Measurement System and River Measurement Method

Abstract

To make it possible to more easily measure the water level at any position in the water area to be measured. 【Solution means】This is solved by a surveying system including a first floating body floating on the water surface, a reflector attached to the first floating body and reflecting electromagnetic waves from a synthetic aperture radar satellite, a GNSS receiver attached to the first floating body and acquiring position information from GNSS, and an RTK receiver acquiring correction information of the multi-copter 10 position information by RTK.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 below discloses a float that is provided with a reflecting portion that reflects radio waves from a synthetic aperture radar satellite and floats on a salt pan.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to diagnose the overtopping risk of a river during a flood, it is important to grasp how the water level and its waterline of the river change during a flood. Among the entire length of the river, the water level at the point where the water level observation station is installed can be measured (observed) actually, but the water levels of other sections will be substituted with estimated water levels (calculated water levels) calculated based on the actually measured values of the water level observation station. However, at present, there is no means to verify the accuracy of this estimated water level.

[0005] In addition, as a means of observing rivers over a wide area, it is conceivable to use images of SAR (Synthetic Aperture Radar) satellites. Since SAR images are created from microwave reflection data, they have the advantage that the observation accuracy is less likely to be affected even at night or in bad weather. On the other hand, since the reflection intensity of microwaves varies depending on the state of the water surface, in order to analyze the position of the waterline of a river, it is necessary to know in advance the water surfaces in various states and the way the reflection intensity appears on the SAR image at that time. However, at present, there is a lack of measured data for organizing such relationships. In addition, there are sometimes trees growing on the riverbanks or in the river, which also makes it difficult to distinguish the waterline. In addition, in order to obtain the altitude and horizontal position (latitude and longitude) of the ground surface using SAR images, it is basically necessary to take multiple images of the same location at different times and obtain the phase difference. In order to obtain detailed information on the ground surface at a single shooting timing such as during a flood of a river, for example, it is necessary to divide the images into the first half and the second half during continuous shooting to ensure the image quality, and treat them as two-time shootings, or to use an SAR satellite equipped with a plurality of antennas arranged at intervals, or an SAR satellite in a formation.

[0006] In view of such problems, the problem to be solved by the present invention is, first, to make it possible to more easily measure the water level at an arbitrary position in the water area to be surveyed, and second, to accumulate measured data associated with the SAR image in order to improve the observation accuracy of the water area by the SAR image.

Means for Solving the Problem

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

[0008] By providing the first floating body floating on the water surface with a reflector, the position of the first floating body in the SAR image can be more clearly identified. And by RTK-correcting the position information of the first floating body obtained by GNSS, the three-dimensional position of the first floating body in the SAR image can be specified relatively accurately. By combining these, it becomes possible to measure the water level and horizontal position at any position in the SAR image.

[0009] Also, to solve the above problems, another surveying system of the present invention includes a first floating body floating on the water surface and flowing from the upstream side to the downstream side along with the water flow in the water area, a GNSS receiver attached to the first floating body for acquiring position information from GNSS (Global Navigation Satellite System), and an L6 receiver for receiving correction information of the position information from QZSS (Quasi-Zenith Satellite System), and the altitude value included in the position information is used for calculating the water level of the water surface on which the first floating body floats.

[0010] By having the first floating body floating on the water surface receive correction information from QZSS (so-called "Michibiki") and correct the position information of GNSS, it becomes possible to measure a relatively accurate three-dimensional position at any position in the water area to be surveyed. Also, by letting the first floating body flow along with the water flow in its basin, the flow velocity of the basin can also be obtained. At this time, the surveying system may further include a scanner device attached to the first floating body for acquiring underwater terrain data. If the flow velocity of the first floating body, the terrain data (cross-sectional area) of the basin through which the first floating body flows, and its water level are known, the flow rate of the basin can be calculated. Also at this time, the surveying system may further include a reflector attached to the first floating body for reflecting electromagnetic waves from a synthetic aperture radar satellite. This makes it possible to clearly identify the position of the first floating body in the SAR image.

[0011] Further, it is desirable that the reflector is a corner reflector. The reflector may be five or more corner reflectors. By using a reflector that is less affected by the rocking of the first floating body floating on the water surface, the position of the first floating body in the SAR image can be identified more clearly.

[0012] Moreover, it is desirable that the surveying system of the present invention further includes a ranging means for acquiring data capable of measuring the position of the waterline of the water area where the first floating body is floating. By actually measuring the distance between the first floating body and the waterline of the water area where it is floating, the position of the waterline in the SAR image becomes clear. At this time, the ranging 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 observing means for acquiring the state of the water surface of the water area where the first floating body is floating. By observing the state of the water surface where the first floating body is floating, it becomes possible to associate the state of the water surface with the way its reflection intensity appears on the SAR image. At this time, the water surface observing means may be an infrared camera or a microwave radar attached to the first floating body.

