Method for transmitting sonar data to an evaluation unit of a sonar system of an underwater vehicle and sonar system therefor

Description

[0001] The invention relates to the field of sonar systems of underwater vehicles used to receive underwater sound.

[0002] Underwater vehicles equipped with sonar systems are known, which detect sound waves propagating underwater. In general literature, a distinction is made between passive and active sonar systems. Passive sonar systems are used exclusively for detecting sound waves, while active sonar systems are designed to transmit sound waves in addition to receiving sound waves.

[0003] US 2011 / 099295 A1 discloses transmitting digitized sonar data to an external processor. The data is quantized and compressed for transmission based on a quantization profile, which can be adapted to a desired quality metric or bit rate.

[0004] EP 2 950 451 A1 discloses a compressed transmission of sensor data (radar or ultrasound) from a road vehicle. Lossy compression is used, with more important data being compressed less; this more important data relates, for example, to targets with higher speed or closer distance.

[0005] In the following, the term sonar system shall include both an active and a passive sonar system, whereby the invention relates to signal processing when receiving underwater sound.

[0006] Sonar systems feature one or more underwater antennas with numerous underwater sound receivers, called hydrophones. The hydrophones are electrically connected to an evaluation unit to transmit the signals picked up by the hydrophones to the evaluation unit. The evaluation unit can then display the received sound waves, for example, graphically or acoustically, based on the hydrophone signals picked up by the hydrophones.

[0007] Due to increasing computing power and the associated expansion of capabilities for evaluating hydrophone signals in the evaluation unit, ever-increasing data transmission rates between the hydrophones and the evaluation unit are becoming increasingly desirable. The desire for higher data transmission rates is further reinforced by the fact that the number of hydrophones used in an underwater antenna is also increasing, as increasingly smaller hydrophones are becoming available.

[0008] However, it is known that the physical properties of an electrical cable—such as its cross-section—limit its data transmission rate. Therefore, if the electrical cables connecting the hydrophones to the evaluation unit are currently at their maximum data transmission rate, additional electrical cables or cables with a comparatively larger cross-section must be used to increase the desired data transmission rate.

[0009] However, the measures just mentioned to increase the data transmission rate are not easily implemented in the field of underwater vehicles. It must be noted that hydrophones are located on the outside of the pressure hull of the underwater vehicle, and the evaluation unit is located inside the pressure hull. Therefore, the electrical cables for electrically connecting the hydrophones to the evaluation unit in a sonar system must run through the pressure hull of the underwater vehicle. However, openings in the pressure hull for the electrical cables represent a weak point in the pressure hull and must therefore be kept as small as possible, or the number of openings must be kept to a minimum.

[0010] In the case of a sonar system on an underwater vehicle, comparatively larger openings or a comparatively larger number of openings in the pressure hull of the underwater vehicle would be necessary to transmit hydrophone signals from the hydrophones to the evaluation unit at a higher data transmission rate. However, increasing the size of such openings or adding more openings would lead to increasing instability of the pressure hull and is therefore undesirable.

[0011] It is therefore an object of the present invention to provide a method and a device that make it possible to resolve one of the problems previously mentioned in the prior art. In particular, a sonar system and a method for a sonar system of an underwater vehicle are to be found in which the increasing amount of data provided by hydrophones can be transmitted to an evaluation unit, ideally without changing the physical properties of the electrical connecting lines or increasing the number of connecting lines.

[0012] For this purpose, a method for transmitting sonar data to an evaluation unit of a sonar system of an underwater vehicle according to claim 1 is proposed.

[0013] According to the method, sound waves are first converted into hydrophone signals using multiple hydrophones. This means that each hydrophone generates a hydrophone signal at its output that is representative of the sound waves.

[0014] The hydrophone signals are then fed to a microcontroller circuit, which converts the hydrophone signals into sonar data. The microcontroller circuit is preferably located in the vicinity of the hydrophones or at least outside a pressure hull of an underwater vehicle that incorporates the sonar system. The microcontroller circuit has signal inputs to which the hydrophone signals are fed. The microcontroller circuit also has outputs from which the sonar data is output. The sonar data is fed to an evaluation unit of the sonar system and evaluated by the evaluation unit.

