### ASA 126th Meeting Denver 1993 October 4-8

## 2aUW12. Modeling and analysis of low-angle ice canopy reverberation in the
Arctic.

**Greg Duckworth
Ted Farrell
Kevin LePage
Cola Atkinson
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*Bolt Beranek and Newman, Inc., 70 Fawcett St., Cambridge, MA 02138
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Recent advances in modeling coherent loss in the Arctic have made it
possible to attempt a constrained inversion of monostatic Arctic reverberation
for the ice scattering matrix. An analysis is presented of low-frequency active
reverberation data collected in the Central Arctic in 1992 where such an
inversion yields meaningful results and compare them to theoretical
predictions. Historical and measured ice roughness statistics collected in
tandem with the acoustic portion of the experiment were used to obtain elastic
perturbation theory predictions of scattering loss and backscatter. These
losses were integrated into the Kraken normal mode model to yield highly
accurate predictions of the coherent signal structure to very long ranges in
the Arctic waveguide, as verified by TL measurements. Based on these
predictions, a significant portion of the time/frequency structure of the
backscattered return received on a 256-element hydrophone array was modeled. To
construct a well-conditioned inverse problem, propagation in 10-Hz bands was
divided into three distinct groups; surface duct, mid depth and RSR. Modeling
of TL and travel time for each band/group made it possible to invert the energy
in the backscattered return for the average scattering cross section of the ice
cover at the three discrete group grazing angles. Comparison of the derived
scattering strengths with the elastic perturbation theory predictions yielded
good agreement. [Work supported by ONR.]