Sonar echo ranging using signals with nonlinear time-frequency characteristics

In this letter, we investigate the applicability of cetacean sounds and frequency-modulated (FM) signals with dispersive characteristics toward the problem of echo ranging of acoustic targets. We derive closed-form expressions of the ambiguity function range resolution profile for nonlinear FM (NFM) pulses with similar time-frequency characteristics as cetacean whistles. We demonstrate that by varying the signal parameters, we can obtain their ambiguity function with a narrow mainlobe and low sidelobes desirable for estimating the time delay and Doppler shift of the received echo. We further test our results by formulating a detection problem using NFM pulses.