Underwater position estimating system, and reception antenna group

Abstract

Provided are an underwater position estimating system and a reception antenna group capable of estimating a position regardless of the orientation of a transmission antenna.　The underwater position estimating system, which employs electromagnetic waves, comprises: an underwater transmission antenna; a reception antenna group that includes a plurality of sets of a plurality of reception antennas that are arranged in the same orientation and are spaced apart at predetermined intervals, the reception antennas being installed at a single location immediately below the water surface and being arranged symmetrically, when viewed from the depth direction, such that the orientations of the plurality of reception antennas are different for each set; and a position estimating device that has a position estimating algorithm for estimating the position of the transmission antenna on the basis of a pattern of values of received power intensity obtained when electromagnetic waves transmitted from the transmission antenna are received by each of the reception antennas.

Description

Underwater positioning system and receiving antennas

[0001] The present invention relates to an underwater position estimation system using electromagnetic waves and a receiving antenna group.

[0002] Traditionally, sound waves have been widely used for underwater communications and exploration because they have little attenuation in seawater, but the problem is that the propagation speed of sound waves in seawater is much slower than that of electromagnetic waves.In recent years, advances in devices, communication technology, and analysis technology have made it possible to ensure a sufficient dynamic range for measuring electromagnetic waves, and technological research into underwater communications and exploration using electromagnetic waves is progressing.

[0003] Electromagnetic waves are suitable for use over short distances because they are highly attenuated in seawater. Furthermore, taking advantage of this large attenuation in seawater, electromagnetic waves have the advantage of being able to ignore the effects of reflected and diffracted waves in seawater. For these reasons, a method of using electromagnetic waves for underwater position estimation technology has been proposed (see Non-Patent Document 1).

[0004] For example, the underwater position estimation system of Non-Patent Document 1 uses a triangulation technique as a method for estimating position in seawater using low-frequency electromagnetic waves. In detail, Non-Patent Document 1 discloses that multiple receiving antennas are floated on the sea surface at intervals of several tens of meters so as to surround a transmitting antenna in seawater, and that a predetermined algorithm is applied to the received signal strength (RSS) value used to estimate the distance between the transmitting antenna and the receiving antenna, thereby enabling position estimation of a horizontally oriented transmitting antenna in seawater.

[0005] Ryosuke Kato., Masaharu Takahashi., Nozomu Ishii. et al. Investigation of a 3D undersea positioning system using electromagnetic waves. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 69, NO. 8 (2021).

[0006] However, in the position estimation system of Non-Patent Document 1, due to the principle of three-point positioning, multiple receiving antennas must be arranged to surround the transmitting antenna, which is the target of position estimation, and the positional relationship between the receiving antennas, which are spaced apart by several tens of meters, must be fixed. Therefore, when used in a real environment, not only is installation difficult due to the influence of waves, tides, etc., but there is also the problem that the position estimation is only possible when the transmitting antenna is in a horizontal position, making it impossible to estimate the position if the attitude of the transmitting antenna changes.

[0007] The present invention has been made in light of these problems, and aims to provide an underwater position estimation system and a group of receiving antennas that can perform position estimation regardless of the attitude of the transmitting antenna.

[0008] To solve the above problems, the seawater position estimation system of the present invention is a seawater position estimation system using electromagnetic waves, comprising: a transmitting antenna underwater; a receiving antenna group installed at a single location just below the water surface, the receiving antenna group having multiple sets of receiving antennas arranged symmetrically as viewed in the depth direction so that the attitudes of the receiving antennas differ for each set; and a position estimation device having a position estimation algorithm that estimates the position of the transmitting antenna based on a pattern of received power intensity values ​​obtained when the electromagnetic waves transmitted from the transmitting antennas are received by each of the receiving antennas. According to this feature, even if the attitude of the transmitting antenna changes, the receiving antenna group installed at a single location can make the multiple RSS value patterns received by each receiving antenna dependent on the position of the transmitting antenna due to differences in the arrangement and attitude of the multiple receiving antennas constituting the receiving antenna group, thereby enabling the position of the transmitting antenna to be estimated using the position estimation algorithm based on the multiple RSS value patterns. This makes it possible to provide a seawater position estimation system that can perform position estimation using a receiving antenna group installed at a single location, i.e., a single receiving antenna group, regardless of the attitude of the transmitting antenna.

[0009] The receiving antennas are all identical in configuration, and the plurality of receiving antennas are arranged at equal intervals. This feature allows for use of not only the difference in the attitude of each receiving antenna set but also the difference in the RSS values ​​of a pair of receiving antennas, thereby improving the accuracy of estimating the position of the transmitting antenna.

[0010] The receiving antenna group has a shape of a regular polygonal prism, and the receiving antennas are arranged on the sides of the top and bottom of the regular polygonal prism so as not to contact each other. This feature makes it possible to widen the position estimation range of the transmitting antenna centered on the receiving antenna group while arranging the receiving antennas symmetrically and compactly.

