JP7431443B2 - Underwater observation system and underwater observation method - Google Patents

Description

The present invention relates to an underwater observation system for observing underwater, and more particularly to an underwater observation system that performs observation while restraining an underwater propulsion device with a power cable centered around an underwater base station.

It is known that Japan's exclusive economic zone is rich in mineral resources such as hydrothermal mineral deposits, energy resources such as methane hydrate, and biological resources such as fish. , there is an urgent need for the development of marine resources. In order to use these marine resources sustainably, it is necessary not only to investigate the abundance and distribution of the resources, but also to correctly understand the mechanisms of resource generation and depletion. There are many. One of the causes of this problem is the inability to measure changes in marine resources and the surrounding environment over time using time-series data.

BACKGROUND ART As one method for investigating the seabed, a technique is known in which a free-fall type unmanned probe remains on the seabed and photographs the surrounding area with a fixed-point camera (for example, see Non-Patent Document 1). Using this technology, it is possible to observe objects over a period of several days to several months, but since the observation range (2 to 3 m ² ) is very narrow and only local changes can be observed, long-term observation of resources is not possible. It is not suitable for

On the other hand, autonomous underwater robots (Autonomous Underwater Vehicles: AUV) are known as other methods of seabed investigation (see, for example, Non-Patent Documents 2 and 3). This AUV is capable of measuring resources over a wide area (10 km ² for acoustic measurement, 1000 m ² for image observation) at low altitude (that is, high resolution). However, since AUVs are self-contained, they have space and power limitations, and unforeseen problems may cause automatic navigation to stop, so a support vessel is essential for transportation to the survey area, deployment, and recovery. be. Existing AUVs, which require support vessels, are expensive to survey, and seabed surveys using AUVs are not carried out frequently, so long-term time-series data on changes in the environment due to seasonal fluctuations is lacking. Therefore, in order to realize long-term observation, a system is being developed that installs an undersea station that serves as a base station on the ocean floor, and performs battery charging and data transfer of AUV (for example, see Non-Patent Document 4). ). By charging the AUV with an undersea station, it is possible to conduct long-term undersea observations.

In addition, related to the above-mentioned techniques, techniques as shown in Patent Documents 1 and 2 are also disclosed. The technology disclosed in Patent Document 1 relates to an underwater exploration device that enables miniaturization of an underwater base for long-term observation of deep sea areas, and is an underwater base installed on the seabed and equipped with exploration equipment. a power station equipped with a transmitter and a power source; a cable connecting the underwater base and the power source of the power station; and an autonomous unmanned vehicle for replenishing power to the power source of the power station. It consists of a running body.

The technology disclosed in Patent Document 2 relates to a seabed exploration method using an underwater station from which an autonomous unmanned vehicle can easily enter and exit, and includes an underwater station lowered from a mother ship, a second transponder on the seabed, and a third transponder. and an autonomous unmanned vehicle having a third receiver, and the underwater station includes a storage section, a power source storage section, a first transponder, first and second receivers, and a plurality of transponders. The signal from the second transponder is received by the third receiver of the vehicle to control the vehicle, and the signal is received by the first receiver to control the thruster of the underwater station. The signal from the third transponder of the moving body is received by the second receiver of the underwater station to correct the control of the thruster.

Japanese Patent Application Publication No. 2003-21684 Japanese Patent Application Publication No. 2003-26090

Etsuro Shimizu, “Investigation of Toyama Bay using the deep-sea probe “Edokko No. 1””, Marine Engineering, Vol.54, No.4, pp.627-630, 2019 Yuya Nishida, Tamaki Ura, Takashi Sakamaki, Junichi Kojima, Yuzuru Ito, Hide Kanaoka, “Dive survey of Smith Caldera in the Izu-Ogasawara area using hovering AUV “Tuna-Sand””, Robotics and Mechatronics Lecture 2013, 2A2-O03, 2013 Masao Nakanishi, "Reliability evaluation of depth sounding using a multi-nano beam echo sounder in waters deeper than 9000 m", Marine Survey Technology, Vol. 23, pp. 11-23, 2011 Toshihiro Maki, Yoshiki Sato, Hayato Mizushima, Takumi Matsuda, Judai Masuda, Nobuyoshi Okada, Takashi Sakamaki, "Deployment method of hovering AUV based on an undersea station - Toward long-term monitoring of the undersea environment", Robotics Mechatronics Lecture 2016, 1A1-17b4, 2016

With the conventional technology described above, it is possible to perform long-term seafloor observation by charging the AUV with a submarine station, but it is necessary to perform advanced processing and control such as self-position estimation, trajectory planning, and position control. There is a risk of docking failure due to changes in the surrounding environment such as tidal currents, or equipment failure due to contact with the seabed or station. In addition, self-propelled AUVs that are not connected to cables are unable to stay at the same location in the event of equipment failure or power outage and are at risk of being lost, making long-term observation using AUVs extremely risky. It becomes a method.

