Sonar system for detecting extensive, delimited inhomogeneities

Abstract

The invention relates to a sonar system (20) for detecting a bubble curtain of spatially extended, delimited inhomogeneities (22) in the water (22), comprising an active sonar (28) and a signal processing unit (30). The active sonar (28) is designed to emit a waterborne sound signal (32) and to receive waterborne sound with reflections (34) of the emitted waterborne sound signal (32) and to convert the waterborne sound into a corresponding electrical signal (36). The signal processing unit (30) is designed to form a working signal on the basis of the electrical signal (36), to detect reverberation of the emitted waterborne sound signal in the working signal and, on the basis of one or more properties of the reverberation of the inhomogeneities, to detect the inhomogeneities, to sense reverberation of the emitted waterborne sound signal (32) in the working signal and, on the basis of properties of the reverberation, to detect the bubble curtain (22). The active sonar (28) is preferably arranged on the bow or laterally on the watercraft.

Description

[0001] Sonar system for the detection of large-scale, localized inhomogeneities

[0002] Description

[0003] The invention relates to the detection of large-scale, localized inhomogeneities using a sonar system. The sonar system can, for example, be used by a torpedo approaching a target. Inhomogeneities can include, for example, a bubble curtain caused by cavitation from the moving underwater vehicle, an oil slick, deliberately emitted bubbles to mask driving noise, or similar phenomena.

[0004] Currently, underwater vehicles equipped with a sonar system for detecting the bubble curtain of other vessels travel below it, emitting sound waves towards the water's surface. Without bubbles between the sound source and the surface, there is a significant reflection of the sound waves. However, with an intervening bubble curtain, this reflection is attenuated or even rendered undetectable. This allows the underwater vehicle to detect whether it is traveling beneath a bubble curtain.

[0005] However, the underwater vehicle cannot detect the direction of a bubble curtain from a distance. This is due to several reasons. First, the sensor, i.e., the active sonar, is located on the top of the underwater vehicle. This means the vehicle can only see towards the water's surface, not forward. Consequently, the active sonar's range is limited to the vehicle's maximum operating depth. This limitation also impacts the hardware design, particularly the selection of the underwater transducers for the active sonar, as well as the software design for signal processing. This includes parameters such as transmit power, resolution, frequency, beamwidth, the number of beams used (for transmit and / or receive beamforming), and the size of the active sonar array.To detect a target, especially a vessel, even when the underwater vehicle or sonar system is not only moving below the bubble curtain created by the vessel, other concepts are needed. It is advantageous to use the same physical properties of the vessel for navigation throughout. That is, there should be no switching between remote detection of the vessel and close-range detection, such as the well-known detection of the bubble curtain. Furthermore, it would be advantageous to be able to detect the bubble curtain or another physical property of the vessel from a distance in order to detect a moving vessel.

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

[0007] 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.

[0008] Exemplary embodiments show a sonar system for detecting spatially extended, particularly large-scale, limited inhomogeneities (hereinafter referred to as inhomogeneities) in water, comprising an active sonar and a signal processing unit. The sonar system can be mounted on any manned or unmanned, autonomous or remotely controlled, watercraft, for example, an underwater vehicle (e.g., a torpedo) or a ship. Inhomogeneities include, for example, a bubble curtain caused by cavitation from the moving underwater vehicle, an oil slick, or even deliberately ejected bubbles to mask navigational noise. The bubbles or oil droplets are considered as individual inhomogeneities and together form a large-scale but limited area of ​​inhomogeneities. The active sonar is configured to transmit an underwater sound signal, receive underwater sound, and convert it into a corresponding electrical signal.The active sonar system comprises multiple underwater transducers, i.e., an underwater transducer array, for transmitting and receiving underwater sound waves. It is possible to use the same transducer(s) for both transmitting and receiving. Alternatively, one or more transducers can be used for transmitting and another or more for receiving. The underwater transducers are designed for a specific frequency range to receive reflections of the transmitted underwater sound signal. Furthermore, the underwater sound waves must be received with temporal reference to the transmitted underwater sound signal in order to detect and classify the reflections and thus also the reverberation of the transmitted underwater sound signal.

