Analysis of multibeam echo-sounder signals from the deep seafloor

The new generation low-frequency echo-sounders, covering the full angular range, are also able to record acoustic images comparable to side-scan sonars. Possibilities of using these systems for sea-floor type identification are currently being investigated. Experimental echoes obtained with a 13 kHz multibeam echo-sounder have been collected and processed for a variety of sea-floor types and water depths. The results of two different analysis methods are presented. The backscattering strength of the sea-floor and its angular variations are known to be strongly dependent on the seabed type. They may be obtained as a function of incident angle from the measured levels averaged in narrow tilted beams, after correcting for the insonified area, the refraction by the sound-speed profile and the sea-floor local slopes. The results of this method make clear large differences between the various investigated seabed classes. The spectral features of backscattered time signals have previously been shown to be a useful tool for identification by side-scan sonars. The authors present the first results obtained by this method for deep sea-floor multibeam echoes: notable discrepancies between the spectral parameters corresponding to various seabeds are shown, enhancing the possibility of using such a technique for low-frequency echo-sounders