Model for Arctic propagation loss using scattering integrals and empirical reflection losses

Abstract

A normal mode program for under ice propagation has been developed. To permit rapid computation, eigenvalues are determined for loss‐less boundaries and attenuation is then added for reflection losses. Scattering from nonspecular angles is included by integration over ray paths from the surface to the source and receiver. Various published shot data were assembled and compared with computed propagation losses, using graphical methods, to determine ice reflection losses. Losses for ranges greater than 100 km gave the most definitive values for ice loss. Losses for shorter ranges, with greater dependence on grazing angles from 0° to 10°, were less definitive. Therefore, a linear function in decibels with 0‐dB loss at 0° was assumed for the ice loss. The slope was then determined by comparison with the data. For Central Arctic data this slope is 1.125 × 10−3 f dB/deg (f is frequency in Hz) for frequencies from 0 to 400 Hz and a constant 0.45 dB/deg above 400 Hz. [Work supported by NORDA, Code 110 A.]