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