Depth-variable trailing sonar and method for operation

Abstract

The present invention relates to a watercraft (10) having a trailing sonar, the trailing sonar having a tow cable region (30) and an antenna region (40), the tow cable region (30) of the trailing sonar being arranged between the watercraft and the antenna region (40) of the trailing sonar, a first submersible body (20) being arranged in front of the antenna region (40) and / or a second submersible body (20) being arranged behind the antenna region (40), characterised in that the submersible body (20) has at least one depth setting device.

Description

[0001] The invention relates to a towed sonar which can be towed behind a watercraft for sound detection, wherein at least the area of ​​the towed sonar with the hydrophones can be adjusted to different water depths.

[0002] Conventional towed sonar systems typically feature a buoyancy-neutral receiving antenna with hydrophones, the operating depth of which is adjusted by the length and / or density of the deployed tow cable and the speed of the towing vessel. The operating depth is always a compromise between water column coverage and maximum horizontal detection range.

[0003] In general, sonar detection performance depends on the sound velocity profile across the water depth. Detection can be disrupted by acoustic anomalies at a so-called thermocline and / or convergence zone (the transition between water layers with different temperatures, pressures, etc.). Due to the locally high refraction of sound waves, a thermocline acts like a reflective horizontal barrier for sonar detection, deflecting underwater sound waves into a series of curves that extend to the water's surface and the seabed. Except at very narrow angles, sonar can only detect sounds on the side of the thermocline on which it is located. Convergence zones arise primarily because sound waves are bent in the water in such a way that blind spots and areas of high density are created.While the densification effect occasionally enables higher detection ranges, blind or shadow zones prevent continuous detection.

[0004] Secondly, a vessel can operate in waters of varying depths. In shallow coastal regions, such as the Baltic Sea, the shallow water depth means that a towed sonar should be towed at a relatively shallow depth. In deep water, for example in parts of the North Sea or the Atlantic Ocean, it can be advantageous to tow the sonar at either a shallow or a greater depth.

[0005] A drum for a trailing antenna is known from DE 10 2016 109 108 A1.

[0006] From DE 10 2015 116 750 A1 a towed sonar with a sound transducer arrangement with a tension frame is known.

[0007] German patent DE 10 2015 115 693 A1 discloses a towed sonar with a first antenna and a second antenna. Coupling elements allow the antennas to be used at different water depths.

[0008] US Patent 5,532,975 A discloses a device for positioning seismic equipment in a predetermined underwater position.

[0009] From WO 2008 / 043823 A1, the arrangement of a depth-variable device on a tow rope is known.

[0010] A towing body with a variable-angle rudder is known from WO 2019 / 121743 A1.

[0011] A towed body with an acoustic transmitter is known from DE 197 19 306 A1.

[0012] A device for controlling a trailed cable is known from US Patent 3,605,674 A.

[0013] The simultaneous towing of several underwater tow vehicles is known from US 4 197 591 A.

[0014] From WO 2008 / 043823 A1 a device for automatically attaching and detaching a towed sonar is known.

[0015] A method for positioning seismic receivers is known from US 2006 / 227 657 A.

[0016] A method for positioning seismic receivers is known from US 2017 / 235 004 A1.

[0017] A method for positioning seismic receivers is known from US 2017 / 106 946 A1.

[0018] For reasons of durability and ease of use, it is desirable to be able to reach different water depths easily and without manual conversion.

[0019] The object of the invention is to provide a towed sonar that can be easily operated at different water depths without having to change the length of the tow cable or the towing speed or the diving depth of a towing vessel.

[0020] This problem is solved by the watercraft with the features specified in claim 1 and by the method with the features specified in claim 10. Advantageous further developments are described in the dependent claims, the following description, and the drawings.

