### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 3aPAa11. Sensitivity analysis of the Green's function parabolic equation
model for atmospheric sound propagation.

**Michael R. Dobry
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*Dept. of Mech. Eng., New Mexico State Univ., Box 30001-3501, Las Cruces,
NM 88004
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**Robert P. Hansen
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*U.S. Military Academy, West Point, NY
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**David H. Marlin
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*U.S. Army Res. Lab., White Sands Missile Range, NM
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A sensitivity analysis was performed on the Green's function parabolic
equation (GFPE) model to determine parameter bounds which maintain model
validity. To determine these bounds, inverse theory was used to determine the
``best'' combination of input parameters over a two-dimensional domain using a
normalized sum of squared residuals. A two-dimensional version of the fast
field program (FFP), a widely accepted atmospheric propagation model, was used
as comparison. Plots of the error surface were then made to show sensitivity
bounds. Upward and downward refracting atmospheres were considered for a range
of frequencies. The GFPE model was found to require a height increment
parameter of about 0.05 wavelengths while the range increment parameter
extended from 10 to 120 wavelengths depending on atmospheric profile and
frequency. The thickness of the attenuation layer was found to be frequency
dependent and ranged from 50 to over 200 wavelengths. The surface wave integral
height was found to be a minimum of 30 and 13 wavelengths for the upward and
downward atmospheres, respectively. The CPU time for the GFPE model ranged from
10 to 60 s, depending on frequency, and was approximately 60--1000x faster than
the two-dimensional FFP.