[0015] When converting the hydrophone signals into sonar data in the microcontroller circuit, the hydrophone signals are digitized and compressed. A compression method is used for compression. According to the invention, the compression method currently used during compression is exchanged by the microcontroller circuit depending on the hydrophone signals.

[0016] Accordingly, the compression method used for compression is interchangeable or variable. The microcontroller circuit is now configured to change the compression method depending on the hydrophone signals, which are preferably viewed over a period in the past.

[0017] For example, a currently used compression method is replaced by a new compression method that is different from the currently used compression method, so that the new compression method is used as the current compression method after the replacement during compression.

[0018] This takes advantage of the fact that different compression methods advantageously lead to optimal compression, preferably lossless compression, in different reception scenarios. In a stationary state, in which an underwater vehicle with the sonar system and targets in the vicinity of the underwater vehicle have unchanged positions relative to each other, a specific compression method can be used that leads to a higher degree of compression than another compression method. However, in a different scenario or in a different situation in which the targets are moving rapidly, the other compression method leads to a comparatively higher degree of compression.

[0019] By exchanging the compression method depending on the current scenario, which can preferably be identified indirectly by the microcontroller circuit on the basis of hydrophone signals already received, a comparatively high degree of compression is always possible in different reception situations.

[0020] In contrast to a universal compression, which uses the same compression method in every situation and thus leads to partially poor compression levels, according to the invention several compression methods are used which, when adapted to the scenario and selected during a given scenario, lead to a comparatively higher compression level.

[0021] Since the degree of compression is now increased overall and continuously across various possible scenarios, a comparatively higher amount of data can be transmitted using relatively unchanged transmission lines.

[0022] According to a first embodiment, several different compression methods are stored in the microcontroller circuit, for example, in a memory of the microcontroller circuit. Depending on the hydrophone signals, the microcontroller circuit then selects one of the stored compression methods and uses the selected compression method as the current compression method when compressing the hydrophone signals.

[0023] Accordingly, compression methods for various scenarios are already stored in the microcontroller circuit. The stored compression methods can then be used as the current compression method by simply selecting the respective compression method. According to a further embodiment, the microcontroller circuit generates a compression method depending on the hydrophone signals, wherein the generated compression method is then used when compressing the hydrophone signals. Instead of simply having to resort to various predefined compression methods that are already stored in the microcontroller circuit, the microcontroller circuit according to this embodiment is therefore additionally capable of generating its own compression methods depending on the situation, namely depending on the hydrophone signals, and using them as the current compression method.

[0024] A high degree of flexibility and adaptability of the compression methods to different scenarios, which are represented by the hydrophone signals and which are recognized in the microcontroller circuit based on the hydrophone signals, is thus possible.

[0025] According to a further embodiment, the compression method is selected or generated as a function of the hydrophone signals by estimating future hydrophone signals. Accordingly, future hydrophone signals are preferably estimated as a function of received hydrophone signals, and then, based on the received and / or estimated hydrophone signals, a compression method is selected or generated that is particularly suitable for the future hydrophone signals. Thus, a compression method is selected or generated that has a higher degree of compression for the future hydrophone signals than at least one alternative compression method of at least one of the stored or previously generated compression methods.

[0026] By estimating future hydrophone signals based on received hydrophone signals, a compression method can advantageously be selected that achieves the highest possible degree of compression even for hydrophone signals received in the future.

[0027] According to a further embodiment, the currently used compression method is evaluated. This evaluation takes place continuously, triggered by an event, or repeated at time intervals. For the evaluation, the compression level of the currently used compression method is determined. According to this embodiment, if the compression level is below a predetermined threshold, the current compression method is replaced.

[0028] Accordingly, the compression level is continuously checked to determine whether the currently selected compression method is still suitable for providing a sufficiently good compression level, depending on the hydrophone reception situation. If a compression level is detected that lies below a threshold and is therefore considered insufficient, the currently used compression method is replaced with another, preferably more suitable compression method. This ensures that a suitable compression method is selected for every situation.

[0029] According to a further embodiment, the currently used compression method is transmitted from the microcontroller circuit to the evaluation unit. In this case, the compression method used includes, for example, coding and is represented in particular by code tables, so that the code tables are then transmitted from the microcontroller circuit to the evaluation unit.

