Target Doppler estimation using wideband frequency modulated signals

The topic of this paper is the design and performance analysis of wideband sonar waveforms capable of estimating both target range and Doppler using as few replicas in the processing as possible. First, it is shown that for conventional Doppler sensitive waveforms, for which the Doppler and delay are uncoupled, the Doppler accuracy is proportional to the reciprocal of the signal duration. As a consequence, Doppler estimation requires a huge number of replicas if long duration signals are transmitted. Second, a design procedure for frequency-modulated signals with a required Doppler tolerance independent of signal duration is presented. Expressions for Doppler tolerance, Doppler and delay accuracy, and delay-Doppler ambiguity in case of high bandwidth duration product signals are derived. Finally, results are applied to low-frequency active sonar. Target range and Doppler have been accurately estimated from data collected during a sea trial in 1997.