Bottom backscattering coefficient estimation from wideband chirp sonar echoes by chirp adapted time-frequency representation

This work is concerned with the estimation of the bottom backscattering coefficient as a function of frequency and of incident angle. Generally, the backscattering coefficient is studied for a given frequency at various angle. But the backscattering depends not only on the angle, but also on the frequency. In our work, a wideband chirp sonar (20140kHz) with -3dB half-angle 12o has been used to collect the lacustrine bottom echoes, that makes it possible to study the backscattering coefficient as a function of frequency and of angle. For this purpose, a Chirp Adapted time-frequency representation is used, which can provide an approximate energy distribution in the time-frequency plane for multicomponent chirp signals. The obtained timefrequency representation is converted to the anglefrequency plane by the relationship between the time and the incident angle. The est imated backscat ter ing coefficients for sand bottom and pebble bottom are analyzed.