JP4968827B2 - Underwater positioning system and underwater positioning method - Google Patents

Description

  The present invention relates to a positioning system for knowing the position of an object existing in water and an underwater positioning method. More specifically, the present invention relates to a positioning system using hyperbolic navigation and an underwater positioning method.

  In recent years, a system for measuring the three-dimensional position of fishing gear and marine survey equipment in water in real time has been required in the fishery field and marine surveys. Until now, for example, the state of fishing gear in the sea has been estimated by developing a model net in a tank and analyzing its movement to estimate the actual state in the sea. However, it has been pointed out that the state of fishing gear in maneuvering in the actual sea area is greatly influenced by the weather and ocean currents and is different from the state in the aquarium experiment. Further, for example, in grasping the behavior of fish and unmanned exploration vehicles (Remotely Operated Vehicles), it is generally required that the behavior range is wide and the position can be traced.

In order to grasp the position of an object existing in the water, a positioning system using an acoustic signal is generally employed regardless of water quality such as fresh water, seawater, brackish water and the like.
Here, “an object present in water” includes not only a stationary object but also a moving body, and the moving body is not limited to an object that can move autonomously, such as fish. It also includes objects that move by leaving the water flow. Also, even if the object itself is stationary, if the person who measures it is moving, it must be noted that this stationary object can also be regarded as a relatively moving object. Don't be. Furthermore, “underwater” refers to the water regardless of the sea, river, or lake. In this specification, “an object existing in water” is understood as an object as described above, and is hereinafter referred to as a “positioning object”.

  In such a positioning system, an acoustic signal transmitter called a pinga is attached to a positioning object, and the position of the positioning object is obtained by receiving the transmitted sound with receivers provided at three or more locations. (For example, refer to Patent Document 1).

  Alternatively, there is a positioning system in which a plurality of acoustic signal devices called transponders are arranged on the seabed, for example, and a positioning target is equipped with an acoustic signal device called a responder (see, for example, Patent Document 2). In this positioning system, the responder that has received the response request acoustic signal transmitted from the transponder transmits the response acoustic signal, and the response acoustic signal is received by the transponder, and the laying position of each transponder and the response request acoustic signal are transmitted. The position of the responder, that is, the position of the positioning object is obtained from the time until the response acoustic signal is received. In addition, for example, when it is desired to obtain the current position of a positioning object such as an unmanned spacecraft, a positioning system in which a transponder is provided on the positioning object and a plurality of responders are laid on the sea floor is being configured. .

Japanese Patent Laid-Open No. 2004-24579 JP 2002-122656 A

  In a conventional positioning system using a transponder or a responder, the transponder or the responder is generally fixed and laid on the seabed, and the sea area where the transponder or the responder is laid is within a range where positioning is possible. Therefore, it is difficult to obtain the position of the positioning object when the positioning object moves outside the sea area where positioning is possible. In addition, there was a problem that it would be very expensive to set up a wider range of positioning capable sea area. Furthermore, since the transponder and the responder generally include not only an acoustic signal transmitting means but also a receiving means thereof, for example, a time synchronizing means for synchronizing each other's clock between the transponders, the size of the transponder and the responder is considerably large. In the case where the positioning object is small or a fish or the like, it is difficult to attach a transponder or a responder.

  Further, in a conventional positioning system using a pinga, when a clock circuit for generating transmission time information of an acoustic signal, a depth measuring means for measuring the depth of the pinga, etc. are mounted on the pinga, the same as above When the positioning object is small, it is difficult to attach a pinga to fish.

  On the other hand, in the case where a clock circuit, depth measuring means, and the like are not mounted on the pingers, the position of the pingers is obtained from the arrival time difference of the acoustic signals from the pingers received by different receivers. For this reason, it is common to install each receiver at a considerable interval so that a significant difference in arrival time can be detected. That is, the position of the pinga is obtained by so-called LBL (Long Base Line) type hyperbolic navigation. In the case of such a positioning system, each receiver is provided in, for example, a separate hull or buoy, and it is necessary to specify the position of each receiver separately, and in accordance with the movement of the positioning object. Tracking mobility is lost.

