Fluctuation Spectra of Signals Transmitted in the Sea and Their Meaning for Signal Detectability

摘要

Spectra have been obtained of the amplitude fluctuation of the sound from a moving low frequency source in the sea at ranges as far as the first convergence zone. The time scale of the observed fluctuation is very broad, extending from the very slow to the very fast. Slow fluctuations having periods roughly of one minute to one hour appear to be due to variable multipath interferences caused by the motion of the source. Faster fluctuations with periods between one and twenty seconds have spectra indicating the moving sea surface to be the dominant cause of the fluctuation. These spectra provide the first estimates for a new fluctuation parameter which, when used with fluctuation-modified ROC curves, enable the effect of a fluctuating signal on target detection to be assessed.