while floating the first floating body from upstream to downstream of the river on the water current of the river, River surveying methods.

9. and acquiring a moving path and a moving speed of the first floating body from the position information corrected by any one of the correction information, and correcting the position of the first floating body in the image captured by the synthetic aperture radar satellite based on the moving path and the moving speed. The river surveying method according to claim 8.

10. a first floating body that is floated on the water surface and photographed by a synthetic aperture radar satellite; a second floating body that floats on the water surface together with the first floating body and is photographed by the synthetic aperture radar satellite; a GNSS (Global Navigation Satellite System) receiving unit attached to the first floating body and configured to acquire position information from a GNSS; A surveying system is used that includes an RTK (Real Time Kinematic) receiver that acquires correction information for the position information, or an L6 receiver that receives correction information for the position information from a QZSS (Quasi-Zenith Satellite System), a step of photographing the first floating body and the second floating body with a synthetic aperture radar satellite while floating them from upstream to downstream of the river on the water current of the river; When the water level is a corrected altitude value, which is a value obtained by correcting the altitude value included in the location information with any of the correction information, or a water surface elevation, which is a value obtained by subtracting the geoid height from the corrected altitude value, (1) the water level of the first floating body, and (2) From the phase difference between the first floating body and the second floating body photographed by the synthetic aperture radar satellite, and calculating the water level at the photographed position of the second floating body. River surveying methods.

Images