Surveying systems and river surveying methods

Abstract

This makes it possible to more easily measure the water level at any point within the body of water being surveyed. [Solution] This problem is solved by a surveying system comprising a first floating body that floats on the water surface, a reflector attached to the first floating body of the multicopter 10 that reflects electromagnetic waves from synthetic aperture radar satellites, a GNSS receiver attached to the first floating body of the multicopter 10 that acquires position information from GNSS, and an RTK receiver that acquires correction information for the position information of the multicopter 10 by RTK.

Description

[Technical Field]

[0001] This invention relates to surveying techniques using floating structures. [Background technology]

[0002] Patent Document 1 below discloses a float that can be floated in a salt field and is equipped with a reflective section that reflects radio waves from a synthetic aperture radar satellite. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-030909 [Overview of the project] [Problems that the invention aims to solve]

[0004] To assess the risk of river overflow during floods, it is crucial to understand how river water levels and their waterlines change during floods. While water levels at stations along the river's length can be measured (observed), water levels in other sections are replaced by estimated water levels calculated based on the measured values ​​at these stations. However, currently, there is no way to verify the accuracy of these estimated water levels.

[0005] Another possible method for observing rivers over a wide area is to utilize images from SAR (Synthetic Aperture Radar) satellites. SAR images are created from microwave reflection data, which has the advantage of being less affected by observation accuracy at night or in bad weather. On the other hand, since the microwave reflection intensity fluctuates depending on the water surface conditions, in order to analyze the position of the river's waterline, it is necessary to know in advance the various conditions of the water surface and how the reflection intensity is represented on the SAR image at those times. However, currently, there is a lack of actual measurement data to organize these relationships. In addition, the presence of trees along the riverbanks and within the river also makes it difficult to determine the waterline. Furthermore, in order to obtain the elevation and horizontal position (longitude and latitude) of the ground surface using SAR images, it is fundamental to take multiple images of the same point at different times and obtain the phase difference. To obtain detailed surface information in a single imaging session, such as during a river flood, it is necessary to either separate the images into the first and second halves of a continuous imaging sequence to ensure image quality and treat them as two separate imaging sessions, or to use SAR satellites equipped with multiple spaced-apart antennas or a convoy of SAR satellites.

[0006] In light of these problems, the issues that this invention aims to solve are, firstly, to enable easier measurement of water levels at any location within a body of water to be surveyed, and secondly, to enable the accumulation of actual measurement data associated with SAR images in order to improve the observation accuracy of that body of water using SAR images. [Means for solving the problem]

[0007] To solve the above problems, the surveying system of the present invention comprises a first floating body that floats on the water surface, a reflector attached to the first floating body that reflects electromagnetic waves from a synthetic aperture radar satellite, a GNSS receiving unit attached to the first floating body that acquires position information from a GNSS (Global Navigation Satellite System), and an RTK receiving unit that acquires correction information for the position information by RTK (Real Time Kinematic).

[0008] By equipping the first floating object, which is suspended on the water surface, with a reflector, the position of the first floating object in the SAR image can be identified more clearly. Furthermore, by correcting the position information of the first floating object acquired by GNSS with RTK, the three-dimensional position of the first floating object in the SAR image can be determined with relatively high accuracy. By combining these methods, it becomes possible to measure the water level and horizontal position at any point in the SAR image.

[0009] Furthermore, in order to solve the above problems, another surveying system of the present invention comprises a first floating body that floats on the water surface and is carried by the water current of the body from upstream to downstream, a GNSS receiving unit attached to the first floating body that acquires position information from a GNSS (Global Navigation Satellite System), and an L6 receiving unit that receives correction information for the position information from a QZSS (Quasi-Zenith Satellite System), wherein the altitude value included in the position information is used to calculate the water level of the water surface on which the first floating body is floating.

[0010] A first floating body, suspended on the water surface, receives correction information from QZSS (the so-called "Michibiki") and corrects the GNSS position information, making it possible to measure the relatively accurate three-dimensional position at any point in the body of water being surveyed. Furthermore, by letting the first floating body drift with the water flow of the watershed, the flow velocity of the watershed can also be obtained. At this time, the surveying system may further include a scanner device attached to the first floating body to acquire underwater topographic data. If the flow velocity of the first floating body, the topographic data (cross-sectional area) of the watershed in which the first floating body drifts, and its water level are known, the flow rate of the watershed can be calculated. At this time, the surveying system may further include a reflector attached to the first floating body that reflects electromagnetic waves from synthetic aperture radar satellites. This makes it possible to clearly identify the position of the first floating body in the SAR image.

[0011] Furthermore, it is preferable that the reflector is a corner reflector. The reflector may also consist of five or more corner reflectors. By using a reflector that is less affected by the oscillation of the first floating object floating on the water surface, the position of the first floating object in the SAR image can be identified more clearly.

[0012] Furthermore, it is desirable that the surveying system of the present invention further comprises a distance measuring means capable of acquiring data that can measure the position of the waterline of the body of water on which the first floating body is floating. By actually measuring the distance between the first floating body and the waterline of the body of water on which it is floating, the position of the waterline in the SAR image becomes clear. In this case, the distance measuring means may be a LiDAR (Light Detection and Ranging) device attached to the first floating body.

