REFLECTION LOSS AND MODE ATTENUATION IN A PEKERIS MODEL

The loss on reflection of a homogeneous acoustic wave from the boundary of an absorbing fluid is derived in several ways, including a calculation based on the attenuation along the beam displacement. For a so-called inhomogeneous plane wave there is an extra term, and the overall effect can be a loss or a gain. The paper considers several approaches to mode attenuation in an isovelocity or Perkeris channel with a lossy lower medium. We compare the horizontal attenuation of a mode with the horizontal attenuation of a ray due to multiple reflection losses. For exact agreement at all angles it is necessary either to include the beam displacement in the cycle distance, or to use the reflection coefficient appropriate to inhomogeneous waves, but these latter provisos are important only for shallow water and modes near cutoff. Beam displacement plays a part in both the reflection loss and the cycle distance calculations, and these aspects may be generalized. © 1979, American Association of Physics Teachers. All rights reserved.