The physical causes of clutter and its suppression via sub-band processing

Seafloor features that cause low-frequency, active sonar clutter are discussed and illustrated with data gathered in the Mediterranean Sea for signals with a 1 kHz bandwidth, centered on 1.3 kHz. A method is proposed to reduce the number of sonar contacts formed due to random returns in the data, i.e. "clutter points". The method uses band-pass filters to split the signal into a number of sub-bands and processes the sub-band data after contact-forming, using knowledge of the physical causes of clutter to reject clutter while retaining real contacts. Comparisons are made between sub-band and full-band processing and the improvements obtainable via the method are illustrated using the measured data with a shipwreck target. It is shown that the proportion of contacts associated with man-made features is increased when sub-band processing is used, relative to the full-band case