[0009] The signal processing unit is designed to generate a working signal based on the electrical signal. Generating the working signal can involve any signal processing. For example, the electrical signal can be digitized by sampling. Additional signal processing steps are also conceivable to generate the working signal. Furthermore, generating the working signal can include representing the information from the electrical signal in a suitable format. For example, the representation can include the intensity of the reflected underwater sound signal and / or the distance or travel time of the underwater sound signal and / or the direction or angle from which the reflection arrives. The signal processing unit can then detect the reverberation of the emitted underwater sound signal within the working signal.When detecting reverberation, a distinction must be made between detecting an echo as a distinct reflection of the underwater sound signal from an object on the one hand, and detecting reverberation as a diffuse reflection of the underwater sound signal from inhomogeneities, or the absence of an echo due to high attenuation of the inhomogeneities, on the other. Unlike detecting an echo from an object, where a location is sought, detecting inhomogeneities seeks the boundaries of an area. The signal processing unit can be implemented in hardware, software, or a combination of both. For example, the signal processing unit could be a computer program running on a computer.

[0010] Reverberation is detected, for example, using suitable image processing methods. The signal processing unit can analyze the spatial distribution of intensity response and / or phase response in the operating signal to distinguish echoes and regions of increased reverberation and thus detect the reverberation. Additionally or alternatively, the signal processing unit can locate reflections with low external Doppler shift in the operating signal to detect the reverberation. External Doppler shift refers to the resulting frequency shift (i.e., Doppler shift) caused by a moving object. This contrasts with intrinsic Doppler shift, which is the frequency shift caused by the moving sonar system with the active sonar.

[0011] Intrinsic Doppler shift and extrinsic Doppler shift together result in the resulting Doppler shift to be measured.

[0012] Based on reverberation properties, the signal processing unit can detect inhomogeneities. For example, as a property of reverberation, the signal processing unit can locate a spatially extended but bounded area of ​​reflections of the underwater sound signal in order to detect the inhomogeneities. This area is also referred to as a trace, and in the case of a bubble curtain, therefore, as a bubble curtain trace. The result is that the inhomogeneities, such as bubbles in the case of a bubble curtain, remain detectable in the water long after the vessel has created them. For example, the signal processing unit can locate and track a gradient in the intensity of the received underwater sound in the operating signal. If the gradient is finite and exceeds a predetermined length, the signal processing unit can detect the area beyond the gradient as a region of inhomogeneities.Alternatively, it is also possible to use artificial intelligence to detect the inhomogeneities based on the operating signal.

[0013] The active sonar is, for example, mounted on the bow or side of the vessel. This makes it possible, in particular, to detect inhomogeneities in front of or alongside the vessel while underway. It can also be advantageous for the underwater sound receivers to detect underwater sound received from the same direction, i.e., at the bow or side of the vessel. Thus, the sonar system can detect inhomogeneities occurring at a distance from the sonar system while underway.

[0014] The idea is to detect inhomogeneities from a distance by recording the reverberation using active sonar positioned in the detection direction. Due to the long detection time of bubble curtains, particularly those caused by a single bubble curtain, in the water, it becomes possible to detect a vessel that passed by some time ago. Furthermore, it is possible to detect not only bubble curtains but also other inhomogeneities generated by vessels.

[0015] To detect the direction of travel and thus the current position of the watercraft, the signal processing unit can, in some embodiments, be configured to determine the contrast within the bubble curtain or other inhomogeneities and to use the direction in which the contrast increases as the direction of travel of the object causing the inhomogeneities. The contrast of the inhomogeneities is a criterion for determining when the inhomogeneities, such as bubbles, originated. The higher the contrast, the more recent the inhomogeneities. At their point of origin, the inhomogeneities appear abruptly and are narrow and concentrated; towards the end, the concentration decreases steadily, and the inhomogeneities spread over a wider area. An echo can sometimes be detected at the beginning.

