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

The invention relates to the field of sonar systems of underwater vehicles, which are used for receiving underwater sound.

Underwater vehicles having sonar systems are known according to the prior art, wherein sound waves which propagate underwater are received using the sonar systems. The general literature differentiates between passive and active sonar systems. Passive sonar systems are used exclusively for receiving sound waves, wherein active sonar systems - in addition to receiving sound waves - are also configured to emit sound waves.

The term sonar system is intended to comprise both an active and also a passive sonar system hereafter, wherein the invention relates to the signal processing upon receiving underwater sound.

Sonar systems have one or more underwater antennas having a plurality of underwater sound receivers, namely so-called hydrophones. The hydrophones are electrically connected to an analysis unit, in order to transfer the signals recorded using the hydrophones to the analysis unit. Using the analysis unit, the received sound waves can then be graphically or acoustically displayed, for example, based on the hydrophone signals recorded using the hydrophones.

Due to increasing computer power and the increasing possibilities accompanying this in the analysis of the signals of the hydrophones in the analysis unit, greater and greater data transfer rates are desired between the hydrophones and the analysis unit. The wish for higher data transfer rates is moreover strengthened in that the number of the hydrophones used in an underwater antenna also increases, since presently smaller and smaller hydrophones are available.

However, it is known that the data transfer rate of an electrical line is limited by the physical properties of the electrical line - for example, the line cross section. Accordingly, if the electrical lines for connecting the hydrophones to the analysis unit are presently completely exhausted with respect to the maximum data transfer rate thereof - to increase the desired data transfer rate, for example, further electrical lines or electrical lines having a comparatively larger line cross section thus have to be used.

However, the above-mentioned measures for increasing the data transfer rate are not readily executable in the field of the underwater vehicles. This is because it has to be noted that hydrophones are arranged on the outer side of the pressure hull of the underwater vehicle and the analysis unit is arranged in the interior of the pressure hull. The electrical lines for electrically connecting the hydrophones to the analysis unit in a sonar system therefore have to lead through the pressure hull of the underwater vehicle. However, openings in the pressure hull for leading through the electrical lines represent a weak point in the pressure hull and therefore have to be selected to be as small as possible and/or the number of the openings has to be kept small.

In the case of a sonar system of an underwater vehicle, comparatively larger openings or a comparatively larger number of openings in the pressure hull of the underwater vehicle would accordingly be necessary to transmit signals of hydrophones at a higher data transfer rate from the hydrophones to the analysis unit. An enlargement of such openings or an addition of further openings would result in increasing instability of the pressure hull, however, and is therefore undesirable.

It would therefore be advantageous if embodiments of the present invention would specify a method and a device which enable one of the above-mentioned problems of the prior art to be remedied. In particular, a sonar system and a method for a sonar system of an underwater vehicle are intended to be found, in which the increasing quantity of data which are provided by hydrophones can be transferred to an analysis unit, as much as possible without changing the physical properties of the electrical connecting lines or increasing the number of the connecting lines.

For this purpose, a method for transferring sonar data to an analysis unit of a sonar system of an underwater vehicle is proposed. According to the method, firstly sound waves are converted using multiple hydrophones into hydrophone signals. This means that each hydrophone generates at its output a hydrophone signal, which is representative of the sound waves.

The hydrophone signals are then supplied to a microcontroller circuit, which converts the hydrophone signals into sonar data. The microcontroller circuit is preferably arranged in the region of the hydrophones or at least outside a pressure hull of an underwater vehicle which comprises the sonar system. The microcontroller circuit comprises signal inputs, to which the hydrophone signals are supplied. Moreover, the microcontroller circuit comprises outputs, from which the sonar data are output. The sonar data are supplied to an analysis unit of the sonar system and analyzed using the analysis unit.

During the conversion of the hydrophone signals into sonar data in the microcontroller circuit, the hydrophone signals are digitized and compressed. A compression method is used for the compression. According to embodiments of the invention, the compression method presently used during the compression is replaced or varied by the microcontroller circuit in dependence on the hydrophone signals.

The compression method used during the compression is accordingly thus replaceable or variable. The microcontroller circuit is now configured to replace or vary the compression method in dependence on the hydrophone signals, which are preferably observed over a time span lying in the past. A presently used compression method is accordingly replaced, for example, by a new compression method, which is different from the presently used compression method, and therefore the new compression method is used as the present compression method during the compression after the replacement.