Furthermore, in order to return from the observation point to the location where the station was installed, highly accurate navigation is required, such as the Inertial Navigation System (INS) and Doppler Velocity Log (DVL). It is necessary to mount an expensive sensor costing several million to tens of millions of yen on the AUV, resulting in extremely high development costs.

The present invention does not perform processes essential for AUV such as self-position estimation, trajectory planning, and position control, and only controls thrust at a low risk (low risk of loss, and even if lost, development costs are minimized). To provide an underwater observation device and an underwater observation method that enable long-term underwater observation over a wide range.

The underwater observation system according to the present application includes an underwater propulsion device that collects information from sensors while propelling the underwater propulsion device, and a power supply means that is fixed and erected on the bottom of the water and supplies electric power for driving the underwater propulsion device. and a power cable connecting the underwater propulsion device and the power supply means, the power cable being connected to a reel disposed at the underwater base station according to the propulsion direction of the underwater propulsion device. is wrapped around or unwound.

As described above, the underwater observation system according to the present invention includes an underwater propulsion device that collects information from sensors while being propelled underwater, and an electric power source that is fixed and erected on the bottom of the water to drive the underwater propulsion device. an underwater base station including a power supply means for supplying power, and a power cable connecting the underwater propulsion device and the power supply means, the power cable being arranged at the underwater base station according to the propulsion direction of the underwater propulsion device. Since the power cable is wound or unwound around the reel, the underwater propulsion device is tied to the power cable, and only thrust control is possible without performing advanced controls such as self-position estimation, trajectory planning, and position control. This has the effect of making it possible to observe underwater over a wide area for a long period of time with low risk.

In the underwater observation system according to the present application, the reel is fixed with the direction in which the underwater base station is installed as an axis, and the underwater propulsion device generates propulsion in the direction of centrifugal force in a circle centered on the axis of the reel. At the same time, it generates propulsion in the tangential direction of the circle.

In this way, in the underwater observation system according to the present invention, the reel is fixed with the direction in which the underwater base station is erected as an axis, and the underwater propulsion device generates a circular centrifugal force centered on the axis of the reel. Since the underwater propulsion device generates propulsion in both directions and in the tangential direction of the circle, it is possible to navigate the same trajectory every time by using power cable restraints by only generating propulsion in two directions. be effective.

In the underwater observation system according to the present application, the underwater propulsion device is provided with a control means for controlling the azimuth and attitude angle as well as the altitude, and the reel is maintained at the same height as the reel under the control of the control means. A circular movement is made around the axis of.

As described above, in the underwater observation system according to the present invention, the underwater propulsion device is provided with a control means for controlling the azimuth and attitude angle, and also controls the altitude, and the underwater propulsion device is provided with a control means for controlling the altitude, and the underwater propulsion device is provided with a control means for controlling the altitude. Since the reel rotates around the axis while being maintained, the reel is observed in the same stable orbit while drawing an involute curve trajectory of forward and reverse rotation on a two-dimensional plane at the height where the reel is placed. This makes it possible to observe the same location over a wide area over a long period of time.

In the underwater observation system according to the present application, the control means changes the altitude of the underwater propulsion device depending on the observation area.

In this way, in the underwater observation system according to the present invention, the control means changes the altitude of the underwater propulsion device according to the observation area, so that, for example, the range that can be imaged by the camera installed at the bottom of the underwater propulsion device is controlled. This has the effect of making it possible to more appropriately acquire the necessary information by adjusting the altitude changes.

In the underwater observation system according to the present application, a plurality of the reels are arranged at different heights at the underwater base station, and a plurality of underwater propulsion devices for each reel are rotated around the axis of the reel. It is something.

