Deep-Sea Ambient-Noise Statistics

Abstract

The statistics of ambient noise in the ocean have been investigated for a single hydrophone at 5200 ft and 14 300 ft. Five frequencies in a 13-oct bands were used in the range from 100 to 1600 Hz. Amplitude samples were taken every 20 msec and were recorded digitally. The data were analyzed in blocks of 500, 1000, and 2000 sample points. Distribution functions and moments were computed up to the fourth moment and the data were tested as to their normality at the 95% and 99% acceptance level using moment tests for skewness and kurtosis and the one-sample Kolmogorov Smirnov test. The two-sample Kolmogorov-Smirnov test was used to test for stationarity. A greater percentage of the smaller samples, i.e., 500 points, fall within the 95% acceptance interval for normality than the longer samples, thus confirming the nonstationarity of ambient sea noise. More than half of all the samples tested were found to be normal.