In active SONAR, frequency agility refers to the transmission, reception, and processing of narrowband waveforms centered at disparate carrier frequencies, which are spaced throughout a wide operational bandwidth. Higher frequencies provide the greatest spatial and Doppler resolution, but are subject to increased attenuation, which limits their useful detection range. Lower frequencies propagate more readily to farther ranges, but their corresponding lower resolution limits their processing gain against reverberation in shallow water sound channels. This study investigates the impact of frequency on the detection performance of a fast-moving forward-looking, fixed aperture SONAR. It develops a model of reverberation as a noise process with a time-dependent power spectrum that is used in conjunction with acoustic ray tracing models to characterize detection performance as a function of target range and Doppler and SONAR frequency. The methodology is demonstrated on two shallow-water acoustic channels.
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