[0011] The regular polygonal prism is a regular octagonal prism, which allows the receiving antennas constituting the receiving antenna group to be arranged at an angle of 45° to each other, thereby efficiently expanding the position estimation range of the transmitting antenna in a circular shape.

[0012] A vertically oriented receiving antenna separate from the receiving antenna is disposed on the bottom surface of the regular octagonal prism so as to intersect perpendicularly with the center of each of the four sides on which the receiving antenna is not disposed. This feature ensures RSS for the vertically oriented receiving antenna disposed in the depth direction, and further widens the position estimation range of the transmitting antenna.

[0013] The vertically oriented receiving antenna is characterized in that its longitudinal center is located at the center of the four sides, which allows the vertically oriented receiving antenna to be compactly arranged while suppressing the influence of other receiving antennas located on the sides.

[0014] The location estimation algorithm is characterized by comprising: a first step of specifying a search position; a second step of calculating an estimated transmitting antenna position for each of the receiving antennas for all of the search positions that can be specified; a third step of calculating and recording the sum of the distances between the estimated transmitting antenna position for each of the receiving antennas and the search positions; and a fourth step of determining the search position at which the distance between the estimated transmitting antenna position for each of the receiving antennas and the search position is the smallest as the final estimated transmitting antenna position. According to this feature, the location of the transmitting antenna can be estimated accurately based on a plurality of RSS value patterns.

[0015] The second step is characterized by comprising: a first substep of calculating a unit vector representing a direction from the geometric center of the regular polygonal prism on which the receiving antennas constituting the receiving antenna group are arranged to the search position; a second substep of calculating a distance between the geometric center of the regular polygonal prism and the transmitting antenna from the relationship between the attitudes of the transmitting antennas and the receiving antennas, the unit vector, and the received power intensity; and a third substep of calculating an estimated transmitting antenna position for each receiving antenna from the unit vector and the distance between the geometric center of the regular polygonal prism and the transmitting antenna. According to this feature, the estimated transmitting antenna position for each receiving antenna can be calculated with high accuracy.

[0016] The receiving antenna group of the present invention is a receiving antenna group used in an underwater position estimation system using electromagnetic waves, and is characterized in that it has multiple sets of receiving antennas arranged at predetermined intervals in the same orientation, and the multiple receiving antennas are arranged symmetrically as viewed in the depth direction so that the orientations of the multiple receiving antennas differ for each set. According to this feature, even if the orientation of the transmitting antenna changes, the multiple RSS value patterns received by each receiving antenna can be made dependent on the position of the transmitting antenna due to differences in the orientation and orientation of the multiple receiving antennas constituting the receiving antenna group, so that position estimation can be performed based on the RSS value patterns regardless of the orientation of the transmitting antenna.

[0017] The receiving antenna is characterized by being one of a dipole antenna, a monopole antenna, and a loop antenna. With this characteristic, since it has simple directivity, electromagnetic waves from a transmitting antenna transmitted from a direction in which the RSS at one receiving antenna is null can be easily covered by another receiving antenna, and multiple RSS value patterns received by the receiving antennas can easily be made dependent on the position of the transmitting antenna.

