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

This work concerns the estimation of the bottom backscattering coefficient as a function of the frequency and incident angle which is important for bottom imaging with wideband sonar. Generally, the backscattering coefficient is studied for a given frequency and a fixed angle. Meanwhile the backscattering depends not only on the angle, but also on the frequency, the conventional methods can not be used for the wideband sonar signals analysis. In our work, a wideband chirp sonar (20-140 kHz) with -3 dB half-angle of 12 degree has been used to collect the lacustrine bottom echoes, so the dependence of the backscattering coefficient on the frequency and the incident angle is studied at the same time. An angle-frequency representation is obtained by using the chirp adapted time-frequency representation which gives an approximate energy distribution for chirp signals. The proposed method is used for sand bottom and pebble bottom analysis