Methods for assessing sonar reflections

Abstract

A procedure for assessing sonar reflections (22) is disclosed comprising the following steps: a) Emitting a sonar signal (24) wherein the sonar signal (24) has a gap (28) in the time domain or in the frequency domain; b) Receiving reflections (22a, 22b) of the sonar signal (24); c) Evaluate the reflections (22a, 22b) of the sonar signal in the gap (28) to assess the reflections (22a, 22b).

Description

[0001] The invention relates to the detection of irregularities using active sonar.

[0002] Active sonar describes the detection of objects based on the reflection of a known, emitted sonar pulse. This includes not only classic active sonar (the same platform transmits and receives) but also bi-static (one platform transmits, a second receives) and multi-static (multiple platforms transmit, another receives). Currently, however, there are increasing efforts to manipulate the reflection of the sonar signal by emitting sound waves. This artificially creates the reflection, thus masking the object's true signature. In particular, a torpedo approaching a target can be deceived, causing it to miss its target or attack the wrong one. Such a decoy device can then, for example, attack the decoy instead of its intended target.

[0003] DE 10 2012 110 943 A1 discloses an underwater signal sequence with at least two acoustic sub-signals, wherein each sub-signal is assigned a transmission time index and an expectation time index.

[0004] US 5 062 083 A reveals a sonar target simulator.

[0005] The object of the present invention is therefore to create an improved concept for the detection of irregularities in reflected sonar pulses.

[0006] The problem is solved by the subject matter of the independent patent claims. Further advantageous embodiments are the subject matter of the dependent patent claims.

[0007] Exemplary embodiments show a method for evaluating sonar reflections comprising the following steps a), b), and c). In step a), a sonar signal is emitted from any platform, in particular a watercraft, and / or an oil rig and / or the base of a wind turbine and / or a harbor wall. The sonar signal is emitted, in particular, by means of an underwater sound transmitter or an array of underwater sound transmitters (i.e., underwater transducers used to transmit underwater sound). The sonar signal exhibits a gap in either the time or frequency domain. That is, in the time domain, there is a pause during the emission of the sonar signal. In the frequency domain, a portion of the frequency spectrum covered by the sonar signal is omitted.

[0008] In step b), reflections of the sonar signal are received, in particular by an underwater sound receiver. The underwater sound receiver can be located on the same platform as the underwater sound transmitter, or on a different platform.

[0009] In step c), the reflections of the sonar signal in the gap are evaluated to assess them. Preferably, classical sonar signal processing takes place first. At an arbitrary point in time, but especially after the usual sonar signal processing, the signal component of the reflection of the sonar signal in the gap is evaluated. Since the object, which is unaware of the emitted signal pulse, also performs sonar signal processing before it can emit its own sonar signal to manipulate the reflection, the background noise present in the gap is inevitably also subjected to sonar signal processing. This sonar signal processing of the background noise reveals that the reflection is a distorted reflection. In other words, the assessment of the reflections involves distinguishing between actual reflections and artificially generated reflections.

[0010] One idea is therefore to create a signal-free area in the emitted sonar signal, which can be used to assess whether the received reflection of the sonar signal has been subjected to sonar signal processing and the actual reflection has thus been manipulated, i.e., the received reflection has been artificially generated.

[0011] In exemplary implementations, evaluating the reflections involves comparing the reflection in the gap with the background noise. For example, evaluating the reflections includes detecting a level increase compared to the background noise. If the received sonar signal in the gap behaves differently from the background noise, it can be assumed that the reflection in the received sonar signal was artificially generated, i.e., did not arise solely due to physical laws.

[0012] Furthermore, a signal processing unit for evaluating sonar reflections is disclosed, comprising a sonar signal processing unit configured to process received reflections of a sonar signal, wherein the emitted sonar signal has a gap in the time domain or frequency domain, and to evaluate the reflections of the sonar signal in the gap in order to assess the reflections. Optionally, the signal processing unit includes a sonar signal generator configured to drive an underwater transducer such that the underwater transducer emits the sonar signal. Advantageously, the signal processing unit is a computer, wherein the sonar signal processing unit and optionally the sonar signal generator are implemented in software.

[0013] Furthermore, a torpedo is disclosed comprising the aforementioned signal processing unit or wherein the torpedo performs the aforementioned method.

[0014] Furthermore, a maritime target detection system, in particular a target destruction system, is disclosed. The target detection system comprises an underwater vehicle, in particular an autonomous or remotely controlled underwater vehicle, and a launching platform for the underwater vehicle, in particular a watercraft, for example a manned underwater vehicle such as a ship or a submarine. The maritime target detection system includes the aforementioned signal processing unit or performs the aforementioned procedure. That is, for example, the underwater vehicle can transmit the sonar signal, receive the reflections, and evaluate them in the gap. However, it is also possible that the launching platform performs all the aforementioned steps or that the aforementioned steps are performed in a distributed manner.An example of a distributed implementation of the steps is that the launching platform transmits an active sonar signal, while the underwater vehicle receives and analyzes the reflections (bi-static). It is also possible for the analysis of the reflections to take place partly on the underwater vehicle and partly on the submersible. In a distributed implementation, it is advantageous if the underwater vehicle is connected to the platform, preferably permanently, via a data cable. If the underwater vehicle is a torpedo, the surface target monitoring system can also be referred to as a surface target destruction system.