[0018] 1A and 1B are a three-dimensional diagram showing an analytical model of the underwater position estimation system according to the first embodiment of the present invention; a front view showing the structure of a receiving antenna group; and a plan view of the analytical model of FIG. 1 as viewed from the depth direction. (a) is a three-dimensional diagram showing eight receiving antennas arranged in a horizontal position among the receiving antennas constituting the receiving antenna group. (b) is an xy plan view of the same as viewed from the z-axis direction. (c) is an xz plan view of the same as viewed from the y-axis direction. (d) is a three-dimensional diagram showing four vertically oriented receiving antennas among the receiving antennas constituting the receiving antenna group. (e) is an xy plan view of the same as viewed from the z-axis direction. (f) is an xz plan view of the same as viewed from the y-axis direction. (a) to (d) are diagrams showing RSS heat maps for receiving antennas 1 to 4 arranged in a horizontal position in the receiving antenna group when the transmitting antenna is in a horizontal (x-axis) position. (e) and (f) are diagrams showing RSS heat maps for receiving antennas 9 and 10 arranged in a vertical position. 8(a) to 8(d) are diagrams showing RSS heat maps for receiving antennas 1 to 4 arranged in a horizontal position in the receiving antenna group when the transmitting antenna is arranged vertically (in the z-axis direction), and 8(e) and 8(f) are diagrams showing RSS heat maps for receiving antennas 9 and 10 arranged vertically and facing upright. 8(a) and 8(b) are flowcharts of a position estimation algorithm. 8(a) and 8(b) are diagrams showing position estimation results using RSS value patterns for the 12 receiving antennas constituting the receiving antenna group of Example 1, where 8(a) is the position estimation result for a horizontally oriented transmitting antenna located at a depth of 2.5 m, and 8(b) is the position estimation result for a vertically oriented transmitting antenna. 8(a) is a diagram showing the error distribution of the position estimation result in FIG. 8(a), and 8(b) is a diagram showing the error distribution of the position estimation result in FIG. 8(b). 10(a) and 10(b) are diagrams showing the results of position estimation using the RSS value patterns of the 12 receiving antennas that make up the receiving antenna group of Example 1, where (a) is the result of position estimation for a horizontally oriented transmitting antenna located at a depth of 4.5 m, and (b) is the result of position estimation for the same transmitting antenna in a vertically oriented position. (a) is a diagram showing the error distribution of the position estimation result in FIG. 10(a), and (b) is a diagram showing the error distribution of the position estimation result in FIG. 10(b).12(a) and 12(b) are diagrams showing position estimation results using RSS value patterns for 12 receiving antennas constituting the receiving antenna group of Example 1, where (a) is the position estimation result for a horizontally oriented transmitting antenna located at a water depth of 6.5 m, and (b) is the position estimation result for the same transmitting antenna in a vertical position. (a) is a diagram showing the error distribution of the position estimation result in FIG. 12(a), and (b) is a diagram showing the error distribution of the position estimation result in FIG. 12(b). (a) is a three-dimensional diagram showing an analytical model of an underwater position estimation system in Example 2 according to the present invention, and (b) is a plan view of the analytical model in (a) as viewed from the depth direction. (b) is a diagram showing position estimation results using RSS value patterns for eight receiving antennas constituting the receiving antenna group of Example 2, where (a) is the position estimation result for a horizontally oriented transmitting antenna located at a water depth of 2.5 m, and (b) is the position estimation result for the same transmitting antenna in a vertical position. 1(c) is a diagram showing the error distribution of the position estimation result in 1(a), and 1(d) is a diagram showing the error distribution of the position estimation result in 1(b). 1(c) is a diagram showing the error distribution of the position estimation result in 1(a), and 1(d) is a diagram showing the error distribution of the position estimation result in 1(b). 1(c) is a diagram showing the error distribution of the position estimation result in 1(a), and 1(d) is a diagram showing the error distribution of the position estimation result in 1(b). 1(c) is a diagram showing the error distribution of the position estimation result in 1(a), and 1(d) is a diagram showing the error distribution of the position estimation result in 1(b). 1(c) is a diagram showing the error distribution of the position estimation result in 1(a), and 1(d) is a diagram showing the error distribution of the position estimation result in 1(b). 1(c) is a diagram showing the error distribution of the position estimation result in 1(a), and 1(d) is a diagram showing the error distribution of the position estimation result in 1(b).

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A mode for carrying out the underwater position estimation system and receiving antenna group according to the present invention will be described below based on examples.

[0020] As shown in FIG. 1, the underwater position estimation system of this embodiment is mainly composed of a transmitting antenna, a group of receiving antennas installed at a single location, and a position estimation device (not shown) equipped with a position estimation algorithm.

[0021] Specifically, the analytical model of the underwater position estimation system in this embodiment uses a pseudo-scale model designed to have actual dimensions of 30 m × 30 m × 9.0 m, as shown in Figure 1, and performs electromagnetic field simulation using the finite integral method (FIT) with the electrical constants of seawater being a relative permittivity εr = 74 and a conductivity σ = 3.53 S / m. The simulation model in this embodiment has a two-layer structure, with a 9.0 m thick seawater layer attached below a 2.0 m thick vacuum layer.

[0022] The pseudo-scale model is a basic principle for conducting experiments in a laboratory that simulate electromagnetic wave propagation in the ocean, and the dimensions of the pseudo-scale model can be reduced to 1 / n in order to reduce calculation time. In this example, the scale factor (n) is set to 100.

[0023] 3, the transmitting antennas in the analysis model are arranged at 15 x 15 = 225 points, which are lattice points spaced at 3.0 m intervals on an xy plane parallel to the horizontal plane, and the group of receiving antennas installed at a single location is located at the origin in the center of the figure. The positions of the transmitting antennas are estimated on a relative coordinate system with the position of the group of receiving antennas as the origin.

[0024] The transmitting antenna is assumed to have two orientations: horizontal (x-axis direction) and vertical (z-axis direction). Note that the horizontal orientation in this embodiment refers to any orientation on the xy plane as long as it does not have a z-axis component. The vertical orientation in this embodiment refers to an orientation that does not have x-axis and y-axis components, i.e., an orientation that is perpendicular to the xy plane.

[0025] The parameter used to estimate the position of the transmitting antenna is the received signal strength (RSS) expressed by the following formula:

[0026]

[0027] The transmitting antenna (Tx) is placed in seawater by, for example, a diver (not shown). The transmitting antenna in this embodiment is a dipole antenna with a length of 0.5 m. Note that in Figure 3, the transmitting antenna is exaggerated and shown larger for ease of explanation.

[0028] In addition, the operating frequency of the transmitting antenna in this embodiment is 10 kHz, and in the pseudo-scale model, the operating frequency is 100 ２ It is set to double the frequency, 100 MHz.