  From the above problems, it is desirable to obtain the position of the pinga by the SBL (Short Base Line) type hyperbolic navigation. In the case of SBL (Short Base Line) type hyperbolic navigation, there is no need to synchronize the time between the receiver and the pinga, and for example, it is possible to adopt a configuration in which a single hull is provided with a plurality of receivers. Even if tracking of an object is excellent, or tracking of a positioning object is unnecessary, it is not necessary to install a receiver in a large-scale range, so that the cost for system construction can be reduced.

  However, in the SBL method, the base line length between the receivers is as short as several meters, for example, so that it is difficult to obtain a significant arrival time difference, and it is difficult to obtain the same positioning accuracy as in the LBL method.

  Accordingly, an object of the present invention is to provide an underwater positioning system and an underwater positioning method with high positioning accuracy that perform positioning of a positioning object by hyperbolic navigation of the SBL (Short Base Line) method.

  In order to solve the above-mentioned problem, in the present invention, the sound emitted from at least three of the transmitting means and the transmitting means that emits an acoustic signal to the water provided in an object (positioning target) existing in the water. The difference between the receiving means capable of receiving an acoustic signal including a signal and the arrival time of the acoustic signals from the transmitting means received by two different receiving means is different, and the combination of the receiving means is different. An underwater positioning system comprising a position specifying means for specifying the position of the positioning object using a plurality of arrival time differences obtained between two receiving means, and received by each receiving means. An AD converter that converts the received acoustic signal into an input signal that is a digital signal, and the position specifying means corresponds to each of the acoustic signals received by the receiving means. Each of the input signals includes signal detection means for detecting whether or not a digital signal corresponding to the acoustic signal transmitted from the transmission means is included, and a digital signal corresponding to the acoustic signal transmitted from the transmission means When detected by the signal detection means, a correlation function calculation is performed for each lag value between the different input signals corresponding to the acoustic signals received by the reception means, and the peak value of the calculation result is given. An underwater positioning system is provided that includes arrival time difference calculating means for obtaining a difference in arrival time of acoustic signals from the transmitting means received by two different receiving means from lag values.

  As described above, when digital signal processing is performed, and further, when a digital signal corresponding to the acoustic signal transmitted from the transmitting unit is detected by the signal detecting unit, each of the acoustic signals received by each receiving unit is handled. By performing a correlation function calculation for each lag value between the input signals, it is possible to realize a resolution according to the sampling rate of the AD converter.

The position specifying means includes decimation means for decimation of each input signal at a sampling rate lower than the sampling rate of the AD converter, and the signal detection means is further received by the reception means. It is good also as what detects whether the digital signal corresponding to the acoustic signal transmitted from the said transmission means is contained in each said input signal corresponding to each acoustic signal by the said decimation means.
This improves signal detection accuracy by performing decimation prior to signal detection as to whether or not a digital signal corresponding to the acoustic signal transmitted from the transmission means is included. In this case, since the sampling rate of the input signal used for the correlation function calculation is larger than the sampling rate of the decimated input signal used for signal detection, accurate arrival time difference calculation is ensured.

  Further, the underwater positioning method of the present invention includes a transmitting step of transmitting an acoustic signal into water by a transmitting means provided on an object (positioning target) existing in water, and an acoustic including the acoustic signal generated from the transmitting means. A reception step of receiving an acoustic signal by at least three receiving means capable of receiving the signal and an arrival time difference of the acoustic signal from the transmitting means received by two different receiving means; An underwater positioning method comprising: a position specifying step for specifying a position of the positioning object using a plurality of the arrival time differences obtained between two different receiving means with different combinations of the receiving means. An AD conversion step of converting the acoustic signal received in the reception step into an input signal which is a digital signal by an AD converter; The position identifying step detects whether or not each input signal corresponding to each acoustic signal received by each receiving means includes a digital signal corresponding to the acoustic signal transmitted from the transmitting means. And when the digital signal corresponding to the acoustic signal transmitted from the transmitting means is detected in the signal detecting step, between the different input signals corresponding to the acoustic signals received by the receiving means. An arrival time difference calculating step for obtaining a difference in arrival time of the acoustic signals from the transmitting means received by two different receiving means from the lag value giving the peak value of the calculation result for each lag value. And a method including:

  According to the present invention, digital signal processing is performed on the acoustic signal received by the receiving unit, and each digital signal corresponding to the acoustic signal transmitted from the transmitting unit is detected by the signal detecting unit. By performing a correlation function calculation for each lag value between each input signal corresponding to each acoustic signal received by the receiving means, it is possible to realize a resolution according to the sampling rate of the AD converter, Even with SBL hyperbolic navigation with a short base line length between receiving means, accurate positioning is realized.

