High repetition rate side looking SONAR

Abstract

Side scan (or side looking) sonar systems are widely used in small object search and detection surveys. Systems with long range (>300 M swath) capabilities are restricted in their ability to detect and resolve small targets at boat speeds in excess of 5 knots. Chirp technology provides for side looking cross track resolution of a few centimeters. This resolution is a function of system bandwidth and signal processing characteristics. Along track resolution is defined by the transducer radiation pattern and transmit repetition rate. The transducer radiation pattern is a function of operating frequency and array length. It takes some number of pings to ensonify a particular target to have a high probability of detection. At any given repetition rate, as the towed transducer vehicle moves through the water at faster and faster speeds, the number of pings ensonifying a target will progressively decrease. Benthos has developed a multiplying enhancement to the SIS-1500 family of side scan sonars which increases the ping repetition rate through the use of orthogonal waveforms. Increasing the transmit repetition rate for any given range scale allows a commensurate increase in boat speed while maintaining the same along track resolution.