[0029] In the underwater position estimation system of this embodiment, the receiving antenna group is located under a float or the like, as shown in FIG. 2 , and is therefore positioned in the seawater just below the water surface. The receiving antenna group in this embodiment is a single receiving antenna group consisting of 12 independently operating receiving antennas (Rx) combined and fixed in a predetermined arrangement. Specifically, the receiving antenna group in this embodiment is configured such that the 12 receiving antennas are combined and fixed in a predetermined arrangement by a frame fixed below a float equipped with a GPS unit, a marine radio unit, a control unit, an RF circuit, and a battery. Although not shown in detail for ease of explanation, each receiving antenna in this embodiment is connected to an RF circuit, and the RF circuit has a circuit for acquiring the received waveform for each receiving antenna, each of which is controlled by the control unit. That is, the receiving antenna group is configured to obtain RSS corresponding to each of the 12 receiving antennas. The receiving antennas in this embodiment are all 0.5 m long dipole antennas with the same configuration as the transmitting antennas. The frame to which the receiving antennas are fixed is preferably made of an insulating material.

[0030] The receiving antenna group includes eight receiving antennas 1 to 8 (see Figures 4(a) to (c)) that are arranged horizontally, i.e., parallel to the xy plane, and four vertically oriented receiving antennas 9 to 12 (see Figures 4(d) to (f)) that are arranged vertically, i.e., perpendicular to the xy plane.

[0031] As shown in Figures 4(a) to 4(c), horizontally oriented receiving antennas 1 to 8 are arranged three-dimensionally on the sides of a regular octagonal prism with a width of 1.0 m and a height of 0.5 m. Specifically, receiving antennas 1, 3, 5, and 7 are arranged symmetrically with respect to the x-axis and y-axis when viewed from the z-axis direction so as not to touch each other on the sides of the top surface of the regular octagonal prism. Furthermore, a pair of receiving antennas 1 and 5 are arranged in the same horizontal orientation in the x-axis direction, and a pair of receiving antennas 3 and 7 are arranged in the same horizontal orientation in the y-axis direction. Furthermore, the spacing between receiving antennas 1 and 5 and the spacing between receiving antennas 3 and 7 are both 1.0 m, and are arranged at equal intervals.

[0032] The receiving antennas 2, 4, 6, and 8 are arranged symmetrically about the x and y axes when viewed from the z axis direction so that they do not touch each other on the sides of the base of the regular octagonal prism. The pair of receiving antennas 2 and 6 are arranged in the same horizontal position with a 45° inclination relative to the x axis, and the pair of receiving antennas 4 and 8 are arranged in the same horizontal position with a 135° inclination relative to the x axis. The spacing between the receiving antennas 2 and 6 and the spacing between the receiving antennas 4 and 8 are both 1.0 m, and they are arranged at equal intervals.

[0033] In this way, the postures of each set of receiving antennas 1 and 5, receiving antennas 3 and 7, receiving antennas 2 and 6, and receiving antennas 4 and 8 are different, and receiving antennas 1, 3, 5, and 7, which are arranged on the sides of the top surface of the regular octagonal prism, and receiving antennas 2, 4, 6, and 8, which are arranged on the sides of the base of the regular octagonal prism, are arranged so that their positions do not overlap when viewed from the depth direction, i.e., the z-axis direction.

[0034] As shown in Figures 4(d) to 4(f), vertically oriented receiving antennas 9 to 12 are arranged at the center of the four sides of the base of the regular octagonal prism where the receiving antennas 2, 4, 6, and 8 are not arranged, so as to intersect perpendicularly. The vertically oriented receiving antennas 9 to 12 are arranged symmetrically with respect to the x and y axes when viewed from the z-axis direction (see Figure 4(e) in particular). The pair of receiving antennas 9, 11 and the pair of receiving antennas 10, 12 are arranged in the same vertical orientation in the z-axis direction. The spacing between the receiving antennas 9, 11 and the spacing between the receiving antennas 10, 12 are both 1.0 m, and are arranged at equal intervals.

[0035] As shown in FIG. 4(f), the receiving antennas 9 to 12 are arranged such that their longitudinal centers are at the centers of the four sides of the bottom surface of the regular octagonal prism where the receiving antennas 2, 4, 6, and 8 are not arranged.

[0036] In the underwater position estimation system of this embodiment, the position estimation device is connected to an observation monitor, for example, on a ship or on land, and has a position estimation algorithm (see Figure 7) that estimates the position of the transmitting antenna based on the RSS value pattern obtained when the electromagnetic waves transmitted from the transmitting antenna are received by the receiving antennas 1 to 12, respectively.

[0037] As shown in Figure 7(a), the position estimation algorithm in the position estimation device of this embodiment includes a first step (S1) of specifying a search position, a second step (S2) of calculating the estimated position of the transmitting antenna (Tx) for each receiving antenna (Rx) for all search positions that can be specified, and a third step (S3) of calculating and recording the sum of the distances between the estimated transmitting antenna positions for each receiving antenna and the search positions, and a fourth step (S4) of repeatedly performing the processes of S1 to S3 for all search positions that can be specified, and then determining the search position at which the distance between the estimated transmitting antenna position for each receiving antenna and the search position is the smallest as the final estimated transmitting antenna position.