[0016] In further embodiments, the active sonar is configured to emit the underwater acoustic signal at a frequency between 9 kHz and 401 kHz, particularly between 15 kHz and 150 kHz. It has been found that the higher the frequency of the emitted underwater acoustic signal, the better the reverberation of inhomogeneities can be detected. The higher frequencies increase the resolution of the operating signal. However, it should be noted that the range of the underwater acoustic signal decreases with higher frequencies. The aforementioned frequency ranges have been found to offer a good compromise between achievable resolution and the range of the underwater acoustic signal, and thus the distance at which inhomogeneities can be detected. Further embodiments show that the signal processing unit is configured to detect bottom and / or surface reflections and to take them into account when measuring the reverberation.This reduces potential sources of interference.

[0017] Further embodiments demonstrate that the active sonar is a sonar for detecting mines and objects. These sonars are high-frequency sonars that scan the surroundings for sea mines and other objects to avoid collisions. The operating signal generated by these sonars can now be used to supplement the detection of reverberation and inhomogeneities.

[0018] Similarly, a method for detecting inhomogeneities with a sonar system is disclosed, comprising the following steps: - Emitting an underwater sound signal predominantly horizontally, in particular from the bow of a watercraft; - Receiving underwater sound with a time reference to the emitted underwater sound signal; - Converting the received underwater sound into an electrical signal; - Generating a working signal based on the electrical signal; - Detecting, i.e., recognizing, the reverberation of the inhomogeneities based on one or more properties of the reverberation of the inhomogeneities. Optionally, a spatial mapping of the inhomogeneities to one or a sequence of spatial segments is performed. Thus, a trace of the inhomogeneities can be determined.

[0019] A further analogous computer program is disclosed, comprising commands which, when executed by a computer, cause the computer to control an active sonar such that the active sonar emits an underwater sound signal from the bow or side of the vessel and, based on an electrical signal generated by the active sonar based on received underwater sound with a time reference to the emitted underwater sound signal, perform the following steps: - generating a working signal based on the electrical signal; - detecting reverberation of inhomogeneities based on one or more properties of the reverberation of the inhomogeneities. Preferred embodiments of the present invention are explained below with reference to the accompanying drawings. The drawings show:

[0020] Fig. 1 : a schematic representation of a sonar system for the detection of inhomogeneities.

[0021] 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.

[0022] Fig. 1 shows a schematic diagram of a sonar system 20 for detecting inhomogeneities 22. The inhomogeneities 22 are generated by a watercraft 24. Here, a surface craft traveling on the water surface 26 is shown. However, the inhomogeneities can also be detected by sonar systems, for example, from manned submarines or unmanned underwater vehicles.

[0023] The sonar system 20 comprises an active sonar 28 and a signal processing unit 30. The active sonar 28 emits an underwater sound signal 32 and receives underwater sound with reflections 34 of the emitted underwater sound signal 32. The reflections 34 are shown as dashed lines because they are not hard reflections (i.e., echoes) but rather many backscattering centers that form the reverberation. The active sonar 28 can convert the received underwater sound into an electrical signal 36. The active sonar 28 is located at the bow of the underwater vehicle 20.

[0024] The signal processing unit 30 processes the electrical signal 36 to detect the inhomogeneities 22. The disclosed (water) transducers are designed for underwater use, 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 underwater sound signal. Furthermore, it is possible for the transducers to convert an applied electrical voltage into underwater sound. The transducers can therefore be used as underwater sound receivers and / or underwater sound transmitters. The transducers can utilize a piezoelectric material, such as a piezoceramic, as the sensing material. The transducers can be used for (active and / or passive) sonar (sound navigation and ranging, dl: sound navigation and range determination).The transducers are preferably not suitable for, or are not used in, medical applications. Likewise, the transducers are preferably not used for, or are not suitable for, the ultrasonic testing of materials.

