Long-period Phase Research Articles

Long-period fluctuations of CW signals in deep and shallow water

In July 1972, as part of the cooperative studies between the Miami and Michigan Project MIMI research groups, continuous fixed-system underwater sound propagation tests at 406 Hz were commenced between a sound source off Eleuthera, Bahamas, and receivers at Bermuda, a distance of 1250 km, and at positions intermediate in range with respect to the 1250-km path. Preliminary studies of long-period CW transmission fluctuations at Bermuda and at one intermediate position have been completed. The long-period phase and amplitude fluctuations are qualitatively quite similar to those observed in the Straits of Florida and in other relatively shallow water locations. Phase fluctuations associated with the ocean tides are a marked feature of the data. With averages taken over two-day time spans, significant variations in the statistical properties of transmission loss have been observed over a five-month time period. Shorter-period fluctuations in acoustic phase (time scale of a few minutes to a few hours) have similar characteristics in the deep and shallow water propagation ranges. [The research was supported by Code 412 of the Office of Naval Research.]