[0021] The watercraft according to the invention features a towed sonar. The towed sonar can, for example, be picked up via a drum. In this case, the watercraft can pick up and deploy the towed sonar. In an alternative embodiment, the towed sonar can be connected to the watercraft, i.e., transported to the deployment site with the aid of another vessel, deployed behind the watercraft, and connected to it. This embodiment is particularly preferred for small watercraft, especially unmanned watercraft. However, there are also submarines that, for mission-related reasons, are connected to a towed sonar that cannot be picked up by the submarine, particularly before the mission in port. This has the advantage of saving space and weight in the submarine.On the other hand, the disadvantage is accepted that the towed sonar is permanently positioned behind the submarine, which must also be taken into account during navigation.

[0022] All vessels used specifically for anti-submarine warfare (ASW) are eligible for towed sonar. These include, but are not limited to, cruisers, destroyers, frigates, corvettes, submarines, and unmanned aerial vehicles (UAVs). However, especially in current times, where static methods are gaining importance due to the decreasing detectability of submarines, towed sonar can also be deployed by other vessels in a convoy. For example, an unmanned aerial vehicle can be deployed from a ship to act as a signal transmitter, and the towed sonar can be connected to the ship. This often results in a higher probability of detecting submarines in the area without revealing the vessel's own position.If the data cannot be evaluated directly on the vessel, it can also be transferred to another vessel, in particular to another vessel equipped with active sonar.

[0023] The towed sonar has a tow cable section and an antenna section. Preferably, the towed sonar may also have an end cable behind the antenna section. The end cable, through its drag, ensures that the towed sonar maintains a straight, extended shape. Additionally, the towed sonar may have a sonar transmitter. This allows the towed sonar to also be used for active sonar methods. However, a disadvantage of all active sonar methods is that the active transmission of sound inevitably reveals the vessel's location, thus posing a risk to the vessel. Therefore, this method is particularly advantageous when the vessel is unmanned.

[0024] The tow cable section of the towed sonar is positioned between the vessel and the antenna section of the sonar. The tow cable section serves two purposes: firstly, it creates a distance between the vessel and the antenna section, minimizing the influence of the vessel's own noise on the antenna section; and secondly, it compensates for any height difference between the vessel and the antenna section. In this section, the tow cable typically runs diagonally through the water to compensate for the height difference. However, for optimal data reception, the antenna section should ideally be positioned horizontally and in as straight a shape as possible.

[0025] According to the invention, a first immersion body is arranged in front of the antenna area and preferably a second immersion body is arranged behind the antenna area. Preferably, a first immersion body is arranged in front of the antenna area and a second immersion body is arranged behind the antenna area, or, more preferably, a first immersion body is arranged in front of the antenna area; most preferably, only a first immersion body is arranged in front of the antenna area. The first immersion body or bodies have at least one depth adjustment device.While conventionally the depth at which the antenna section is towed is set via the parameters of the watercraft's towing speed, the density of the antenna section, the density of the tow cable section, and the length of the tow cable section (often varied by the length supplied from a drum), the submersible body(s) with a depth-adjustment device allow for active depth adjustment, at least partially independent of the aforementioned parameters. The first submersible body has at least one first environmental sensor for detecting an environmental measurement.

[0026] An environmental measurement is a quantity measured in relation to the environment, the surrounding water, such as pressure, temperature, or salinity. It can also include, for example, the speed of sound, which is influenced by factors like temperature and salinity. An environmental measurement therefore does not include any property, state, or control variable of the submerged object itself, such as the angle of a rudder.