As described above, in the underwater observation system according to the present invention, a plurality of the reels are arranged at different heights at the underwater base station, and a plurality of underwater propulsion devices for each reel are arranged around the axis of the reel. Because of the orbiting motion, it is possible to collect information from multiple different heights, resulting in the ability to obtain multifaceted information.

FIG. 1 is a schematic diagram of an underwater observation system according to a first embodiment. It is a diagram showing an example of the structure of a base station in the underwater observation system according to the first embodiment. FIG. 3 is a diagram showing a connection structure between a drum-type reel and a CUV in the underwater observation system according to the first embodiment. It is a figure showing the navigation trajectory of CUV in the underwater observation system concerning a 1st embodiment. FIG. 2 is a first diagram showing a simulation result of a navigation trajectory of a CUV in an underwater observation system according to a first embodiment. FIG. 2 is a second diagram showing simulation results of the navigation trajectory of the CUV in the underwater observation system according to the first embodiment. FIG. 7 is a third diagram showing a simulation result of the navigation trajectory of the CUV in the underwater observation system according to the first embodiment. It is a figure which shows the case where the altitude of CUV in the underwater observation system based on other embodiment is controlled according to an observation area. FIG. 7 is a diagram showing a case where information is acquired at different altitudes for each CUV in an underwater observation system according to another embodiment.

(First embodiment of the present invention)
The underwater observation system according to this embodiment will be explained using FIGS. 1 to 7. The underwater observation system according to this embodiment is used to observe and investigate underwater conditions, and is particularly suitable for investigating marine mineral resources such as mineral resources, energy resources, and biological resources under the sea. It is something that The underwater observation system according to this embodiment can be used for underwater observation in the sea, lake, pond, river, water treatment facility, etc., but in the following description, underwater observation will be explained. Specifically, for example, in shallow waters, this system can be deployed in areas with seaweed beds and coral reefs to measure data such as the growth status of marine plants and corals, while in deep waters, it can be deployed in areas with hydrothermal areas, hydrothermal mineral deposits, etc. This system can be deployed in areas such as methane hydrate areas and manganese nodules to measure time-series changes such as resource accumulation and decline.

FIG. 1 is a schematic diagram of an underwater observation system according to this embodiment. The underwater observation system 1 according to the present embodiment includes a base station 2 that is fixedly installed on the seabed in an area to be observed, and an underwater propulsion device 3 (hereinafter referred to as CUV3) that observes the seabed while navigating. CUV 3) and a power cable 4 that connects the base station 2 and the CUV 3. The base station 2 has a very large underwater weight and a low center of gravity so that it does not tilt or move due to external forces such as ocean currents. Although details will be described later, for example, a large capacity battery or the like may be mounted below the base station 2 in order to lower the center of gravity. A drum-shaped reel 5 for winding the power cable 4 is disposed above the base station 2, and is fixed with the direction in which the base station 2 is erected as a central axis. That is, the power cable 4 is wound horizontally around the central axis of the drum-shaped reel 5 and unwound.

The CUV 3 has one or more thrusters 3a for generating thrust, and the thruster 3a generates thrust in the direction of centrifugal force in a circle centered on the central axis of the drum-type reel 5. Generates thrust in one tangential direction. Observation is performed while the power cable 4 is wound around and unwound around the drum-shaped reel 5 as the CUV 3 moves.

When the base station 2 is located relatively close to land, it is possible to supply power to the CUV 3 by connecting an external power source (not shown) in the management facility 6 to the base station 2 using a power transmission cable 7. It is. Further, by connecting a communication line to the power transmission cable 7, the data observed by the CUV 3 may be transmitted to the management facility 6 at any time. The driving power for CUV3 can be obtained from an external power supply from land, a large-capacity battery that enables navigation for several months or more, an underwater power generation device that uses hot water, etc., and connection to submarine cables. The power is supplied as driving power to the CUV 3 via a power supply means such as a power converter mounted on the base station 2. Further, the large capacity battery may be a secondary battery, and the secondary battery may be configured to be rechargeable from an external power source.

FIG. 2 is a diagram showing an example of the structure of the base station 2. As shown in FIG. In the base station 2, a support 10, which is fixed to the seabed and has a large weight, and a drum-shaped reel 5 are connected by a support 8, and the support 8 and the support 10 are reinforced and connected with an auxiliary member 9. The support body 10 is formed as a rectangular body with a plurality of columns, and a large capacity battery 11 is installed inside. As described above, this large capacity battery 11 desirably has a capacity that can drive the CUV 3 for several months or more. The power cable 4 electrically connects the large-capacity battery 11 and the CUV 3, and is connected from the large-capacity battery 11 to the CUV 3 via the drum-shaped reel 5.