[0015] Furthermore, a computer program is disclosed, comprising instructions which, when the program is executed by a computer, cause it to process received reflections of an emitted sonar signal, wherein the emitted sonar signal has a gap in the time domain or in the frequency domain and evaluates the reflections of the sonar signal in the gap in order to assess the reflections.

[0016] Preferred embodiments of the present invention are explained below with reference to the accompanying drawing. It shows: Fig. 1: A schematic representation of a signal processing unit in a scenario for assessing sonar reflections.

[0017] 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.

[0018] Fig. Figure 1 shows a schematic diagram of a signal processing unit 20 in a scenario for evaluating sonar reflections 22a, 22b. The sonar reflections 22a, 22b are based on a known, previously transmitted sonar signal 24. The sonar reflection 22a is a purely natural reflection from an object in the water, while the sonar reflection 22b is, at least partially, actively generated to obscure the actual contour or the backscattering area. For example, a decoy can disguise itself as a larger ship and thus, for instance, confuse an approaching torpedo.

[0019] The sonar signal 24 can be emitted, as shown, by the signal processing unit 20 (active sonar) but also by a sonar on another platform (bi-static) or several platforms (multi-static). It is important that the emitted sonar signal 24 has a gap 28 in the time domain (see figure). Fig. 1) or alternatively in the frequency domain. Due to its simpler representation, in Fig. 1. The signal, and thus the gap 28, was initially represented in the frequency domain as a graph of amplitude over time. However, signal processing is somewhat simpler in the frequency domain, so the gap 28 is preferably used there. In principle, though, both forms (gap 28 in the time domain or in the frequency domain) are possible to implement the idea.

[0020] In the transmission channel, the transmitted signal 24 is superimposed with (background) noise 30. Thus, at objects 26a, 26b, where the transmitted signal 24 is reflected, a signal arrives in which only noise is present in the gap 28; otherwise, the transmitted signal 24 is superimposed with noise.

[0021] The first object 26a passively reflects the transmitted signal 24, i.e., the reflection complies with the laws of physics (see graph for signal 22a). Therefore, in the gap 28, the signal processing unit 20, which receives the reflection, will only detect noise.

[0022] The second object 26b actively reflects the emitted sonar transmit signal 24. That is, it subjects the transmit signal 24, including noise 30, to signal processing and actively sends back a resulting signal 22b that superimposes the reflection to imitate a modified reflection. Since only noise 24 is present in the gap 28, the noise 24 in the gap 28 is also subjected to the signal processing of the second object 26b. In particular, the transmit signal 24 is amplified by the second object 26b, which also amplifies the noise in the gap 28. The signal processing applied to the noise in the gap 28, for example, the amplification as in Fig. As shown in Figure 1, the noise 30' in the gap 28 is also amplified. The signal processing, for example amplification, of the noise in the gap can be detected by the signal processing unit 20. Thus, modified, i.e., simulated, reflections can be detected.

[0023] The disclosed (underwater) sound transducers are designed for underwater use, i.e., in the maritime environment, 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 underwater sound transmitters.The transducers can be made of a piezoelectric material, such as a piezoceramic, to act 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. 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, the ultrasonic testing of materials.

[0024] 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.

[0025] 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. Reference symbol list: 20 Signal processing unit 22 sonar reflections 24 Sonar signal 26 reflective objects 28 gap 30 noise 32 Sonar signal processing unit

Claims

Method for evaluating sonar reflections (22) comprising the following steps: a) Emitting a sonar signal (24) wherein the sonar signal (24) has a gap (28) in the time domain or in the frequency domain; b) Receiving reflections (22a, 22b) of the sonar signal (24); c) Evaluating the reflections (22a, 22b) of the sonar signal in the gap (28) to evaluate the reflections (22a, 22b). Method according to claim 1, wherein the evaluation of the reflections (22a, 22b) comprises the distinction between actual reflections (22a) and artificially generated reflections (22b). Method according to one of the preceding claims, wherein the evaluation of the reflections (22a, 22b) comprises a comparison of the reflection (22a, 22b) in the gap (28) and the background noise (30). Method according to one of the preceding claims, wherein the evaluation of the reflections (22a, 22b) comprises a detection of a level increase relative to the background noise (30). Signal processing unit (20) for evaluating sonar reflections (22) with the following features: - a sonar signal processing unit (32) configured to process received reflections (22a, 22b) of a sonar signal (24), wherein the emitted sonar signal (24) has a gap (28) in the time domain or in the frequency domain and evaluates the reflections (22a, 22b) of the sonar signal (24) in the gap (28) in order to evaluate the reflections (22a, 22b). Signal processing unit (20) according to claim 5, comprising a sonar signal generator (34) configured to control an underwater sound transducer such that the underwater sound transducer emits the sonar signal (24). torpedo comprising the signal processing unit (20) according to one of claims 5 or 6 or wherein the torpedo performs the method according to one of claims 1 to 4. Maritime target monitoring system comprising an underwater vehicle and a launching platform, in particular a watercraft, for the underwater vehicle, wherein the maritime target monitoring system comprises the signal processing unit (20) according to one of claims 5 or 6 or performs the method according to one of claims 1 to 4. Maritime sea target monitoring system according to claim 8, wherein the underwater vehicle is a torpedo. Computer program comprising instructions which, when executed by a computer, cause it to: - process received reflections (22a, 22b) of an emitted sonar signal (24), wherein the emitted sonar signal (24) has a gap (28) in the time domain or in the frequency domain; - evaluate the reflections (22a, 22b) of the sonar signal (24) in the gap (28) in order to assess the reflections (22a, 22b).

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