[0027] The first environmental sensor could be selected from the group comprising pressure sensors, salinity sensors, sound velocity sensors, temperature sensors, conductivity sensors, optical sensors, and flow sensors. The first environmental sensor could be further selected from the group comprising pressure sensors, salinity sensors, sound velocity sensors, temperature sensors, conductivity sensors, and flow sensors. According to the invention, the first environmental sensor is selected from the group comprising salinity sensors, sound velocity sensors, temperature sensors, and conductivity sensors. In particular, layers of water with different temperatures or salinity can act as a barrier to sound due to changes at the layer boundary. The speed of sound in water changes with temperature and salinity, so that reflective layers form at discontinuities, preventing sound from being detected through such layers, or at least preventing reliable detection.Such layers can even cause local turbidity, making them optically perceptible and detectable. It can therefore be advantageous to directly measure the factor causing this effect, such as temperature or salinity, to ensure that the probe remains safely below or above such a layer, for example, below or above a thermocline. This allows for more reliable targeting of these layers, as their height is variable. The salinity, for instance, can be determined either directly, using sodium-ion-selective sensors, or indirectly, for example, using a conductivity detector. However, a simple depth measurement, such as with a pressure sensor, is easier to implement. This sensor could be redundant, i.e., duplicated.Similarly, an optical sensor, particularly an upward-facing one, could determine the diving depth by measuring the absorption of sunlight, especially in conjunction with a second optical sensor on board the vessel. A sensor measuring the speed of sound would have the advantage of directly capturing the essential parameter, regardless of whether it changes due to temperature or salinity variations. Sonar can be used, provided it is specifically designed for bottom detection. This allows, for example, maintaining a safe distance above the bottom in shallow water, thus preventing damage to the towed sonar.

[0028] According to the invention, the first submersible body has at least one second environmental sensor, wherein the second environmental sensor is different from the first environmental sensor and wherein the second environmental sensor is selected from the group consisting of pressure sensor, salinity sensor, sound velocity sensor, temperature sensor, conductivity sensor, optical sensor, flow sensor, and sonar.

[0029] The watercraft according to the invention makes it possible to use a towed sonar in both shallow and deep water without requiring any modifications or significant restrictions on speed at different depths. Furthermore, the antenna section of the towed sonar can be selectively positioned at a specific water depth, for example, either above or below a thermocline. Thus, the invention enables the flexible use of a towed sonar, for example, on a frigate, in both deep water, such as the Atlantic Ocean, and shallow water, such as the Baltic Sea. Similarly, if a submarine is selected as the watercraft, the invention can be used to position the submarine, for example, on one side of a thermocline and the antenna section of the towed sonar correspondingly above or below it on the other side of the thermocline.

[0030] In a further embodiment of the invention, the depth adjustment device is selected from the group comprising a diving plane and a ballast tank. Preferably, the diving body has both a diving plane and at least one, preferably two, ballast tanks. With the aid of a diving plane and / or a ballast tank, the diving body can precisely change its diving depth. This causes the associated antenna section to descend to this depth, so that the depth of the antenna section can be selected and adjusted via the diving body. In this way, the area from which sound can be received can also be precisely selected. The combination of a diving plane and a ballast tank is particularly advantageous because the diving plane enables a rapid, precise change in depth. On the other hand, the diving depth can be kept stable over a long period of time using a ballast tank.Additionally, this eliminates the need for continuous steering with a diving plane, which increases drag, thereby increasing the watercraft's energy consumption and reducing its top speed. Ideally, the submersible hull features only the diving plane and no ballast tank as a depth adjustment device, as this allows the system to be kept simple and compact.

[0031] In a further embodiment of the invention, the first submersible body additionally features a rudder. This additional rudder allows the antenna section to be shifted laterally parallel to the direction of travel of the vessel. This offers significant advantages, particularly in two operational scenarios. In shallow water, it makes it possible to move the antenna section out of the wake of the towing vessel. Secondly, this lateral distance between the vessel's path and the antenna section's trail can, in the case of an active sonar, mislead a potential adversary about the towing vessel's position, as they would expect the towing vessel to be directly in front of the actively transmitting towed sonar.Even if a potential enemy takes this possibility into account, there is a significantly increased uncertainty about the position of the towing vessel, as it is unclear, for example, whether the towed sonar is shifted to starboard or port.

[0032] In a further embodiment of the invention, the first submersible body has a control device. The control device is designed to read the first environmental sensor and to control the depth adjustment device. The first submersible body can therefore automatically monitor a predetermined depth-correlated environmental measurement, which can also be the depth itself, and, if necessary, actively control it.