[0013] Furthermore, it is desirable that the surveying system of the present invention further includes a water surface observation means for acquiring the state of the water surface in the body of water on which the first floating body is floating. By observing the state of the water surface on which the first floating body is floating, it becomes possible to correlate the state of the water surface with how its reflection intensity appears on the SAR image. In this case, the water surface observation means may be an infrared camera or microwave radar attached to the first floating body.

[0014] Furthermore, the surveying system of the present invention may further include a second floating body that floats on the water surface together with the first floating body, and the reflector may be attached to the second floating body. By floating multiple reflectors in the water area to be surveyed, the amount of information obtained in a single SAR image can be increased.

[0015] Furthermore, it is desirable that the first floating object be an unmanned aerial vehicle capable of landing on the water surface. This would allow the worker (surveyor) to remotely control the first floating object from a safe location, increasing the flexibility of the water area and location where the survey is conducted.

[0016] Furthermore, it is desirable for the RTK receiver to acquire the correction information via the Internet. Alternatively, it is desirable for the RTK receiver to acquire the correction information via a mobile communication network. This eliminates the need to set up an RTK reference station near the body of water being surveyed, making surveying easier.

[0017] Furthermore, the surveying system of the present invention may further include a data analysis unit, wherein the data analysis unit may be configured to use as the water level at that position of the first floating body a corrected altitude value, which is a value obtained by correcting the altitude value included in the position information with the correction information, or a water surface elevation, which is a value obtained by subtracting the geoid height from the corrected altitude value. In this case, the system may further include a distance measuring means that can measure the position of the waterline of the body on which the first floating body is floating, and it is desirable that the data analysis unit is configured to estimate the likely position of the waterline of the body from (1) the position of the waterline of the body identified from the water level of the first floating body and pre-prepared 3D topographic data of the body, and (2) the position of the waterline of the body identified by the distance measuring means. By estimating the waterline from multiple types of measured values, the position of the waterline can be determined more accurately.

[0018] Furthermore, in order to solve the above problems, the gist of the river surveying method of the present invention is to include the step of using the surveying system of the present invention to photograph the first floating body with a synthetic aperture radar satellite while it is floating down the river from upstream to downstream, carried by the river's current. The position of the first floating body in the SAR image is clarified by the reflector, and by combining this with the corrected 3D position information of the first floating body, it becomes possible to identify the river's waterline in the SAR image with higher accuracy. In addition, although it generally takes several seconds to capture one SAR image, as the first floating body floats down the river during the capture of the SAR image, the position of the first floating body may appear as a line or dotted line on the SAR image. This makes it possible to obtain the flow velocity (movement speed of the first floating body) in the section in which the first floating body was photographed.

[0019] At this time, the river survey method of the present invention may include a step of obtaining the movement path and movement speed of the first floating body from the position information corrected by the correction information, and correcting the position of the first floating body in the image taken by the synthetic aperture radar satellite based on the movement path and movement speed. During the shooting of the SAR image, when the first floating body flows down (moves) in the river, the position of the first floating body shown in the SAR image may be shifted due to Doppler shift or blurred. By considering the movement path and movement speed of the first floating body that have been previously determined, the original position of the first floating body on the SAR image can be identified.

[0020] Further, the river survey method of the present invention uses the survey system of the present invention to flow the first floating body and the second floating body from the upstream to the downstream of the river along with the water flow of the river, and when the correction altitude value is the value obtained by correcting the altitude value included in the position information with the correction information, or the water surface elevation which is the value obtained by removing the geoid height from the correction altitude value is defined as the water level, (1) the water level of the first floating body, and (2) the phase difference between the reflector of the first floating body and the reflector of the second floating body photographed by the synthetic aperture radar satellite, a step of calculating the water level at the photographed position of the second floating body may be included. Thereby, the amount of information obtained by one shooting of the SAR image can be increased.

Effects of the Invention

[0021] As described above, according to the survey system and the river survey method of the present invention, it becomes possible to more easily measure the water level at an arbitrary position in the water area to be surveyed, and it also becomes possible to accumulate the measured data associated with the SAR image.

Brief Description of the Drawings

[0022] [Figure 1] It is a schematic diagram showing the configuration of the multicopter 10 used in the survey system S. [Figure 2] It is a perspective view and a plan view showing the structure of the reflector 70 and the reflector set 71. [Figure 3]This is a block diagram showing the functional configuration of the surveying system S. [Figure 4] This is a schematic diagram showing other installation examples of the LiDAR device 51 and infrared camera 52. [Figure 5] This block diagram shows the autopilot functions provided by the FC / BC20. [Figure 6] This is a schematic diagram illustrating the outline of a river surveying method using a multicopter 10. [Figure 7] This is a schematic diagram showing how a Doppler shift or blur occurs in the position of the multicopter 10 as captured in the SAR image. [Figure 8] This is a schematic diagram illustrating a river surveying method using a multicopter 10 and multiple sub-floats 11 equipped with reflectors 70. [Figure 9] This is a block diagram showing the functional configuration of the surveying system Sb. [Figure 10] This is a schematic cross-sectional view showing the multicopter 10b floating on the surface of a river. [Figure 11] This is a reference diagram to explain the cross-sectional area CS used when determining river flow rate. [Modes for carrying out the invention]

