Range localication of 10-100 km shots by means of an endfire array and a waveguide invariant

During a shallow-water acoustic experiment, signals from small explosions were recorded on an endfire horizontal array. The experiment took place in open waters with relatively slow changes of the water depth with range. The array in question (820 m) proved to be too short for measuring group speeds of individual modes, but resolved the phase speeds well. By means of the “β waveguide invariant” relationship between group and phase speed, the ranges of the shots were estimated from the phase speeds and the arrival time differences, and compared to the ranges obtained by navigation. Similarly, β values were estimated for the individual shots and compared to theoretical values computed according to assumptions such as the adiabatic approximation.