GB2071322A - Improvements in or relating to sonar apparatus - Google Patents

Abstract

A submersible vessel for sonar survey applications has a structure (5a, 6, 7, 8a, 9, 10) adapted to receive a towing cable (4). The structure carries sonar signal transmitter transducer means (11) and at least one acoustic reflector (2, 3) and receiver transducer means (5, 8). The transducer means (5, 8) are positioned to receive acoustic echo signals reflected in use from the acoustic reflector (2, 3) and originating from targets illuminated with acoustic energy by the transmitter transducer means (11). <IMAGE>

Description

SPECIFICATION Improvements in or relating to sonar apparatus This invention relates to sonar apparatus.

For many sonar applications it is desirable that sonar transducers should be positioned between the sea bed and a surface vessel carrying out a sonar survey. This is normally achieved by means of a sonar transducer transmitter/receiver array which is carried by an underwater vessel towed by the surface vessel carrying out the survey. Sonar transducers of this kind are usually described as towed arrays and comprise a number of transducer elements, signals from which are conveyed to the surface vessel via a towing cable.

A relatively large number of elements are normally used to form the array whereby beam forming utilising signal processing techniques is facilitated.

According to the present invention a submersible vessel for sonar survey applications comprises a structure adapted to receive a towing cable, and carried by the structure, sonar signal transmitter transducer means, at least one acoustic reflector and receiver transducer means positioned to receive acoustic echo signals reflected in use from the acoustic reflector and originating from targets illuminated with acoustic energy by the transmitter transducer means.

The acoustic reflector or reflectors are preferably curved whereby received acoustic echo signals are effectively focused onto the receiver transducer means.

In this way a beam forming effect is produced obviating the need for a complex signal processing apparatus receiving signals from a multi-element receiver transducer array.

The structure may be arranged to carry two receiver transducers each operatively associated with at least one acoustic reflector.

The structure may comprise an elongate body including two acoustic reflectors positioned on opposing elongate sides thereof, the two receiver transducers being spaced apart from the elongate body.

The receiver transducers may be supported by struts connected to the elongate body.

The transmitter transducer means may comprise two transducers arranged in use to radiate acoustic energy one being positioned on each side of the body.

The two acoustic reflectors may be part circular or curved parabolically, and they may be arranged to produce a line focus rather than a point focus.

Each of the two reflectors may have associated with it an intermediate reflector via which acoustic energy is reflected on to its associated receiver transducer.

The struts and/or the body may be faired or streamlined so as to minimise drag when the vessel is towed.

Some embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a generally perspective view of a submersible sonar survey vessel; Figure 2 is a part plan view of the vessel of Figure 1; Figure 3 is a part sectional view of the vessel shown in Figures 1 and 2, and Figure 4 is a part sectional view similar to Figure 3 but employing an intermediate reflector between main reflector and transducer.

Referring now to the drawings, wherein corresponding part of the various Figures bear the same numerical designations, the vessel comprises a faired body 1 constructed of an aluminium alloy or any other suitable material which is preferably non-corrosive and which facilitates acoustic signal reflection. The body 1 is shaped to define on each side thereof a pair of acoustic reflectors 2 and 3 and is adapted to receive a towing cable 4 which also accommodates electrical wires for carrying signals to or from transducers carried in or operatively associated with the body 1. The acoustic reflectors 2 and 3 are curved in one plane only as shown in the drawings to produce a line focus of received acoustic energy.The focal line of the mirror 2 is centred on a receiver transducer array 5 carried by a pair of struts 6 and 7 which are secured to the body 1 anci the focal line of the mirror 3 is arranged to be centred on a similar receiver transducer array 8 which is supported by struts 9 and 10 similarly connected to the body 1.

Two transmitting transducers 11 and 12 are provided, which are positioned to radiate energy one on each side of the body 1. In order to reduce drag when the vessel is towed, the struts 6, 7, 9 and 10 and the body 1 are streamlined and supporting pads 5a and 8a, on which the receiver transducers 5 and 8 respectively are mounted, are also streamlined as shown most clearly in Figure 3. Signals received by the transducers 5 and 8 may be transmitted, along wires concealed in the struts, to the towing cable 4 and drive signals for the transmitter transducers 11 and 12 may be similarly transmitted via the tow cable 4.