[0023] <Surveying System Overview> Embodiments of the present invention will be described below with reference to the drawings. The surveying system S and river surveying method described below are characterized by their ability to clarify the position of the multicopter in the captured SAR image by mounting a reflector that reflects microwaves from a SAR satellite on a multicopter floating on a river, and by measuring the altitude of the multicopter at the time the SAR image was taken, i.e., the high-precision three-dimensional position including the water level of the river on which the multicopter was floating, thereby improving the accuracy of SAR image analysis. This characteristic and other characteristics associated therewith will be described below through embodiments. In the following description, "surveying" is not limited to the meaning defined in the Surveying Act, but refers to measuring and observing the water level of rivers, the waterline (water surface width), the shape of the river channel (topography), the flow velocity, the flow rate, or the water surface condition, etc.

[0024] Figure 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. Figure 1(a) is a plan view of the multicopter 10, and Figure 1(b) is a plan view of a modified example thereof.

[0025] As shown in Figure 1, the multicopter 10 in this embodiment is a so-called hexacopter, with rotors 41 fixed to the ends of six arms that extend radially in a plan view. The multicopter 10 is equipped with a pair of boat-shaped floats 43 for floating on the water surface, and a pair of thrusters 42 are fixed to each float 43 for adjusting the position of the multicopter 10 on the water surface.

[0026] The multicopter 10 in Figure 1(a) has a reflector 70 mounted on the upper surface of its fuselage to reflect microwaves from the SAR satellite. The reflector 70 in this configuration is a so-called corner reflector. The specific structure of the reflector 70 and other options will be described later. The reflector 70 in Figure 1(a) is supported by a stabilizer 79 that directs its reflective surface toward the SAR satellite. The stabilizer 79 is a three-axis stabilizer that automatically cancels out the pitch, roll, and yaw oscillations of the reflector 70, keeping the reflector 70 always pointed toward a single point (towards the SAR satellite). By equipping the multicopter 10 with such a reflector, the position of the multicopter 10 in the SAR image can be identified more clearly.

[0027] Figure 1(b) shows an example of a configuration in which the stabilizer 79 is omitted. In the example in Figure 1(b), five reflector sets 71, each consisting of four reflectors 70, are distributed on the multicopter 10'. Each reflector set 71 is composed of four reflectors 70 arranged with their apertures facing outwards. Each reflector set 71 has a different arrangement angle when viewed from above. This allows for the reflection of microwaves from all directions in the celestial sphere even without the stabilizer 79.

[0028] (Reflector) Figure 2 shows perspective and plan views of the reflector 70 and reflector set 71. The reflector 70 in this embodiment is a roughly triangular pyramidal reflector with a hollow structure and 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, and microwaves incident on the opening (inner surface) of the reflector 70 are reflected multiple times within the reflector 70 and are finally sent out (returned) in the direction of incidence. The reflector set 71 is a structure in which four reflectors 70 are arranged back to back, that is, a structure in which two sides of each reflector 70 other than the bottom surface are in contact with the sides of the other two reflectors 70. In theory, it seems that one reflector set 71 can retroreflect microwaves from almost all directions of the celestial sphere, but depending on the reflector 70, sufficient reflection intensity may not be obtained unless the ideal incidence angle is around ±10°. In the example shown in Figure 1(b), the intensity and reliability of retroreflection are further enhanced by arranging five reflector sets 71 with their orientations shifted by 20° in plan view. In this way, the surveying system S of this embodiment allows for the clear identification of the position of the multicopter 10 in the SAR image, even when the multicopter 10,10' is oscillating on the water surface, by supporting the reflector 70 with a three-axis stabilizer 79 or by using five or more reflectors 70.

[0029] Furthermore, the reflector of the present invention may be any material 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) with a shape like one of the eighth sections of a hollow cube, as shown in Figure 2(c). If reflector 70 and reflector 70b have the same height, the reflective surface area of ​​reflector 70b will be approximately twice that of reflector 70, and therefore higher reflective performance can be expected. Therefore, if there is sufficient installation space and payload capacity, reflector 70b should be used. In addition, for example, retroreflective materials with many fine beads or prisms embedded in them, or film-type or coated-type retroreflective materials can also be considered.

[0030] <Functional Configuration> Figure 3 is a block diagram showing the functional configuration of the surveying system S. As shown in Figure 3, the surveying system S in this configuration mainly consists of a multicopter 10 and an analysis device 60. The multicopter 10 and the analysis device 60 are connected via the Internet for communication. In this configuration, the operator terminal U of the surveying system S also communicates with each device via the Internet.

[0031] (Multicopter) The multicopter 10 in this configuration consists of a control device, a flight controller / boat controller 20 (hereinafter referred to as "FC / BC20"), a network RTK-compatible GNSS receiver 30 (hereinafter simply referred to as "GNSS receiver 30") connected to the FC / BC20, a LiDAR (Light Detection And Ranging) device 51, a rotor 41, a thruster 42, an infrared camera 52, a reflector 70 supported by the aforementioned three-axis stabilizer 79, and floats 43. The FC / BC20 in this configuration includes a dedicated IMU (Inertial Measurement Unit), a barometric pressure sensor, an electronic compass, etc.