In addition, when power is supplied from the outside, it is not necessarily necessary to have the large capacity battery 11, and it is sufficient to be able to connect to the power transmission cable 7 from the outside. At this time, it is preferable that a heavy object be loaded inside the support body 10 in order to move the center of gravity of the base station 2 downward.

FIG. 3 is a diagram showing a connection structure between a drum-type reel and a CUV. The drum-shaped reel 5 is joined to the support column 8 with the center axis 5a extending in the direction in which the base station 2 is erected (the direction in which the support column 8 stands up). The drum-shaped reel 5 is fixedly joined to the support 8, so that the central shaft 5a does not move relative to the support 8. End members 5b and 5c are connected to the end surfaces of the drum-shaped reel 5, that is, to both ends of the central shaft 5a to secure the power cable 4 inside the drum-shaped reel 5. It is tapered toward the part where the power cable 4 is wound, so that the power cable 4 can be wound and unwound smoothly.

The gap distance D between the end members 5b and 5c satisfies d≦D<2d, where d is the diameter of the power cable 4, and the power cable 4 is wound in a single layer. By doing so, it is possible to prevent the power cable 4 from becoming tangled. The terminal end of the power cable 4 is connected to the CUV 3, which supplies power from the large-capacity battery 11 to the CUV 3 and restricts the movement of the CUV 3 within the range in which the power cable 4 extends.

The CUV 3 has one or more thrusters for its own movement, and generates a propulsive force that creates a tension greater than the extent to which the power cable 4 is fully extended in the direction of a circular centrifugal force centered on the central axis 5a of the drum-shaped reel 5. It also generates thrust in the tangential direction of the circle. That is, it controls the thrusters for sailing in the centrifugal force direction of a circle centered on the central axis 5a of the drum-shaped reel 5, in one tangential direction of this circle, and in the other tangential direction reversed by 180 degrees. Sailing while In addition, the CUV 3 is equipped with an observation sensor 3b such as a camera or sonar that images the downward direction to observe resources, etc., and is also equipped with a control sensor 3c such as an IMU and an altitude sensor that can measure the true direction and attitude angle. There is. The CUV 3 uses the control sensor 3c to maintain a stable posture at the same altitude as the drum-shaped reel 5, performs thruster control, and moves around the central axis 5a of the drum-shaped reel 5 using the observation sensor 3b. Collect observation information. The collected information may be stored in the CUV 3 and collected together with the main body, or may be sent to the administrator in real time if a communication line is connected.

The CUV 3 sails while drawing a trajectory close to an involute curve as shown in FIG. The power cable 4 is wound around and unwound around the central shaft 5a of the drum-shaped reel 5. When sailing in one tangential direction, the power cable 4 is wound around the central shaft 5a, and when sailing in the other tangential direction, which is reversed by 180 degrees, the power cable 4 is unwound from the central shaft 5a. That is, from the state in which the power cable 4 is wound around the central axis 5a, the CUV 3 starts sailing near the central axis 5a, and gradually moves away from the central axis 5a while drawing the involute curve shown in FIG. 4 and unwinding the power cable 4. After all the power cables 4 have been unwound, the CUV 3 starts sailing in the opposite direction, draws the involute curve shown in FIG. 4 again, and gradually approaches the center axis 5a while winding the power cables 4 around the center axis 5a. Once all the power cables 4 are wound around the central shaft 5a, the same operation is repeated again. By repeating such operations, the CUV3 can orbit in almost the same orbit for a long period of time, making it possible to stably collect time-series data.

As mentioned above, the CUV 3 always needs to generate thrust in the direction of centrifugal force in order to maintain the restrained state in which the power cable 4 is fully extended, but since the thrust in the direction of centrifugal force hardly contributes to the movement of the CUV 3, The greater the thrust, the more power is wasted. Further, depending on the position and connection method of the power cable 4 connected to the CUV 3, the CUV 3 may swing or meander during navigation. Therefore, a control means may be provided that calculates the vector and magnitude of the thrust force that the CUV 3 must generate according to the environment of the sea area, and appropriately controls the direction of the thruster and the thrust force. Furthermore, in order to eliminate the effects of twisting and hardness (dynamic characteristics), the power cable 4 may be made of, for example, hard-twisted and flexible high-density polyethylene fiber (HDPE).