[0030] The microcontroller circuit is thus configured to send or transmit additional data to the evaluation unit in addition to the sonar data generated from the hydrophone signals immediately after digitization and compression. According to the present embodiment, this additional data contains information about the compression method currently being used. This information includes, for example, the type of compression method and / or code tables and / or constants and / or variables used in the compression method, as well as additional information required by the evaluation unit to decompress or decode the compressed hydrophone signals in the sonar data so that an evaluation can take place in the evaluation unit.

[0031] Preferably, the transmission of the compression method from the microcontroller circuit to the evaluation unit only takes place when the current compression method is varied or replaced. For example, as soon as the microcontroller circuit detects that the compression level of the currently used compression method is below the predefined threshold and the currently used compression method is varied or replaced, the microcontroller circuit notifies the evaluation unit, essentially in parallel with the replacement, that the variations or replacement of the currently used compression method has occurred or will occur.In addition, the microcontroller circuit informs the evaluation unit of the time of the exchange and the compression method, i.e. information about the compression method that is now being used or is to be used as the new current compression method instead of the compression method currently in use.

[0032] According to a further embodiment, the compression method comprises spatial compression, in which the relative positions of at least two or all of the hydrophones are taken into account during compression. This eliminates the need to transmit the complete signal profile of each hydrophone signal with the sonar data.

[0033] According to a particularly advantageous embodiment, to take the relative positions into account, the propagation time differences and / or amplitude differences of at least two of the hydrophone signals resulting from the different positions of the hydrophones are determined. Thus, at least the determined propagation time difference and / or amplitude difference of the at least two hydrophone signals is added to the sonar data during compression.

[0034] It is therefore conceivable, for example, that a single hydrophone signal from a single hydrophone, along with all the time-of-flight and / or amplitude differences of the other hydrophone signals, could be incorporated into the sonar data. This allows all hydrophone signals to be reconstructed in the evaluation unit without the need to transmit all the complete hydrophone signal waveforms from the microcontroller unit.

[0035] According to a further embodiment, the compression method includes temporal compression. During temporal compression, repetitive signal profiles of the individual hydrophone signals are taken into account. Advantageously, the fact that the hydrophone signals record sounds with constant frequencies in the form of sound waves is exploited. Due to the sinusoidal shape of sound waves, the temporal profiles of the signals also repeat. These repetitions can be used for compression.

[0036] According to a further embodiment, to account for the repetitive signal waveforms, time windows are determined for one or more of the hydrophone signals in which the signal waveforms essentially repeat. From this, sonar data for the respective hydrophone are then generated during compression, which at least contains the repetitive signal waveform in a reconstructable manner. Furthermore, the sonar data contains the number of time windows in which the signal waveform essentially repeats.

[0037] This means that a hydrophone signal waveform that has already been transmitted once does not need to be transmitted a second time if it occurs identically a second time. Rather, it is sufficient to report that the signal waveform occurs a second time, namely in a second time window.

[0038] According to a further embodiment, the compression method may also include a spatial and temporal compression simultaneously, in which on the one hand the relative positions of two or all hydrophones are taken into account and on the other hand the temporally repeated signal curve of each individual or at least several of the hydrophones is taken into account.

[0039] According to a further embodiment, at least one of the compression methods comprises a comparison of at least two hydrophone signals in order to detect matches between the hydrophone signals and to select a suitable compression method on the basis of these matches between different hydrophone signals.

[0040] Preferably, the hydrophone signals are compared using a correlation method, i.e., by correlating the hydrophone signals. A correlation method offers the advantage of an easily implemented mathematical method for the microcontroller circuit that can reliably determine the agreement or similarity of hydrophone signals.

[0041] According to a further embodiment, at least one of the compression methods comprises an audio data compression method that is preferably lossless. In particular, the "Free Lossless Audio Codec (FLAC)" method is used, for example.

[0042] According to a further embodiment, at least one of the hydrophone signals from at least one hydrophone is generally compressed losslessly. This ensures that an intercept, i.e., a ping, which is a short, high-amplitude tone, is detected reliably and without significant time delay.