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

[0015] Also, it is desirable that the first floating body is an unmanned aerial vehicle that can land on the water surface. As a result, an operator (surveyor) can remotely control the first floating body from a safe location, and the degree of freedom in the water area and position where the surveying is performed is increased.

[0016] Further, it is desirable that the RTK receiver obtains the correction information via the Internet. Alternatively, it is desirable that the RTK receiver obtains the correction information via a mobile communication network. This eliminates the need to install an RTK reference station near the water area to be surveyed, enabling more convenient surveying.

[0017] Moreover, the surveying system of the present invention further includes a data analysis unit. The data analysis unit may be configured such that the corrected altitude value, which 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 excluding the geoid height from the corrected altitude value, is used as the water level at the position of the first floating body. At this time, the surveying system further includes a distance measuring means for obtaining data capable of measuring the position of the water line of the water area where the first floating body is floating. The data analysis unit preferably estimates the probable position of the water line of the water area from (1) the water level of the first floating body and the position of the water line of the water area specified from the three-dimensional terrain data of the water area prepared in advance, and (2) the position of the water line of the water area specified by the distance measuring means. By estimating the water line from multiple types of measured values, the position of the water line can be specified more accurately.

[0018] In order to solve the above problems, the river surveying method of the present invention mainly includes a step of using the surveying system of the present invention to photograph the first floating body while letting it float along the water flow of the river from the upstream to the downstream of the river with a synthetic aperture radar satellite. By clarifying the position of the first floating body in the SAR image with a reflector and combining it with the corrected three-dimensional position information of the first floating body, it becomes possible to specify the water line of the river in the SAR image with higher accuracy. Also, generally, it takes several seconds to photograph one SAR image. However, when the first floating body flows down the river during the photographing of the SAR image, the position of the first floating body may appear as a line or a dotted line on the SAR image. Thus, it is also possible to obtain the flow velocity (the moving speed of the first floating body) in the section where the first floating body is 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] Also, 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, which 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 excluding 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 water level at the photographed position of the second floating body are calculated from 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. This can increase the amount of information obtained from a single shooting of the SAR image.

Advantages 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 any 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]

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Embodiments for Carrying Out the Invention

[0023] <Overview of the Measurement System> Hereinafter, embodiments of the present invention will be described with reference to the drawings. The measurement system S and the river survey method described below are characterized in that by mounting a reflector that reflects the microwave of the SAR satellite on a multicopter floating on a river, the position of the multicopter in the captured SAR image is clarified, and a high-precision three-dimensional position including the altitude of the multicopter when the SAR image was taken, that is, the water level of the river on which the multicopter is floating, is actually measured to improve the analysis accuracy of the SAR image. Hereinafter, this feature and other features associated therewith will be described through embodiments. Note that the "survey" in the following description is not limited to the meaning defined in the survey method, and refers to measuring and observing the water level, water line (water surface width), river channel shape (topography), flow velocity, flow rate, or water surface state of a river or the like.

[0024] FIG. 1 is a schematic diagram showing the configuration of the multicopter 10 used in the surveying system S of the present embodiment. The multicopter 10 is an example of the first floating body and the unmanned aircraft 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.

[0025] As shown in FIG. 1, the multicopter 10 of the present embodiment is a so-called hexacopter in which rotors 41 are fixed to the tips of six arms extending radially in plan view. The multicopter 10 is provided with a pair of pontoon-shaped floats 43 for floating its fuselage on the water surface, and a pair of thrusters 42 for adjusting the position of the multicopter 10 on the water surface are fixed to each float 43.

[0026] In the multicopter 10 of FIG. 1(a), a single reflector 70 that reflects microwaves from the SAR satellite is installed on the upper surface of its fuselage. The reflector 70 of the present embodiment is a so-called corner reflector. The specific structure and other options of the reflector 70 will be described later. The reflector 70 in FIG. 1(a) is supported by a stabilizer 79 that directs its reflecting surface toward the SAR satellite side. The stabilizer 79 is a three-axis stabilizer that automatically cancels out the rocking of the reflector 70 in the pitch, roll, and yaw directions and always directs the reflector 70 toward one point (the SAR satellite side). By the multicopter 10 being provided with such a reflector, the position of the multicopter 10 in the SAR image can be more clearly identified.

[0027] FIG. 1(b) is an example of a configuration in which the stabilizer 79 is omitted. In the example of FIG. 1(b), five sets of reflector sets 71 each composed of four reflectors 70 are dispersedly arranged on the multicopter 10'. Each reflector set 71 is a combination of four reflectors 70 with their openings facing outward. The arrangement angles of these reflector sets 71 are different when viewed in plan view. Thereby, even without the stabilizer 79, microwaves from all directions of the celestial sphere can be reflected.