[0025] 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 is also to 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.

[0026] 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. List of reference numerals:

[0027] 20 sonar systems

[0028] 21 Underwater vehicle 22 Inhomogeneities

[0029] 24 Watercraft

[0030] 26 Water surface

[0031] 28 Active sonar

[0032] 30 Signal processing unit 32 Emitted underwater sound signal

[0033] 34 Reflections

[0034] 36 electrical signal

Claims

Patent claims 1. Sonar system (20) for detecting spatially extended, limited inhomogeneities (22) in water with the following features: - an active sonar (28) designed to emit an underwater sound signal (32), receive underwater sound and convert it into a corresponding electrical signal (36); - a signal processing unit (30) configured to generate a working signal based on the electrical signal (36), to detect an afterglow of the emitted underwater sound signal in the working signal, and to detect inhomogeneities based on one or more properties of the afterglow of the inhomogeneities; - wherein the active sonar (28) is located at the bow or on the side of the sonar system (20).

2. Sonar system (20) according to claim 1, wherein the active sonar (28) is configured to emit the underwater sound signal (32) at a frequency between 9 kHz and 401 kHz, in particular between 29 kHz and 101 kHz.

3. Sonar system (20) according to one of the preceding claims, wherein the signal processing unit (30) is configured to locate, as a property of the reverberation, a spatially extended but limited area with reflections (34) of the underwater sound signal (32) in order to detect the inhomogeneities (22).

4. Sonar system (20) according to claim 3, wherein the signal processing unit (30) is configured to detect and track a gradient in the intensity of the received underwater sound in the operating signal and, if the gradient is finite and exceeds a predetermined length, to detect the area behind the gradient as an area with inhomogeneities (22).

5. Sonar system (20) according to one of the preceding claims, wherein the signal processing unit (30) is configured to determine a contrast in the inhomogeneities (22) and to determine the direction of travel of the object that the Inhomogeneities (22) cause the direction in which the contrast increases.

6. Sonar system (20) according to one of the preceding claims, wherein the signal processing unit (30) is configured to analyze a spatial distribution of intensity response and / or phase response in the operating signal in order to distinguish echoes and regions of increased reverberation and to detect the reverberation.

7. Sonar system (20) according to one of the preceding claims, wherein the signal processing unit (30) is configured to detect reflections (34) with low extraneous Doppler shift in the working signal in order to detect the reverberation.

8. Sonar system (20) according to one of the preceding claims, wherein the signal processing unit (30) is configured to detect ground and / or surface reflections and to take them into account when recording the reverberation.

9. Sonar system (20) according to one of the preceding claims, wherein the signal processing unit (30) is configured to use artificial intelligence to detect the inhomogeneities (22) based on the operating signal.

10. Sonar system (20) according to one of the preceding claims, wherein the active sonar (28) is a sonar for detecting mines and objects.

11. Method for detecting inhomogeneities (22) using a sonar system comprising the following steps: - Emitting an underwater sound signal (32) from the bow or side of a watercraft; - Receiving underwater sound with a time reference to the emitted underwater sound signal; - Converting the received underwater sound into an electrical signal; - Forming a working signal based on the electrical signal; - Detecting, i.e., recognizing, the reverberation of the emitted underwater sound signal in the working signal - Detecting inhomogeneities based on one or more properties of the reverberation of the inhomogeneities.

12. Computer program comprising instructions which, when executed by a computer, cause the computer to control an active sonar (28) such that the active sonar (28) emits an underwater sound signal (32) from the bow or side of a watercraft and, based on an electrical signal generated by the active sonar (28) based on received underwater sound with a time reference to the emitted underwater sound signal, perform the following steps: - generating a working signal based on the electrical signal; - Detecting inhomogeneities based on one or more properties of the reverberation of the inhomogeneities.

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