Patent ID: 12248112

DESCRIPTION OF EMBODIMENTS

Terminology used for describing particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that the terms “comprises” and/or “comprising” specify the presence of stated features but do not preclude the presence or addition of one or more other features. It will be further understood that when a particular step of a method is referred to as subsequent to another step, it can directly follow said other step or one or more intermediate steps may be carried out before carrying out the particular step, unless specified otherwise. Likewise it will be understood that when a connection between structures or components is described, this connection may be established directly or through intermediate structures or components unless specified otherwise.

The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown.

In the drawings, the absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments may be described with reference to schematic and/or cross-section illustrations of possibly idealized embodiments and intermediate structures of the invention. In the description and drawings, like numbers refer to like elements throughout. Relative terms as well as derivatives thereof should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the system be constructed or operated in a particular orientation unless stated otherwise.

FIG.1illustrates a top view of a preferred embodiment for a marine survey system100for mapping a marine bottom below a body of water “W”.

In a preferred embodiment, the system100is suitable for ultrahigh resolution UHR mapping of the marine bottom and sub-bottom. Thereto, the system100preferably comprises a frame20to be towed as a whole by one or more towing cables12at some distance “Xf” behind a marine vessel10as shown inFIG.1. Typically the vessel10moves over or through the water “W” in a movement direction at a steady velocity “V”, e.g. along a predetermined trajectory or sail line.

The system100preferably comprises a plurality of acoustic receivers31for registering the acoustic waves reflected from the marine bottom and sub-bottom. Typically, the acoustic receivers31comprise transducers, e.g. hydrophones, configured to register the particulars such as timing and amplitude of the acoustic wave in the water and convert these into electrical signals for analysis. For example, a time between the emission and receipt of an acoustic wave can be used to determine a distance to a reflecting structure at the marine bottom “B”, or there below e.g. within the sediment.

In a preferred embodiment, e.g. as shown with continued reference toFIG.1, the system100comprises a plurality of so-called streamers30. A streamer30typically comprises a number of acoustic receivers31towed in a line behind the vessel10. As shown the acoustic receivers31are thus linearly arranged in the movement direction “V” of the vessel10. For example, the system comprises at least two streamers30, preferably at least four streamers30, or more. Streamers may also comprise other features such as buoys14,15and/or respective drogues16at the end of each streamer. Preferably, the drogues16are kept at different distances along the movement coordinate “X” to further prevent tangling.

Preferably the acoustic receivers31are arranged at a relatively low receiver-to-receiver distance “Xr” for distinguishing the bottom regions with an ultrahigh resolution Rx also in a tangential direction X parallel to the movement direction “V” of the vessel10. For example, the receiver-to-receiver distance “Xr” is less than four meter, preferably less than three meter, more preferably two meters, or less, e.g. two meter, to map the marine bottom and sub-bottom with an ultrahigh resolution Rx of one meter, or, e.g. one meter, to map the marine bottom and sub-bottom with an ultrahigh resolution Rx of half a meter, in the movement direction “V”.

Typically, each acoustic receiver31is configured for individual readout of acoustic signal registered by the respective acoustic receiver31. Furthermore each streamer30may comprises more than ten, more than twenty, or even more than forty separately acoustic receivers31. In a preferred embodiment, as shown inFIG.1, at least two streamers30are attached to the frame20. For example, the two streamers are attached at outer ends of the frame in the transverse direction “Y”. In such embodiments it is furthermore preferred that the plurality of independent acoustic sources21are all arranged in the transverse direction “Y” between the two adjacent streamers30attached to the frame20.

As also illustrated inFIG.1, it is preferred in some embodiments that at least two inner streamers30are attached to the frame20and at least two outer streamers are towed directly by the vessel10without attachment to the frame20. For example, the outer streamers30are towed by spreader bars extending outward from each side of the vessel10to improve the covered area for surveying.

Typically, the system100comprises a controller50. For example, the controller50is configured (i.e. arranged and/or programmed) to perform the operational acts in accordance with the marine survey as described herein. The controller50may be placed on board the vessel10in some embodiments as illustrated inFIG.1. In some embodiments, the controller50is configured to control the acoustic sources21to emit the respective acoustic waves “A”. In other or further embodiments, the controller50is configured to receive and/or process signals from the acoustic receivers31.

FIGS.2A-2Cillustrate various views of an embodiment of a frame20with acoustic sources.

