Underwater antenna for measuring underwater sound

Abstract

The invention relates to an underwater antenna (20) for measuring underwater sound (56) for seismic measurements, comprising the following features: - a three-dimensional array (24) of underwater transducers (26, 28), - wherein the underwater transducers (26, 28) of the array (24) of underwater transducers (26) are each designed to convert underwater sound (56) into a digitizable signal corresponding to the sound pressure; - wherein the underwater transducers are at a defined distance from one another; and - a securing element (30) which is designed to secure the underwater antenna (20) to the bottom of the body of water (22) so that the antenna is stationary during measurement.

Description

[0001] Underwater antenna for measuring underwater sound

[0002] Description

[0003] The invention relates to an underwater antenna for the stationary detection of underwater sound, particularly for seismic measurements, i.e., the analysis of the seabed, but also for the continuous, especially passive, detection of underwater sound to map the environment in the water above the seabed, for example, for monitoring critical infrastructure. "Stationary detection" refers to the fact that the underwater antenna, unlike, for example, a towed antenna or sonar mounted on a watercraft, is fixed in place during the measurements.

[0004] There are various types of seismic measurements, each currently requiring different measuring equipment. Examples include 2D, 3D, and 4D (change over time) surveying of large-scale geological structures, so-called Vertical Seismic Profiling (VSP), and the detection of objects in the subsurface, as well as, in principle, the monitoring of critical infrastructure. To date, each type of measurement requires its own measuring equipment and, in some cases, complex measurement procedures.

[0005] The object of the present invention is therefore to create an improved concept for underwater antennas for stationary detection of underwater sound.

[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 an underwater antenna for measuring underwater sound, particularly for conducting seismic measurements. The underwater antenna comprises a three-dimensional array of underwater sound transducers. A three-dimensional array of underwater sound transducers is characterized by a first set of underwater sound transducers arranged in a plane and a second set of underwater sound transducers arranged outside the plane. That is, the first set of underwater sound transducers can be called the first sub-array and the second set of underwater sound transducers can be called the second sub-array. In particular, the second sub-array is a line array or a plurality of line arrays.

[0008] Advantageously, the plane of operation of the underwater antenna is essentially parallel to the water surface. "Essentially" here refers to deviations due to positioning inaccuracies, for example up to 15°, as well as deviations due to wave action, etc. The antenna's orientation during measurement can be determined on the unmounted antenna, for example, by observing a mounting element used to secure it to the bottom of the water body.

[0009] Advantageously, the underwater transducers of the second set of transducers, i.e., one or more second sub-arrays, are arranged essentially (i.e., particularly with regard to positioning accuracy underwater) perpendicular to the first array of underwater transducers. This makes it possible to perform a spatially three-dimensional scanning of the wave. The perpendicular arrangement allows for the largest possible array aperture for a given edge length. In other words, the perpendicular arrangement of the underwater transducers enables efficient creation of a large array aperture. Furthermore, this allows scanning across a wide range of detection angles. Thus, more meaningful signal processing is achieved with an optimized aperture. In other words, this facilitates a simplified transition from a quantitative measurement (e.g., hard soil / soft soil) to a qualitative measurement, e.g., the exact...

[0010] Soil parameters. The underwater sound transducers are each designed to convert underwater sound into a digitizable signal corresponding to the sound pressure, i.e., in particular an electrical or optical signal.

[0011] An array of underwater transducers refers to a spatial arrangement of individual underwater transducers, preferably exhibiting an omnidirectional reception characteristic. The underwater transducers are preferably located at fixed, particularly predetermined, positions within the array. It is not necessary for the underwater transducers to be equidistant from adjacent transducers. However, the underwater transducers maintain a defined distance from each other; that is, the distance remains constant during measurements and for subsequent measurements.