[0032] (FC / BC) The FC / BC20 drives the rotors 41 and thrusters 42 while checking the output values ​​of each sensor device in response to instructions from operator U or the autopilot function described later, to fly or navigate the multicopter 10. Here, "navigation" means that the multicopter 10 moves on the water surface, and this includes movement by the multicopter 10 being carried downstream by the current of a river. The multicopter 10 in this configuration is equipped with six rotors 41, which are thrust sources for moving through the air, and two thrusters 42, which are thrust sources for adjusting its position on the water surface. The FC / BC20 can 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 by instruction from operator U. Operator U remotely controls the multicopter 10 by visual observation if the multicopter 10 is within visual range, and by relying on data transmitted from the LiDAR device 51 and infrared camera 52 when the multicopter 10 is outside visual range. It is also conceivable to mount a visible light camera separately on the multicopter 10 for remote control by operator U.

[0033] (GNSS receiver and RTK receiver) The GNSS receiver 30 in this configuration incorporates an RTK receiver 31. The RTK receiver 31 acquires correction information via a network to correct positioning errors in the GNSS signal. The RTK receiver 31 may be a separate device from the GNSS receiver 30. The RTK receiver 31 in this configuration 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) around the survey site in the survey system S of this configuration, allowing for faster and simpler wide-area surveying. In addition to the LTE line, the RTK receiver 31 may also use other mobile communication networks such as 5G, 3G, and WiMAX (Worldwide Interoperability for Microwave Access). Furthermore, the GNSS receiver 30 in this configuration supports signals from various GNSS satellites, including GPS, GLONASS, Galileo, BDS (BeiDou Navigation Satellite System), and QZSS.

[0034] In this configuration, the FC / BC20 can acquire altitude from the GNSS receiver 30 and continue to acquire correction information with the RTK receiver 31 even after the rotor 41 has stopped. Conventional unmanned aerial vehicles use GNSS primarily to acquire latitude and longitude, and acquire altitude during flight using a barometric pressure sensor or a downward-facing rangefinder built into the flight controller. In other words, the altitude value obtained from GNSS is basically not used during flight, and even less so after landing. On the other hand, in this configuration of surveying system S, the GNSS receiver 30 and RTK receiver 31 are also used to acquire water level, so they continue to operate even after landing on the water (when the rotor 41 has stopped).

[0035] (LiDAR device) The LiDAR device 51 is an example of the ranging means of the present invention. Its laser is directed from the body of the multicopter 10 floating on the river toward at least both riverbanks, and it acquires point cloud data that can identify the position of the river's waterline. The multicopter 10 has a SLAM (Simultaneous Localization and Mapping) program 231, which will be described later, and this maps the positional relationship between the multicopter 10 and its surrounding objects. By measuring the distance between the multicopter 10 and the waterline of the body on which it is floating, the position of the waterline in the SAR image, i.e., the width of the water surface, can be identified, and a threshold of reflection intensity for distinguishing the water surface from land on the SAR image can be found. The ranging means of the present invention is not limited to the LiDAR device 51, as it is not limited to any device that can acquire data that can measure the position of the waterline of the body on which the multicopter 10 (first floating body) is floating. For example, other options may include laser rangefinders other than the LiDAR device 51, rangefinders using other electromagnetic waves such as infrared or millimeter waves, rangefinders using ultrasound, stereo cameras, or depth cameras.

[0036] (Infrared camera) The infrared camera 52 is an example of a water surface observation means of the present invention, and is a camera that photographs the state of the water surface on which the multicopter 10 is floating. By observing the state of the water surface, that is, the state of the waves, when SAR images are being taken, it becomes possible to correlate the roughness of the water surface with how its reflection intensity appears on the SAR image. In this embodiment, because an infrared camera 52 is used as the water surface observation means instead of a visible light camera, the state of the water surface can be observed with stable quality even at night or in bad weather. The water surface observation means of the present invention is not limited to the infrared camera 52, as it is a means that can identify the state of the water surface with the naked eye or mechanically. For example, it may be a visible light camera, or it may be a microwave radar.

[0037] In this embodiment of the surveying system S, the LiDAR device 51 and infrared camera 52 are mounted on the multicopter 10 itself, but they can also be installed in a location separate from the multicopter 10. Figure 4 is a schematic diagram showing other installation examples of the LiDAR device 51 and infrared camera 52. As shown in Figure 4, the infrared camera 52 may be pre-installed as a fixed camera 54 along the body of water to be surveyed, and the state of the water surface of the body of water to be surveyed may be observed from the image of this fixed camera 54. Alternatively, the width w of the water surface and the state of the water surface of the body of water to be surveyed may be acquired separately from above using a so-called aerial photography drone 53 equipped with the LiDAR device 51 and infrared camera 52.

[0038] (Analysis device) Returning to Figure 3, let's continue the explanation. 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 prepares it in a format that can be used to interpret SAR images. The analysis device 60 may be a single device or a combination of multiple devices. Alternatively, the operator U's control terminal may have the functions of the analysis device 60.

