Computer modelling of a passive sonar system

Describes the graphical computer simulation of a passive sonar digital signal processing system. The simulation, written chiefly in FORTRAN to run on a MicroVAX, is used alongside a theoretical noise study to predict the effects of digital noise in the sonar in the presence of analogue input noise. In particular, they yield a figure for the minimum input signal-to-noise ratio required for reliable detectability, and can be used to identify potential bottlenecks in system performance. The simulation is restricted to the stages of the (dual channel) sonar that come after the hydrophones. The system comprises various components such as a beamformer, filters and a correlator, each of which uses several different word lengths and connects to the next via an adjustable bit-field. The sources of digital noise are therefore truncation of the digital word both in and between components, especially in multipliers. The simulation uses variable wordlengths at every stage so that the effects of a change can easily be monitored