[0012] Optionally, the underwater antenna includes a fixing element, ensuring that the orientation of the transducers in the first array remains constant relative to those in the second array. The fixing element allows the second array to be anchored to or within the bottom of the water body. Furthermore, the fixing element can be designed as a (essentially rigid) rod or plate, secured in such a way that water currents cause virtually no change in the position of the transducers in the second array. It is also possible for each transducer, individually or in groups, to be fixed in place by means of a fixing element. For example, multiple additional arrays of transducers, i.e., multiple transducers analogous to the first array, can be arranged in parallel.The structure that holds the first set of waterborne transducers in the first layer and the subsequent waterborne transducers (arranged analogously to the first set) in their position in the further layers can, in this case, be referred to as a fixing element. In this case, a mechanical connection between the individual fixing elements of the second array of waterborne transducers may not be necessary.

[0013] A mounting element for the underwater antenna is designed to secure the antenna to the bottom of the body of water during measurement. This mounting element can be anchored directly to or within the bottom of the body of water, or it can be connected to a mounting partner permanently attached to or within the bottom of the body of water. In the latter case, one possible embodiment allows the mounting element to be detached from the mounting partner and connected to another mounting partner at a different location. This means that the mounting partners can be installed at predetermined locations on or within the bottom of the body of water. The underwater antenna can then be placed on these mounting partners for stationary measurement.

[0014] The three-dimensional arrangement of the underwater transducers allows for the determination of the direction of incidence of underwater sound in both horizontal and vertical directions. This enables the same or even a better aperture of the underwater antenna to be achieved with a smaller horizontal extent compared to a two-dimensional array, and in the simplest case, a three-dimensional representation of the seabed can be obtained with just one measurement. The aperture refers to the opening angle of the underwater antenna.

[0015] This underwater antenna is now suitable for performing 2D, 3D, and 4D measurements, as well as vertical seismic profiling and the detection of subsurface objects. A 4D measurement refers to a temporal sequence of 3D measurements. Currently, 3D measurements utilize multiple towed antennas, essentially in parallel (towed by a vessel), which receive the reflection of underwater sound waves emitted by one or more underwater transducers (i.e., underwater sound transmitters) and reflected off the seabed. However, for 4D measurements, the measurements must be performed with high repeatability at different times. The positioning of the underwater sound transmitters can be achieved by placing them directly on, or at least very close to, a vessel.However, towed antennas are located far from the towing vessel and, for example, cannot be precisely positioned for two measurements at different times due to the current. With underwater antennas, or even with multiple underwater antennas positioned within a search area, the underwater acoustic receivers are positioned at precisely the same location. This works for acoustic measurements in hydrocarbon exploration (e.g., for oil) that operate at very low frequencies around 20 Hz. For higher frequencies above 500 Hz or 750 Hz, particularly above 1 kHz, preferably above 2 kHz, and more preferably above 3 kHz up to, for example, 4.5 kHz, which are used, for example, for acoustic measurements of sediments, such as measuring rock layers located closer to the surface than hydrocarbon deposits, 4D measurement achieves previously unattainable levels of accuracy.

[0016] In coil shooting, a watercraft equipped with one or more underwater sound transducers and a towed underwater sound receiver essentially travels in concentric circles (particularly for navigation accuracy and during transitions between circles). This allows for a 360° mapping of the seabed. However, stones, also known as boulders, are too small to reflect the incident sound waves. Instead, ambiguities arise due to the scattering of the sound waves. Using the underwater antenna, these ambiguities can be resolved by the three-dimensional arrangement of the arrays of underwater sound transducers, the different viewing angles to the stone, and the stationary positioning during the measurement (i.e., while the circles are being traveled with the underwater sound transducer(s)). This allows the stone to be detected as such.

[0017] The classic Vertical Seismic Profiling (VSP) method utilizes boreholes drilled to great depths of over 500 meters. Transducers are inserted into the borehole and used to record sound waves generated above the borehole. The recorded signals result in a higher vertical resolution of the subsurface layers due to their highly vertical sound propagation path, which minimizes attenuation and signal conversion. However, this method is not applicable at depths below 200 meters because the borehole wall is not sufficiently stable and is prone to immediate collapse. Therefore, the underwater antenna with its three-dimensional array of underwater transducers in the water column represents an unprecedented capability for recording such high-resolution signals.

