Acoustic reflection from a sea bottom with linearly increasing sound speed.

We calculate the acoustic reflection coefficient for plane waves, in a homogeneous fluid half-space, incident at arbitrary angle upon an underlying half-space of unconsolidated bottom sediments. The lower half-space, treated here as a fluid, has constant density and a sound speed that increases linearly with depth. An exact formal expression is found for the complex reflection coefficient R, in terms of a modified Bessel function. With no absorption, | R | is unity for all angles except at normal incidence, as would also be expected from ray theory. Assuming bottom absorption, we derive an analytical approximation for R, valid for incident angles [variant_greek_theta] (measured from the interface normal) in the range 10°<=[variant_greek_theta]<=70°, for acoustic frequencies f>=10 Hz, and to about 80° for f>=70 Hz. A high-frequency limit and a small-angle approximation are found. Use of a pseudolinear gradient, suitable at large angles, could extend [variant_greek_theta] to 90°. A more realistic model having layers in the upper part of the bottom is discussed briefly. [ABSTRACT FROM AUTHOR]