Embodiments of the present invention will be described with reference to the drawings.
First, the underwater positioning system of the present invention obtains the position of a positioning object by SBL hyperbolic navigation. In the SBL method, a plurality of receiving means (for example, hydrophones [ultrasonic wave receivers]) are arranged so that the base line length between two different hydrophones is about several meters. The number of hydrophones can vary depending on the type and number of known information and the type and number of information required. For example, when the time is not accurately synchronized between the pinga side and the hydrophone side, and it is desired to know the three-dimensional position of the pinga, at least four hydrophones are used. In addition, when the time is not accurately synchronized between the pinga side and the hydrophone side and it is desired to know the two-dimensional position of the pinga, at least three hydrophones are used. In the following description, a positioning system and method using four hydrophones will be described taking the case of measuring a three-dimensional position as an example. When positioning a two-dimensional position using three hydrophones, it should be understood by excluding 4 in the hydrophone (4) and indexes i and j described below.

  FIG. 1 shows the positional relationship between the pinga (5) as a transmitting means and the hydrophones (1) to (4) as four receiving means. The four hydrophones (1) to (4) do not necessarily have to be on the same plane. Acoustic signals (in this embodiment, ultrasonic pulses) emitted from the pinga (5) are received by the hydrophones (1) to (4). In the SBL method, for example, the arrival time difference of ultrasonic pulses from the pinga (5) received by the hydrophone (1) and the hydrophone (2), the pinga (1) received by the hydrophone (1) and the hydrophone (3) (3) These three arrival time differences are obtained using the difference in arrival times of ultrasonic pulses from 5) and the arrival time difference of ultrasonic pulses from pinga (5) received by hydrophone (1) and hydrophone (4). The intersection of three hyperboloid surfaces obtained from the distance difference corresponding to is the position of the pinga (5) to be obtained [hyperbolic navigation].

The position coordinates of the four hydrophones (1) to (4) are (x _i , y _i , z _i ) [i = 1, 2, 3, 4], and the position coordinates of the pinga (5) are (x, y, When z), the time t _i to reach the pinger (5) ultrasonic pulses emitted from the i-th hydrophone (i) is given by equation (1). c is the speed of sound in water.

The arrival time difference Δt _j1 [j = 2, 3, 4] of the ultrasonic pulse from the pinga (5) received by the hydrophone (1) and the hydrophone (j) is given by Expression (2).

The arrival time difference Δt _j1 is obtained as an actual measurement value. Therefore, in order to obtain the position of the pinga (5) from the measured arrival time difference, the position (x, y, z) of the pinga (5) is obtained by repeatedly performing calculation by giving an arbitrary initial position by, for example, the successive approximation method. Find it.

  Here, the position coordinates of the pinga (5) and the hydrophones (1) to (4) are expressed as the reference coordinate system when the hydrophones (1) to (4) are installed on the hull, for example. Can do. For example, the bow direction is the x-axis, the starboard direction is the y-axis, and the vertical direction is the z-axis. In addition, the structure which installs each hydrophone in a buoy etc. may be sufficient, and what is necessary is just the structure installed in the same object in short. Of course, any arrangement that has a short baseline length is sufficient, and a configuration in which each hydrophone is installed on a separate object is also possible. However, considering tracking of the positioning object, it is preferable to have a flexible configuration, and if all hydrophones are installed on the same object, the baseline length will not change, so additional equipment for measuring the baseline length will be added. From the viewpoint of eliminating the need for the above, a configuration in which all hydrophones are installed on the same object is preferable.

  The conversion from the hull coordinates to the earth coordinates can be performed using, for example, a GNSS (Global Navigation Satellite System) compass. The GNSS compass can measure not only the heading but also the hull motion (rolling and pitching).

