Abstract
Nearly all acoustic systems used for fisheries and biological oceanographic studies have to date used systems that transmit short CW tone pulses. One of the characteristics of this type of system is that the user of the system is forced to trade-off spatial resolution with ability to minimize the adverse effects of noise. This paper describes the application of a different type of signal, the FM slide or chirp, for fisheries and oceanographic acoustic assessment. These systems have the characteristic that the signal parameters can be selected to provide both good spatial resolution and good noise immunity. The basic theory of FM slides as well as some of the factors that must be considered when implementing this signal type in actual systems are described. Laboratory measurements and field results are presented that show the potential advantage of the FM slide or chirp signals over the more conventional CW tone pulse.