Patent ID: 6314053
Filing Date: 2001-11-06
Classification: G01S

Abstract:
A process for detecting moving objects by an active sonar moving at a velocity V, in which a signal of duration T is transmitted, which signal is reverberated by the transmission medium, having a spectral spread due to the actual speed of the sonar and this reverberated signal is processed by correlation with a set of frequency-shifted copies of the transmission signal in order to correspond to the set of Doppler shifts capable of affecting the reverberated signal, characterized in that the transmitted signal is broadband encoded in order to present a spectrum having a comb-of-lines structure at successive frequencies f.sub.i, the interval separating two successive lines f.sub.i and f.sub.i+1 of which is a function of the velocity V in order to be at least equal to the spectrum spread by satisfying the formula: ##EQU32##where a is an integer between 1 and 2, c is the speed of acoustic waves in water and in that the transmission signal also comprises two pulses at pure frequencies f.sub.m and f.sub.M intended to make it possible to detect fast moving objects, the echoes from which are located beyond the frequency band occupied by the reverberated signal, both when receding and when approaching, these frequencies being given by the equations: ##EQU33##where V.sub.c.sup.max is the maximum velocity of the target.