[0038] As shown in FIG. 7B, the position estimation algorithm includes a first substep (S2-1) for calculating a unit vector representing the direction from the geometric center C (see FIG. 4) of the regular octagonal prism in the receiving antenna group to the search position to calculate the estimated transmitting antenna position for each receiving antenna from the search position, the attitude of the transmitting antenna, and the RSS; a second substep (S2-2) for calculating the relationship between the attitudes of the transmitting antenna and the receiving antenna, the unit vector, and the antenna-to-antenna distance, which is the distance between the geometric center C of the regular octagonal prism in the receiving antenna group and the transmitting antenna; and a third substep (S2-3) for calculating the estimated transmitting antenna position for each receiving antenna from the unit vector and the antenna-to-antenna distance. Note that the antenna-to-antenna distance is estimated using a machine learning model (support vector regression), enabling highly accurate estimation. The search area is limited by comparing the magnitude of the RSS values ​​for each receiving antenna.

[0039] In this way, the position estimation algorithm of this embodiment applies the principle of three-point positioning to express the antenna angle characteristics, i.e., the relative angle characteristics of each receiving antenna based on the position and attitude of the transmitting antenna, and by using it in combination with the group of receiving antennas installed in a single location as described above, high-precision position estimation is possible regardless of the attitude of the transmitting antenna.

[0040] In addition, the position estimation algorithm of this embodiment sets an RSS lower limit value, thereby excluding RSS data below that RSS lower limit value from the evaluation of the search position, and extracting only RSS that is sufficient for estimating the position of the transmitting antenna.

[0041] Furthermore, the receiving antenna group of this embodiment is configured so that the group of receiving antennas whose RSS is equal to or greater than the RSS lower limit value varies depending on the positions and attitudes of the transmitting antenna and receiving antennas 1 to 12, and so that a different RSS heat map, i.e., RSS value pattern (see Figures 5 and 6), is obtained for each attitude of the receiving antenna in the receiving antenna group.

[0042] Specifically, as shown in Figures 5 and 6, the RSS value patterns of receiving antennas 1, 2, 3, 4, 9, and 10 groups for transmitting antennas at the same position are different, which confirms that the RSS value pattern changes depending on the attitude of the transmitting antenna.

[0043] Below, we will explain the results of a position estimation test conducted using the underwater position estimation system of this embodiment to estimate the position of a transmitting antenna (Tx) in a horizontal (x-axis direction) and vertical (z-axis direction) orientation in a pseudo-scale model (see Figure 1).

[0044] The location estimation algorithm was implemented using support vector regression implemented in Scikitlearn, a Python machine learning library. The location estimation range is the plane shown in Figure 3, with a group of receiving antennas installed at a single location at the origin. The training data used was integer-valued data from 225 locations, which are lattice points spaced 3.0 m apart on the xy plane shown in Figure 3, at depths of 2.0 to 7.0 m. Test data was also similarly arranged, using data at depths of 2.5 m, 4.5 m, and 6.5 m. Taking into account the dynamic range of the measurement, the RSS lower limit was set to -150 dB. Search positions were spaced 0.5 m apart.

[0045] First, Fig. 8(a) shows the position estimation results (i.e., estimated position distribution) of a horizontally oriented transmitting antenna located at a depth of 2.5 m, and Fig. 8(b) shows the position estimation results of a vertically oriented transmitting antenna. Furthermore, Fig. 9(a) and Fig. 9(b) show the error distributions of the position estimation results of Fig. 8(a) and (b), respectively.

[0046] As shown in Figures 8(a) and 9(a), it was confirmed that for a horizontally oriented transmitting antenna located at a depth of 2.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular range of approximately 12 m in radius, with the receiving antenna group located at the center of Figure 3 as the origin.

[0047] Furthermore, as shown in Figures 8(b) and 9(b), it was confirmed that for a vertically oriented transmitting antenna located at a depth of 2.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular range with a radius of approximately 12 m, with the receiving antenna group as the origin.

[0048] Next, Fig. 10(a) shows the position estimation result of a horizontally oriented transmitting antenna located at a depth of 4.5 m, and Fig. 10(b) shows the position estimation result of a vertically oriented transmitting antenna. Fig. 11(a) and Fig. 11(b) show the error distributions of the position estimation results of Fig. 10(a) and Fig. 10(b), respectively.

[0049] As shown in Figures 10(a) and 11(a), it was confirmed that for a horizontally positioned transmitting antenna located at a depth of 4.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular range with a radius of approximately 12 m, with the receiving antenna group as the origin.

[0050] Furthermore, as shown in Figures 10(b) and 11(b), it was confirmed that for a vertically oriented transmitting antenna located at a depth of 4.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular range with a radius of approximately 12 m, with the receiving antenna group as the origin.

[0051] Next, Fig. 12(a) shows the position estimation result of a horizontally oriented transmitting antenna at a depth of 6.5 m, and Fig. 12(b) shows the position estimation result of a vertically oriented transmitting antenna. Furthermore, Fig. 13(a) and (b) show the error distributions of the position estimation results of Fig. 12(a) and (b), respectively.