A simulation was performed on the operating trajectory of CUV3 described above. In order to simulate a trajectory using the restraint of the power cable 4, a trajectory drawn by an involute curve shown in the following equation (1) was used as a base.

The simulation conditions are shown in Table 1 below.

The simulation results for each condition are shown in FIGS. 5, 6, and 7. 5 shows the simulation results for the power cable 4 under condition 1, FIG. 6 shows the simulation results under condition 2, and FIG. 7 shows the simulation results under condition 3. FIGS. 5 to 7 show the trajectory of the CUV 3 as it moves while unwinding the power cable 4, with the power cable 4 being wound around the center shaft 5a as the initial position, and the power cable 4 becomes thicker. It can be seen that the diameter of the involute curve increases as the distance increases, and the orbital spacing becomes approximately equal under each condition.

In this embodiment, the power cable 4 has a structure in which a single cable is wound in one layer as shown in FIG. 3, but a structure in which a plurality of cables are wound in parallel in one layer may good. In that case, although a guide or the like is required to properly wrap the power cable 4 without tangling, the influence of the thickness of the power cable 4 on the trajectory is reduced, making analysis and other processing easier.

As described above, in the underwater observation system according to the present embodiment, the CUV 3 maintains the restraint state by the power cable 4 and generates thrust so as to move forward or backward, thereby achieving advanced self-position estimation using sensors. It is possible to continue navigating the same trajectory according to the kinematics of the power cable 4 and the drum-shaped reel 5 even without motion control. It becomes possible to thoroughly observe the seafloor area within a circle with the same radius as the length.

Furthermore, if the kinematics of the power cable 4 and the drum-shaped reel 5 are known, the self-position of the CUV 3 can be estimated from the number of windings of the power cable 4 through very simple motion control without the need for expensive sensors. It will be able to observe a wider area tens to hundreds of times more than a spacecraft. In other words, the underwater observation system according to this embodiment is a very effective system for long-term observation of marine resources, and it is capable of acquiring time-series data on marine resources and the surrounding environment that could not be measured up to now. It becomes possible to promote resource development.

(Other embodiments)
The underwater observation device according to this embodiment will be explained using FIGS. 8 and 9. The underwater observation device according to this embodiment is capable of acquiring information according to necessity by changing the altitude of the CUV 3. Note that in this embodiment, explanations that overlap with those of the first embodiment will be omitted.

FIG. 8 is a diagram showing a case where the altitude of the CUV is controlled according to the observation area, and FIG. 9 is a diagram showing a case where multiple CUVs are provided at different altitudes and information is acquired at different altitudes for each CUV. . FIG. 8(A) is a schematic diagram when the base station 2 and CUV 3 are viewed from the side, and FIG. 8(B) is a diagram showing altitude information for each observation area. As shown in area A in Fig. 8(B), for example, when you want to observe a part of the entire observation target area near the seabed (for example, when you want to zoom in and capture a detailed image) ), control is performed to lower the altitude of the CUV 3 as shown by the broken line in FIG. 8(A) only when passing through that part of the area. Conversely, as shown in area B of FIG. 8(B), in order to avoid obstacles such as rocks, control is performed to raise the altitude of the CUV 3 only in that area as shown by the dashed line in FIG. 8(A).

The altitude of the CUV 3 can be easily controlled by, for example, providing a vertically movable thruster.

In the case of FIG. 9, a plurality of drum-shaped reels 5 are provided at different heights of the support 8, and the CUV 3 corresponding to each drum-shaped reel 5 is connected by a power cable 4, and each CUV 3 maintains a constant height. Observations will be made while This makes it possible to observe the same region (same area) at different resolutions, making it possible to perform multifaceted analysis. In addition, at this time, it is desirable to control so that continuous observation can be performed with as little time interval as possible by shifting the timing of movement of each CUV 3.

In this way, in the underwater observation system according to the present embodiment, in order to change the altitude of the CUV 3 according to the observation area, for example, the range that can be imaged by the camera installed at the bottom of the CUV 3 is adjusted by changing the altitude, and as needed. This makes it possible to more appropriately acquire the information that is required.