In the hull coordinate system, the bow direction is the x-axis, the starboard direction is the y-axis, the vertical direction is the z-axis, the bow direction is θ _c , the hull rolling angle is θ _r , and the hull pitching angle is θ _p . In the earth coordinate system, the north direction is the X axis, the longitude direction is the Y axis, and the vertical direction is the Z axis.
At this time, the coordinate conversion from the hull coordinate system to the earth coordinate system based on the heading is given by Equation (3) and Equation (4).

Further, since the rolling angle θ _{r of} the hull and the pitching angle θ _p of the hull are measured in hull coordinates, the pitching angle θ ′ _p in the earth coordinate system is given by the equation (5).

Therefore, the coordinate transformation from the hull coordinate system to the earth coordinate system by pitching is given by Equation (6) and Equation (7) using Equation (5). X obtained by Expression (6) is the X coordinate of the positioning object in the earth coordinate system.

Further, the coordinate transformation from the hull coordinate system to the earth coordinate system by rolling is given by Equation (8) and Equation (9). Y obtained by Expression (8) is the Y coordinate of the positioning object in the earth coordinate system, and Z obtained by Expression (9) is the Z coordinate of the positioning object in the earth coordinate system.

In the SBL method, compared to the LBL method, the base line length (broken lines B ₁ , R ₄ ) is longer than the distance (solid lines R ₁ , R ₂ , R ₃ , R ₄ ) between the pinga (5) and each of the hydrophones (1) to (4). _{B 2, B 3, B 4} , B 5, B 6) is short. Therefore, as described above, it is often difficult to recognize a significant difference between, for example, the above three arrival time differences, as is apparent when the positioning object is far from each hydrophone. Accordingly, sufficient positioning accuracy cannot be obtained by simple time difference measurement such as time difference measurement in a conventional LBL type positioning system. Specifically, conventionally, an ultrasonic pulse received by a hydrophone is amplified by an analog amplifier, an SN ratio is increased by an analog filter, and a difference in signal reception time is defined as an arrival time difference.

  On the other hand, in the present invention, digital processing is performed on an acoustic signal received by a receiver (hydrophone) which is a receiving means. In positioning systems that require high speed and real-time performance, the difference in arrival time has been measured with an analog circuit. Recently, however, digital processing capability (the processing capability of arithmetic processing units such as CPUs, bus transmission performance, memory performance, etc.) (Read-write speed, etc.) has improved dramatically, and real-time performance comparable to digital processing can be secured. In addition, a digital filter realized in digital processing can easily realize a steep cutoff characteristic as compared with an analog filter, and has an increase in the degree of freedom for selecting a different pinga having a different frequency and an effect of improving the SN ratio. Measurement performance can be improved.

The underwater positioning system according to the present embodiment includes a pinga (transmitting means) that emits an acoustic signal in water and four hydrophones that can receive an acoustic signal including the acoustic signal emitted from the pinga. (Receiving means) and position specifying means (50) for specifying the position of the positioning object to which the pinga is attached using the difference in arrival time of acoustic signals from the pinga received by two different hydrophones. And an underwater positioning system (see FIGS. 1 and 2).
On the side where the position of the positioning object is specified, the position specifying means (50) includes an AD converter that converts the acoustic signal received by each hydrophone into an input signal that is a digital signal. A signal detection unit (signal detection means) that detects whether each input signal corresponding to each acoustic signal received by each hydrophone includes a digital signal corresponding to the acoustic signal transmitted from the pinga; When a digital signal corresponding to the acoustic signal transmitted from the pinga is detected by the signal detection unit, a correlation function calculation is performed for each lag value between each input signal corresponding to each acoustic signal received by each hydrophone. The acoustic signal from the pinga received by the two different hydrophones from the lag value giving the peak value of the calculation result Configured to include the arrival time difference calculating section for determining the arrival time difference and the (arrival time difference calculating means).
In more detail, in this embodiment, a frequency mixer that performs quadrature detection, a decimator that performs decimation, and a low-pass filter that is a digital filter are explicitly included as components of the position specifying means (50). It has become.