The fact is utilized in this case that in various reception scenarios, various compression methods advantageously result in an optimum compression, preferably a lossless compression. In a stationary state, in which, for example, an underwater vehicle having the sonar system and targets in the surroundings of the underwater vehicle have unchanged positions in relation to one another, for example, a certain compression method is usable, which results in this situation in a higher degree of compression than another compression method. In contrast, the other compression method results, however, in another scenario or in another situation, in which, for example, the targets move rapidly, in a comparatively higher degree of compression.

Due to the replacement of the compression method in dependence on the present scenario, which can preferably be identified indirectly by the microcontroller circuit on the basis of already received hydrophone signals, a comparatively high degree of compression is thus always possible in various reception situations.

In contrast to a universal compression, which thus uses the same compression method in every situation and therefore sometimes results in poor degrees of compression, according to embodiments of the invention multiple compression methods are thus used, which, adapted to the scenario and upon selection during a present scenario, result in a comparatively higher degree of compression.

Since the degree of compression is thus now increased as a whole and continuously over various possible scenarios, a comparatively higher quantity of data is transmittable simultaneously using comparatively unchanged transmission lines.

According to a first embodiment, multiple different compression methods are stored in the microcontroller circuit, for example, in a memory of the microcontroller circuit. The microcontroller circuit then selects one of the stored compression methods in dependence on the hydrophone signals and uses the selected compression method as the present compression method during the compression of the hydrophone signals.

Accordingly, compression methods are already stored in the microcontroller circuit for various scenarios. The stored compression methods can then be used by simply selecting the respective compression method as the present compression method. According to a further embodiment, the microcontroller circuit generates a compression method in dependence on the hydrophone signals, wherein the generated compression method is then used during the compression of the hydrophone signals. Instead of solely having to make use of various already fixedly predefined compression methods, which are already stored in the microcontroller circuit, according to this embodiment, the microcontroller circuit is therefore additionally capable of generating its own compression methods in dependence on the situation, namely in dependence on the hydrophone signals and using them as the present compression method.

A high level of flexibility and adaptability of the compression methods to various scenarios, which are depicted by the hydrophone signals and recognized in the microcontroller circuit on the basis of the hydrophone signals, is thus possible.

According to a further embodiment, the selection or generation of the compression method is performed in dependence on the hydrophone signals by estimating future hydrophone signals. Accordingly, future hydrophone signals are preferably estimated in dependence on received hydrophone signals and a compression method is thereupon selected or generated on the basis of the received and/or estimated hydrophone signals, which is particularly suitable for the future hydrophone signals. For this purpose, a compression method is therefore selected or generated which comprises 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 already previously generated compression methods.

By estimating future hydrophone signals on the basis of received hydrophone signals, a compression method can advantageously be selected which also achieves the greatest possible degree of compression for hydrophone signals received in the future.

According to a further embodiment, the presently used compression method is evaluated. This evaluation takes place continuously, triggered by an event, or repeated at time intervals. For the evaluation, the degree of compression of the presently used compression method is determined. According to this embodiment, in the case in which the degree of compression is below a predetermined threshold value, the present compression method is replaced or varied.

It is accordingly thus continuously checked by determining the degree of compression whether the compression method currently selected as the present compression method is still suitable to offer a sufficiently good degree of compression in dependence on the reception situation of the hydrophones. If a degree of compression is detected in this case which is below a threshold value and is therefore considered to be inadequate, the currently used compression method is replaced by another, preferably better suitable compression method. In this way, it is ensured that a suitable compression method is selected for every situation.

According to a further embodiment, the presently used compression method is transferred from the microcontroller circuit to the analysis unit. In this case, the compression method used comprises, for example, a coding and is represented in particular by code tables, and therefore the code tables are then transferred from the microcontroller circuit to the analysis unit.

The microcontroller circuit is therefore configured to also transmit or transfer further data to the analysis unit in addition to the sonar data, which are generated immediately after the digitization and compression from the hydrophone signals. According to the present embodiment, these further data include items of information about the presently used compression method. These items of information comprise, for example, the type of the compression method and/or code tables and/or constants and/or variables, which are used in the compression method, and also further items of information which the analysis unit requires to decompress or decode the compressed hydrophone signals in the sonar data again, so that an analysis can take place in the analysis unit.