[0028] (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 substantially triangular pyramid-shaped reflector that is hollow and has an opening, and is composed of three right-angled isosceles triangular plates that are orthogonal to each other. The inner surface of the reflector 70 serves as a reflecting surface for reflecting the microwaves of the SAR satellite. The microwaves incident on the opening (inner surface) of the reflector 70 are repeatedly reflected a plurality of times within the reflector 70 and are finally sent out (returned) in the incident direction. The reflector set 71 has a structure in which four reflectors 70 are arranged back to back with each other, that is, a structure in which two side surfaces other than the bottom surface of each reflector 70 are combined so as to be in contact with the side surfaces of the other two reflectors 70. Theoretically, it seems that almost all the microwaves from all directions of the celestial sphere can be retroreflected by one reflector set 71, but depending on the reflector 70, sufficient reflection intensity may not be obtained unless the ideal incident angle is around ±10°. In the example of FIG. 1(b), by arranging five reflector sets 71 while shifting their orientations by 20° each in plan view, the intensity and certainty of retroreflection are further enhanced. Thus, in the surveying system S of this embodiment, by supporting the reflector 70 with a three-axis stabilizer 79 or using five or more reflectors 70, even when the multicopters 10, 10' swing on the water surface, the position of the multicopter 10 in the SAR image can be clearly identified.

[0029] Furthermore, the reflector of the present invention only needs to be a member capable of retroreflecting electromagnetic waves from an SAR satellite, and its form is not limited to the reflector 70. For example, it may be a reflector 70b (so-called corner cube reflector) having a shape such as one of the hollow cubes divided into 1 / 8 as shown in Fig. 2(c). When the heights of the reflector 70 and the reflector 70b are the same, the reflector 70b is expected to have higher reflection performance because the area of its reflecting surface is about twice that of the reflector 70. Therefore, if there is room in the installation space and payload, the reflector 70b may be adopted. In addition, for example, it is also conceivable to adopt a retroreflective material in which a large number of fine beads or prisms are embedded, or a film-type or coating-type retroreflective material.

[0030] <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 mainly includes a multicopter 10 and an analysis device 60. The multicopter 10 and the analysis device 60 are communicably connected via the Internet. In addition, in this embodiment, the operation terminal of the operator U of the surveying system S also communicates with each device via the Internet.

[0031] (Multicopter) The multicopter 10 of this embodiment includes a flight controller / boat controller 20 (hereinafter referred to as "FC / BC20") which is a control device, 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, rotors 41, thrusters 42, an infrared camera 52, the reflector 70 supported by the above-mentioned three-axis stabilizer 79, and a float 43. The FC / BC20 of this embodiment includes a dedicated IMU (Inertial Measurement Unit), a barometric pressure sensor, an electronic compass, and the like.

[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 the instructions of the operator U or the automatic flight control function described later, and makes the multicopter 10 fly and navigate. The "navigation" mentioned here means that the multicopter 10 moves on the water surface, including the movement of the multicopter 10 flowing downstream along the water flow of the river. The multicopter 10 of this embodiment is provided with six rotors 41 as thrust sources for moving in the air and two thrusters 42 as thrust sources for adjusting the position on the water surface. The FC / BC20 can automatically or according to the instruction from the operator U switch between the "flight mode" of moving in the air with the rotors 41 and the "navigation mode" of moving on the water surface with the thrusters 42. If the multicopter 10 is within the visual range, the operator U can remotely control the multicopter 10 visually, and outside the visual range, rely on the data transferred from the LiDAR device 51 and the infrared camera 52. It is also conceivable to separately install a visible light camera on the multicopter 10 for remote control by the operator U.

[0033] (GNSS Receiver and RTK Receiver Unit) The GNSS receiver 30 of this embodiment incorporates an RTK receiver unit 31. The RTK receiver unit 31 acquires correction information for correcting the positioning error of the GNSS signal via the network. The RTK receiver unit 31 may be a device separate from the GNSS receiver 30. The RTK receiver unit 31 of this embodiment acquires the correction information provided as a service on the Internet through an LTE (Long Term Evolution) line. Thereby, in the surveying system S of this embodiment, it is not necessary to install an RTK base station (fixed station) around the surveying area, and a wider range of surveying can be performed more quickly and simply. Note that the RTK receiver unit 31 may use other mobile communication networks such as 5G, 3G, and WiMAX (Worldwide Interoperability for Microwave Access) in addition to the LTE line. Also, the GNSS receiver 30 of this embodiment is compatible with signals from various GNSS satellites such as GPS, GLONASS, Galileo, BDS (BeiDou Navigation Satellite System), and QZSS.

[0034] Here, the FC / BC 20 of this embodiment can acquire altitude from the GNSS receiver 30 and continue to acquire correction information from the RTK receiver 31 even after the rotor 41 stops. General unmanned aircraft use GNSS solely for acquiring longitude and latitude, and the altitude during flight is acquired by a barometric pressure sensor built into the flight controller, a ranging sensor directed downward, or the like. That is, the altitude value obtained from GNSS is basically not used even during flight, and even less so after landing. On the other hand, in the surveying system S of this embodiment, since the GNSS receiver 30 and the RTK receiver 31 are also used for acquiring water level, these are kept operating even after water landing (when the rotor 41 stops).