Hereinafter, with reference to FIG. 2 and FIG. 3, the positioning method of a positioning target object is demonstrated.
First, the pinga (5) transmits an acoustic signal underwater asynchronously with the position specifying means (50) for about 10 ms (milliseconds) about once per second, for example (step S1). And an acoustic signal is received by four hydrophones (1)-(4) (step S2). It should be noted that since the pinga repeats transmission / non-transmission alternately, the acoustic signal received by each hydrophone may or may not include an ultrasonic pulse from the pinga. Don't be.

Next, AD conversion is performed on the acoustic signal received by the hydrophone (step S3).
The AD converter (10) that performs AD conversion is configured as a known technique. A sampling frequency (hereinafter also referred to as a sampling rate) in AD conversion can be arbitrarily set. For example, sampling is performed at 1 MHz. The acoustic signal received by the hydrophone is sampled by the AD converter (10) and input signal s _i [i = 1, 2, 3, 4 as a digital signal, and the subscript i is a code indicating the hydrophone. It corresponds to. ] Is converted.

Next, the frequency mixers (12) and (13) perform quadrature detection on the input signal s _i (step S4).
The frequency mixers (12) and (13) are configured as well-known techniques. The reference signal used for quadrature detection is generated by the reference signal generator (11), and the frequency thereof is the frequency of the pinga (5) (the frequency of a general pinga available on the market is about 25 kHz to 85 kHz. ). The frequency mixer (12) outputs an I component that is in-phase with the reference frequency, and the frequency mixer (13) outputs a Q component that is a quadrature component that is 90 ° out of phase with the reference frequency. The input signal s _i is stored and stored in storage means (not shown) such as a memory.

Next, the decimators (15) and (16) perform decimation on the I component output from the frequency mixer (12) and the Q component output from the frequency mixer (13) (step S5).
Decimators (15) and (16) are configured as well-known techniques. The decimator (15) decimates the I component and the decimator (16) decimates the Q component. In this decimation, band limitation and downsampling are performed by a low-pass filter taking antialiasing into consideration. The downsampling rate can be arbitrarily set.

Subsequently, the I component output from the decimator (15) and the Q component output from the decimator (16) are subjected to band limitation by the low pass filters (18) and (19) (step S6).
Noise and double frequency signals are removed by band limitation by the low-pass filters (18) and (19). Through the above processing, the I component and Q component of the baseband signal are extracted.

As described above, the acoustic signal received by the hydrophone is subjected to digital quadrature detection and then extracted as an I component and a Q component of the baseband signal, and a complex number having the I component as a real part and the Q component as an imaginary part. Considering this, these are stored and stored in a storage means (not shown) such as a memory as a pair of amplitude information and phase information. If the I component is represented by I and the Q component is represented by Q, the amplitude information a is obtained by a = √ (I ² + Q ² ), and the phase information θ is obtained by θ = tan ⁻¹ (Q / I).

  In the above, an example in which a general circuit configuration of analog quadrature detection is also applied to digital quadrature detection has been described. However, for example, a circuit configuration using a Hilbert transform filter may be used. From the viewpoint of saving the storage capacity of the storage means, the processes in steps S2 to S6 are periodically performed to update the amplitude information and phase information stored in the storage means, so that the latest amplitude information and phase information are always updated. It may be stored and saved. In this case, the time length of the amplitude information and the phase information stored and stored is preferably at least longer than the transmission time of the ultrasonic pulse of the pinga (5). For example, if the transmission time of the ultrasonic pulse of the pinga (5) is 10 ms, the amplitude information and the phase information stored in the storage means are set to 20 ms longer than 10 ms.

  Moreover, each process of said step S1-S6 is each performed simultaneously about the acoustic signal received by each hydrophone (1)-(4), respectively (refer FIG. 2).

  Here, the essential points of the digital processing in the present invention have been described, but for example, a process for adjusting the gain of the signal may be interposed between the processes of Step S2 and Step S3, and quantization in AD conversion may be performed. It is also possible to apply general digital signal processing techniques related to each processing described above according to the design items of the positioning system.