[0033] In another alternative embodiment of the invention, the watercraft has a control device. This control device is designed to read the first environmental sensor and to control the depth adjustment device. The advantage is that all information is thus available directly and immediately at the operations center. Additionally, this information is particularly relevant for evaluating the sonar data from the slack sonar, especially during larger depth adjustments, since a straight, horizontal arrangement of the hydrophones can no longer be assumed with significant changes.

[0034] In a further embodiment of the invention, the first submersible unit can be reversibly and detached from the towed sonar. Preferably, the first submersible unit is deployable and connectable to the towed sonar unmanned, and particularly preferably autonomously. Especially in applications on a submarine, it is not possible to manually couple or decouple components, such as a transmitter for an active sonar or a submersible unit itself, when deploying or retrieving the towed sonar. The towed sonar must therefore be able to be wound onto a drum in a simple manner. However, in this form, it becomes technically difficult to arrange a submersible unit within the towed sonar. Therefore, the first submersible unit is preferably equipped with a propulsion system and preferably has the shape of a torpedo. In this way, the first submersible unit can be deployed from a gun tube.The first submersible body can then be moved to the towed sonar unit, either by wire guidance or autonomously, and coupled to it. If guided by wire, the wire is then cut to close the weapon tube. The propulsion system can also be used to make even faster elevation changes of the antenna array.

[0035] In a further embodiment of the invention, the towed sonar runs through the first submersible body. The first submersible body can be reversibly detached during the winding process and reversibly connected to the towed sonar during the winding process. Examples of such connections are known to those skilled in the art, for example, from WO 2008 / 043823 A1. This is particularly preferred if the watercraft is a submarine. In this case, the first submersible body remains outside the submarine after the towed sonar has been wound up. In a further embodiment of the invention, the towing cable section has a

[0036] A data connection is established between the vessel and the first submersible, allowing the first submersible to be controlled via this connection. Data lines run along the tow cable to transmit sonar data from the antenna area to the vessel. Therefore, integrating a corresponding data connection for the first submersible is very straightforward. This enables direct control and thus adjustment of the antenna's diving depth directly from the sonar system. Optionally, a connection to the first submersible's power supply can also be provided. Alternatively, the various systems can be connected to the vessel via separate power supplies through the tow cable area, allowing control solely through the power supplied to each individual system.For example, a pump in the first submersible body can be temporarily powered to draw water from a ballast tank, thus reducing the diving depth. Similarly, a servo motor for a diving plane or rudder can be powered to effect the resulting change. Information is therefore transmitted solely through the transfer of energy. The data connection can be established using an electrically conductive cable. This can be a data connection only. Alternatively, a power-carrying cable can be used to transmit data along with power over the same line. The data connection can also be established using a fiber optic cable.

[0037] In a further alternative embodiment of the invention, a data connection between the watercraft and the first submersible body is established by means of an acoustic modem, wherein the first submersible body can be controlled via the data connection. This embodiment allows for retrofitting existing systems without having to modify the towing cable.

[0038] In a further embodiment of the invention, the first submersible body has an active sonar. This can be particularly advantageous when the towed sonar is being pulled on the opposite side of a thermocline from where the watercraft is located.

[0039] In a further embodiment of the invention, the watercraft has two towed sonar units, at least one of which has a first submersible element; preferably, both towed sonar units are each equipped with at least one first submersible element. This makes it possible, for example, to deploy a first towed sonar unit above a thermocline and the second towed sonar unit below a thermocline. This makes it extremely difficult for an enemy submarine to evade detection.

[0040] In a further embodiment of the invention, the first submersible body has no gas-filled regions. Preferably, the first submersible body is completely encapsulated or flushed with water. By omitting gas-filled regions, a sudden change in the speed of sound at the boundary between solid and gaseous states is avoided, thus reducing the reflectivity for sound waves and consequently the signature of the first submersible body. This embodiment is particularly preferred for the passive embodiment. In the case of an active sonar on board the first submersible body, its position is already revealed by the emission of sound waves, making signature optimization unnecessary.