[0043] Furthermore, the invention relates to a sonar system for an underwater vehicle according to claim 14.

[0044] The sonar system is preferably configured to carry out the method according to one of the aforementioned embodiments. The sonar system serves to receive and evaluate underwater sound and, for this purpose, has several hydrophones. The hydrophones convert sound waves into hydrophone signals. Furthermore, the sonar system comprises an evaluation unit for evaluating sonar data.

[0045] The sonar system also includes at least one microcontroller circuit for converting the hydrophone signals into sonar data. Converting the hydrophone signals involves digitizing and compressing the hydrophone signals. Furthermore, the microcontroller circuit is configured to exchange a compression method currently used during compression depending on the hydrophone signals.

[0046] Further embodiments will become apparent from the exemplary embodiments explained in more detail in the figures. Fig. 1 shows an embodiment of a sonar system, Fig. 2 shows the sequence of a method according to an embodiment, Fig. 3 shows the steps of conversion according to an embodiment and Fig. 4 shows a signal curve of a hydrophone signal.

[0047] Fig. 1shows an embodiment of a sonar system 10. The sonar system comprises an underwater antenna 12 configured to receive sound propagating underwater and convert it into electrical signals. For this purpose, the sonar system includes underwater microphones, also called hydrophones 14.

[0048] The underwater antenna 12 in the present embodiment comprises 16 hydrophones 14, although according to further alternative embodiments, underwater antennas 12 with more than 16 hydrophones 14 are also possible. The hydrophones 16 have relative positions 15 to one another.

[0049] The hydrophones 14 are connected to a microcontroller circuit 18 via electrical lines 16. Each of the hydrophones 14 is connected via its corresponding electrical line 16 to an analog input 20 of the microcontroller circuit 18. Accordingly, hydrophone signals are fed to the microcontroller circuit 18 through the electrical lines 16 via the analog inputs 20.

[0050] In the microcontroller circuit 18, the analog hydrophone signals are first digitized and then compressed. For this purpose, each of the analog inputs 20 includes an analog-to-digital converter, which is not shown here for clarity. The digital hydrophone signals are then fed to a processor, which generates a compressed signal from the digital hydrophone signals, referred to herein as sonar data.

[0051] The sonar data is then output in digital form at an output 22 of the microcontroller circuit 18. The output 22 of the microcontroller circuit 18 is further connected to an evaluation unit 24 via an electrical data line 26. In the evaluation unit 24, the compressed hydrophone signals are decompressed and evaluated so that they are displayed graphically on a display 28 or acoustically via headphones 30. Instead of the headphones 30, a simple loudspeaker according to another embodiment is also possible.

[0052] The electrical data line 26 between the microcontroller circuit 18 and the evaluation unit 24 leads through an opening 32 in the wall 34 of the pressure hull of an underwater vehicle.

[0053] Accordingly, the microcontroller circuit 18, the underwater antenna 12, and the electrical lines 16 between the underwater antenna 12—namely, the hydrophones 14 of the underwater antenna 12—and the microcontroller circuit 18 are located outside the pressure hull and thus outside the wall 34 of the underwater vehicle. The evaluation unit 24, as well as the display 28 and the headphones 30, are located inside the pressure hull, i.e., on the other side of the wall 34 of the pressure hull of the underwater vehicle. Since, at great diving depths of the underwater vehicle, a high compressive force is exerted on the wall 34 by the water pressure, it is advantageous to select the opening 32 as small as possible and to keep the number of such openings 32 to a minimum in order to counteract the implosion of the pressure hull.

[0054] In the Fig. 1A single microcontroller circuit 18 is shown, which is connected to an underwater antenna 12 via electrical lines 16. This invention is not limited to the use of a single microcontroller and a single underwater antenna. Rather, multiple microcontroller circuits 18 are also conceivable, each connected to a number of hydrophones 14. However, preferably all electrical data lines of the additional microcontroller circuits 18 are connected to the same evaluation unit 24. The electrical data lines 26 of the additional microcontroller circuits 18 are routed either through the same opening 32 or through additional openings 32.