[0052] As shown in Figures 12(a) and 13(a), it was confirmed that for a horizontally positioned transmitting antenna located at a depth of 6.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular area with a radius of approximately 12 m, with the receiving antenna group as the origin.

[0053] Furthermore, as shown in Figures 12(b) and 13(b), it was confirmed that for a vertically oriented transmitting antenna located at a depth of 6.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular range with a radius of approximately 12 m, with the receiving antenna group as the origin.

[0054] As described above, the underwater position estimation system of this embodiment was confirmed to enable highly accurate position estimation within a circular range of approximately 12 m radius centered on a single receiving antenna group at a depth of 2 to 7 m, regardless of the orientation of the transmitting antenna. In a receiving antenna group in which three receiving antennas are arranged perpendicular to the edges of a 0.5 m cube so that they face the x-axis, y-axis, and z-axis directions without touching each other, the RSS of the receiving antenna facing the z-axis direction easily falls below the lower RSS limit (-150 dB), so the position estimation range was limited to a circular range of approximately 6 m radius centered on the receiving antenna group. However, it was confirmed that the position estimation device with the receiving antenna group configuration and position estimation algorithm of this embodiment can expand the position estimation range to approximately twice the circular range regardless of the orientation of the transmitting antenna.

[0055] As described above, in the underwater position estimation system of this embodiment, even if the attitude of the transmitting antenna changes, the multiple RSS value patterns received by each of the receiving antennas 1 to 12 constituting the receiving antenna group installed at a single location can be made dependent on the position of the transmitting antenna depending on the differences in the arrangement and attitude of the receiving antennas 1 to 12, so that the position of the transmitting antenna can be estimated using a position estimation algorithm based on the multiple RSS value patterns. This makes it possible to provide an underwater position estimation system that can estimate the position using a single receiving antenna group regardless of the attitude of the transmitting antenna.

[0056] Furthermore, the receiving antennas 1 to 12 are all identical in configuration, and pairs of receiving antennas 1 to 12 are arranged at equal intervals, so that not only the difference in attitude of each set of receiving antennas 1 to 12 but also the difference in RSS values ​​of a pair of receiving antennas, for example, a pair of receiving antennas 1 and 5, can be used, thereby improving the accuracy of estimating the position of the transmitting antenna.

[0057] Furthermore, by arranging the receiving antennas 1 to 12 on the sides of the top and bottom surfaces of a regular polygonal prism, particularly a regular octagonal prism, so that they do not come into contact with each other, the receiving antennas 1 to 8 that make up the receiving antenna group can be arranged symmetrically and compactly, while expanding the position estimation range of the transmitting antenna centered on the receiving antenna group installed in a single location.

[0058] Furthermore, by arranging the receiving antennas 1 to 8 on the sides of the top and bottom surfaces of the regular octagonal prism so that they do not come into contact with each other, adjacent receiving antennas 1 to 8 that make up the receiving antenna group can be arranged at a 45° angle to each other, thereby efficiently expanding the position estimation range of the transmitting antenna in a circular shape.

[0059] Furthermore, by arranging vertically oriented receiving antennas 9 to 12 on the bottom surface of the regular octagonal prism so that they intersect perpendicularly with the centers of the four sides on which no receiving antennas are located, RSS can be ensured for the vertically oriented receiving antennas 9 to 12, thereby further expanding the position estimation range of the transmitting antenna.

[0060] Furthermore, the vertically oriented receiving antennas 9 to 12 are arranged with their longitudinal centers at the centers of the four sides of the base of the regular octagonal prism on which the above-mentioned receiving antennas 2, 4, 6, and 8 are not arranged, thereby making it possible to arrange the vertically oriented receiving antennas 9 to 12 compactly while suppressing the influence of the receiving antennas 1 to 8 arranged on the sides, in other words, their mutual interaction.

[0061] Furthermore, since receiving antennas 1 to 8 and vertically oriented receiving antennas 9 to 12 are dipole antennas, they have simple directivity, so that electromagnetic waves from a transmitting antenna transmitted from a direction in which the RSS of one receiving antenna becomes NULL can be easily covered by other receiving antennas, making it easy to make the multiple RSS value patterns received by the receiving antennas dependent on the position of the transmitting antenna.

[0062] Next, an underwater position estimation system according to a second embodiment will be described with reference to Fig. 14 and Fig. 17. Note that a description of the same configuration as in the first embodiment will be omitted. In this second embodiment, an electromagnetic field simulation is performed with the electrical constants of seawater set to a relative permittivity εr = 80 and a conductivity σ = 4.0 S / m.

[0063] As shown in Figure 14(a), the underwater position estimation system of this Example 2 differs from Example 1 in that the receiving antenna group does not have vertically oriented receiving antennas 9 to 12, but is composed of eight receiving antennas 1 to 8 that are arranged on the sides of the top and bottom of a regular octagonal prism so as not to touch each other.

