Estimates of Two Point, Broadband Temporal Coherence Using a z-Transform Technique
Abstract
Values of broadband coherence versus time delay are presented for two horizontally separated receivers in water overlying a rigid bottom. These values are given for different source azimuth angles (from broadside to endfire) and for (a) surface-bottom (SB) paths, (b) bottom-surface (BS) paths, and (c) a combination of SB and bottom-reflected (B) paths. The acoustic wavelength band considered is the passband from 0.2-1.0 m. The water depth and range are both 5 km. The source and receivers are all at 200 m depth, with the receivers separated by 25 m. The ocean bottom is assumed to be rigid and flat. Scattering from the ocean surface is modeled using the time-domain, facet-ensemble method applied to a long-crested wave model of the ocean surface using actual wave- height measurements with an rms value of 1 m. A z-transform algorithm is used to perform broadband filtering and to compute coherence. Results demonstrate how signals that arrive endfire via SB paths possess greater coherence (with values near 0.8) than signals that arrive via BS paths (values near 0). This is because the SB path involves scattering off areas on the ocean surface that are close together and physically similar. Keywords: Sonar sound analyzers; Reprints.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1988
- Accession Number
- ADA199694
Entities
People
- C. Feuillade
- W. A. Kinney
Organizations
- United States Naval Research Laboratory