Subsequent to the processing in step S3, the signal detection unit (20) obtains from the acoustic signal received by the hydrophone (1) having a predetermined time length (20 ms in the above example) stored and stored in the storage unit. amplitude information a _1, the amplitude information a ₂ obtained from the acoustic signal received by the hydrophone _(2), amplitude information a ₃ obtained from acoustic signals received by the hydrophone _(3), in hydrophone (4) by using the amplitude information a ₄ obtained from the received acoustic signal, to detect these on whether include digital signal corresponding to the outgoing ultrasonic pulses from pinger (5) (step S7).
Prior to the processing of step S7, since the processing of step S5 and step S6 is performed, signal detection that is unlikely to cause erroneous determination is possible.
As a specific example, the signal detection unit (20) outputs a digital signal corresponding to an ultrasonic pulse transmitted from the pinga (5) when any amplitude information exceeds a trigger level which is a preset threshold. Detect triggers. Or a signal detection part (20) calculates | requires the cumulative distribution of the amplitude information which has the maximum level, and detects the said trigger by the steep change of a cumulative value. The trigger detection result of the signal detection unit (20) is notified to the control unit (22).

  In the case of the trigger detection result that the trigger is detected, the control unit (22) performs control so that the arrival time difference calculation process by the arrival time difference calculation unit (24) is performed, and the trigger detection result that the trigger is not detected. In this case, control is performed so that the processing after step S1 is performed (step S8).

When the trigger is detected, the arrival time difference calculation unit (24) reads the input signal s _i obtained by converting the acoustic signal received by each hydrophone into digital data from the storage means (in FIG. 2, a circle symbol A , B, C, and D.), a correlation function is calculated between them to calculate the arrival time difference (step S9).
A specific example will be described here. Assume that an input signal given amplitude information having the maximum level is a reference input signal, for example, an input signal s ₁ corresponding to the acoustic signal received by the hydrophone (1). The arrival time difference calculation unit (24) calculates the cross-correlation function R _j1 of the equation (10) with the input signal s ₁ and the input signal s ₂ , the input signal s ₁ and the input signal s ₃ , and the input signal s ₁ and the input signal s _4. (M) is calculated. However, j = 2, 3, and 4. N is the number of sampling points of the input signal. Furthermore, the lag value m that gives the peak point of the cross-correlation function R ₂₁ (m) is m ₂ , the lag value m that gives the peak point of the cross-correlation function R ₃₁ (m) is m ₃ , and the cross-correlation function R ₄₁ ( The arrival time difference calculation unit (24) calculates the equation (11) and outputs the arrival time difference Δt _j1 with the lag value m giving the peak point of m) as m ₄ . Here, f _s is the sampling rate of the input signal.

As described above, according to the present invention, the detection of the arrival time difference is performed by performing the correlation function calculation at the sampling rate of the input signal s _i while performing the signal detection of the acoustic signal transmitted from the pinga at the down-sampled sampling rate. The accuracy is comparable to the sampling rate of AD conversion, and a resolution according to the sampling rate of the AD converter can be realized. For this reason, the position of the pinga can be measured with better accuracy.
As a specific example, when the sampling rate of AD conversion is 100 kHz, the resolution is 10 μs, and when the acoustic signal speed in water is 1500 m / s, the resolution corresponds to a distance of 1.5 cm. On the other hand, when the decimation accompanying signal detection is thinned by 1/100, the sampling rate is 1 kHz. This is 1 ms resolution, and the same acoustic signal speed as described above corresponds to a resolution of 1.5 m distance.
Theoretically, the position specifying error can be suppressed to about several centimeters. However, it must be noted that since the position is specified by hyperbolic navigation, the actual positioning accuracy differs depending on the positional relationship between the pinga and the hydrophone.

The position determination unit (26) receives the arrival time difference Δt _j1 as an input, and obtains the position of the pinga (5) in the hull coordinate system using the expressions (1) and (2) (step S10). When determining the position of the pinga (5) in the Earth coordinate system, the GNSS compass (27) determines the heading and hull motion (rolling and pitching) from the GPS information obtained by the GPS antenna (28). The information is also input to the position determination unit (26), and the position of the pinga (5) is obtained by the above formulas (3) to (9). The position coordinates of the pinga (5) are displayed by display means such as a liquid crystal display.

  Here, the example of obtaining the position of one pinga (5) has been described. However, when obtaining the positions of a plurality of pinga, for example, the transmission frequency may be changed for each pinga. In this case, the reference signal frequency of the quadrature detection may be switched according to the frequency of the pinga whose position is to be specified. Or if the said positioning system which performs the position specification of a specific pinga is prepared for every pinga, the position specification of a several pinga can be performed simultaneously.