The transfer of the compression method from the microcontroller circuit to the analysis unit preferably only takes place if the present compression method is varied or replaced. Thus, for example, as soon as the microcontroller circuit detects that the degree of compression of the presently used compression method is below the predefined threshold value and the presently used compression method is varied or replaced, essentially parallel to the exchange, the analysis unit is informed by the microcontroller circuit that the variations or the replacement of the presently used compression method is occurring or will occur. Moreover, the microcontroller circuit informs the analysis unit of the point in time of the replacement and the compression method, i.e., items of information about the compression method, which now is or should be used instead of the presently used compression method as the new present compression method.

According to a further embodiment, the compression method comprises a spatial compression, in which the relative positions of at least two or all of the hydrophones are taken into consideration during the compression. In this way, it is made possible that the complete signal curve of each hydrophone signal does not have to be transferred with the sonar data.

According to one particularly advantageous embodiment, to take into consideration the relative positions, the runtime differences and/or amplitude differences of at least two of the hydrophone signals resulting due to the different positions of the hydrophones are determined. Therefore, at least the determined runtime difference and/or amplitude difference of the at least two hydrophone signals are appended to the sonar data during the compression.

It is accordingly conceivable, for example, that a single hydrophone signal of a single hydrophone and all runtime differences and/or amplitude differences of the other hydrophone signals are incorporated into the sonar data. In this way, all hydrophone signals may be reconstructed in the analysis unit, without all complete signal curves of the hydrophone signals having to be transferred from the microcontroller unit.

According to a further embodiment, the compression method comprises a chronological compression. Repeating signal curves of the individual hydrophone signals are taken into consideration during the chronological compression. The fact is thus advantageously utilized that the hydrophone signals record noises having constant frequencies in the form of sound waves. The chronological curves of the signals accordingly also repeat due to the sinusoidal curve of sound waves. These repetitions can be used for the compression.

According to a further embodiment, time windows are determined for one or more of the hydrophone signals, in which the signal curves essentially repeat, to take into consideration the repeating signal curves. Sonar data for the respective hydrophone are then generated therefrom during the compression, which contain at least the repeating signal curve in a form which can be reconstructed. Moreover, the sonar data contain the number of time windows in which the signal curve essentially repeats.

It is thus taken into consideration that a signal curve of a hydrophone signal which has already been transferred once does not have to be transferred a second time if it occurs identically a second time. Rather, it is sufficient to communicate that the signal curve occurs a second time, namely in a second time window.

According to a further embodiment, the compression method can also contain a spatial and chronological compression simultaneously, in which, on the one hand, the relative positions of two or all hydrophones are taken into consideration and, on the other hand, the chronologically repeating signal curve of each individual one or at least a plurality of the hydrophones is taken into consideration.

According to a further embodiment, at least one of the compression methods comprises a comparison of at least two hydrophone signals, to detect correspondences of the hydrophone signals and to select a suitable compression method on the basis of these correspondences of different hydrophone signals. The comparison of the hydrophone signals is preferably performed by a correlation method, i.e., by correlation of the hydrophone signals. A correlation method offers the advantage of an easily implementable mathematical method for the microcontroller circuit, which can reliably determine a correspondence or similarity of hydrophone signals.

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

According to a further embodiment, at least one of the hydrophone signals of at least one hydrophone is compressed in a fundamentally lossless manner. In this way, it is ensured that an intercept, i.e., a ping, which is a short tone having a high amplitude, is detected reliably and without substantial time delay.

Moreover, in an embodiment, the invention relates to a sonar system for an underwater vehicle. The sonar system is preferably configured to execute the method according to the invention according to one of the above-mentioned embodiments. The sonar system is used for receiving and analyzing waterborne sound and has multiple hydrophones for this purpose. Sound waves are converted into hydrophone signals using the hydrophones. Moreover, the sonar system comprises an analysis unit, which is used for analyzing sonar data.

The sonar system moreover comprises at least one microcontroller circuit, which is used for converting the hydrophone signals into sonar data. The conversion of the hydrophone signals comprises in this case a digitization and compression of the hydrophone signals. Moreover, the microcontroller circuit is configured to replace or vary a compression method which is presently used during the compression in dependence on the hydrophone signals by way of the microcontroller circuit.