[0035] (LiDAR device) The LiDAR device 51 is an example of the ranging means of the present invention. Its laser is directed at least in both directions of the banks of the river from the body of the multicopter 10 floating on the river, and it acquires point cloud data capable of specifying the position of the waterline of the river. The multicopter 10 has a SLAM (Simultaneous Localization and Mapping) program 231, which will be described later, and thereby maps the positional relationship between the multicopter 10 and the surrounding objects. By actually measuring the distance between the multicopter 10 and the waterline of the water area on which it floats, the position of the waterline in the SAR image, that is, the water surface width, can be specified, and a threshold value of the reflection intensity for distinguishing between the water surface and the land on the SAR image can be found. Note that the ranging means of the present invention only needs to be able to acquire data capable of measuring the position of the waterline of the water area on which the multicopter 10 (the first floating body) floats, and is not limited to the LiDAR device 51. For example, it may be a laser ranging sensor other than the LiDAR device 51, a ranging sensor using other electromagnetic waves such as infrared rays and millimeter waves, a ranging sensor using ultrasonic waves, a stereo camera, or a depth camera.

[0036] (Infrared camera) The infrared camera 52 is an example of the 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 when the SAR image is being taken, that is, the state of the waves, it becomes possible to associate the roughness of the water surface with the way its reflection intensity appears on the SAR image. In this embodiment, as the water surface observation means, an infrared camera 52 is adopted instead of a visible light camera, so that the state of the water surface can be observed with stable quality even at night or in bad weather. Note that the water surface observation means of the present invention may be any means capable of identifying the state of the water surface visually or mechanically, and is not limited to the infrared camera 52. For example, this may be a visible light camera, or a microwave radar may also be considered.

[0037] 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 these can also be installed at a location away from the multicopter 10. FIG. 4 is a schematic diagram showing other installation examples 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 to be surveyed may be observed from the image of this fixed camera 54. Also, with a so-called aerial drone 53 equipped with the LiDAR device 51 and the infrared camera 52, the water surface width w and the state of the water surface of the water area to be surveyed may be separately acquired from above.

[0038] (Analysis device) Returning to FIG. 3 to continue the explanation. The analysis device 60 is a dedicated computer device such as a server computer or a PC, and is a device that analyzes and integrates the data collected by the multicopter 10 and arranges it in a form that contributes to the interpretation of the SAR image. The analysis device 60 may be a single device, or may be a combination of multiple devices. Also, the function of the analysis device 60 may be provided in the operation terminal of the operator U.

[0039] The analysis device 60 of this embodiment acquires, from the multicopter 10, in addition to the longitude and latitude information corrected by the correction information of the RTK receiver 31, a corrected altitude value that is the altitude value 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 it as the water level at the position of the multicopter 10. For the geoid height, for example, the gravity geoid model data provided by the Geospatial Information Authority of Japan may be used. The water surface elevation may be calculated within the multicopter 10 and transmitted to the analysis device 60. Also, in the surveying system S of this embodiment, the water surface elevation is used as the water level at each position of the river, but it is also conceivable to treat the corrected altitude value as the water level. Here, in order to obtain the elevation of the water surface from the SAR image, it is common to employ interferometric technology (InSAR: Interferometric Synthetic Aperture Radar), but it is difficult to obtain the elevation of the water surface from only the SAR image taken at a single time. According to the surveying system S of this embodiment, it is possible to acquire a highly accurate water level even from only the SAR image taken at a single time.

[0040] In addition, the analysis device 60 also collects the captured video of the infrared camera 52 and the point cloud data of the LiDAR device 51 from the multicopter 10. The analysis device 60 of this embodiment identifies the position of the waterline of the river from the water level at the position where the multicopter 10 is floating and the three-dimensional terrain data regularly surveyed by the river office of the river, and also identifies the position of the waterline from the point cloud data of the LiDAR device 51. Then, by comparing and integrating these, a more accurate position of the waterline is calculated.

[0041] The surveying system S of this embodiment is equipped with a configuration (analysis device 60) specialized in collecting and integrating the data acquired by each sensor device of the multicopter 10, so that the loads and functions of each device are appropriately distributed in the entire system. Further, the analysis device 60 serves as a hub for accumulating survey results and sharing them with other related parties and researchers. Note that an independent analysis device 60 is not essential for the surveying system S. For example, the multicopter 10 may be provided with a processing function corresponding to the analysis device 60, and the results of various calculations performed within the multicopter 10 may be transmitted to the operator U, and the operator U may separately accumulate and share this data.