[0018] In exemplary embodiments, the underwater antenna comprises a frame, also referred to as a structure, on which the underwater transducers of the array and the mounting element are arranged. That is, the underwater transducers are preferably attached directly to the frame. For example, the underwater transducers of the first array can be mounted on or within struts of the frame. Mounting within the struts is possible, for instance, if the struts are designed as hollow struts. Furthermore, it is advantageous, particularly when the underwater transducers are arranged within the struts, that the struts have a similar refractive index to the surrounding water. Glass fiber reinforced plastics (GFRP) are suitable for this purpose. Electrical connections to the underwater transducers can also run along or within the struts of the frame.For example, it is possible to brace a multitude of linear underwater antennas, each of which could also be used as a towed antenna, along or between the struts of the frame to form the first set of underwater transducers in the plane. A linear antenna typically comprises a multitude of underwater transducers arranged linearly during operation, for example, in a tube. Preferably, the underwater transducers have an omnidirectional receiving characteristic. In other words, the frame forms the basic mechanical structure of the underwater antenna.

[0019] In some embodiments, a float is attached to the frame in such a way that it floats on the water's surface. That is, the float is attached to the frame by means of a tensioning device, for example, a rope, a strap, or a telescopic pole. The float can serve various purposes.

[0020] For example, in some embodiments, the float can have a buoyancy greater than the downward buoyancy of the entire underwater antenna. This makes it possible to move the underwater antenna to its destination by floating. That is, the underwater antenna can be towed, for example, by a ship. Advantageously, the float is attached to the frame by means of a winch. A traction element, in particular a rope or strap, can be wound onto the winch before the underwater antenna is moved. Likewise, the traction element can be unwound by the winch to secure the underwater antenna to the seabed using the mounting element. Thus, the underwater antenna can be lifted from and lowered onto the seabed using the winch. In some embodiments, the underwater antenna has a communication interface through which electrical signals are transmitted to a base station.The communication interface can be, for example, an antenna. Advantageously, the communication interface is positioned so that it remains permanently above the water's surface. Preferably, the communication interface is located on the float. This ensures that the electrical signals, or more generally, the collected information, can be transmitted to the base station. A communication adapter, such as a cellular or satellite communication adapter, can convert the electrical signals into a transmittable format, i.e., in particular, embed them in a transmission protocol. Using the communication interface, it is possible to send the electrical signals as raw data, i.e., without prior data processing to gain information, to the base station and evaluate them there.Data processing for transmitting the raw data, for example for (lossless) compression of the data, i.e., the electrical signals, is still possible. Usually, the evaluation of the data is not time-critical, so the data can first be collected in the base station and processed there, often using various data processing methods to gain insights.

[0021] In further embodiments, the waterborne transducers of the first set of waterborne transducers form a ring array, which is formed from a plurality of linearly arranged waterborne transducers forming a polygon. That is, a plurality of linear antennas can be arranged in a polygon to form the first sub-array of waterborne transducers. The term "ring array" refers to a closed, but not necessarily circular, shape of the array of waterborne transducers. The edges of the polygon can each contain a plurality of waterborne transducers.

[0022] The second set of water-based transducers, i.e., the second sub-array, is in exemplary embodiments a linear array formed from a plurality of linearly arranged water-based transducers. The linear array can preferably be arranged perpendicular to the plane in which the water-based transducers of the first set of water-based transducers are arranged. In particular, the water-based transducers of the second set can comprise a plurality of parallel linear arrays. That is, the linear arrays of the second array of water-based transducers can be arranged at various points of the first array of water-based transducers perpendicular to it. For example, the linear arrays can be arranged at at least two, preferably at least three, more preferably at least four, and again more preferably at least five or more vertices or other points of the polygon.

[0023] In exemplary embodiments, the frame spans a further (second) plane parallel to the plane in which the waterborne sound transducers of the first set of waterborne sound transducers are arranged, to which the fixing element fixes at least some, in particular at least one-third, preferably at least half of the waterborne sound transducers of the second set of waterborne sound transducers. Thus, the waterborne sound can be detected in different planes.