The position specifying means (50) for performing the position specifying process as a digital process can be realized by, for example, a general computer. An example of the hardware configuration of such a computer is as follows (see FIG. 4).
The position specifying means (50) can connect an input unit (51) to which an input device such as a keyboard can be connected, an output unit (52) to which a display device such as a liquid crystal display can be connected, and an AD converter. A signal input unit (53) that receives an input of the input signal obtained by the converter, and a CPU (Central Processing Unit; 54) [cache memory or the like may be provided. RAM (Random Access Memory) (55) as a memory, Read Only Memory (ROM) (56), an external storage device (57) as a hard disk, and their input unit (51), output unit (52), A CPU (54), a RAM (55), a ROM (56), a bus (58) connected so as to exchange data between the external storage devices (57), and the like are provided. Further, if necessary, the position specifying means may be provided with a device (drive) that can read and write a storage medium such as a CD-ROM.
The external storage device (57) of the position specifying means (50) stores and stores a program for enabling each processing of steps S4 to S10 and data necessary for the processing of the program. Further, data obtained by the processing of these programs is appropriately stored in the RAM (55) or the like.

  Using a training boat “Hiyodori” (19 tons of drainage) from Tokyo University of Marine Science and Technology, a positioning object was measured using the underwater positioning system of the present invention. This experiment was conducted in a sea area of about 20m in the northern part of Tokyo Bay. The weather during the experiment was clear, the water temperature was 18.9 ° C., and the sound speed during the experiment was calculated to be about 1518 m / s.

  FIG. 5 shows the positional relationship between the arrangement of the hydrophone and the pinga in this experiment. For convenience, it was assumed that ultrasonic pulses from a pinga attached to a fishing rod were received by four hydrophones suspended from the side of the “hidori”. In consideration of the “hidori” hull form and positioning accuracy, one hydrophone was placed at a position where the water depth was lower than the other three hydrophones. Pinga emits an acoustic signal in water for about 10 ms (milliseconds) once a second.

  An example of the AD conversion result (input signal) of the acoustic signal received by four hydrophones is shown in FIG. In FIG. 6, in order to display four input signals corresponding to each hydrophone side by side on the vertical axis of the graph, each input signal is displayed with a bias. Note that FIG. 7 and FIG. 8 described later are displayed corresponding to FIG. FIG. 7 shows a case where the input signal shown in FIG. 6 is subjected to quadrature detection and the amplitude information (reception level) is displayed as an absolute value. Further, FIG. 8 shows the absolute value of the reception level after performing decimation processing and band limitation processing for trigger detection. Of the four decimated input signals shown in FIG. 8, channel 1 having the maximum level (corresponding to the acoustic signal received by hydrophone (1)) was obtained to determine the cumulative distribution and perform signal detection. This is shown in FIG.

The signal detection is successful and the input signal corresponding to the acoustic signal received by each hydrophone is read from the memory for 20 ms. FIG. 10 shows these input signals (digital data). As shown in FIG. 10, it can be seen that each of the hydrophones (2), (3), and (4) receives an ultrasonic pulse from the pinga at about the same timing as the signal detection time for channel 1. In analog processing, it is difficult to accurately obtain these arrival time differences, but this problem can be solved by performing digital processing. In addition, since the arrival time difference is calculated using the input signal of the sampling rate when AD conversion is performed, the arrival time difference can be obtained with high accuracy. Here, the cross-correlation calculation with other channels (corresponding to the acoustic signals received by the hydrophones (2), (3), and (4)) is performed with the channel 1 as a reference. The cross correlation calculation result is shown in FIG.
The lag value giving three peak values corresponds to the arrival time difference between channel 1 and the other channels. In FIG. 11, when the number of sample points of channel 1 is 2000, the peak value of channel 2 is 2188 data points, the peak value of channel 3 is 2310 data points, the peak value of channel 4 is data points. The peak value of channel 2 is given when the lag value is 188, the peak value of channel 3 is given when the lag value is 310, and the peak value of channel 4 is given when the lag value is 319. I understand. At this time, a specific arrival time difference is obtained by Expression (11). Further, the position of the pinga, that is, the position of the positioning object can be obtained by repetitive calculation in the near future according to equations (1), (2) or equations (3)-(9).

