Position determination system for determining positions of a plurality of sonar buoys

Abstract

The invention relates to a position determination system for determining positions of a plurality of sonar buoys (22a, 22b, 22c), comprising a data processing unit (24). The data processing unit is configured to evaluate waterborne sound of a plurality of sonar buoys in order to detect, for each of the plurality of sonar buoys, a waterborne sound signal of a sound transmitter in the waterborne sound, ascertain, for each of the plurality of sonar buoys that has received the waterborne sound signal, a property of the waterborne sound signal in respect of the sonar buoy that has received the waterborne sound signal, and determine the positions of the sonar buoys based on differences in the property of the waterborne sound signals of different sonar buoys.

Description

[0001] Positioning system for determining the position of a large number of sonar buoys

[0002] Description

[0003] The invention relates to the determination of the position of a sonar buoy that is not fixed in place, in particular a self-deployed one.

[0004] Sonar buoys are deployed temporarily, for a few days, often only a few hours, in a body of water, especially the sea. After this time, the sonar buoys can no longer be used. They are either abandoned or destroyed. For this reason, sonar buoys are manufactured as cheaply as possible, and often, elaborate anchoring to the seabed is omitted. Without anchoring, however, the buoys are exposed to the elements. After deployment, the sonar buoys drift, particularly due to currents and wind, and leave their original deployment position.

[0005] For this reason, sonar buoys are usually equipped with GPS (Global Positioning System) sensors. However, the GPS system can fail or be disrupted in times of crisis, or the GPS sensors themselves, especially the cheaper ones, can malfunction. Without a current position of the sonar buoy, the position of a detected target, which can only be determined relative to the buoy, can no longer be reliably ascertained. This effect increases over time due to the natural drift of the sonar buoy.

[0006] The object of the present invention is therefore to create an improved concept for determining the position of sonar buoys.

[0007] The problem is solved by the subject matter of the independent claims. Further advantageous embodiments are the subject matter of the dependent claims. Exemplary embodiments show a positioning system for determining the position of a plurality of sonar buoys. The positioning system comprises a data processing unit configured to evaluate underwater sound received by a plurality of sonar buoys in order to detect an underwater sound signal from a sound transmitter in the underwater sound for each sonar buoy of the plurality of sonar buoys. The underwater sound signal is the same signal emitted by the sound transmitter in each case. However, the underwater sound signal arrives at the sonar buoys with a time delay depending on the relative position of the sonar buoy to the sound transmitter. Upon arrival, the underwater sound is received by one or more underwater sound transducers in the sonar buoys. The positioning system can, for example,The sonar buoys can be located in one of the sonar buoys or in a base station. Optionally, the sonar buoys can also be part of the positioning system, for example, in the form of a distributed system if the positioning system is located in the base station. The sonar buoys and / or the sound transmitter can be freely movable, i.e., not anchored, in a body of water, i.e., floating in or on the water.

[0008] Furthermore, the data processing unit is configured to determine, for each sonar buoy among the multitude of sonar buoys that received the underwater sound signal, a property of the underwater sound signal with respect to the receiving sonar buoy and, based on differences in the underwater sound signal property of different sonar buoys, to determine the position of the sonar buoys. The properties described below include the time of reception, particularly for a short-term signal (e.g., a sonar ping), and the direction of incidence, particularly for a continuous signal (e.g., a rotating ship propeller). A DIFAR (Directional Frequency Analysis and Recording) buoy, for example, can be used to determine the direction of incidence. Advantageously, the data processing unit is configured to verify that the underwater sound signal is direct sound, i.e., not a reflection.In particular, the property is determined only for the first arriving underwater sonar signal. A more comprehensive check for the presence of direct sound can, for example, include a plausibility check of the property, i.e., the detection of outliers in the property. The idea is to track the position of the sonar buoys, especially in the event of GPS failure, based on the received sonar signals, starting from their known deployment position. Specifically, the position is determined continuously. For this to work, it is only necessary that the sonar buoys receive the same underwater sonar signal. If, as is common, several different underwater sonar signals are received, i.e., underwater sonar signals from different transmitters, one of the underwater sonar signals must be selected. The different properties that the underwater sonar signal exhibits with respect to the receiver can be used to determine the position of the sonar buoys.

