EFFECTS OF INTERNAL WAVES ON SOUND PULSE-PROPAGATION IN THE STRAITS OF FLORIDA

An unexplained result of broad-band transmission experiments made more than ten years ago by DeFerrari in the Straits of Florida (center fre quency similar to 500 Hz, bandwidth similar to 100 Hz, water depth sim ilar to 200-m, range similar to 20 km) is that the measured pulse resp onse functions failed to show the expected multipath replicas of the t ransmitted pulse and instead were smeared into a single broad cluster (duration similar to 50-similar to 350 ms) in which the unresolved mul tipaths fluctuated rapidly in geophysical time (coherence time (much l ess than 12 min) leaving only a relatively stable envelope that is use ful for oceanographic inversion. It is demonstrated here that the effe cts of internal waves on sound pulse propagation in the Straits of Flo rida can explain these observed results, and it is suggested that simi lar instabilities of acoustic multipaths due to internal waves are to be expected in other shallow-water propagation conditions, The demonst ration is based on numerical simulations with the broad-band UMPE acou stic model that includes multiple forward scattering from volume inhom ogeneities induced by internal wave fluctuations that are described by a broad spectrum of excitation, The simulated temporal variability, s tability, and coherence of acoustic pulse arrivals are displayed on ge ophysical time scales from seconds to many hours and are qualitatively in agreement with the measured data in the Straits of Florida.