In a first aspect of the present invention, there is provided a method for transferring sonar data to an analysis unit of a sonar system of an underwater vehicle, comprising the following steps:

- converting sound waves into hydrophone signals using multiple hydrophones;

- converting the hydrophone signals into sonar data using at least one microcontroller circuit,

- transferring the sonar data to an analysis unit, and

- analyzing the sonar data in the analysis unit,

wherein the conversion of the hydrophone signals comprises a digitization and compression of the hydrophone signals using one of multiple different compression methods, and wherein a compression method presently used during compression is replaced by the microcontroller circuit in dependence on the hydrophone signals,

wherein at least one of the compression methods comprises a spatial compression, which takes into consideration relative positions of at least two or all of the hydrophones during the compression, and/or at least one of the compression methods comprises a chronological compression and chronologically repeating signal curves of the hydrophone signals are taken into consideration during the compression, and/or at least one of the compression methods used during the compression comprises a comparison of at least two hydrophone signals wherein in particular a correlation method is used to compare the hydrophone signals.

In a second aspect of the present invention, there is provided a sonar system for an underwater vehicle for receiving and analyzing waterborne sound, the sonar system comprising:

- multiple hydrophones for converting sound waves into hydrophone signals,

- an analysis unit for analyzing sonar data,

- at least one microcontroller circuit for converting the hydrophone signals into sonar data, wherein the microcontroller circuit is configured to digitize the hydrophone signals received from the hydrophones, compress them using one of multiple different compression methods, and output them as sonar data, wherein the microcontroller circuit is moreover configured to replace or vary the compression method presently used during the compression in dependence on the hydrophone signals by way of the microcontroller circuit; and wherein at least one of the compression methods comprises a spatial compression, which takes into consideration relative positions of at least two or all of the hydrophones during the compression, and/or at least one of the compression methods comprises a chronological compression and chronologically repeating signal curves of the hydrophone signals are taken into consideration during the compression, and/or at least one of the compression methods used during the compression comprises a comparison of at least two hydrophone signals wherein in particular a correlation method is used to compare the hydrophone signals.

Further embodiments result on the basis of the exemplary embodiments explained in greater detail in the figures. In the figures:

Figure 1 shows an exemplary embodiment of a sonar system,

Figure 2 shows the sequence of a method according to one exemplary embodiment, Figure 3 shows the steps of the conversion according to one exemplary embodiment, and Figure 4 shows a signal curve of a hydrophone signal.

Figure 1 shows an exemplary embodiment of a sonar system 10. The sonar system comprises an underwater antenna 12, which is configured to receive sound propagating underwater and convert it into electrical signals. For this purpose, the sonar system comprises underwater microphones, which are also called hydrophones 14.

The underwater antenna 12 in the present exemplary embodiment comprises 16 hydrophones 14, wherein according to further alternative exemplary embodiments, underwater antennas 12 having more than 16 hydrophones 14 are also possible. The hydrophones 16 have relative positions 15 in relation to one another.

The hydrophones 14 are connected via electrical lines 16 to a microcontroller circuit 18. Each of the hydrophones 14 is connected with its corresponding electrical line 16 to one analog input 20 of the microcontroller circuit 18. Accordingly, hydrophone signals are supplied to the microcontroller circuit 18 through the electrical lines 16 via the analog inputs 20.

The analog hydrophone signals are firstly digitized and then compressed in the microcontroller circuit 18. For this purpose, each of the analog inputs 20 comprises an analog-to-digital converter, which is not shown here for a better overview. The digital hydrophone signals are then supplied to a processor, which generates a compressed signal, which is referred to here as sonar data, from the digital hydrophone signals.

The sonar data are then output in digital form at an output 22 of the microcontroller circuit 18. The output 22 of the microcontroller circuit 18 is furthermore connected to an analysis unit 24 via an electrical data line 26. The compressed hydrophone signals are decompressed and analyzed in the analysis unit 24, and therefore they can be graphically displayed via a display 28 or acoustically displayed via headphones 30. Instead of the headphones 30, a simple loudspeaker is possible according to another exemplary embodiment.

The electrical data line 26 between the microcontroller circuit 18 and the analysis unit 24 leads in this case through an opening 32 in the wall 34 of the pressure hull of an underwater vehicle.