[0041] In a further embodiment of the invention, the power supply is provided via a power cable in the pull cable area, wherein the power cable has at least four conductors and wherein the power cable has two conductors of the same polarity, with conductors of opposite polarity being adjacent to each other. In the case of four conductors, this results in two conductors with a high potential (+) and two with a low potential (-). These four conductors are arranged at the corners of a square, so that conductors with the same potential are diagonally opposite each other. This achieves a reduction of the electromagnetic signature.

[0042] In another aspect, the invention relates to a method for operating a watercraft according to the invention. The method comprises the following steps: a) Deploying the towed sonar, b) Specifying a depth-correlated environmental measurement, whereby a temperature or salinity is specified, so that the first submersible remains precisely below or above a stratification, c) Controlling the depth resulting from the depth-correlated environmental measurement by the first submersible using the depth control device, d) Continuously measuring a measurement correlated to the depth-correlated environmental measurement with the first environmental sensor, e) Evaluating the measurement and checking whether a depth adjustment needs to be performed and, if necessary, controlling the depth control device.

[0043] The depth-correlated environmental measurement specified in step b) is therefore an ambient temperature, an ambient conductivity or a salinity.

[0044] Naturally, the depth-correlated environmental measurement can be changed at any time, for example, to continue the search with the towed sonar at a different depth and thus, for instance, in a different layer. The procedure then jumps back to step b), followed by the command to the new depth in step c). However, a local change in the environmental measurement can also be specified, which is particularly advantageous. This can be beneficial, for example, if the towed sonar is to be positioned below a first thermocline, i.e., a first layer of significant temperature change. Since the exact location of this thermocline is usually not precisely known due to seasonal variations, for example, it can also be specified that the towed sonar should be kept at a depth just below a sudden change in, for example, temperature, salinity, or the speed of sound.In this case, the towed sonar is lowered until the measured environmental parameter shows a corresponding predefined change. This makes it possible to correctly position a towed sonar even if the exact stratification of the water is initially unknown.

[0045] Steps d) and e) constitute a control loop to maintain the towed sonar in the desired position. The continuous measurement in step d) does not need to be uninterrupted. Instead, it can occur at intervals, with the interval lengths being adjustable. In particular, the interval length can be made dependent on the variability of the measured quantity. For example, if only very small fluctuations occur, measurements are taken at one-minute intervals; if larger changes occur, the interval is changed to, for example, 10 seconds, or, in the case of even larger changes, to 1 second or continuous.

[0046] According to the invention, the use of such a control loop also makes it possible to remain specifically below or above a stratification by specifying a temperature or salinity, regardless of the water depth at which it is located.

[0047] In a further embodiment of the invention, the depth profile of the measured variable is determined during step c). Often, the temperature or salinity profiles are only partially known. It is therefore advantageous to capture this profile in the current situation and to be able to use this information to adapt the subsequent mission. The determination of the depth profile can be repeated regularly whenever the depth changes.

[0048] In another embodiment, a first depth is initially specified, and during step c) the depth profile of the measured quantity is determined. From this depth profile, the ideal position for the hydrophones is then determined, and the temperature or salinity of this position is then specified as a depth-correlated environmental measurement. For this purpose, a sufficiently deep first depth is selected in the first step to ensure that the desired transition in the water is traversed and thus measured.

[0049] In a further embodiment of the invention, the watercraft has a first submersible body and a second submersible body, wherein a coordination for simultaneous depth changes between the first submersible body and the second submersible body takes place.

[0050] The watercraft according to the invention is explained in more detail below with reference to an embodiment shown in the drawings. Fig. 1 Watercraft with towed sonar and submerged body Fig. 2 Diving body Fig. 3 Submarine with towed sonar and diving body

[0051] In Fig. 1 A watercraft 10, for example a frigate, equipped with a towed sonar. The towed sonar has a tow cable section 30 and an antenna section 40. Additionally, the towed sonar has a first submersible body 20, which is located in Fig. 2 The first submersible body 20 is shown enlarged. The submersible body 20 is detachably connected to the antenna section 40 and the towing cable section 30. To roll up the towed sonar on a winch on the vessel 10, the first submersible body 20 is detached. The first submersible body 20 has a diving plane 50, a rudder 70, and a ballast tank 60. These components are controlled by the vessel 10 via a data line in the towing cable section 30, allowing the diving depth of the antenna section 40 to be precisely adjusted.