[0042] As described above, in the surveying system S of this embodiment, since the multicopter 10 is adopted as the first floating body, the degree of freedom in the water area and position for performing surveying is increased, and the operator U can easily perform river surveying from a safe remote location. Note that the first floating body of the present invention does not necessarily have to be the multicopter 10, and any object that can float on the water surface and is provided with a reflector capable of retroreflecting electromagnetic waves from an SAR satellite may be used. For example, it may be something like the floating ring 19 provided with a plurality of reflector sets 71 shown in FIG. 8(a) described later. Since the data collected by the multicopter 10 is optimized and accumulated in the analysis device 60 for the interpretation of SAR images, it is expected that the analysis accuracy of SAR images will be improved as the surveying system S is used. For example, when actual measurement data and comparison data are accumulated in the surveying system S and the analysis accuracy of SAR images is sufficiently improved, it is considered possible to accurately identify the waterline and water level of a river from the SAR image and its orthoimage.

[0043] <Automatic flight function> FIG. 5 is a block diagram showing the automatic flight function provided in the FC / BC20. The multicopter 10 of this embodiment includes, as its automatic flight function, 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. Hereinafter, each automatic flight function provided in the FC / BC20 will be described.

[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 including a takeoff (water takeoff) point, a landing (water landing) point, waypoints which are a plurality of waypoints constituting a flight route between these points, the flight altitude at each waypoint, parameters such as the flight speed between each waypoint, etc., specified on the map data of the GCS (Ground Control Station).

[0045] The autonomous navigation program 22 is a function that automatically moves the multicopter 10 on the water surface along a pre-prepared cruise plan (navigation plan). The cruise plan is data including parameters of a starting point, an ending point, and waypoints which are a plurality of waypoints constituting a navigation route, specified on the map data of the GCS. It may move by flying or by navigating until the starting point of the cruise plan. When the multicopter 10 is floated on the water surface, the FC / BC 20 switches the multicopter 10 from the flight mode to the navigation mode. As described above, the FC / BC 20 continues to operate the GNSS receiver 30 and the RTK receiving unit 31 even after switching the multicopter 10 to the navigation mode (after stopping the rotor 41). The autonomous navigation program 22 automatically controls the thruster 42 so that the multicopter 10 floating on the river current and going down the river moves along the navigation route.

[0046] The collision avoidance program 23 and the SLAM program 231 are functions that prevent the multicopter 10 from colliding with floating objects or surrounding objects on the water surface in the navigation mode. The SLAM program 231 identifies the positional relationship between the body of the multicopter 10 and surrounding objects based on the output data of the LiDAR device 51. The collision avoidance program 23 automatically controls the thruster 42 based on the analysis result of the SLAM program 231 so that the distance between the multicopter 10 and surrounding objects does not become less than a predetermined interval and so that it does not deviate from the navigation route as much as possible. The collision avoidance program 23 and the SLAM program 231 can also be used in the flight mode.

[0047] The heading control program 24 is a function that controls the heading (nose) direction of the aircraft to a specified direction by means of an electronic compass provided in the FC / BC 20.

[0048] The flight detour program 25 is a function for a multicopter 10 that rides on the water flow of a river and detours by flying over structures such as water intakes and dams that cannot be passed through. When the multicopter 10 reaches a predetermined position in the river, the flight detour program 25 automatically takes off and flies the multicopter 10 and lands it at another position further downstream from that position. In this embodiment, the takeoff point and landing point of the flight detour program 25, the flight altitude between these two points, etc. are specified as waypoints of the cruise plan.

[0049] As described above, the multicopter 10 of this embodiment is equipped with various automatic flight functions, and even an inexperienced operator U or a survey conducted out of sight can perform the survey with a quality above a certain level.

[0050] <River survey method> FIG. 6 is a schematic diagram showing an outline of a river survey method using the multicopter 10. In the example of FIG. 6, it is assumed that the survey is carried out at night or during bad weather (flood). The multicopter 10 is placed on the water surface in accordance with the shooting time of the reserved SAR satellite and is carried by the water flow of the river from the upstream side to the downstream side.

[0051] As shown in Fig. 6, the multicopter 10 placed on the river rides on the water flow of the river and goes downstream. The autonomous navigation program 22 automatically controls the thruster 42 so that the multicopter 10 goes downstream along the navigation route R1 of the cruise plan. When the multicopter 10 deviates from the navigation route R1, it gradually returns to the navigation route R1 while going downstream (R3). Regarding the intake weir B1, which is an impassable structure in the middle of the navigation route R1, when the multicopter 10 reaches a predetermined position downstream in the river, it flies and detours by the flight detour program 25 (R2). Incidentally, since the altitude of the multicopter 10 while the flight detour program 25 is operating does not represent the water level of the river, the analysis device 60 excludes the water level during this period from the analysis target. For the pier B2 in the middle of the navigation route R1, the SLAM program 231 detects it, and the collision avoidance program 23 passes through it with a minimum deviation (R4).