The microcontroller circuit 18, the underwater antenna 12, and the electrical lines 16 are accordingly located between the underwater antenna 12, namely the hydrophones 14 of the underwater antenna 12, and the microcontroller circuit 18 outside the pressure hull and thus outside the wall 34 of the underwater vehicle. The analysis unit 24 and the display 28 and the headphones 30 are located, in contrast, 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 depth of the underwater vehicle, a high pressure force is exerted on the wall 34 by the water pressure, it is advantageous to select the opening 32 to be as small as possible and to keep the number of such openings 32 low, to counteract an implosion of the pressure hull.

A single microcontroller circuit 18 is shown in Figure 1, which is connected to an underwater antenna 12 via electrical lines 16. Embodiments of this invention are not restricted to using a single microcontroller and a single underwater antenna. Rather, multiple microcontroller circuits 18 are also conceivable, which are each connected to a number of hydrophones 14. In this case, however, all electrical data lines of the further microcontroller circuits 18 are preferably connected to the same analysis unit 24. In this case, the electrical data lines 26 of the further microcontroller circuits 18 are led either through the same opening 32, or through further openings 32.

Figure 2 shows the fundamental sequence of the method, as is executed, for example, using a sonar system 10, as shown in Figure 1. In a reception step 40, sound waves are received by hydrophones 14 and converted into electrical signals, namely hydrophone signals. The hydrophone signals are supplied to a microcontroller circuit 18 and converted into sonar data in a conversion step 42 following the reception step 40. The sonar data are then transferred to an analysis unit 24 from the microcontroller circuit 18 in a transfer step 44. In a decompression step 46, the sonar data are decompressed, such that they are analyzed in an analysis step 48. In the output step 50, the analyzed sonar data are then acoustically or optically output.

In Figure 3, the conversion step 42, as is executed in the microcontroller circuit 18, is now shown in detail. The hydrophone signals 52 are supplied to the conversion step 42 and converted in an analog-to-digital conversion step 54 into digital signals 56. The digital signals 56 are compressed in a compressing step 58, which can also be called compression step 58, by means of a compression method and output as sonar data 60.

The hydrophone signals 56 digitally converted in the analog-to-digital conversion step 54 are moreover supplied to an estimation step 62. In the estimation step 62, future hydrophone signals 64 are estimated on the basis of the hydrophone signals. In the selection step 66, one of multiple compression methods, preferably stored in a memory, is selected on the basis of the estimated hydrophone signals 64 and the selected compression method is supplied to the compressing step 58 as the present compression method 68. In the compressing step 58, the compression of the digital signals 56 is accordingly carried out by means of the selected compression method 68.

It is illustrated on the basis of Figure 4 how, for example, a hydrophone signal can be estimated. For this purpose, a chronological signal sequence of a digitized hydrophone signal 56 is shown via a time axis 70 and an amplitude axis 72 in the time span 74. It is established by analyzing this time span 74 that the signal sequence which is contained in the time span 76 repeats in the time span 78.

A time window 76 is accordingly established. Furthermore, it can be established that the signal sequence has a lower amplitude in the window 78 than in the time window 76. The individual amplitudes of the time spans 76 and 78 accordingly have the difference 79. It can accordingly now be presumed that with great probability in the time span 80 following the time span 78, this signal sequence will also be repeated, wherein the amplitudes drop further by the difference 79 in relation to the time span 78. This also applies to the time spans following the time span 80. Therefore, instead of the hydrophone signal illustrated here, the signal sequence of the time span 76 can now also be transferred and solely the amplitude differences of the signals from the preceding time window are transferred for the following time spans 80.

For the case in which a signal sequence completely different from the signal sequence illustrated here is now transferred, 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 degree of compression, and another compression method is selected.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features in various embodiments of the invention.

Modifications and variations as would be apparent to a skilled addressee are determined to be within the scope of the present invention.

List of reference numerals 10 sonar system

12 underwater antenna

14 hydrophones

16 electrical lines

18 microcontroller circuit

20 analog input

22 output

24 analysis unit

26 electrical data line

28 display

30 headphones

32 opening

34 wall

40 reception step

42 conversion step

44 transfer step

46 decompression step

48 analysis step

50 output step

52 hydrophone signals

54 analog-to-digital conversion step

56 signals

58 compressing step

62 estimation step

64 estimated hydrophone signals

66 selection step

68 compression method

70 time axis

72 amplitude axis

74, 78, 80 time span

79 amplitude difference