Accession Number : AD0774907

Title :   Fluctuations in Sonar: A Short Survey.

Descriptive Note : Final rept.,


Personal Author(s) : Urick,R. J.

Report Date : 19 NOV 1973

Pagination or Media Count : 25

Abstract : Sonar fluctuations recieved intensive study during the hectic days of World War II, when the causes of fluctuation were identified and some quantitative data was obtained at the frequencies and ranges of current interest. Since then, in the search for mean values of the sonar parameters, fluctuations have tended to be neglected as a subject of serious study. They are the results of the mobile, varying nature of the medium and the objects within it. For example, echoes fluctuate because of the constantly changing heading of a submarine underway; the ambient background fluctuates because of changing ship traffic, wind speed and biological activity; CW signals fluctuate because of a changing multipath structure of the medium. Examples of these effects, as observed in NOL field work, will be presented. Their effect on detection is to improve detection at low mean S/N ratios and to cause lost contacts at high S/N ratios. Quantitatively, this behavior can be expressed by means of ROC curves modified to include fluctuations. However, much more work needs to be done on the second-order statistics of underwater sound before their magnitude can be predicted and their effects understood. (Author)

Descriptors :   *Sonar signals, Signal to noise ratio, Ambient noise, Background noise, Marine biological noise, Underwater sound, Sound transmission, Variations, Reviews

Subject Categories : Physical and Dynamic Oceanography
      Acoustic Detection and Detectors

Distribution Statement : APPROVED FOR PUBLIC RELEASE