[0064] In addition, the location estimation algorithm in this example was implemented using Gaussian process regression implemented in Scikitlearn, one of Python's machine learning libraries. The location estimation range was the quarter plane shown in Figure 14(b), in which a group of receiving antennas installed at a single location was placed at the origin. For training data, data from 64 grid points at 3.0 m intervals on the xy plane shown in Figure 14(b), and integer values ​​from water depths of 2.0 to 7.0 m, were used. Test data was also similarly arranged and used at water depths of 2.5 m, 4.5 m, and 6.5 m. Taking into account the dynamic range of the measurement, the RSS lower limit was set to -150 dB. Search positions were spaced 0.5 m apart.

[0065] First, Fig. 15(a) shows the position estimation result of a horizontally oriented transmitting antenna located at a depth of 2.5 m, and Fig. 15(b) shows the position estimation result of a vertically oriented transmitting antenna. Fig. 15(c) and (d) show the error distributions of the position estimation results of Fig. 15(a) and (b), respectively.

[0066] As shown in Figures 15(a) and (c), it was confirmed that for a horizontally positioned transmitting antenna located at a depth of 2.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular area with a radius of approximately 12 m, with the receiving antenna group located at the center of Figure 14(a) as the origin.

[0067] Furthermore, as shown in Figures 15(b) and (d), it was confirmed that for a transmitting antenna in a vertical position located at a water depth of 2.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular range with a radius of approximately 9 m, with the receiving antenna group as the origin.

[0068] Next, Fig. 16(a) shows the position estimation result of a horizontally oriented transmitting antenna located at a depth of 4.5 m, and Fig. 16(b) shows the position estimation result of a vertically oriented transmitting antenna. Fig. 16(c) and (d) show the error distributions of the position estimation results of Fig. 16(a) and (b), respectively.

[0069] As shown in Figures 16(a) and (c), it was confirmed that for a horizontally oriented transmitting antenna located at a depth of 4.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular range of approximately 12 m in radius, with the receiving antenna group as the origin.

[0070] Furthermore, as shown in Figures 16(b) and (d), it was confirmed that for a vertically oriented transmitting antenna located at a depth of 4.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular range with a radius of approximately 9 m, with the receiving antenna group as the origin.

[0071] Next, Fig. 17(a) shows the position estimation result of a horizontally oriented transmitting antenna at a depth of 6.5 m, and Fig. 17(b) shows the position estimation result of a vertically oriented transmitting antenna. Fig. 17(c) and (d) show the error distributions of the position estimation results of Fig. 17(a) and (b), respectively.

[0072] As shown in Figures 17(a) and (c), it was confirmed that for a horizontally oriented transmitting antenna located at a depth of 6.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular range of approximately 12 m in radius with the receiving antenna group as the origin.

[0073] Furthermore, as shown in Figures 17(b) and (d), it was confirmed that for a vertically oriented transmitting antenna located at a depth of 6.5 m, a position estimation accuracy of less than 2.0 m, which is the target error, can be achieved within a circular range with a radius of approximately 9 m, with the receiving antenna group as the origin.

[0074] As described above, it was confirmed that the underwater position estimation system of this embodiment can estimate positions with high accuracy at depths of 2 to 7 m within a circular range with a radius of approximately 12 m, with the origin at a group of receiving antennas installed at a single location, for a horizontally oriented transmitting antenna, and within a circular range with a radius of approximately 9 m, with the origin at a group of receiving antennas installed at a single location, for a vertically oriented transmitting antenna. Note that this position estimation range is significantly wider than the position estimation range (radius of approximately 6 m) when using the above-mentioned receiving antenna group consisting of three receiving antennas.

[0075] In this embodiment, the position estimation range for the vertically oriented transmitting antenna is narrower by about 3 m in radius compared to the first embodiment. This indicates that the position estimation range for the vertically oriented transmitting antenna is expanded by the vertically oriented receiving antennas 9 to 12 in the first embodiment.

[0076] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention also includes modifications and additions that do not deviate from the gist of the present invention.

[0077] For example, in the above embodiment, the receiving antennas constituting the receiving antenna group were described as being arranged so as not to come into contact with the sides of the top and bottom of a regular octagonal prism, but this is not limited thereto, and the receiving antenna group may have multiple sets of receiving antennas arranged in the same orientation at a predetermined interval, and the orientations of the multiple receiving antennas are different for each set so that they are symmetrically arranged when viewed from the xy plane, for example, two sets of receiving antennas may be arranged so as not to come into contact with the sides of the top and bottom of a quadrangular prism.In this way, it goes without saying that the configuration of the receiving antennas in the receiving antenna group may be changed as appropriate depending on the performance required in the usage environment.

[0078] In the above embodiment, a pair of receiving antennas, i.e., two receiving antennas, is described as one set, but the present invention is not limited to this, and a set may consist of three or more receiving antennas. In this case, it goes without saying that by optimizing the number and arrangement of sets according to the number of receiving antennas constituting one set, it is possible to improve the accuracy of estimating the position of the transmitting antenna and to widen the position estimation range.