[0039] In this configuration, the analysis device 60 acquires corrected altitude values ​​from the multicopter 10, which are altitude values ​​corrected by the correction information of the RTK receiver 31, in addition to the latitude and longitude information corrected by the same correction information. The analysis device 60 calculates the water surface elevation, which is the value obtained by subtracting the geoid height from this corrected altitude value, and uses this as the water level at that position on the multicopter 10. For example, the geoid height can 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 this configuration of the surveying system S, the water surface elevation is used as the water level at each position in the river, but it is also conceivable to treat the corrected altitude value as the water level. Here, in order to obtain the water surface elevation from SAR images, it is common to use interferometry technology (InSAR: Interferometric Synthetic Aperture Radar), but it is difficult to obtain the water surface elevation from SAR images taken at a single time. According to this type of surveying system S, high-precision water levels can be obtained even from SAR images taken at a single time period.

[0040] The analysis device 60 also collects images from the infrared camera 52 and point cloud data from the LiDAR device 51 from the multicopter 10. In this configuration, the analysis device 60 identifies the location of the river's waterline from the water level at the position where the multicopter 10 is floating and from 3D topographic data that the river's river office periodically surveys, as well as from the point cloud data of the LiDAR device 51. By comparing and integrating these, it calculates a more accurate location of the waterline.

[0041] This configuration of the surveying system S includes a configuration (analysis device 60) specifically designed to collect and integrate data acquired by each sensor device of the multicopter 10, thereby appropriately distributing the load and function of each device throughout the entire system. Furthermore, the analysis device 60 acts as a hub for accumulating surveying results and sharing them with other stakeholders and researchers. It should be noted that a separate 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 separately accumulate and share this data.

[0042] Thus, in this embodiment of the surveying system S, the use of a multicopter 10 as the first floating body increases the degree of freedom in the water area and location to be surveyed, allowing the operator U to easily survey rivers from a safe remote location. It should be noted that the first floating body of the present invention does not necessarily have to be a multicopter 10; it can be anything that can float on the water surface and is equipped with a reflector capable of retroreflecting electromagnetic waves from SAR satellites. For example, it could be something like the floating ring 19 equipped with multiple reflector sets 71, as shown in Figure 8(a) later. The data collected by the multicopter 10 is optimized for SAR image interpretation and stored in the analysis device 60, so it is expected that the accuracy of SAR image analysis will improve the more the surveying system S is used. For example, when actual measurement data and comparison data are stored in the surveying system S and the accuracy of SAR image analysis is sufficiently improved, it is considered that it will be possible to accurately identify the river's waterline and water level from the SAR image and its orthomosaic image.

[0043] <Autopilot function> Figure 5 is a block diagram showing the autopilot functions of the FC / BC20. The multicopter 10 in this configuration is equipped with 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 detour program 25 as its autopilot functions. The following describes each of the autopilot functions of the FC / BC20.

[0044] The autonomous flight program 21 is a function that automatically flies the multicopter 10 according to a pre-prepared flight plan. The flight plan is data that includes parameters such as the takeoff (water takeoff) point and landing (water landing) point specified on the GCS (Ground Control Station) map data, waypoints which are multiple waypoints that make up the flight route between these points, the flight altitude at each waypoint, and the flight speed between each waypoint.

[0045] 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. The cruise plan is data that includes parameters for the starting point, ending point, and waypoints, which are multiple waypoints that make up the navigation route, as specified on the GCS map data. The multicopter may fly or sail to the starting point of the cruise plan. Once the multicopter 10 is floating on the water surface, the FC / BC 20 switches the multicopter 10 from flight mode to navigation mode. As mentioned above, the FC / BC 20 continues to operate the GNSS receiver 30 and RTK receiver 31 even after switching the multicopter 10 to navigation mode (after stopping the rotor 41). The autonomous navigation program 22 automatically controls the thrusters 42 so that the multicopter 10, riding the river current downstream, moves along the navigation route.

[0046] Collision avoidance program 23 and SLAM program 231 are functions that prevent the multicopter 10 from colliding with floating objects on the water surface or surrounding objects in flight mode. Based on the output data of the LiDAR device 51, SLAM program 231 determines the positional relationship between the multicopter 10 and its surrounding objects. Based on the analysis results of SLAM program 231, collision avoidance program 23 automatically controls the thrusters 42 so that the distance between the multicopter 10 and its surrounding objects does not fall below a predetermined interval, and so that it does not deviate from the flight path as much as possible. Collision avoidance program 23 and SLAM program 231 can also be used in flight mode.

[0047] The heading control program 24 is a function that uses the electronic compass of the FC / BC20 to control the aircraft's heading (nose) direction to a specified orientation.

[0048] The flight detour program 25 is a function that allows a multicopter 10, traveling downstream on the river current, to fly around structures it cannot pass through, such as water intake weirs or dams. When the multicopter 10 reaches a predetermined position downstream, the flight detour program 25 automatically takes off from the water and flies to another location further downstream. In this configuration, the takeoff point, landing point, and flight altitude between these two points are designated as waypoints in the cruise plan.

[0049] Thus, this configuration of the multicopter 10 is equipped with various autopilot functions, enabling even inexperienced operators U or when conducting surveys beyond visual line of sight to perform surveys with a certain level of quality or higher.