[0052] Here, the flow velocity of the river may vary depending on the position in the river width direction. For example, even where the river is flowing straight, in areas with a deeper water depth, due to the influence of two spiral flows arranged in the river width direction, the flow velocity in the center of the river is faster than that on both banks. Also, when the water volume of the river increases, the water level in the center of the river rises, and a flow occurs on the water surface from the center towards both banks. When the water volume of the river decreases, conversely, the water level in the center of the river drops, and a flow occurs on the water surface from both banks towards the center. Also, in areas where the river is curved, the flow velocity on the outer side of the curved part is faster than that on the inner side. And a floating object with a certain depth will naturally be induced towards the direction where the flow velocity is the fastest if it faces that direction. Therefore, when it is possible to let the multicopter 10 flow along the course with the fastest flow velocity in the river, a margin (width) may be provided for the longitude and latitude values specified in the automatic navigation program 22.

[0053] Since the reflector 70 is installed on the multicopter 10 of this embodiment, it is relatively easy to identify the position of the multicopter 10 in the SAR image. By combining this with the corrected three-dimensional position of the multicopter 10 and the point cloud data of the LiDAR device 51, the water level and water line of the river in the SAR image can be identified with high accuracy. Furthermore, by matching the state of the water surface at each position photographed by the infrared camera 52, the state of the water surface and the way its reflection intensity appears on the SAR image can be associated with each other.

[0054] FIG. 7 is a schematic diagram showing a state where a Doppler shift or blur occurs at the position of the multicopter 10 shown in the SAR image. In the river survey method of this embodiment, the multicopter 10 is flown in the river while being photographed by a SAR satellite. When the multicopter 10 moves during the shooting of the SAR image, a Doppler shift or blur may occur at the position of the multicopter 10 shown in the captured SAR image.

[0055] As shown in FIG. 7(a), when the SAR satellite and the multicopter 10 are moving in an orthogonal direction, the position of the multicopter 10 on the SAR image may be shifted due to the Doppler shift. The amount of Doppler shift is calculated by 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 : Moving speed of the multicopter 10 V D : Relative speed (moving speed of the multicopter 10 / moving speed of the 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 blurred 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 shooting 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 so 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 along the flow of the river.

[0059] In the example of Fig. 8, it is assumed that a SAR satellite equipped with a plurality of antennas arranged at intervals or a formation of SAR satellites is used for imaging. That is, it is assumed that position information including the phase difference at each point can be obtained through a single imaging. The multicopter 10 and the sub-floats 11 are arranged on the water surface in accordance with the reserved imaging time of the SAR satellite and are carried downstream from the upstream side along with the flow of the river. The multicopter 10 and each sub-float 11 flow down the river starting from different positions of the river. The sub-floats 11 are thrown into the river by workers.

[0060] The sub-float 11 is provided with a reflector 70 (reflector set 71), and its position can be relatively easily specified in the SAR image. On the other hand, since no sensor device such as a GNSS receiver is mounted on the sub-float 11, its three-dimensional position cannot be directly obtained. 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 Fig. 8(b)) between the position of the multicopter 10 and the position of each sub-float 11 in the SAR image. Thereby, the amount of information obtained by a single imaging of the SAR image can be increased. In the case where 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. Also, when using a SAR satellite with a single antenna, that is, when using a SAR satellite that cannot obtain the phase information of the ground surface (water surface) in a single imaging, a separate GNSS receiver or the like may be mounted on the sub-float 11 to obtain its three-dimensional position.

[0061] Of the total length of the river, the water level at the point where the water level observation station GS is installed can be measured (observed) directly, while the water levels in other sections will be replaced by estimated water levels calculated based on the measured values at the water level observation stations. Currently, the accuracy of these estimated water levels cannot be guaranteed. Whether during surveying using only the multicopter 10 or during surveying including the sub-float 11, the correctness of the measured values can be verified by passing through the position where the water level observation station GS is installed. And if the correctness of the measured values can be verified, the accuracy of the estimated water levels can also be verified by comparing the measured values with the estimated water levels.

[0062] <Other Embodiments> FIG. 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 description, the same components as those in the above embodiment are denoted by the same reference numerals and their description is omitted. Note that in FIG. 9, the infrared camera 52 is omitted, but it may be provided.

[0063] The main feature of the surveying system Sb is that the multicopter 10b floating on the river and carried by the water flow from the upstream side to the downstream side is equipped with a GNSS receiver 30b compatible with the CLAS (Centimeter Level Augmentation Service) or MADOCA-PPP (Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis - Precise Point Positioning) service provided by QZSS. It receives correction information transmitted from QZSS to correct the positioning error of the GNSS signal, and uses the altitude value for calculating the three-dimensional position and water level of the multicopter 10b. The reflector 70 is not essential for the surveying system Sb of this embodiment. Hereinafter, this feature and other features associated therewith will be described using CLAS as an example. Note that for the configurations other than the differences described below, it may be considered the same as or similar to the above embodiment. For example, the multicopter 10b has the same automatic flight control function as the multicopter 10.

