Partitioned and modified chirp Z-transform: Signal processing technique for simultaneous multifrequency evaluation of the surface reradiated spectrum in slowly varying environments

The partitioned and modified chirp Z-transform (PAM-CZT) is a signal processing technique for computing the Z-transform of a sequence at equally spaced samples on a sector of the unit circle in the Z-plane. Unlike the computationally cumbersome classical technique (4), the PAM-CZT utilizes the fast Fourier transform (FFT) that allows real time implementation with state of the art minicomputers. Another advantage of the PAM-CZT is its partitioning capability; long sequences can be processed in short-time-ordered sequences, thereby providing spectral analysis to any frequency resolution by allowing large time records. This signal processing technique will aid in the analysis of acoustically propagated noises in the ocean. Classical experiments utilize a monochromatic probe set at different frequencies for each of several orthogonal time records. However, the quasi-stationarity of the ocean inhibits reaching conclusions as to the frequency dependence of the surface reradiated spectrum´ because the measurements are corrupted by the slowly varying characteristics of the ocean. An alternative approach is to simultaneously probe the ocean surface with several sinusoids and perform a PAM-CZT analysis of the results.