[0052] In Fig. 3 An example of a Type 12 submarine is shown. Unlike the one in Fig. 1 In the example shown, the first submersible body 20 is laterally coupled to the towed sonar. The submersible body 20 is deployed separately from the towed sonar via the weapon tube of the submarine 12 and only coupled underwater. Of course, coupling at the water's surface with a surfaced submarine 12 is also theoretically conceivable. Reference sign

[0053] 10 Watercraft 12 Submarine 20 First diving hull 30 Towing cable area 40 Antenna area 50 Diving plane 60 Ballast tank 70 Rudder

Claims

1. Watercraft (10) with a towed sonar, wherein the towed sonar has a tow cable section (30) and an antenna section (40), wherein the tow cable section (30) of the towed sonar is arranged between the watercraft (10) and the antenna section (40) of the towed sonar, wherein a first submerged body (20) is arranged in front of the antenna section (40) and, preferably, a second submersible body (20) is arranged behind the antenna section (40), wherein the first or the submersible body (20) submersible bodies (20) have at least one depth adjustment device, wherein the first submersible body (20) has at least one first environmental sensor for detecting an environmental measurement variable, characterized in that the first environmental sensor is selected from the group comprising a salinity sensor, a sound velocity sensor, a temperature sensor, a conductivity sensor, wherein the first submersible body (20) has at least one second environmental sensor, wherein the second environmental sensor is different from the first environmental sensor and wherein the second environmental sensor is selected from the group comprising a pressure sensor, salinity sensor, sound velocity sensor, temperature sensor, conductivity sensor, optical sensor, flow sensor, sonar.

2. Watercraft (10) according to claim 1, characterized in that the depth adjustment device is a depth rudder (50).

3. Watercraft (10) according to one of the preceding claims, characterized in that the first submersible body (20) additionally has a rudder (70).

4. Watercraft (10) according to one of the preceding claims, characterized in that the first submerged body (20) has a control device, wherein the control device is designed to read out the first environmental sensor and to control the depth adjustment device.

5. Watercraft (10) according to one of claims 1 to 3, characterized in that the watercraft has a control device, wherein the control device is designed to read out the first environmental sensor and to control the depth adjustment device.

6. Watercraft (10) according to one of the preceding claims, characterized in that the first diving body (20) can be reversibly detachably connected to the towed sonar.

7. Watercraft (10) according to claim 5, characterized in that the towed sonar runs through the first submerged body (20), wherein the first submerged body (20) is reversibly detachable when being wound up and reversibly connectable to the towed sonar when being wound down.

8. Watercraft (10) according to one of the preceding claims, characterized in that the tow cable section (30) has a data connection between the watercraft (10) and the first submersible body (20), wherein the first submersible body (20) can be controlled via the data connection.

9. Watercraft (10) according to one of the preceding claims, characterized in that the first submerged body (20) has an active sonar.

10. Method for operating a watercraft (10) according to one of the preceding claims, wherein the method comprises the following steps: a) deploying the towed sonar, b) specifying a depth-correlated environmental measurement variable, wherein a temperature or a salinity is specified so that the first submersible body (20) remains specifically below or above a stratification, c) controlling the depth resulting from the depth-correlated environmental measurement variable by the first submersible body (20) with the aid of the depth adjustment device, d) continuous measurement of a measured variable correlated with the depth-correlated environmental measured variable using the first environmental sensor, e) evaluating the measured variable and checking whether a depth adjustment must be performed and, if necessary, controlling the depth adjustment device.

11. Method according to claim 10, characterized in that during step c), the depth profile of the measured variable is determined.

12. Method according to one of claims 10 to 11, characterized in that the watercraft (10) has a first diving body (20) and a second diving body (20), wherein coordination for simultaneous depth change takes place between the first diving body (20) and the second diving body (20).

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