Abstract: Systems are described which make it possible to carry out a 3D seismic survey from the surface of the sea. The systems include individual standalone assemblies each including an electrically propelled fish which tows each seismic streamer the other end of which is positioned by a tail fish. These assemblies are connected, electrically and mechanically, via an electro-towing cable to the streamlined cables for towing the diverging paravanes.

Abstract: A system for underwater seismic prospecting or exploration on seafloors, especially deep seafloors, including streamers designed to contain the measurement devices and to lie on the seafloor, in the form of an inner tube that is non-stretching and non-compressible and an outer tube that is extensible to a certain extent. Through the injection of liquid between these two tubes, the buoyancy of each streamers is made positive. This enables it to be detached from the seafloor and towed to the next measuring position.

Abstract: A device for transmitting acoustically toward the bottom of the sea includes an arrangement of a cable 404 containing vertically suspended electro-acoustic transducers 403 wherein each of said transducers are assigned to a frequency of the pulse spectrum to be emitted. The transducers are attached to the cable at such positions whereby the wave transmitted toward the sea floor is in phase with the reflective wave on the surface of the sea The superimposition of different elementary signals constitutes a single strong pulse. The device replaces air gun devices for oil exploration.

Abstract: A process of acoustic emission for sonar with a separate emission array from the receiving array. The emission array has the shape of a linear acoustic array and can either be towed simultaneously with linear acoustic receiving array or be suspended from a helicopter to form a "dipping" type sonar. Detection using this type of sonar is facilitated by increasing the sound level via the directivity index, while reducing the level of reverberation originating from the bed and from the surface of the sea.

Abstract: In a method of formation of channels for a sonar, after having sampled at a frequency T=1/4f.sub.0 (where f.sub.0 is the receiving center frequency of the sonar) the signals from the hydrophones of the sonar and having translated them to baseband, the signals thus translated are subsampled with a period T.sub.SE =kT (wherein k is an integer) substantially equal to 1.25 B, where B is the reception bandwidth of the sonar. A first set of signals is subsampled at identical times to form a frontal sector. Two further sets of signals are subsampled with delays between the signals from two adjacent hydrophones equal to T, which determines two side sectors adjacent to the frontal sector. The subsampled signals are then transmitted serially by the towing cable of the sonar device towed array and are processed in FFT circuits which allow to form in each sector a set of channels covering the sector.

Abstract: In a sonar used to determine the characteristics of the underwater mines, the emission diagram in the vertical plane is modified to obtain two main lobes separated by a central zero value. At reception, the bearing/frequency display system shows a dark strip separated by two luminous strips. When the echo from a mine persists, in going through the dark zone, it is recognized that it pertains to a moored mine floating in the water, thus enabling moored mines to be identified and their submersion depth measured.

Abstract: A system of emission array with several pairs of emitting transducers to emit simultaneously and covering contiguous frequency sub-bands of a band B. The sub-bands have a width which is less than or at most equal to the width inducing an acceptable displacement of the directivity lobes of the emission pattern of a pair of arrays. The emitters of a single pair are spaced by a distance of L.sub.i and emit signal pulses at frequency f.sub.i and of duration .tau..sub.e 1/.DELTA.f, the products L.sub.i f.sub.i being equal for all the pairs of emitters.The emission patterns of the various pairs of emitters accordingly coincide precisely, and, as the emitters are supplied with signals emerging from the oscillators which are in phase at the center of the pulse of duration .tau..sub.e, the pulse resulting from the superposition of the emitted signals is compressed in time.

Abstract: A sonar transducer comprising a stack of an even number of antennae with identical linear networks. The stack is driven by a reciprocating rotary movement of low amplitude, with the antennae alternately emitting and receiving with each half wavelength of the rotary movement. The emitting antennae as well as the receiving antennae are mutually staggered by an angle equal to the angle of rotation of the assembly. The assembly of receiving antennae are staggered with respect to the assembly of emitting antennae by an angle equal to the phase delay of an emission lobe with respect to the corresponding reception lobe.

Abstract: An interferometric sonar in non-linear acoustics for high-resolution observations of objects located in the vicinity of the sea floor includes two end transducers for simultaneous transmission at two high frequencies F.sub.1 and F.sub.2 of the order of 200 kHz. Reception is performed by hydrophones placed between the sending transducers at the low frequency F.sub.2 -F.sub.1 of the order of 20 kHz. Angular channels are formed during two transmission sequences. Transmission takes place in phase at the frequency F.sub.2 -F.sub.1 in one sequence and in phase opposition in the other sequence in the case of the two sources generated by non-linear effects.

Abstract: An array with high resolving power and low secondary lobe levels, comprising a receiving array formed of transducers along its length L.sub.R, two of these transducers, separated by a distance L.sub.E, also forming the transmitters. The change from transmission to reception and back is effectuated by switches. Signals received by transducers are weighted by resistors before being delivered to beam forming circuits, containing multi-terminal phase shifters and a wiring matrix and adders. The weighting function and ratio L.sub.E /L.sub.R are chosen to ensure that the overall transmission-reception system diagram has high resolving power and low secondary lobe levels.

Abstract: A high resolving power arrangement of transmitting and receiving transducer for arrays the detection of targets in a wave detection system such as sonar. The arrangement includes a transmitting array including two transducers (T.sub.1) and (T.sub.n) transmitting in synchronism or alternatively in phase opposition and a receiving array including transducers T.sub.1, T.sub.2 . . . T.sub.n associated respectively with multiple connector phase shifters (D.sub.1), (D.sub.2) . . . (D.sub.n).