ACOUSTIC IMAGING OF SEA-BED GEOMETRY - A HIGH-RESOLUTION REMOTE TRACKING SONAR (HRRTS-II)

A High Resolution Remote Tracking Sonar (HRRTS II) is described which is capable of measuring a 2-D profile of the sea-bed over a maximum distance of 5 m under conditions of significant sediment transport. The backscattered signal from a pulsed (30 mus) 5 MHz sonar provides acoustic range measurements of the small-scale topography generated by bedforms at any point in time as well as changes in this small-scale topography and the average elevation of sections of the sea-bed over time. Bedform height and spacing can be determined accurately although bedform shape is distorted by ''smoothing'' of large slope changes as a result of the finite size of the ''footprint'' of this narrow-beamed (0.74-degrees) sonar. The system operates on command from a shore-based micro-computer and topographic resolution of the order of a few millimetres is possible. Resolution deteriorates as wave energy increases to levels where vibration of the transducer and large concentrations of sediment in the water column result in signal attenuation and a decrease in the signal-to-noise ratio.