[0024] In further embodiments, one or more additional layers of waterborne transducers are arranged parallel to the layer of waterborne transducers. This can also be referred to as a layer stack of waterborne transducers. If the stack of layers consists of at least three layers, a second set of waterborne transducers can be formed from these stacked layers.

[0025] Furthermore, a system with an underwater antenna is disclosed. The system further comprises a watercraft with an underwater sound transmitter configured to emit underwater sound, which is received by the underwater sound transducers of the underwater antenna. Thus, the aforementioned methods of coil shooting, VSP, and 4D measurement can be performed. For receiving underwater sound, the underwater antenna is fixed in position. This means, in particular, that the watercraft and the underwater antenna are not connected to each other during the measurement. Preferred embodiments of the present invention are explained below with reference to the accompanying drawings. These show:

[0026] Fig. 1 : a schematic representation of an underwater antenna, wherein Fig. 1a is a schematic perspective view and Fig. 1b is a schematic top view of the underwater antenna;

[0027] Fig. 2: Figs. 2a, 2b and 2c show different embodiments of the underwater antenna as depicted in Fig. 1a;

[0028] Fig. 3: a schematic representation of a system with an underwater antenna and a watercraft with an underwater sound transmitter.

[0029] 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.

[0030] Fig. 1 shows a schematic representation of an underwater antenna 20 for measuring underwater sound. Fig. 1a shows the underwater antenna 20 in a schematic perspective view and Fig. 1b in a schematic top view of the underwater antenna 20.

[0031] The underwater antenna 20 comprises a three-dimensional array 24 of underwater sound transducers 26, 28 and a mounting element 30. A first set of underwater sound transducers 26 forms a first sub-array and is arranged in a plane. During the measurement, the plane is oriented essentially parallel to a water surface (see reference numeral 37 in Fig. 2c and Fig. 3). The underwater sound transducers 26 can each convert underwater sound into a digitizable signal corresponding to the sound pressure. The digitizable signal can be an (analog) electrical signal or an optical signal. Fig. 1 shows an exemplary arrangement of the underwater sound transducers 26 along the legs of a hexagon. That is, the underwater sound transducers 26 form a polygon. The underwater sound transducers are also shown along the legs, purely by way of example, where typically a larger number of underwater sound transducers can be used per leg.However, in the following illustrations, the depiction of the individual water transducers 26 is omitted for the sake of clarity.

[0032] The second set of underwater sound transducers 28 is aligned in a third dimension with respect to the plane in which the underwater sound transducers of the first set of underwater sound transducers 26 are located. The underwater sound transducers 26, 28 are spaced a defined distance apart from each other, i.e., they are fixed in position, at least during the measurement(s). This can be achieved, for example, by means of a fixing element 32. In Fig. 1a, the fixing element 32 is anchored to or in the bottom 23 of the body of water by way of example; however, there are other options for arranging the underwater sound transducers at a defined distance. That is, in the case shown in Fig. 1a, the orientation of the underwater sound transducer of the second set of underwater sound transducers 28 is perpendicular to the plane in which the underwater sound transducers 26 of the first set of underwater sound transducers are arranged. Any external forces, such as the current in the body of water, are also unable to significantly change the orientation relative to each other.The second set of water transducers 28 is shown as an example linear array.

[0033] The underwater antenna can be fixed in a stationary position on the bottom of the body of water 22 during the measurement by means of the fastening element 30.

[0034] For example, the mechanical structure of the underwater antenna 20 can be constructed using a frame 34. The struts of the frame 34 can mechanically connect the underwater transducers 26, 28 and the mounting element 30. In particular, the underwater transducers 26 of the first set of underwater transducers can run in or along the struts of the frame 34. In Fig. 1, the frame 34 forms the edges of a funnel with a hexagonal opening. Advantageously, however, the funnel has no outer surface. Fig. 2 schematically shows three different embodiments of the underwater antenna 20 as depicted in Fig. 1a. However, only the differences from the embodiment in Fig. 1a will be discussed here.

