Wide band, high resolution sonar techniques

Abstract

Introduction.Current generation sonar imaging systems use large aperture sensor arrays and wide processing bandwidths to resolve difficult targets. A typical submarine obstacle avoidance sonar, for example, may use transducer arrays consisting of several hundred staves of hydrophones and coded transmissions with bandwidths in excess of 100 kHz.Recent developments in the use of composite ceramics for high frequency arrays have reached the stage where large area, high frequency sonar receiver arrays can be produced cost effectively [1]. Typically these consist of hundreds of individual sensors with excellent element-to-element matching, in both gain and phase, over bandwidths in excess of an octave centred on frequencies in the range 30 to 500 kHz (See Figure 1). This composite sensor technology allows high performance sonar imaging systems to be developed with good spatial and angular resolution and wide angular cover. A typical system may use a hydrophone array of say 200 staves, each quantised to around 18-20 bits and processed in the frequency band 100 to 200 kHz to provide 1 degree wide beams over say a +/-80 degree angle of cover. Replica correlation must be provided on each beam output for target detection, followed by some overall feature extraction and image display system.