In a preferred embodiment, the frame20comprises a rigid framework23and a plurality of independent acoustic sources21. For example, the rigid framework23preferably comprises a truss structure as shown inFIGS.2A-2C. The acoustic sources21are kept fixated by the rigid framework23at a source-to-source distance “Ys” in a transverse direction “Y” perpendicular to the movement direction “V” of the vessel10for distinguishing the bottom regions with a corresponding resolution Ry. As shown, the acoustic sources21are preferably linearly arranged in the transverse direction “Y” parallel to the water surface Sw.

As shown e.g. inFIG.2A, a transverse distance “Ysr” between a respective streamer30attached to the frame (20) and nearest acoustic source21is preferably half the source-to-source distance “Ys”. Accordingly, the streamer-to-streamer distance “Yr” in the transverse direction “Y” is a little more than a total width spanned by the plurality of acoustic sources21. Typically the streamer-to-streamer distance “Yr” can be equal to the number of acoustic sources21times the respective source-to-source distance “Ys” there between. For example, for a frame20with four acoustic sources21placed at a source-to-source distance “Ys” of two meters, the streamer-to-streamer distance “Yr” can be eight meters. Generally, N sources together span a width of (N−1)*Ys to which is added two times half the distance Ys at each end of the spanned length for attaching the streamers.

With continued reference toFIGS.2A-2C, the frame20may comprise one or more floatation devices22. Preferably the frame20is kept at least partially afloat with the acoustic sources21at a fixed source depth Zs below a surface Sw of the water “W” as shown particularly inFIG.2B. Preferably, the source depth Zs is adjustable e.g. by adjusting a relative depth of the acoustic sources21with respect to the one or more floatation devices22.

Preferably, the system100comprises one or more positioning units24, e.g. operating on the basis of a Global Position System GPS, preferably differential GPS, e.g. Real Time Kinematic RTK. For example, as shown inFIG.2C, at least one, preferably two, positioning unit24are attached to the frame20with a known relative position or positions with respect to the acoustic sources21. Advantageously, two positioning unit24can be attached at spaced apart locations on the frame20to determine the position of more than two, e.g. four acoustic sources21, in some embodiments.

With continued reference toFIG.2C, preferably the frame20comprises a wireless transmitter and/or receiver25configured to transmit data between the frame20and the vessel10. In some embodiments, control data can be sent wirelessly from a controller50on the vessel10to a transceiver25on the frame20to control the acoustic sources21.

Alternatively, or in addition, the sources may also be under (partial or full) control of a local control unit (not shown) on the frame20itself. In some embodiments, measurement data can be sent wirelessly from a transceiver25on the frame20to a controller50and/or other processing unit on the vessel10to receive and/or process the measurement data. For example, the measurement data may include acoustic signals recorded by the acoustic receivers31, positioning information from the one or more positioning units24, depth information of the sources and/or receivers, et cetera.

Alternatively, or in addition to wireless connections there can also be wired connections between the vessel10and frame20. In particular, electrical energy supply can be provided from a generator or battery on the vessel10to the equipment on the frame20and/or streamers30. Using wireless data transfer instead of wired data transfer can be advantageous to prevent interference especially from high voltage electrical wiring which is typically used to supply the acoustic sources21, .e.g. sparkers.

FIG.3illustrates the propagation of acoustic waves “A” via the marine bottom “B” between the acoustic sources21and acoustic receivers31in some embodiments.

Each acoustic source21is preferably independently controllable to emit a separate acoustic wave “A”. Each of the acoustic waves A may thus propagates along its own (unique) path through the water “W” to reflects off respective bottom regions at (or inside) the marine bottom “B” for the mapping thereof. Typically, the resolution Ry in the transverse direction “Y” is half the source-to-source distance “Ys” in transverse direction “Y”. This can be understood e.g. fromFIG.3which shows that the half way points of shortest reflected paths between the respective sources and receivers are spaced apart by half the distance between the sources.

To attain desired high resolution, the source-to-source distance “Ys” is preferably less than four meter, more preferably less than three meter, most preferably two meters, or less, to map the marine bottom with a transverse resolution Ry of one meter, or less. On the other hand the source-to-source distance “Ys” is typically at more than half a meter, preferably more than one meter e.g. to keep the acoustic waves “A” and/or originating sources21apart.

