### ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

## 2aUW2. Theoretical approaches for computing FAT spreads.

**Diana F. McCammon
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*Appl. Res. Lab. and the Graduate Prog. in Acoust., Penn State Univ., P.O.
Box 30, State College, PA 16804
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FAT (frequency, angle, and time) spreading is approached theoretically
through the Helmholtz integral equation for scattering from random rough
surfaces. Using the Kirchhoff approximation, angle spread is readily found to be
related to the probability of surface slopes. Various approximate evaluations
are discussed for modeling time spread, from numerical ray tracing to integrals
over pulse shapes. Solving for the half-power points of the intensity shows the
link between angle and time spread. Frequency spread functions are discussed,
illustrating the difficulty of using Fresnel phase approximations for
higher-order corrections to the Doppler shift.