[0035] The embodiment according to Fig. 2a shows the frame 34 with a second level 34'. The waterborne transducers 26 of the second set of waterborne transducers are not located in the base, but are attached to the second level 34' of the frame 34 by means of the fixing element 32. In addition to or as an alternative to the second level 34' of the frame 34, the embodiment according to Fig. 2a discloses the arrangement of (two) further linear arrays 28', 28", which are optionally arranged at the corners of the polygon. Optionally, further waterborne transducers can also be arranged along the second level 34' of the frame. These waterborne transducers in the second level can be considered part of the second set of waterborne transducers. For example, a further (third) sub-array of waterborne transducers can be formed parallel to the first sub-array of waterborne transducers.

[0036] The embodiment according to Fig. 2b reveals a plurality of further levels 34', 34", 34'" of the framework 34. The three points 34a indicate that the levels are distributed, in particular equidistantly, over the entire height of the underwater antenna 20. In this embodiment, the second sub-array, as well as further sub-arrays of the underwater transducers 28 of the second set of underwater transducers, are formed from underwater transducers arranged one above the other, i.e., perpendicular to the plane in which the underwater transducers 26 of the first set of underwater transducers are arranged. In principle, the number of sub-arrays, i.e., the linear antennas formed from the second set of underwater transducers, corresponds to the number of underwater transducers per level 34.

[0037] A multi-level embodiment, for example from Fig. 2a or Fig. 2b, enables higher sampling densities due to the larger number of underwater transducers, resulting in higher resolution and a better signal-to-noise ratio. Positioning and statistics are also improved, and a larger number of transducers allows for the detection of steeper sound paths and 3-dimensional sound detection without a trailing configuration.

[0038] The embodiment shown in Fig. 2c discloses a float 36 attached to the mounting element 30. The attachment can be effected by means of a traction element 38. The float 36 floats on the surface of a body of water 37. Preferably, the float 36 has a buoyancy greater than the downward buoyancy of the entire underwater antenna 20. Optionally, the float 36 is attached to the mounting element by means of a winch 40, the winch 40 being configured to wind up the traction element 38 before the underwater antenna 20 changes position and to unwind the traction element 38 in order to secure the underwater antenna 20 to the bottom of the body of water by means of the mounting element 30. The arrow 41 indicates the directions of movement of the underwater part of the underwater antenna. The attachment to the bottom of the body of water can be effected directly or by means of a mounting partner 42 permanently attached to or in the bottom of the body of water.

[0039] Fastening element 30 and fastening partner 42 can form a detachable connection to easily allow the underwater antenna 20 to be relocated.

[0040] In addition to or as an alternative to the winch, a communication interface 44 can be arranged on the float 36 to send the electrical signals to a base station.

[0041] Fig. 3 shows a schematic representation of a system 50 with the underwater antenna 20 and a watercraft 52 with an underwater sound transmitter 54. The underwater sound transmitter 54 can emit underwater sound 56, the reflections 56', 56" of which are received by the underwater antenna 20.

[0042] The disclosed (water) sound transducers are designed for underwater use, particularly in the sea. The transducers can convert underwater sound into a digitizable 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 as underwater sound transmitters. Advantageously, the transducers can comprise a pressure-sensitive material, in particular a piezoelectric material, for example, a piezoceramic.

[0043] In addition to piezoelectric materials, other transducers can also be used, for example, transducers with a PVDF (polyvinylidene fluoride) membrane or optical transducers. These transducers are preferably not suitable for, or are not used in, medical applications.

[0044] 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.