[0009] First, the embodiment with the reception time as a property of the underwater sound signal in relation to the sonar buoys is described. The data processing unit can determine the reception time of the underwater sound signal at the sonar buoy as a property of the underwater sound signal and determine the position of the sonar buoys that received the underwater sound signal relative to the sound source based on the difference in reception times using the Time Delay of Arrival (TDoA) method. The Time Delay of Arrival method is a way to determine the position of at least three different receivers relative to the position of the source by evaluating the signal travel time differences.

[0010] In this method, probability profiles (in the form of lines) are generated, particularly virtually, containing possible points from which the underwater sonar signal could have been emitted, assuming the signal has the measured time-of-flight difference between two sonar buoys. Due to the uncertainty of the actual positions of the sonar buoys, the buoys must be moved until the lines (which change with each movement) intersect at the position of the underwater sonar transmitter. The position of the sonar buoys thus determined then corresponds to their (actual) current position. A known initial starting value for the positions of the sonar buoys shortens the iterative moving process. However, the initial position of the sonar buoys upon deployment is known and can be used as the initial starting value.The position of the sonar buoys can then be tracked, especially continuously, provided a corresponding underwater sound signal is received.

[0011] In this case, the data processing unit can use the time of arrival of the short-term signal as the reception time. A short-term signal is, for example, a sonar ping.

[0012] The supplementary or alternative embodiment uses the direction of incidence of the underwater sound signal at the sonar buoys as a property of the underwater sound signal with respect to the sonar buoys. The data processing unit can determine the direction of incidence of the underwater sound signal at the sonar buoy as a property of the underwater sound signal. A previously known position of the sonar buoys, used as an initial starting value, can be tracked by virtually shifting the positions of the sonar buoys that received the underwater sound signal by optimizing an intersection cloud. That is, the current position of the sonar buoys can be determined by an iterative optimization process of the intersection cloud of the reception directions. The intersection cloud is defined as the polygon that encloses all intersections of the reception directions. The optimization of the intersection cloud aims to minimize its size.Theoretically, the intersection cloud can be reduced to a single intersection point that combines all reception directions.

[0013] However, it is advantageous to also include boundary conditions in the optimization. One boundary condition can be a maximum deviation from the previously known position. This maximum deviation can depend on the time difference between the determination of the last known position and the current position determination. Advantageously, the position deviation may also increase with the increasing difference between the measurement times. Another boundary condition can be that intersections of the reception directions that are too far from the center of the intersection points of the reception directions—a so-called outlier—are not considered in the optimization. Such an outlier can occur, for example, if a reflection of the underwater sound signal is detected instead of the direct sound. The distance of the sonar buoy to the underwater sound transmitter is, however, variable. This can, for example,Position determination is achieved by using a second underwater sonar signal with a known position. The intersection of the two reception directions then represents the current position of the sonar buoy. Alternatively, an estimate can be made, for example, by determining the shortest distance from the last known position to the reception direction and estimating this position as the current position of the sonar buoy. Other methods for determining the distance include the joint optimization of the resulting intersection clouds from different transmitters or tracking the lines over time in case of transmitter drift.

[0014] This method preferably uses a continuous signal, such as the sound of a ship's propeller. Since sonar buoys often determine direction based solely on the gradient (i.e., using a dipole, cf. DIFAR buoy) of the underwater sound signal, direction finding is more accurate with a continuous signal than with a short-term signal. Integration can further reduce uncertainties. The data processing unit can then determine the direction of incidence of a continuous signal.

[0015] Similarly, a method for determining the position of a plurality of sonar buoys is disclosed, comprising the following steps: a) evaluating underwater sound from a plurality of sonar buoys; b) detecting, for each sonar buoy of the plurality of sonar buoys, an underwater sound signal from a sound transmitter in the underwater sound; c) determining a property of the underwater sound signal with respect to the sonar buoy receiving the underwater sound signal; d) determining the position of the sonar buoys of the plurality of sonar buoys based on differences in the property of the underwater sound signal from different sonar buoys.

[0016] Furthermore, a computer program is disclosed, comprising instructions that, when executed by a computer, cause the computer to perform the method. Preferred embodiments of the present invention are explained below with reference to the accompanying drawings. These show:

[0017] Fig. 1: a schematic representation of the Time Difference of Arrival method; and

[0018] Fig. 2: a schematic representation of the method for determining the position of the sonar buoys based on the direction of incidence of an underwater sound signal.