The figure which shows the positional relationship of a pinga and a hydrophone. The functional block diagram which illustrates the processing function of the underwater positioning system of this invention. The flowchart which shows the flow of the process in the underwater positioning method of this invention. The figure which shows the hardware structural example at the time of implement | achieving the position specific means which comprises the underwater positioning system of this invention with a computer. The figure which shows the positional relationship of the arrangement | positioning of a hydrophone and a pinga in the experiment of an Example. The graph which shows an example of AD conversion result (input signal) of the acoustic signal received with four hydrophones. FIG. 7 is a graph in which the input signal shown in FIG. 6 is orthogonally detected and amplitude information (reception level) is displayed as an absolute value. The graph which performed the decimation process and the band limitation process on the input signal shown in FIG. 7, and showed the absolute value of the reception level. The cumulative distribution of channel 1 having the maximum level among the four decimated input signals shown in FIG. The graph which showed each input signal equivalent to the acoustic signal received with each hydrophone when signal detection succeeded. The graph which shows the correlation calculation result which performed the cross correlation calculation with the other channel on the basis of the channel 1. FIG.

Explanation of symbols

1, 2, 3, 4 Hydrophone 5 Pinga 10 AD converter 12, 13 Frequency mixer 15, 16 Decimator 18, 19 Low pass filter 20 Signal detection unit 24 Correlation function calculation unit 26 Position determination unit 27 GNSS compass 28 GPS antenna

Claims (2)

A transmission means for emitting an acoustic signal in water, provided on an object (positioning object) existing in water;
At least three receiving means capable of receiving an acoustic signal including an acoustic signal emitted from the transmitting means;
Calculate the arrival time difference of the acoustic signals from the transmitting means received by two different receiving means, and obtain a plurality of the obtained different two receiving means with different combinations of the receiving means. An underwater positioning system comprising position specifying means for specifying the position of the positioning object using the difference in arrival time,
An AD converter that converts the acoustic signal received by each receiving means into an input signal that is a digital signal;
The position specifying means is
At a lower sampling rate than the sampling rate of the AD converter, have row decimation of the input signals, a decimation means for generating a decimation signal,
Corresponding to acoustic signals received by said each receiving means, the upper Symbol each decimation signal, a signal detecting means for detecting whether the digital signal corresponding to the acoustic signal transmitted from said transmitting means is included,
When the digital signal corresponding to the acoustic signal transmitted from said transmitting means is detected by the signal detecting means performs a correlation function calculation for each lag value between different said input signal, the peak value of the calculation result An underwater positioning system comprising: an arrival time difference calculating means for obtaining a difference in arrival time of acoustic signals from the transmitting means received by two different receiving means from given lag values. A transmission step of emitting an acoustic signal into the water by a transmission means provided on an object (positioning object) existing in water;
A receiving step of receiving an acoustic signal by at least three receiving means capable of receiving an acoustic signal including an acoustic signal emitted from the transmitting means;
Calculate the arrival time difference of the acoustic signals from the transmitting means received by two different receiving means, and obtain a plurality of the obtained different two receiving means with different combinations of the receiving means. An underwater positioning method including a position specifying step for specifying the position of the positioning object using the arrival time difference,
An AD conversion step of converting the acoustic signal received in the reception step into an input signal which is a digital signal by an AD converter;
The location step is
At a lower sampling rate than the sampling rate of the AD converter, it has row decimation of the input signals, and decimation step of generating a decimation signal,
Corresponding to acoustic signals received by said each receiving means, to the respective decimation signal, a signal detecting step of detecting whether the digital signal corresponding to the acoustic signal transmitted from said transmitting means is included ,
When the digital signal corresponding to the acoustic signal transmitted from said transmitting means is detected in the signal detection step, performs correlation function calculation for each lag value between different said input signal, the peak value of the calculation result An underwater positioning method, comprising: an arrival time difference calculating step of obtaining an arrival time difference between acoustic signals from the transmitting means received by two different receiving means from given lag values.

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