Acoustic propagation of AFAR: Theory and experiment

We examine the statistics of the second and fourth moments of the acoustic field measured at the Azores Fixed Acoustic Range (AFAR). The results are from pulse transmissions during 1973 and 1975 of several acoustic frequencies over two volume‐refracted paths in different scattering regimes: a 2.9‐km geometric and a 35‐km partially saturated path. The Garrett‐Munk internal wave model is used to specify the index‐of‐refraction fluctuations; model parameters are entirely determined by environmental observations. Predictions based upon the path‐integral formulation [Sound Transmission through a Fluctuating Ocean, edited by S. M. Flatté(1979)] compare favorably with the acoustic observations. The arrival time (phase) fluctuations are predominantly geometric. However at 35 km, microray effects in the phase can be identified. The 2.9‐km amplitude behavior appears geometric although comparison is hampered by a short time series. At 35 km, log‐amplitude and intensity fluctuations are due largely to microray effects; the power spectra of log‐amplitude are described by a single parameter model where the parameter is related to the intensity decorrelation caused by the microrays. [Work supported by ONR, Code 425UA.]