[0055] Fig.2 shows the basic procedure as it is used, for example, with a sonar system 10 as shown in Fig. 1is shown. In a receiving step 40, sound waves are received by hydrophones 14 and converted into electrical signals, namely hydrophone signals. The hydrophone signals are fed to a microcontroller circuit 18 and converted into sonar data in a conversion step 42 following the receiving step 40. The sonar data is then transmitted to an evaluation unit 24 from the microcontroller circuit 18 in a transmission step 44. In a decompression step 46, the sonar data is decompressed so that it is evaluated in an evaluation step 48. In the output step 50, the evaluated sonar data is then output acoustically or optically.

[0056] In Fig. 3The conversion step 42, as executed in the microcontroller circuit 18, is now shown in detail. The hydrophone signals 52 are fed to the conversion step 42 and converted into digital signals 56 in an analog-to-digital conversion step 54. The digital signals 56 are compressed using a compression method in a compression step 58, which can also be called compression step 58, and output as sonar data 60.

[0057] The hydrophone signals 56 digitally converted in the analog-to-digital conversion step 54 are also fed to an estimation step 62. In the estimation step 62, future hydrophone signals 64 are estimated based on the hydrophone signals. In the selection step 66, one of several compression methods, preferably stored in a memory, is selected based on the estimated hydrophone signals 64, and the selected compression method is fed to the compression step 58 as the current compression method 68. In the compression step 58, the compression of the digital signals 56 is carried out accordingly using the selected compression method 68.

[0058] Based on Fig. 4It is shown how, for example, a hydrophone signal can be estimated. For this purpose, a temporal signal sequence of a digitized hydrophone signal 56 is represented over a time axis 70 and an amplitude axis 72 in the period 74. By evaluating this period 74, it is determined that the signal sequence contained in the period 76 repeats in the period 78.

[0059] Accordingly, a time window 76 is defined. However, it can also be determined that the signal sequence in window 78 has a lower amplitude than in time window 76. The individual amplitudes of time periods 76 and 78 therefore have a difference of 79. It can therefore now be assumed that, with a high probability, this signal sequence will also be repeated in time period 80 following time period 78, with the amplitudes continuing to decrease by the difference of 79 relative to time period 78. The same applies to the time periods following time period 80. Thus, instead of the hydrophone signal shown here, the signal sequence of time period 76 can now also be transmitted, and for the subsequent time periods 80, only the amplitude differences of the signals from the previous time window are transmitted.

[0060] If a signal sequence completely different from the one shown here is transmitted, these differences become so large that the compression method used here is no longer optimal. This is then detected by the microcontroller, which regularly checks the compression level, and a different compression method is selected. List of reference symbols

[0061] 10Sonar system 12Underwater antenna 14Hydrophones 16Electrical cables 18Microcontroller circuit 20Analog input 22Output 24Evaluation unit 26Electrical data line 28Display 30Headphones 32Opening 34Wall 40Reception step 42Conversion step 44Transmission step 46Decompression step 48Evaluation step 50Output step 52Hydrophone signals 54Analog-to-digital conversion step 56Signals 58Compression step 62Estimation step 64Estimated hydrophone signals 66Selection step 68Compression method 70Time axis 72Amplitude axis 74, 78, 80Period 79Amplitude difference

Claims

1. Method for transmitting sonar data (60) to an evaluation unit (24) of a sonar system (10) comprising the steps of: - Converting sound waves into hydrophone signals (52) with several hydrophones (14); - Converting (42) the hydrophone signals (52) into sonar data (60) with at least one microcontroller circuit (18), - Transmitting (44) the sonar data (60) to an evaluation unit (24), and - Evaluation (48) of the sonar data (60) in the evaluation unit (24), the conversion (42) of the hydrophone signals (52) comprising digitizing (44) and compressing (58) the hydrophone signals (52), characterized in that the sonar system (10) is the sonar system (10) of an underwater vehicle and the compression method (68) currently used during compression (58) is exchanged as a function of the hydrophone signals (52) by the microcontroller circuit (18) as follows: - Use of a compression method in the stationary state, wherein the compression method results in a higher degree of compression than another compression method in the stationary state in which the sonar system and targets in the environment have an unchanged position relative to each other; - Use of the other compression method when the targets are moving quickly, whereby the other compression method results in a higher degree of compression than the compression method in this situation.