[0064] (L6 Receiver Section) As shown in Fig. 9, the GNSS receiver 30b of the multicopter 10b incorporates an L6 receiver section 31b that receives the L6D signal of CLAS. The L6 receiver section 31b receives correction information for correcting the positioning error of the GNSS signal from QZSS. The L6 receiver section 31b may be a device separate from the GNSS receiver 30b. Thus, in the surveying system Sb of this embodiment, without installing an RTK base station (fixed station) around the survey site or subscribing to a network RTK service such as VRS-RTK (Virtual Reference Station Real-Time Kinematic), relatively high-precision surveying can be performed anywhere within the coverage area of QZSS. As described above, the L6 receiver section 31b can also receive the L6E signal of MADOCA-PPP. Similarly to the above-described embodiment, the GNSS receiver 30b of this embodiment is also compatible with signals from various GNSS satellites such as GPS, GLONASS, Galileo, BDS, and QZSS.

[0065] The analysis device 60b of this embodiment receives, in addition to the longitude and latitude information corrected by the correction information of CLAS, a corrected altitude value that 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 this corrected altitude value. In the surveying system Sb, this water surface elevation is also treated as the water level at each point of the river.

[0066] (Multi-beam Sonar) The multicopter 10b of this embodiment is equipped with a sonar unit 55 for acquiring underwater terrain data (cross-sectional shape of the river channel) after landing on the water. The sonar unit 55 is an example of the scanner device of the present invention. The sonar unit 55 is a multi-beam acoustic sounding device that transmits acoustic beams of different frequencies fan-shaped into the water and receives their reflected waves to acquire the terrain data of the river.

[0067] The sonar unit 55 is a unit equipped with a transmitting section in which a plurality of sonars are arranged, a receiving section for receiving reflected waves, a dedicated IMU, a surface sound velocity meter, and the like. Ultrasonic measurement is less affected by turbidity compared to optical cameras and green lasers, and more accurate topographic data can be obtained even under difficult conditions. Note that the scanner device installed on the multicopter 10b only needs to be able to acquire underwater topographic data after the multicopter 10b lands in water, and is not limited to the sonar unit 55. For example, if only measuring highly transparent and stationary water areas, it is considered that topographic data can be acquired even with a scanner device using an optical camera or a laser.

[0068] Figure 10 is a cross-sectional schematic diagram showing the state of the multicopter 10b floating on the water surface of a river. As shown in Figure 10, the multicopter 10b that has landed in the river and has been switched to the navigation mode starts an underwater scan by the sonar unit 55. The sonar unit 55 transmits a sound wave beam in a fan shape over the set swath width θ and acquires point cloud data representing the topography of the river channel RC. If the swath width θ of the sonar unit 55 is set to 180° or more, the cross-sectional shape of the entire current water area can be acquired. The heading control program 24 (see Figure 5) of the FC / BC20 automatically controls the thruster 42 so as to maintain the state in which the sonar array direction of the sonar unit 55 intersects the traveling direction of the navigation route R1 (see Figure 6) as much as possible.

[0069] (Calculation of flow rate) Figure 11 is a reference diagram for explaining the cross-section CS when determining the flow rate of a river. The "flow rate" in this embodiment means the volume of water flowing through a certain cross-section of a river in a predetermined unit 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 measurement unit is cubic meters per second (m 3 / s). More specifically, although there are many calculation formulas, the flow rate is calculated by the following formula or the like. The flow velocity can be calculated from the longitude and latitude acquired by the GNSS receiver 30b, its correction value, and the acquisition time. Flow rate Q (m 3 / s) = Flow velocity V (m / s) × Cross-sectional area A (m 2 ) Manning's formula

Equation

[0070] As described above, according to the survey system Sb of this embodiment, it is possible to easily obtain the water level and flow velocity of a river in the coverage area of QZSS. And by providing the sonar unit 55, it is also possible to measure the actual terrain data and flow rate of the river channel RC. In addition, by providing the reflector 70 on the multicopter 10b of the survey system Sb, it is also possible to use various data collected by the multicopter 10b to improve the analysis accuracy of SAR images.

[0071] ​Although the 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 gist of the invention. For example, in each of the above embodiments, only a river is cited as an example of the water area to be surveyed, but the water area to be surveyed is not limited to a river, and other water areas such as the sea, dams, lakes, etc. may also be applicable.