[0045] 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:

[0046] 20 underwater antennas

[0047] 22 bottom of water

[0048] 24 three-dimensional array

[0049] 26 first set of water transducers / first sub-array

[0050] 28 second set of water transducers / second and optionally further sub-

[0051] Arrays

[0052] 30 Fastening element

[0053] 32 fixing element

[0054] 34 scaffolding

[0055] 36 swimmers

[0056] 37 Water surface

[0057] 38 traction elements

[0058] 40 winches

[0059] 41 Movement arrow

[0060] 42 fastening partners

[0061] 44 Communication interface

[0062] 50 System

[0063] 52 Watercraft

[0064] 54 underwater sound transmitters

[0065] 56 Water sound

Claims

1. Patent claims 1. Underwater antenna (20) for measuring underwater sound (56) for seismic measurements with the following features: - a three-dimensional array (24) of water transducers (26, 28); - wherein the water sound transducers (26, 28) of the array (24) are each configured to convert water sound (56) into a digitizable signal corresponding to the sound pressure; - wherein the water transducers are spaced a defined distance apart; and - a fastening element (30) designed to fix the underwater antenna (20) stationary on the bottom of the water (22) during the measurement.

2. Underwater antenna (20) according to one of the preceding claims, wherein the underwater antenna (20) comprises a first set of underwater sound transducers (26) arranged in a plane and wherein the underwater antenna comprises a second set of underwater sound transducers (28) arranged outside the plane, in particular perpendicular to the plane.

3. Underwater antenna (20) according to claim 2, wherein the plane is arranged substantially parallel to a water surface (37).

4. Underwater antenna (20) according to one of claims 2 or 3, wherein the underwater transducers (26) of the first set of underwater transducers form a ring array formed from a plurality of linearly arranged underwater transducers (26) forming a polygon.

5. Underwater antenna (20) according to one of claims 2 to 4, wherein the underwater transducers (28) of the second set of underwater transducers form a linear array or a plurality of parallel linear arrays, wherein a linear array is formed from a plurality of linearly arranged underwater transducers (26).

6. Underwater antenna (20) according to claim 4 or 5 in its reference to claim 4, wherein the linear arrays are arranged at at least two points, in particular corners, of the polygon.

7. Underwater antenna (20) according to one of the preceding claims, wherein the underwater antenna comprises a frame (34) on which the underwater transducers (26, 28) of the array of underwater transducers and the fastening element (30) are arranged.

8. Underwater antenna (20) according to claim 7, wherein a float (36) is attached to the frame (34) and / or the fastening element (30) such that the float (36) floats on the surface of the water (37).

9. Underwater antenna (20) according to claim 8, wherein the float (36) has a buoyancy that is greater than the downward force of the entire underwater antenna.

10. Underwater antenna (20) according to claim 9, wherein the float (36) is attached to the frame (34) and / or the fastening element (30) by means of a winch (40), wherein the winch (40) is configured to wind up a traction element (38) before the underwater antenna changes location and to unwind the traction element (38) in order to secure the underwater antenna to the bottom of the water (22) by means of the fastening element.

11. Underwater antenna (20) according to one of the preceding claims, wherein the underwater antenna has a communication interface (44) configured to send the electrical signals to a base station.

12. Underwater antenna (20) according to claim 11 as referring back to any one of claims 8 to 10, wherein the communication interface (44) is arranged on the float (36).

13. Underwater antenna (20) according to one of the preceding claims, wherein the fastening element (30) is designed to be connected to a fastening partner (42) permanently attached to or in the bottom of the water.

14. Underwater antenna (20) according to claim 13, wherein the fastening element (30) is designed to be detached from the fastening partner (42) in order to be connected to another fastening partner (42) at another location.

15. Underwater antenna (20) according to one of the preceding claims, wherein the underwater antenna has a fixing element (32) to keep the orientation of the underwater transducers (26, 28) in the array of underwater transducers constant.

16. Underwater antenna (20) according to claim 7 and claim 15, wherein the frame (34) spans a further plane (34') parallel to the plane, on which the fixing element (32) fixes at least some of the underwater transducers (28) of the second set of underwater transducers.

17. Underwater antenna (20) according to one of the preceding claims, wherein one or more further planes (34', 34“, 34'“) of underwater transducers (26) are arranged parallel to the plane of underwater transducers (26).

18. System (50) with the following features: - an underwater antenna (20) according to one of the preceding claims; - a watercraft (52) with a water sound transmitter (54) designed to emit water sound (56) which is received by the water sound transducers (26) of the underwater antenna.

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