Measured Effects of Ice Roughness on under-Ice Transmission Loss

Coincident measurements of under-ice transmission loss over a frequency range of 100–1000 Hz and top ice roughness were made from aircraft. The acoustic measurements were made with calibrated sonobuoys and explosive charges, while top ice roughness measurements were made using a laser profiler along several 100-km tracks. The resulting ice roughness data is expressed in terms of ridge density. As expected, low-frequency transmission loss increases with top ice ridge density. According to a preliminary analysis of top and bottom ice roughness data, top ice ridge density is a quantitative indicator of bottomside ridge density and rms roughness. The data are compared with theoretical predictions and previous measurements. Some possible acoustic scattering mechanisms at the water-ice interface are suggested.