Patent ID: 7218574

Claim:
An underwater communications method for modulating and demodulating communications signals while compensating for the effects of range rate, said method comprising the steps of: generating a communication signal with a nonlinear frequency modulated acquisition component for providing an initial estimate of the range rate, wherein said nonlinear frequency modulated acquisition component is a hyperbolic frequency modulated signal the frequency of which varies in accordance with the expression ( 1 + v c ) ⁢ f , where ν is the constant velocity between the transmitter and receiver, c is the velocity of propagation of sound in water, f is the frequency of modulation which varies from a first frequency to a last frequency, f 1 ≦f≦f n ; generating a set of single-frequency tonals and acquiring them using said initial estimate of range rate to obtain a more precise estimate of range rate; and demodulating said communication signal using said more precise estimate of range rate to compensate for the effects of range rate to make said communication signal appear as though range rate effects were not present in said communication signal.