Concurrent underwater acoustic wave front fluctuations at two frequencies over a 75‐nmi path

An experiment was performed to investigate the fluctuations in wave front shape of signals transmitted over a distance of about 75 nmi from a ship‐suspended sound source to a bottomed set of receivers. An experimental set of eight receivers, spanning a distance of about 2300 ft in both the downslope and cross‐slope directions, was laid on a 26° slope southwest of Bermuda at about 5000‐ft depth. Pulses of 200‐ and 400‐Hz signals were transmitted alternately from the projector, by the second‐order RSR mode; these were recorded on an oscillograph, and delays in arrival time at each receiver were measured. Plane wave fronts were fitted to the delay data, and the azimuth and elevation angles for the wave fronts were calculated. The effect of ship motion and stationary effects were removed from the raw delays. Plane wave front fits to the adjusted data were made, and deviations from these wave fronts were found for each receiver. The wave fronts are characterized by two actions: (1) gross wave front rocking and...