The STOKES (Version 4) Normal-Mode Shallow Water Transmission Loss Program
Abstract
The STOKES program calculates the Normal-Mode-Sum solution to the acoustic wave equation for an arbitrary sound-speed profile in a water column overlying a seabed that consists of a liquid layer and a solid half-space. The water column sound-speed profile may be arbitrary except that the sound-speed adjacent to the sea-floor must not be significantly greater than that at the depths of the sound transducers. For the seabed, the user can either supply values for each geoacoustic parameter, or if the seabed is unconsolidated sediment, supply the mean grain-size. In the latter case, STOKES uses published regression equations and models to estimate the geoacoustic parameters. The mode phase-speed eigenvalues are the zeroes of a characteristic function that depends on the depth function at the sea-floor and the reflectivity of the sea-floor. STOKES calculates the mode eigenvalues to great accuracy, and is superior to SNAP if the seabed has a significant shear-speed. STOKES has been successfully run for realistic cases with bottom depths of from 60 to 120 m, and for frequencies from 32 Hz to 2 kHz. It has also performed very well when compared with bench-marks. At very low frequencies, near the cut-off frequency of the sound-speed profile as a whole (usually of the order of 10 Hz in practical cases), the imaginary part of any eigenvalue is large, and in some cases this prevents STOKES, which uses a simple root-finding procedure, from finding any mode. In such a case the Transmission Loss (at ranges of at least a few kilometres) would be exceptionally high, and its precise value would not be of practical interest.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1993
- Accession Number
- ADA268772
Entities
People
- Marshall V. Hall
Organizations
- Defence Science and Technology Group