[0019] Before exemplary embodiments of the present invention are explained in detail below with reference to the drawings, it should be noted that identical, functionally equivalent or equivalent elements, objects and / or structures in the different figures are provided with the same reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0020] Figures 1 and 2 each show a schematic representation of a positioning system 20, which uses different methods for determining the position of sonar buoys 22a, 22b, 22c. The positioning system 20 includes a data processing unit 24 for executing these methods. The data processing unit 24 can evaluate the underwater sound received from a plurality of sonar buoys in order to detect an underwater sound signal from a sound transmitter 28 in the underwater sound for each sonar buoy 22a, 22b, 22c. Furthermore, the data processing unit 24 can, for each sonar buoy 22a, 22b, 22c that has received the underwater sound signal, determine a property of the underwater sound signal in relation to the sonar buoy 22a, 22b, 22c that received the underwater sound signal and, based on differences in the property of the underwater sound signal from different sonar buoys, determine the position of the sonar buoys 22a, 22b, 22c.The data processing unit 24 is shown by way of example in a base station 25, in particular on a surface vessel such as a ship. Three sonar buoys 22a, 22b, 22c are shown by way of example. However, it is also possible to use more than three sonar buoys.

[0021] Fig. 1 reveals a schematic representation of the position determination system 20 for carrying out a method for determining the position of the sonar buoys 22a, 22b, 22c based on the Time Delay of Arrival (TDoA) method with the data processing unit 24. In this case, the time of reception of the underwater sound signal is used as a property of the underwater sound signal with respect to the sonar buoys receiving the underwater sound signal; the difference in the properties of the underwater sound signal from different sonar buoys is the difference in the time of reception (travel time difference) between different sonar buoys.

[0022] The lines t1, t2, and t3 (probabilities of presence) are shown schematically, uniting the points whose travel time differences between a first sonar buoy 22a and a second sonar buoy 22b (t1), the second sonar buoy 22b and a third sonar buoy 22c (t2), and the first sonar buoy 22a and the third sonar buoy 22c (t3) are represented. The final position of the sonar buoys, set by the data processing unit 24 by (virtually) shifting the previous position of the sonar buoys through setting a single common resulting intersection point 26 of the lines on the underwater sound transmitter 28, is also shown.

[0023] Fig. 2 shows a schematic representation of the position determination system 20 for carrying out a method supplementing or alternative to the method from Fig. 1 for determining the position of the sonar buoys 22a, 22b, 22c. The data processing unit 24 can determine the direction of incidence 30a, 30b, 30c of the underwater sound signal at the sonar buoys 22a, 22b, 22c as a property of the underwater sound signal with respect to the sonar buoys and optimize a previously known position 22a', 22b', 22c' of the sonar buoys by virtually shifting the position of the sonar buoys that received the underwater sound signal, creating an intersection cloud 32 of the directions of incidence in order to determine a current position of the sonar buoys 22a, 22b, 22c. In other words, the data processing unit 24 can now shift the position of the sonar buoys 22a, 22b, 22c in such a way that the intersection cloud 32 of the directions of incidence is reduced in size.The image shows a 32' intersection cloud that is almost concentrated on a single intersection point.

[0024] The sonar buoys 22a, 22b, 22c are therefore shown at two positions. The current (actual) positions, determined by the method using data processing unit 24, are shown with dashed lines; the last known positions of the sonar buoys are indicated by an additional apostrophe in the reference symbol. The directions of incidence 30a, 30b, 30c belonging to the sonar buoys are also indicated with an apostrophe relative to the previous positions of the sonar buoys. In contrast to the lines in Fig. 1, the directions of incidence are shifted parallel to each other. The shift in positions is indicated by an arrow.

[0025] To receive underwater sound, the sonar buoys can be equipped with underwater sound transducers. The disclosed underwater sound transducers are designed for use underwater, particularly in the sea. The transducers can convert underwater sound into an electrical signal (e.g., voltage or current) corresponding to the sound pressure, the (received) underwater sound signal. Furthermore, it is possible for the transducers to convert an applied electrical voltage into underwater sound. The electrical voltage can follow a predefined pattern and then be referred to as the (transmitted) sonar signal, while the underwater sound resulting from the sonar signal to be transmitted is referred to as the (transmitted) sonar signal. Examples of sonar signals are a chirp (frequency-modulated signal) or, as a special case of the chirp, a sweep (linearly frequency-modulated signal). The transducers can therefore be used as underwater sound receivers and / or as underwater sound transmitters.The transducers can use a piezoelectric material, such as a piezoceramic, as the sensor material. A plurality of underwater transducers, or one or more underwater transducers in conjunction with a signal processing unit, can be referred to as a sonar system.