[0050] <River surveying method> Figure 6 is a schematic diagram illustrating the outline of a river surveying method using a multicopter 10. In the example shown in Figure 6, the survey is assumed to be conducted at night or during inclement weather (flooding). The multicopter 10 is positioned on the water surface in accordance with the scheduled SAR satellite imaging time and is carried downstream by the river current from upstream to downstream.

[0051] As shown in Figure 6, the multicopter 10 positioned on the river travels downstream along the river current. The autonomous navigation program 22 automatically controls the thrusters 42 so that the multicopter 10 travels downstream along the cruise route R1 of the cruise plan. If the multicopter 10 deviates from the cruise route R1, it gradually returns to the cruise route R1 while traveling downstream (R3). For the intake weir B1, an impassable structure located along the cruise route R1, the flight detour program 25 is used to fly around it once the multicopter 10 has reached a predetermined position in the river (R2). Note that the altitude of the multicopter 10 while the flight detour program 25 is operating does not represent the river water level, so the analysis device 60 excludes the water level during this period from the analysis. For the bridge pier B2 located along the cruise route R1, the SLAM program 231 detects it, and the collision avoidance program 23 avoids it with the minimum necessary deviation (R4).

[0052] Here, the flow velocity of a river can vary depending on the location 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 the flow velocity 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 the flow velocity on the inside. And, a floating object in water will naturally be guided towards the faster flow if it is facing the direction with the fastest flow velocity. Therefore, if it is sufficient to guide the multicopter 10 along the fastest flow course in the river, a margin (width) may be allowed in the latitude and longitude values ​​specified in the automatic navigation program 22.

[0053] Since the multicopter 10 in this configuration is equipped with a reflector 70, it is relatively easy to pinpoint the position of the multicopter 10 within the SAR image. By combining the corrected 3D position of the multicopter 10 with the point cloud data from the LiDAR device 51, the water level and shoreline of the river within the SAR image can be identified with high accuracy. Furthermore, by comparing the water surface conditions at each location captured by the infrared camera 52, it is possible to correlate the water surface conditions with how their reflection intensity appears in the SAR image.

[0054] Figure 7 is a schematic diagram showing how Doppler shift or blur occurs in the position of the multicopter 10 as captured in the SAR image. In this river surveying method, the multicopter 10 is floated down the river while SAR satellite imaging is performed. As the multicopter 10 moves during SAR image capture, Doppler shift or blur may occur in the position of the multicopter 10 as captured in the SAR image.

[0055] 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 shift 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 velocity (speed of multicopter 10 / speed of SAR satellite) And the movement speed of the multicopter 10 and the relative velocity V D The following relationships exist: V R =V D ×V S V R : Multicopter 10 movement speed V D : Relative velocity (speed of multicopter 10 / speed of SAR satellite) V S : Moving speed of the SAR satellite

[0056] Also, as shown in Fig. 7(b), when the SAR satellite and the multicopter 10 are moving in a parallel direction, the position of the multicopter 10 on the SAR image is displayed with blur in the azimuth direction Az of the SAR image. The amount of this blur is calculated by the following formula. V = x / T V: Moving speed of the multicopter 10 x: Length of the blur T: Imaging time of the SAR image

[0057] As described above, in this embodiment, since the corrected three-dimensional position of the multicopter 10 is obtained, the moving path (moving direction) and moving speed (flow speed) of the multicopter 10 at the time of taking the SAR image are known. Therefore, by applying known values to the above formulas, the original position of the multicopter 10 on the SAR image can be specified.

[0058] Fig. 8 is a schematic diagram showing a river survey method using the multicopter 10 and a plurality of sub-floats 11 provided with reflectors 70. The sub-float 11 is an example of the second floating body of the present invention. As shown in Fig. 8(a), the sub-float 11 is a simple floating body in which five reflector sets 71 are installed on a general floating ring 19. The five reflector sets 71 are arranged such that their orientations are shifted by 20° each, similar to the example of Fig. 1(b). The sub-float 11 has no drive source such as a thruster, and also does not carry sensors such as a GNSS receiver. The sub-float 11 only flows down following the flow of the river.

[0059] In the example shown in Figure 8, SAR satellites equipped with multiple spaced-apart antennas, or SAR satellites arranged in a convoy, are used for imaging. In other words, positional information including the phase difference of each point can be obtained through a single imaging session. The multicopter 10 and sub-floats 11 are positioned on the water surface in accordance with the scheduled imaging time of the SAR satellites and are carried downstream by the river current from upstream to downstream. The multicopter 10 and each sub-float 11 drift down the river starting from different locations in the river. The sub-floats 11 are thrown into the river by workers.

[0060] The sub-float 11 is equipped with a reflector 70 (reflector set 71), making it relatively easy to locate its position within the SAR image. However, since the sub-float 11 does not have sensor equipment such as a GNSS receiver, its 3D position cannot be directly obtained. Nevertheless, since the multicopter 10 of this configuration 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 and the position of each sub-float 11 in the SAR image. This increases the amount of information that can be obtained in a single SAR image capture. If the aforementioned Doppler shift or blurring is a concern, the sub-float 11 may be moored and fixed, or a separate GNSS receiver may be mounted on the sub-float 11. Furthermore, when using a single-antenna SAR satellite, that is, when using a SAR satellite that does not provide phase information of the Earth (water) surface in a single capture, a separate GNSS receiver may be mounted on the sub-float 11 to obtain its 3D position.

