Multipole analysis of the directionality of ambient noise in the Arctic

Abstract

We present an analysis of the directionality properties of ambient noise in Arctic regions based on the premise that ambient noise in the sea originates at its surface. Placing conceptual and suitable distributions of acoustic multipole sources at the sea surface, each one emitting sound with its own typical radiation pattern, it was possible to obtain predictions for the directional characteristics of arctic ambient noise, whatever its cause may be. An available theoretical model [R. J. Talham, J. Acoust. Soc. Am. 36, 1541–1544 (1964)] and ray-tracing programs were extended and modified to calculate the sound-intensity levels reaching a receiver per unit solid angle in the vertical plane for any receiver location. The results are valid for receivers looking toward the sea surface or the bottom, and the effects of a lossy ice surface and a lossy bottom were incorporated into the analysis. The angular distribution of intensity at the receiver is displayed in a variety of graphs for six (deep and shallow) geographical locations within the Attic region, various receiver depths, and several types of surface radiators and/or environmental parameters. Under several simplifying conditions satisfied only in rare instances, these elaborate calculations agree well with a straight forward analytical prediction discussed by Urick; otherwise, the elaborate calculations are a must.