[0026] The transducers can be used for (active and / or passive) sonar (sound navigation and ranging). The transducers are preferably not suitable for, or are not used for, medical applications. Likewise, the transducers are preferably not used for, or are not suitable for, ultrasonic testing of materials.

[0027] Although some aspects have been described in connection with a device, it is understood that these aspects also constitute a description of the corresponding process, so that a block or component of a device can also be understood as a corresponding process step or as a feature of a process step. Similarly, aspects described in connection with or as a process step also constitute a description of a corresponding block, detail, or feature of a corresponding device.

[0028] Depending on the implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be carried out using a digital storage medium, for example, a magnetic or optical storage medium, on which electronically readable control signals, e.g., a computer program, are stored. These signals can interact with a programmable computer system (CPU and / or GPU) in such a way that the respective method is carried out. For this reason, the digital storage medium should be computer-readable. Embodiments can therefore include a data carrier that has electronically readable control signals capable of interacting with a programmable computer system in such a way that one of the methods described herein is carried out.

[0029] In some embodiments, a programmable logic device (for example, a field-programmable gate array, an FPGA) can be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field-programmable gate array can interact with a microprocessor to perform one of the methods described herein. Generally, in some embodiments, the methods are performed by any hardware device. This can be general-purpose hardware such as a computer processor (CPU) or a graphics processing unit (GPU), or hardware specific to the method, such as an ASIC. Distributed execution across the CPU and GPU is also possible.

[0030] The embodiments described above merely illustrate the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be obvious to other people skilled in the art. Therefore, it is intended that the invention be limited only by the scope of protection set forth in the following claims and not by the specific details presented herein by way of description and explanation of the embodiments.

[0031] Reference symbol list:

[0032] 20 Position determination system

[0033] 22 sonar buoys, 24 data processing units

[0034] 26 Intersection

[0035] 28 underwater sound transmitters

[0036] 30 reception directions

[0037] 32 Intersection cloud

Claims

Patent claims 1. Position determination system (20) for determining the position of a plurality of sonar buoys (22) with the following features: - a data processing unit (24) which is designed to evaluate underwater sound from a plurality of sonar buoys (22) in order to detect an underwater sound signal from a sound transmitter in the underwater sound for each sonar buoy of the plurality of sonar buoys; - wherein the data processing unit (24) is configured to determine, for each sonar buoy of the plurality of sonar buoys that has received the underwater sound signal, a property of the underwater sound signal in relation to the sonar buoy that received the underwater sound signal, and to determine the position of the sonar buoys based on differences in the property of the underwater sound signal of different sonar buoys.

2. Position determination system (20) according to claim 1, wherein the data processing unit (24) is configured to determine, as a property of the underwater sound signal, the time of reception of the underwater sound signal at the sonar buoy and to determine the position of the sonar buoys (22) that have received the underwater sound signal relative to the sound transmitter (28) based on a difference in the times of reception using the Time Delay of Arrival (TDoA) method.

3. Position determination system (20) according to claim 2, wherein the data processing unit (24) is configured to use the time of arrival of a short-time signal as the time of receipt.

4. Position determination system (20) according to claim 1, wherein the data processing unit (24) is configured to determine the direction of incidence (30) of the underwater sound signal at the sonar buoy as a property of the underwater sound signal and to optimize a previously known position of the sonar buoys (22) by virtually shifting the position of the sonar buoys (22) that have received the underwater sound signal to create an intersection cloud (32) in order to determine a current position of the sonar buoys.

5. Position determination system (20) according to claim 4, wherein the data processing unit (24) is configured to determine the direction of incidence of a continuous signal.

6. Position determination system according to one of the preceding claims, wherein the sonar buoys of the plurality of sonar buoys are movably arranged in a body of water.

7. Position determination system according to one of the preceding claims, wherein the sonar transmitter is movably arranged in the water.

8. Method for determining the position of a plurality of sonar buoys (22) comprising the following steps: a) evaluating underwater sound from a plurality of sonar buoys (22); b) detecting, for each sonar buoy of the plurality of sonar buoys, an underwater sound signal from a sound transmitter (28) in the underwater sound; c) determining a property of the underwater sound signal with respect to the sonar buoy receiving the underwater sound signal; d) determining the position of the sonar buoys of the plurality of sonar buoys based on differences in the property of the underwater sound signal from different sonar buoys.

9. Computer program comprising instructions which, when the program is executed by a computer, cause it to execute the method according to claim 8.

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