Average low-frequency under-ice reflection amplitudes and phases in the central Arctic were estimated from long-range (260-km) signals from fixed continuous wave (cw) sources detected on a long (1-km) vertical array (the FRAM IV experiment), using conventional and minimum variance estimators in conjunction with matched-field processing. Theoretical computation of the trial source fields for all assumed ranges and depths was based on a normal-mode code into which were incorporated the under-ice reflection amplitudes and phases by functional dependence on grazing angle. These were varied iteratively to achieve maximum matched-field processor gain with minimum range and depth errors. The resultant best data-fitting amplitudes and phases, which differ significantly from expectations based on existing under-ice scattering models, provide a new benchmark for testing and, it is hoped, a stimulus for the development of refined theories.

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