Explanation of Reference Numerals

[0072] S, Sb: Surveying system, U: Operator, RC: River course, CS: Cross section, GS: Water level observation point, R1 - 4: Navigation route, B1: Water intake weir, B2: Bridge pier, 10, 10b: Multi - copter (first floating body, unmanned aerial vehicle), 11: Sub - float (second floating body), 19: Floating ring, 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: Network RTK - compatible GNSS receiver (GNSS receiving unit, RTK receiving unit), 30b: CLAS - compatible GNSS receiver (GNSS receiving unit, L6 receiving unit), 31: RTK receiving unit, 31b: L6 receiving unit, 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. A first floating body that is floated on the water surface; A reflector attached to the first floating body and configured to reflect electromagnetic waves from a synthetic aperture radar satellite; A GNSS receiver attached to the first floating body and configured to acquire position information from a Global Navigation Satellite System (GNSS); An RTK (Real Time Kinematic) receiving unit that acquires correction information for the position information by RTK; and a distance measuring means for acquiring data capable of measuring the position of the waterfront of the water area in which the first floating body is floated. Surveying system.

2. A first floating body that can be floated on the water surface; A reflector attached to the first floating body and configured to reflect electromagnetic waves from a synthetic aperture radar satellite; A GNSS receiving unit that is attached to the first floating body and acquires position information from a Global Navigation Satellite System (GNSS); An RTK (Real Time Kinematic) receiving unit that acquires correction information for the position information by RTK, The first floating body is an unmanned aerial vehicle capable of landing on the water surface. Surveying system.

3. A first floating body that is floated on the water surface and carried by the water current of the water area from the upstream side to the downstream side; A GNSS receiver attached to the first floating body and configured to acquire position information from a Global Navigation Satellite System (GNSS); An L6 receiver that receives correction information for the position information from a QZSS (Quasi-Zenith Satellite System); a reflector attached to the first floating body and configured to reflect electromagnetic waves from a synthetic aperture radar satellite; 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 floated. Surveying system.

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

5. The reflector is a corner reflector. A surveying system according to any one of claims 1 to 3.

6. The reflector is five or more corner reflectors. A surveying system according to any one of claims 1 to 3.

7. The first floating body further includes 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. The surveying system according to claim 3.

8. The ranging means is a LiDAR (Light Detection and Ranging) device attached to the first floating body, A surveying system according to claim 1 or 7.

9. The water surface observation means further includes a water surface observation means for acquiring a state of the water surface of the water area in which the first floating body is floated. A surveying system according to any one of claims 1 to 3.

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 device further includes a second float that can be floated on the water surface together with the first float, The reflector is attached to the second floating body. A surveying system according to any one of claims 1 to 3.

13. The first floating body is an unmanned aerial vehicle capable of landing on the water surface. The surveying system according to claim 3.

14. The RTK receiving unit acquires the correction information via the Internet. The surveying system according to claim 1 or 2.

15. The RTK receiving unit acquires the correction information via a mobile communication network. The surveying system according to claim 1 or 2.

16. Further comprising a data analysis unit, The data analysis unit determines 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, as the water level at the position of the first floating body. A surveying system according to any one of claims 1 to 3.

17. The first floating body further includes 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, 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 16.

18. A first floating body that can be floated on the water surface; A reflector attached to the first floating body and configured to reflect electromagnetic waves from a synthetic aperture radar satellite; A GNSS receiver attached to the first floating body and configured to acquire position information from a Global Navigation Satellite System (GNSS); A surveying system including an RTK (Real Time Kinematic) receiver that acquires correction information for the position information by RTK, a step of photographing 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, River surveying methods.

19. a step of photographing the first floating body with the synthetic aperture radar satellite while floating the first floating body on the water current of the river from the upstream to the downstream using the surveying system according to claim 3, River surveying methods.

20. and acquiring a moving path and a moving 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 an image captured by the synthetic aperture radar satellite based on the moving path and the moving speed.

20. A river surveying method according to claim 18 or 19.

21. A first floating body that can be floated on the water surface; A second float that floats on the water surface together with the first float; a reflector attached to the first floating body and the second floating body, the reflector reflecting electromagnetic waves from a synthetic aperture radar satellite; A GNSS receiver attached to the first floating body and configured to acquire position information from a Global Navigation Satellite System (GNSS); A surveying system including an RTK (Real Time Kinematic) receiver that acquires correction information for the position information by RTK, a step of photographing the first floating body and the second floating body by a synthetic aperture radar satellite while floating them on the water current of the river from upstream to downstream of the river; When the water level is the corrected altitude value obtained by correcting the altitude value included in the position information with the correction information, or the water surface elevation 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 reflector of the first floating body and the reflector of 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.

22. a step of photographing the first floating body and the second floating body with a synthetic aperture radar satellite while floating the first floating body and the second floating body on the water current of the river from the upstream to the downstream of the river using the surveying system according to claim 12; When the water level is the corrected altitude value obtained by correcting the altitude value included in the position information with the correction information, or the water surface elevation 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 reflector of the first floating body and the reflector of 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