[0061] While the water level at points along the river where water level observation stations (GS) are installed can be measured (observed), the water level in other sections is replaced by an estimated water level calculated based on the measured values ​​at the water level observation stations. Currently, the accuracy of this estimated water level cannot be guaranteed. In both surveys using only the multicopter 10 and surveys including the sub-float 11, the accuracy of the measured values ​​can be verified by having them pass over the locations where water level observation stations (GS) are installed. Once the accuracy of the measured values ​​has been verified, the accuracy of the estimated water level can be verified by comparing these measured values ​​with the estimated water level.

[0062] <Other Embodiments> Figure 9 is a block diagram showing the functional configuration of surveying system Sb, which is another embodiment of the surveying system of the present invention. In the following description, components identical to those in the above embodiment are denoted by the same reference numerals and their descriptions are omitted. Although the infrared camera 52 is omitted in Figure 9, it may be included.

[0063] The main feature of the surveying system Sb is that the multicopter 10b, which floats on the river and is carried downstream by the current, is equipped with a GNSS receiver 30b that supports 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. It receives correction information transmitted from QZSS to correct the positioning error of the GNSS signal, and uses the resulting altitude value to calculate the 3D position of the multicopter 10b and the water level. In this configuration of the surveying system Sb, a reflector 70 is not required. The following will explain this feature and other related features using CLAS as an example. Note that the configuration other than the differences described below can be considered to be the same as or similar to the above embodiment. For example, the multicopter 10b has the same autopilot function as the multicopter 10.

[0064] (L6 receiver) As shown in Figure 9, the GNSS receiver 30b of the multicopter 10b incorporates an L6 receiver 31b that receives the CLAS L6D signal. The L6 receiver 31b receives correction information from QZSS to correct the positioning error of 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 configuration to perform relatively high-precision surveys anywhere within the QZSS coverage area without installing RTK base stations (fixed stations) around the survey site or subscribing to network RTK services such as VRS-RTK (Virtual Reference Station Real-Time Kinematic). As mentioned above, the L6 receiver 31b can also receive the MADOCA-PPP L6E signal. Furthermore, similar to the above embodiment, the GNSS receiver 30b of this configuration also supports signals from various GNSS satellites, including GPS, GLONASS, Galileo, BDS, and QZSS.

[0065] In this configuration, the analysis device 60b receives not only latitude and longitude information corrected by CLAS correction information, but also corrected altitude values, which are altitude values ​​corrected by the same correction information. It then calculates the water surface elevation, which is the value obtained by subtracting the geoid height from this corrected altitude value. The surveying system Sb also treats this water surface elevation as the water level at each point in the river.

[0066] (Multibeam sonar) The multicopter 10b in this configuration is equipped with a sonar unit 55 for acquiring underwater topographic data (cross-sectional shape of the river channel) after landing on the water. The sonar unit 55 is an example of a scanner device of the present invention. The sonar unit 55 is a multibeam acoustic depth sounder that transmits sound wave beams of different frequencies into the water in a fan shape and acquires river topographic data by receiving the reflected waves.

[0067] The sonar unit 55 is a unit equipped with 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 measurement is less affected by turbidity than optical cameras or green lasers, and can obtain more accurate topographic data even under difficult conditions. The scanner device installed on the multicopter 10b does not have to be the sonar unit 55; any device that can acquire underwater topographic data after the multicopter 10b hits the water is acceptable. For example, if only areas of clear, still water are being surveyed, topographic data can be acquired using a scanner device that uses an optical camera or laser.

[0068] Figure 10 is a schematic cross-sectional view showing the multicopter 10b floating on the surface of a river. As shown in Figure 10, once the multicopter 10b has landed on the river and switched to navigation mode, it begins scanning the underwater surface with the sonar unit 55. The sonar unit 55 transmits a fan-shaped sound wave beam over a set swath width θ to acquire point cloud data representing the topography of the river channel RC. By setting the swath width θ of the sonar unit 55 to 180° or more, the cross-sectional shape of the entire current water area can be acquired. The heading control program 24 of the FC / BC20 (see Figure 5) automatically controls the thrusters 42 to maintain, as much as possible, the state in which the sonar array direction of the sonar unit 55 intersects with the direction of travel of the navigation route R1 (see Figure 6).

[0069] (Calculation of flow rate) Figure 11 is a reference diagram illustrating the cross-sectional area CS used when determining river flow rate. In this embodiment, "flow rate" refers to the volume of water that passes through a certain cross-sectional area of ​​a river in a given unit of time. For example, it refers to the volume of water that passes through the river cross-sectional area CS shown in Figure 11 in one second. River flow rate is calculated by multiplying the flow velocity by the cross-sectional area of ​​the cross-sectional area CS. The unit of measurement is cubic meters per second (m³). 3 It is ( / s). More specifically, there are many calculation formulas, but the flow rate is calculated using the following formula, etc. The flow velocity can be calculated from 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 style

number

[0070] Thus, with this configuration of the surveying system Sb, river water level and flow velocity can be easily acquired within the QZSS coverage area. Furthermore, by incorporating the sonar unit 55, actual topographic data and flow rate of the river channel RC can also be measured. In addition, by equipping the multicopter 10b of the surveying system Sb with a reflector 70, the various data collected by the multicopter 10b can be used to improve the accuracy of SAR image analysis.

