Communications – electrical: acoustic wave systems and devices – Echo systems – Speed determination
Patent
1996-02-28
1997-12-02
Lobo, Ian J.
Communications, electrical: acoustic wave systems and devices
Echo systems
Speed determination
367 90, 367153, 7317013, G01S 1560
Patent
active
056943725
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to sonar systems which make it possible either to measure the currents within the water, thus forming a current meter, or to measure the speed with respect to the sea bed of the boat on which such a sonar is mounted, thus producing a Doppler log.
2. Discussion of the Background
These known apparatuses are very much alike and both operate by measuring the Doppler effect on the acoustic waves backscattered either by the sea bed or by the water strata. Any differences between the two apparatuses lie in regard to the electronics for processing the signal received and possibly in regard to the frequencies used.
These apparatuses are usually designed according to the so-called Janus configuration represented diagrammatically in FIG. 1, in which the acoustic antenna fixed under the hull of a boat 101 is used to emit 4 acoustic beams 102 to 105. The two beams 102 and 103 are inclined with respect to the vertical by an angle .alpha. respectively fore and aft of the boat in a vertical plane parallel to the axis of this boat. This makes it possible to obtain the longitudinal speed of the boat with respect to the sea bed, or the speed of the marine currents over the depth of water between the surface and the sea bed. The other two beams 104 and 105 are themselves inclined by an angle .alpha. but to port and to starboard of the boat in a vertical plane perpendicular to the axis of the boat and hence to the previous plane. The lateral speed of the boat or of the marine currents is thus obtained. Combining these two speeds therefore gives the true speed together with the drift angle.
SUMMARY OF THE INVENTION
The main drawback of this device is that, to form these beams, a set of plane transducers oriented in the requisite direction is generally used for each beam, that is to say in total one antenna formed by 4 sectors substantially forming the 4 faces of a relatively flat pyramid. This antenna is therefore of relatively large size, this generally requiring a fairly big hole to be made in the hull in order to fix a thick liquid-filled housing containing the antenna. This housing communicates with the exterior via an acoustic window. This device is a potential source of leaks.
To obviate these drawbacks, the invention proposes a sonar system for current meter and Doppler log, which comprises a set of transducers situated on a plane base intended to be fixed horizontally on the bottom of the hull of a carrier boat, and means for feeding these transducers with signals exhibiting a first and second successive distinct frequencies and phases making it possible to obtain in at least a first plane perpendicular to the plane of the base, a first emission lobe at the first frequency forming an angle .alpha. with the perpendicular to the plane of this base and a second emission lobe at the second frequency forming an angle -.alpha. with this perpendicular, and means of summation of the signals received by the transducers in order to obtain two reception signals in the emission plane separated by their frequencies, principally characterized in that the transducers are aligned in rows spaced apart by a distance d and grouped in twos with a feed polarity inverted from one group to the next, and that the feed means make it possible to deliver, for each frequency, signals A and B which are 90.degree. out of phase, these signals being delivered to the transducers in a first sequence A, B, A, B . . . with the first frequency and in a second sequence A', -B', A', -B'. . . with the second frequency; these two sequences determining the two emission lobes.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the invention will emerge clearly in the following description given by way of non-limiting example with regard to the appended figures which represent:
FIG. 1 a perspective view of a boat fitted with a four-beam sounder;
FIG. 2 a plan view of an antenna according to the invention in a one-dimensional mode;
FIG. 3 a feed scheme for th
REFERENCES:
patent: 3618006 (1971-11-01), Wright
patent: 3924259 (1975-12-01), Butler et al.
patent: 4104912 (1978-08-01), Clavelloux et al.
patent: 4138657 (1979-02-01), Shave
patent: 4270191 (1981-05-01), Peynaud
"Thomson-CSF"
Lobo Ian J.
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