Subsea image interpretation-a problem in remote sensing

Although remote sensing is generally associated with satellite imagery, it can also be applied to sea-floor imagery collected by acoustic surveying techniques. Sea-floor surveying is important in environmental and oceanographic research, and for mineral prospecting and marine civil engineering projects. The main instrument for sea-floor mapping is the side-scan sonar. This generates an image of the sea-floor by recording the backscattered energy at shallow grazing angles from a short acoustic pulse, which is transmitted along a fan shaped beam, narrow in azimuth but wide in elevation. Typical carrier frequencies are in the region of 100 kHz and chirp sources are becoming available. Seismic profiling is used to obtain information of the sub-bottom by transmitting an acoustic pulse into the seabed and recording the reflected signals. The seismic sensor looks directly downwards at the sea-floor and operates at much lower frequencies, typically 1-3 kHz. This paper is confined to the classical remote sensing problems of delineating boundaries between different regions of the images and classifying the domains within these boundaries