Further, a plurality of drum-shaped reels 5 are arranged at different heights on the support 8, and for each drum-shaped reel 5, a plurality of CUVs 3 are rotated around the central axis 5a of the tram-shaped reel 5. Therefore, it becomes possible to collect information from multiple different heights, making it possible to obtain multifaceted information.

1 Underwater observation system 2 Base station 3 CUV
3a Thruster 3b Observation sensor 3c Control sensor 4 Power cable 5 Drum-shaped reel 5a Central shaft 5b, 5c End member 6 Management facility 7 Power transmission cable 8 Support column 9 Auxiliary member 10 Support part 11 Large capacity battery

Claims (6)

An underwater propulsion device that collects information from sensors while propelling underwater;
an underwater base station that is fixedly erected on the bottom of the water and includes a power supply means that supplies power for driving the underwater propulsion device;
comprising a power cable connecting the underwater propulsion device and the power supply means,
The power cable is wound or unwound around a reel disposed at the underwater base station depending on the propulsion direction of the underwater propulsion device ,
The reel includes a central shaft around which the power cable is wound or unwound, and a pair of end members respectively joined to both ends of the central shaft for retaining the power cable within the reel,
The pair of end members has a region in which the power cable is accommodated, and where d≦D<2d, where D is the gap distance between the end members and d is the diameter of the power cable; An underwater observation system characterized by having a region tapered toward the inside where the power cable is wound, on the outside in the radial direction of the region . An underwater propulsion device that collects information from sensors while propelling underwater;
an underwater base station that is fixedly erected on the bottom of the water and includes a power supply means that supplies power for driving the underwater propulsion device;
comprising a power cable connecting the underwater propulsion device and the power supply means,
The power cable is wound or unwound around a reel disposed at the underwater base station depending on the propulsion direction of the underwater propulsion device,
The reel includes a central shaft around which the power cable is wound or unwound, and a pair of end members respectively joined to both ends of the central shaft for retaining the power cable within the reel,
The pair of end members has a region in which the power cable is accommodated, and where d≦D<2d, where D is the gap distance between the end members and d is the diameter of the power cable; a region tapered toward the inner side around which the power cable is wound, on the radially outer side of the region;
An underwater observation system characterized in that a navigation trajectory of the underwater propulsion device is set based on a trajectory drawn by an involute curve according to the diameter of the central axis and the diameter of the power cable. An underwater propulsion device that collects information from sensors while propelling underwater;
an underwater base station that is fixedly erected on the bottom of the water and includes a power supply means that supplies power for driving the underwater propulsion device;
comprising a power cable connecting the underwater propulsion device and the power supply means,
The power cable is wound or unwound around a reel disposed at the underwater base station depending on the propulsion direction of the underwater propulsion device,
A plurality of the reels are disposed at different heights at the underwater base station while their central axes are coaxial,
An underwater observation system characterized in that a plurality of underwater propulsion devices for each of the reels rotate around the axis of the reel while maintaining intervals between the plurality of underwater propulsion devices. The underwater observation system according to any one of claims 1 to 3 ,
the reel is fixed with the direction in which the underwater base station is erected as an axis;
An underwater observation system in which the underwater propulsion device generates propulsion in the direction of centrifugal force of a circle centered on the axis of the reel, and also generates propulsion in the tangential direction of the circle . The underwater observation system according to claim 4 ,
The underwater propulsion device includes a control means for controlling the azimuth and attitude angle as well as the altitude,
An underwater observation system in which a rotational movement is performed around the axis of the reel while maintaining the same height as the reel under the control of the control means . A power cable is wound around a reel disposed at an underwater base station that is fixed and erected on the bottom of the water, and the reel is connected to the central axis around which the power cable is wound or unwound, and a pair of end members joined to both ends of the reel for securing the power cable within the reel; When the air gap distance is D and the diameter of the power cable is d, there is a region that satisfies d≦D<2d, and a tapered shape on the radially outer side of the region toward the inside where the power cable is wound. An underwater propulsion device is connected to the tip of the power cable, and the underwater propulsion device is driven by electric power from the power supply means of the underwater base station, and the underwater propulsion device is connected to the reel. While winding or unwinding the power cable by orbiting on a navigation trajectory set based on a locus drawn by an involute curve according to the diameter of the central axis and the diameter of the power cable, An underwater observation method that collects information from sensors installed in the propulsion device.