Digital signal processing of high resolution within-pulse sector scanning sonars

Abstract

The characteristics of three scanning sonars, presently in use at the Admiralty Marine Technology Establishment, and operating at frequencies of 300kHz, 150kHz and 75kHz are described. The performance of a system for digitally recording the information from these sonars is detailed. A six bit (64 levels) analogue to digital conversion is employed at such a rate as to maintain the basic accuracy of the sonars. This data is recorded onto digital cassettes following ECMA 34 standards. The recorded information can be replayed into a PDP 11/40 computer via a digital highway for subsequent laboratory analysis. The processed data is then presented in various graphical three dimensional formats, examples of which are shown. The use of this analysis and representation is illustrated with reference to the use of the scanning sonar in three different modes of operation, namely echo sounding, forward search and depth scanning. A system is described that continuously records whole successive frames of sonarinformation onto an instrument recorder using a multitrack digital recording technique. This system can also capture a frame of data into a random access memory of 512 pixels by 512 pixels of eight bit resolution (256 levels) and display the sonar picture in B scan format on a conventional colour TV monitor. The range and bearing are represented by the vertical and horizontal positions of a point whilst the echo intensity can be represented as one of 127 colour levels using a colour look-up table technique.