DEMONSTRATION OF A LOW-FREQUENCY, LONG-RANGE ACOUSTIC COMMUNICATIONS-SYSTEM

An acoustic communications system employing low frequencies to attain greater communications ranges is described. The waveforms are incohere nt so that greater reliability can be obtained at the expense of poten tially higher bit rates. The waveform generation process is described as are the results of three at-sea expeditions in which the system was tested in both bottom-limited and deep water conditions as well as in surface duct and convergence zone environments. The primary objective of the at-sea tests was to measure the attainable data rate from any fixed or moving transmitter to any fixed or moving receiver at a range of 100 nmi. The attainable data rate was measured as a function of se veral parameters, including the relative Doppler shift, error correcti on overhead, the acoustic environment, and trade-offs of time for band width in the data modulation process.