Abstract: A method for achieving omnidirectional transmission using of a towed linear antenna of length L greater than the wavelength ? of the signal transmitted. The antenna has a plurality of P projectors. The spacing between projectors is substantially less than ?/2. The method includes applying, to each projector, a transmit signal coming from a common transmit signal. The common signal is assigned a delay based upon a calculation that includes a non-linear term as a function of the position of the projector in the antenna, thereby allowing the angular aperture of the transmission pattern to be modulated. the method permits sonar detection systems comprising transmit and receive antennas having substantially identical diameters, which thereby can be reeled onto the same winch without it being necessary to separate them.

Abstract: The present invention is directed to a method of allowing a computational load caused by the implementation of conventional signal processing methods operating by multicopy correlation, by simultaneous correlation of the spectrum of the received signal to copies of the signal, each of the copies having a different Doppler shift. The multicopy correlation operation is a time-frequency transformation of the received signal. Synthetic spectra are found by selection of spectral lines and concatenation, starting from the spectrum of the received signal. An inter-spectral product is computed, in other words by the product of each synthetic spectrum with the concatenated conjugate spectrum of the corresponding Doppler copy. A frequency-time transformation of the inter-spectral products is performed.

Abstract: The present invention is directed to a method of allowing a computational load caused by the implementation of conventional signal processing methods operating by multicopy correlation, by simultaneous correlation of the spectrum of the received signal to copies of the signal, each of the copies having a different Doppler shift. The multicopy correlation operation is a time-frequency transformation of the received signal. Synthetic spectra are found by selection of spectral lines and concatenation, starting from the spectrum of the received signal. An inter-spectral product is computed, in other words by the product of each synthetic spectrum with the concatenated conjugate spectrum of the corresponding Doppler copy. A frequency-time transformation of the inter-spectral products is performed.

Abstract: The disclosure relates to a signal processing method for a towed linear antenna, notably to resolve right-left ambiguity, said antenna comprising a set of hydrophone multiplets each with n?3 hydrophones spread over a straight section of the longitudinal axis of said antenna, wherein the roll angle of each multiplet relative to the vertical is measured, the signals of said hydrophones and said roll angles are used to synthesize p?3 linear sub-antennas, then M azimuth channels are formed with each sub-antenna and 2 adaptive right-left channels are formed from said p sub-antennas for each direction corresponding to each azimuth channel. The invention resolves right-left ambiguity with optimal performance in detection and for long antennas.

Abstract: The disclosure relates to a signal processing method for a towed linear antenna, notably to resolve right-left ambiguity, said antenna comprising a set of hydrophone multiplets each with n≧3 hydrophones spread over a straight section of the longitudinal axis of said antenna, wherein the roll angle of each multiplet relative to the vertical is measured, the signals of said hydrophones and said roll angles are used to synthesize p≧3 linear sub-antennas, then M azimuth channels are formed with each sub-antenna and 2 adaptive right-left channels are formed from said p sub-antennas for each direction corresponding to each azimuth channel. The invention resolves right-left ambiguity with optimal performance in detection and for long antennas.

Abstract: A process for making it possible to detect moving objects by an active sonar operating by the Dopper effect. The process uses, as a transmission signal, a burst of N pulses encoded so as to present a spectrum having a comb-of-lines structure. In this way, the “signal/reverberation” ratio of the useful signal intensity to the reverberated intensity is increased, thereby increasing the efficiency of the sonar. The process allows objects moving in a reverberating transmission medium to be detected more easily.

Abstract: The invention relates to methods which make it possible to measure the Doppler shift of the echoes of a detection system. That is, the present invention modulates the frequency of the pulses of the transmissions of this system by a pseudohyperbolic function such that a restricted number of copies of the transmission signal can be used to perform the correlation operations on reception and to have them followed by an interpolation operation.

Abstract: The invention relates to towed sonars. It consists in compensating electronically for the movement of the antenna in order to suppress the Doppler shift of the fixed echoes. In order to do that in a towed linear antenna (203) comprising N sensors (205), M (M<N) successive sensors are selected which are switched electronically in order to make them travel synthetically over the antenna in the direction opposite to the movement of the latter at a speed equal to twice the forward speed of the antenna. In order not to have too large a number of physical sensors, the signals from the latter are interpolated in order to obtain synthetic sensors which are sufficient in number to reduce the increment of the movement of the synthetic sub-antenna in such a way as to suppress the parasitic lobes due to the incremental nature of this movement. It makes it possible to increase the sensitivity of sonars without increasing their power. FIG. 2.

Abstract: A sonar that enables an already localized object to be found again uses a transmission antenna fitted out to transmit only the two .+-.first order secondary lobes. This antenna is supplied with a set of frequencies tiered so that each of these lobes determines a series of channels at transmission corresponding to these frequencies and filling two sub-sectors located to the right and to the left of the antenna. The reception is done by forming two wide channels, each of which covers one of the two transmission sub-sectors. The discrimination in bearing at reception is done by the discrimination of the frequencies. To cover a more extensive sector, including especially the central part located between two sub-sectors, the antenna can be made to rotate mechanically. This enables the construction of a simplified sonar which can be used in a consumable way.