[0079] Furthermore, in the above embodiment, the orientation of the transmitting antenna for which position estimation is performed by the underwater position estimation system has been described as being horizontal and vertical, but it goes without saying that this is not limited to this, and the position of the transmitting antenna can be estimated when the transmitting antenna is in an orientation having components in the x-axis direction, y-axis direction, and z-axis direction, respectively.

[0080] In the above embodiment, the receiving antenna group is described as being placed just below the water surface, but more specifically, it is preferable that the geometric center C of the regular octagonal prism be placed at a water depth of 0.5 to 2.0 m.

[0081] In addition, in the above embodiment, the receiving antenna is described as being arranged so as to be linearly symmetric with respect to the x-axis and y-axis when viewed from the z-axis direction, but this is not limited to this, and the receiving antenna may be arranged so as to be point-symmetric with respect to the geometric center C.

[0082] The transmitting and receiving antennas are not limited to dipole antennas, but may be other antennas with simple directivity, such as monopole antennas, loop antennas, etc. The transmitting and receiving antennas may also be half-sheathed dipole antennas, which have been confirmed to be operable in seawater.

[0083] Furthermore, the transmitting antenna and the receiving antenna may be a combination of the various antennas described above, but it is preferable to use the same type of antennas from the viewpoint of stabilizing the RSS value pattern.

[0084] The present invention has industrial applicability because it enables position estimation of transmitting antennas within a circular position estimation range centered on the receiving antenna group using a single receiving antenna group, regardless of the orientation of the transmitting antennas. Since the position of the receiving antenna group does not need to be fixed, when used in real environments such as the ocean, it is less susceptible to the effects of waves and tides, and can be easily installed and retrieved. Furthermore, by adding receiving antenna groups to each position estimation range, it is possible to expand the position estimation area horizontally and / or in the depth direction by connecting the position estimation ranges of a single receiving antenna group. Furthermore, the underwater position estimation system of the present invention not only improves the welfare and safety of divers, but also has a wide range of applications, such as contributing to resource exploration, construction, and surveillance in the sea by using underwater drones, etc.

Claims

1. An underwater position estimation system using electromagnetic waves, comprising: a transmitting antenna underwater; a group of receiving antennas installed at a single location just below the water surface, each set having a plurality of receiving antennas arranged at predetermined intervals with the same orientation, the receiving antennas being arranged symmetrically when viewed in the depth direction so that the orientations of the receiving antennas differ for each set; and a position estimation device having a position estimation algorithm that estimates the position of the transmitting antenna based on the pattern of received power intensity values ​​obtained when the electromagnetic waves transmitted from the transmitting antennas are received by the receiving antennas.

2. The underwater position estimation system according to claim 1, characterized in that all of the receiving antennas have the same configuration, and the multiple receiving antennas are arranged at equal intervals.

3. The underwater position estimation system described in claim 2, characterized in that the group of receiving antennas is in the shape of a regular polygonal prism, and the receiving antennas are arranged on the sides of the top and bottom of the regular polygonal prism so as not to come into contact with each other.

4. The underwater position estimation system according to claim 3, wherein the regular polygonal prism is a regular octagonal prism.

5. The underwater position estimation system described in claim 4, characterized in that a vertically oriented receiving antenna separate from the receiving antenna is arranged at the bottom of the regular octagonal prism so as to intersect perpendicularly with the centers of the four sides on which the receiving antenna is not arranged.

6. The underwater position estimation system according to claim 5, wherein the longitudinal center of the vertically oriented receiving antenna is positioned at the center of the four sides.

7. A seawater position estimation system as described in any one of claims 1 to 6, characterized in that the position estimation algorithm comprises: a first step of specifying a search position; a second step of calculating an estimated transmitting antenna position for each of the receiving antennas for all of the search positions that can be specified; a third step of calculating and recording the sum of the distances between the estimated transmitting antenna position for each of the receiving antennas and the search positions; and a fourth step of determining the search position at which the distance between the estimated transmitting antenna position for each of the receiving antennas and the search position is smallest as the final estimated transmitting antenna position.

8. The underwater position estimation system described in claim 7, characterized in that the second step comprises: a first substep of calculating a unit vector representing the direction from the geometric center of the regular polygonal prism on which the receiving antennas constituting the receiving antenna group are arranged to the search position; a second substep of calculating the distance between the geometric center of the regular polygonal prism and the transmitting antenna from the relationship between the attitudes of the transmitting antenna and the receiving antenna, the unit vector and the received power intensity; and a third substep of calculating the estimated position of the transmitting antenna for each receiving antenna from the unit vector and the distance between the geometric center of the regular polygonal prism and the transmitting antenna.

9. A receiving antenna group used in an underwater position estimation system using electromagnetic waves, characterized in that it has multiple sets of receiving antennas arranged at predetermined intervals with the same attitude, and the receiving antennas are arranged symmetrically when viewed from the depth direction so that the attitudes of the multiple receiving antennas differ for each set.

10. The group of receiving antennas according to claim 9, wherein the receiving antennas are either dipole antennas, monopole antennas or loop antennas.

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