where 8 is the backward shift. In the case of a stationary Gaussian process, DO , FAN., 1473 EDITION OF' I MOV o is OUOLETE S/N 0102-LF-014-6601 SECURITY CLASSIFICATION OF THIS PAGE (ften Date Itntored) SECURITY CLASSFICATION Of THIS PAGE (Whm Dra EaeMO 20. Abstract (continued) the expected zero-crossing rate indexed by a E (-1,1), is always decreasing, completely determines the correlation generating function, and is equal to a constant if and only if the process is a pure sinusoid with probability one. When the process is a sinusoid plus white noise, a sequence {E[D], j = 1,2 .... } is constructed that after proper normalizaj tion converges to the frequency of the sinusoid regardless of the signal to noise ratio. A real data example is given in tracking the vocal sound of a meuaptera novaeangZiae whale.