According to a preferred embodiment of the invention however, the front of the body includes space for buoyancy chambers and a watertight compartment 13 containing apparatus 14 for processing signals received by the receiver transducer arrays 5 and 6 and for providing signals for the transmitter transducers 11 and 12. Thus in this preferred embodiment, the cable may be arranged to carry a minimum number of signals and may therefore be reduced in size so as to minimise drag.

The transmitter transducers may comprise single transducers or a plurality of transducers in the form of an array and the receiver transducers preferably comprise a small transducer array comprising relatively few transducer elements in the form of a single line of spaced elements or a double line of staggered elements.

By utilising reflectors which produce a vertical line focus rather than a point focus it will be appreciated that the effects of roll produced during towing are minimised.

It will also be appreciated that signals originating from targets positioned at 900 to the towing direction are normally focused on the centre of the receiving transducer array, but it may be arranged, by transducer element switching, for signals to be received from transducers positioned on one side or the other of the centre line, whereby some degree of beam steering is facilitated, so that yaw of the towed vessel may be compensated for.

Each of the two reflectors may have associated with it an intermediate reflector via which acoustic energy is reflected onto its associated receiver transducer. Such an arrangement is shown in Figure 4, one side only of the arrangement being iilustrated. In this arrangement acoustic echo signals are reflected by the reflector 3 onto an intermediate reflector 1 5 which is carried by the supporting pad 8a. The intermediate reflector then focusses the received echo signals onto the transducer 8 which is positioned in the body above the reflector 3. In this way the length of the arm 10 can be reduced as the focussing path length is approximately twice the arms length. A further advantage of this arrangement is that all of the electrical connections are inside the body and there is no need to route leads along the arms 9 or 10.

Arrangements as just before described have the advantage that beam forming is produced in the water by acoustic reflection techniques rather than by complex signal processing and a system is thereby afforded which is relatively frequency independent.

Claims (14)

1. A submersible vessel for sonar survey applications, comprising a structure adapted to receive a towing cable, and carried by the structure, sonar signal transmitter transducer means, at least one acoustic reflector and receiver transducer means positioned to receive acoustic echo signals reflected in use from the acoustic reflector and originating from targets illuminated with acoustic energy by the transmitter transducer means.

2. A vessel as claimed in claim 1, wherein said at least one reflector is/are curved to effect focussing of acoustic echo signals onto the receiver transducer means.

3. A vessel as claimed in claim 2, wherein said at least one reflector is/are of part circular form.

4. A vessel as claimed in claim 2, wherein said at least one reflector is/are of parabolic form.

5. A vessel as claimed in claim 2, 3 or 4, wherein said at least one reflector is/are arranged to produce a line focus of received echo signals.

6. A vessel as claimed in any one of the preceding claims, wherein the receiver transducer means comprises an in line array of spaced transducer elements.

7. A vessel as claimed in claim 6, wherein the receiver transducer means comprises a double line of staggered transducer elements.

8. A vessel as claimed in any one of the preceding claims, wherein said transmitter transducer means comprises an array of transducer elements.

9. A vessel as claimed in any one of the preceding claims, comprising two receiver transducers mounted on said structure each of which transducers is operatively associated with at least one of said acoustic deflectors.

10. A vessel as claimed in claim 9, wherein each of the two reflectors has associated with it an intermediate reflector via which acoustic energy is reflected onto its associated receiver transducer.

11. A vessel as claimed in claim 9, wherein said structure comprises an elongate body including two acoustic reflectors positioned on opposing elongate sides thereof, the two receiver transducers being spaced apart from the elongate body.

12. A vessel as claimed in claim 11, including struts connected to said elongate body and arranged to support the receiver transducers.

13. A vessel as claimed in claim 11 or 12, wherein the transmitter transducer means comprises two transducers arranged in use to radiate acoustic energy one being positioned on each side of the body.

14. A vessel as claimed in any one of claims 11, 12 or 13, wherein a watertight compartment is provided in the body and processing apparatus is mounted in the compartment the processing apparatus being responsive to signals received by the receiver transducers.

1 5. A submersible vessel for sonar survey applications substantially as described herein with reference to, and as illustrated in, the drawings.