[0071] 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, only rivers are given as examples of bodies of water to be surveyed, but the bodies of water to be surveyed are not limited to rivers, but may be other bodies of water such as the sea, dams, lakes, etc. [Explanation of Symbols]

[0072] S, Sb: Survey system, U: Operator, RC: River channel, CS: Cross section, GS: Water level observation station, R1-4: Navigation route, B1: Intake weir, B2: Bridge pier, 10, 10b: Multicopter (1st floating body, unmanned aerial vehicle), 11: Sub-float (2nd floating body), 19: Lifebuoy, 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 detour program, 30: Net 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: analysis device (data analysis unit), 70, 70b: corner reflector (reflector), 71: reflector set, 79: stabilizer

Claims

1. The first floating body is placed on the water surface, A reflector attached to the first floating body, which reflects electromagnetic waves from a synthetic aperture radar satellite, A GNSS receiver unit, which is attached to the first floating body and acquires position information from GNSS (Global Navigation Satellite System), The system includes an RTK receiving unit that acquires correction information for the position information using RTK (Real Time Kinematic), Surveying system.

2. A first floating body is placed on the water surface and carried by the water currents of that area from upstream to downstream, A GNSS receiver unit, which is attached to the first floating body and acquires position information from GNSS (Global Navigation Satellite System), The system includes an L6 receiving unit that receives correction information for the position information from the QZSS (Quasi-Zenith Satellite System), The altitude value included in the aforementioned position information is used to calculate the water level on the water surface in which the first floating body is floating. Surveying system.

3. The first floating body is further equipped with a scanner device that acquires underwater topographic data. The surveying system according to claim 2.

4. The first floating body is further equipped with a reflector that reflects electromagnetic waves from a synthetic aperture radar satellite, The surveying system according to claim 2.

5. The aforementioned reflector is a corner reflector. The surveying system according to claim 1 or 4.

6. The reflector is a corner reflector of five or more parts. The surveying system according to claim 1 or 4.

7. The system further includes a distance measuring means for acquiring data that can measure the position of the waterline in the body of water where the first floating body is located. The surveying system according to claim 1 or 4.

8. The distance measuring means is a LiDAR (Light Detection and Ranging) device attached to the first floating body. The surveying system according to claim 7.

9. The system further comprises a water surface observation means for acquiring the state of the water surface in the body of water on which the first floating body is located. The surveying system according to claim 1 or 4.

10. The water surface observation means is an infrared camera attached to the first floating body. The surveying system according to claim 9.

11. The water surface observation means is a microwave radar attached to the first floating body. The surveying system according to claim 9.

12. The system further comprises a second floating body which floats on the water surface together with the first floating body, The reflector is attached to the second floating body. The surveying system according to claim 1 or 4.

13. The first floating object is an unmanned aerial vehicle capable of landing on the water surface. The surveying system according to claim 1 or 4.

14. The RTK receiver acquires the correction information via the Internet. The surveying system according to claim 1.

15. The RTK receiving unit acquires the correction information via a mobile communication network. The surveying system according to claim 1.

16. Furthermore, it includes a data analysis department, The data analysis unit uses the corrected altitude value, which is the altitude value included in the position information corrected with the correction information, or the water surface elevation, which is the corrected altitude value minus the geoid height, as the water level at that position of the first floating body. The surveying system according to claim 1 or 4.

17. The system further comprises distance measuring means for acquiring data that can measure the position of the waterline of the body of water in which the first floating body is floating, The aforementioned data analysis unit, (1) The water level of the first floating body and the position of the waterline of the water body identified from the three-dimensional topographic data of the water body prepared in advance, (2) The position of the waterline of the body of water identified by the distance measuring means, To estimate the likely location of the waterline of the aforementioned body of water, The surveying system according to claim 16.

18. The process includes using the surveying system described in claim 1 or 4 to photograph the first floating body with the synthetic aperture radar satellite while it is being carried downstream by the river's current from the upstream to the downstream of the river. River surveying methods.

19. The process includes obtaining the movement path and movement speed of the first floating body from the position information corrected by 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 movement path and movement speed. The river surveying method according to claim 18.

20. The process involves using the surveying system described in claim 12 to photograph the first floating body and the second floating body with a synthetic aperture radar satellite while they are being carried downstream by the river's current from the upper reaches of the river, When referring to the water level as the corrected altitude value, which is the altitude value included in the position information corrected with the correction information, or the water surface elevation, which is the corrected altitude value minus the geoid height, (1) The water level of the first floating body, and (2) From the phase difference between the reflector of the first floating structure and the reflector of the second floating structure, as captured by the synthetic aperture radar satellite, The process includes calculating the water level at the position where the second floating body was photographed, River surveying methods.

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