In some embodiments, each acoustic source21comprises a respective array of acoustic transducers. In such embodiments, the acoustic transducers of the respective array are configured to fire in unison to collectively emit the separately detectable respective acoustic wave “A”, as described herein. For example, each acoustic source21comprises at least three, typically many more, acoustic transducers. Typically, the transducers making up such an acoustic source21are relatively close together to determine an spatial extent of the acoustic source21. For example, the array of transducers in a respective acoustic source21are arranged within half a meter, within thirty centimeters, or less, from each other, so that they can collectively fire the acoustic wave by constructive and destructive interference of their respective waves. For example, the extent of each acoustic source21is less than half, preferably less than a quarter of the distance between the acoustic sources21. In some embodiments, the acoustic transducers comprise so-called sparkers which use a high electric potential to cause a discharge in to the water creating a short-lived plasma causing pressure waves, i.e. acoustic signals. Of course also other acoustic sources/transducers can be used such as air guns.

In a preferred embodiment, the acoustic waves of the independent acoustic sources21are fired sequentially with a time interval there between. A minimum interval between subsequent acoustic waves may be determined e.g. by a depth Zb of the marine bottom “B” or depth of structures to be detected there below. For example, for a depth of 50 m and a sound velocity in water of 1500 m/s, the sound wave may take at least 2*50/1500=0.07 seconds to reflect straight from the bottom and longer if the reflection comes from below the bottom or at an angle. On the other hand, a maximum interval between subsequent acoustic waves may be determined e.g. by a movement velocity of the vessel10, number of independent acoustic sources21, and the distance between acoustic receivers31.

Preferably, each of the acoustic sources has an opportunity to emit its acoustic wave within the time interval that it takes the vessel to move the distance “Xr” between the acoustic receivers. For example for a system with a receiver-to-receiver distance of 1 m and a towing velocity of 2 m/s, it takes half a second for each source to move the distance to the previous position of the adjacent source. So for example in a system with four independent acoustic sources firing within half a second, the interval between acoustic waves is 0.5/4=0.125 seconds, or less. So for marine survey of relatively shallow water of fifty meters or less, and a moderate velocity of two meters per second, the interval between subsequent acoustic waves can be chosen e.g. at about a tenth of a second, or at least in a range between 0.01 and 1 second.

This may also means that the (collective) acoustic waves “A” themselves may be shorter than one tenth of a second, preferably much shorter, e.g. less than ten millisecond, less than one millisecond, or less. Accordingly, for an acoustic source comprising an array of transducers, the transducers should typically all fire in unison within that time period to generate the collective wave. The duration or wavelength of the acoustic wave “A” may also be related to the resolution which can be attained, with shorter waves typically allowing better resolution.

In some aspects, a marine vessel10or equipment on board such vessel may form part of the marine survey system100as described herein. In a preferred embodiment, one or more towing cables12are attached to the frame20for towing the frame20at a distance “Xf” behind the vessel10, wherein the distance “Xf” between the frame20and the vessel10is set to avoid a region of turbulence Tin the water T caused by the vessel10. For example, the distance “Xf” is more than ten meters, more than twenty meters, more than fifty meters, more than more than hundred meters, or more. Preferably at least two towing cables12are attached between the frame20and the vessel10at spaced apart locations on the frame for preventing rotational movement of the frame20being towed through the water “W”. Aspects as described herein may also be embodied as a marine survey method for ultrahigh resolution UHR mapping of a marine bottom “B” below a body of water “W” by means of a frame20towed as a whole by one or more towing cables12at a distance “Xf” behind a marine vessel10. Some aspects can also be embodied as a machine readable medium storing software instructions that, when executed e.g. by a controller50of a marine survey system100, cause the execution of the marine survey methods as described herein.

For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

Of course, it is to be appreciated that any one of the above embodiments or processes may be combined with one or more other embodiments or processes to provide even further improvements in finding and matching designs and advantages. In interpreting the appended claims, it should be understood that the word “comprising” does not exclude the presence of other elements or acts than those listed in a given claim; the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements; any reference signs in the claims do not limit their scope; several “means” may be represented by the same or different item(s) or implemented structure or function; any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise. Where one claim refers to another claim, this may indicate synergetic advantage achieved by the combination of their respective features. But the mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot also be used to advantage. The present embodiments may thus include all working combinations of the claims wherein each claim can in principle refer to any preceding claim unless clearly excluded by context.