2. Method according to claim 1, wherein several different compression methods (68) are stored in the microcontroller circuit (18) and the microcontroller circuit (18) selects one of the compression methods (68) as a function of the hydrophone signals (52) and the selected compression method (66) is used when compressing (58) the hydrophone signals (52).

3. The method according to claim 1, wherein the microcontroller circuit (18) generates a compression method (68) depending on the hydrophone signals (52) and the generated compression method (68) is used in compressing (58) the hydrophone signals (52).

4. Method according to claim 2 or 3, wherein the compression method (68) is selected (66) or generated as a function of the hydrophone signals (52), in which future hydrophone signals (64) are estimated (62) as a function of received hydrophone signals (52) and a compression method (68) is selected (66) or generated on the basis of the received hydrophone signals (52) and / or the estimated hydrophone signals (64), which compression method (68) has a degree of compression suitable for the estimated hydrophone signals.

5. Method according to one of the preceding claims, wherein the currently used compression method (68) is evaluated continuously, triggered by an event or at time intervals by determining a degree of compression and, in the event that the degree of compression is below a predetermined threshold value, the compression method (68) currently used during compression (58) is exchanged.

6. Method according to one of the preceding claims, wherein the currently used compression method (68) is transmitted from the microcontroller circuit (18) to the evaluation unit (24), wherein the used compression method (68) is defined in particular by code tables.

7. The method according to any one of the preceding claims, wherein the compression method (68) comprises a spatial compression that takes into account the relative positions (15) of at least two or all of the hydrophones (14) in the compression (58).

8. Method according to claim 7, wherein, in order to take into account the relative positions (15), transit time differences and / or amplitude differences resulting from the different positions are determined for at least two of the hydrophone signals (52) and the sonar data (60) contain at least the determined transit time differences and / or amplitude differences.

9. The method according to any one of the preceding claims, wherein the compression method (68) comprises a temporal compression and the compression (58) takes into account temporally repeating signal characteristics of the hydrophone signals (52).

10. The method according to claim 9, wherein time windows (76, 78) are determined for one or more of the hydrophone signals (52) in which a signal curve is substantially repeated in order to take the signal curves into account, and sonar data are generated for the hydrophone signals (52) of a hydrophone (14) during compression (58), which sonar data contain at least the repeating signal curve and in particular also a number of windows (76, 78) in which the signal curve is substantially repeated.

11. The method according to any one of the preceding claims, wherein at least one of the compression methods (68) used in the compression (58) comprises a comparison of at least two hydrophone signals (52), and wherein a correlation method is used in particular to compare the hydrophone signals.

12. The method according to any one of the preceding claims, wherein at least one of the compression methods (68) uses an audio data compression method which is preferably lossless, in particular the Free Lossless Audio Codec (FLAC) method.

13. The method according to any one of the preceding claims, wherein the hydrophone signals (52) of at least one hydrophone (14) are compressed without loss.

14. Sonar system (10) for receiving and evaluating waterborne sound, the sonar system (10) being designed in particular for carrying out a method according to one of the preceding claims, and comprising the sonar system (10): - a plurality of hydrophones (14) for converting sound waves into hydrophone signals (52), - an evaluation unit (24) for evaluating sonar data (60), - at least one microcontroller circuit (18) for converting the hydrophone signals (52) into sonar data (60), the microcontroller circuit (18) being arranged to digitize and compress the hydrophone signals (52) received from the hydrophones (14) and to output them as sonar data (60), characterized in that in that the sonar system (10) is the sonar system (10) of an underwater vehicle and the microcontroller circuit (18) is also set up to exchange the compression method currently used during compression as a function of the hydrophone signals by the microcontroller circuit (18), wherein the microcontroller circuit is adapted to use one compression method in the stationary state, the compression method resulting in a higher degree of compression than another compression method in the stationary state in which the sonar system and targets in the environment have unchanged positions relative to each other, and to use the other compression method when the targets are moving rapidly, the other compression method resulting in a higher degree of compression than the compression method in this situation.

15. The sonar system according to claim 14, wherein the microcontroller circuit (18) is an FPGA, preferably with 16, 64, or 256 inputs (20).