Subcritical Detection of Targets Buried Under a Rippled Interface: Calibrated Levels and Effects of Large Roughness
Abstract
This paper describes results of an ongoing modeling and measurement effort investigating shallow grazing angle acoustic detection of targets buried in sand. The measurements were performed in a 13.7-meter deep, 110-meter long, 80-meter wide test pool with a 1.5-meter layer of sand on the bottom. A silicone-oil-filled target sphere was buried under a rippled surface with contours formed by raking the sand with a machined rake. Broadband (10 to 50 kHz) transducers were placed onto the shaft of a tilting motor, which in turn was attached to an elevated rail that enabled this assembly to be translated horizontally, permitting acquired data to be processed using synthetic aperture sonar (SAS) techniques. Acoustic backscatter data were acquired at subcritical grazing angles for various ripple wavelengths and heights. Also, the backscattered signals from a free-field sphere and the transmitted signals received with a free-field hydrophone were recorded. For each bottom configuration, the seabed roughness over the buried target was measured to determine the ripple parameters and to estimate the small-scale roughness spectrum. This roughness information is used in scattering models to calculate the backscattered signal levels from the target and bottom. In previous work, measured signal-to-reverberation ratios were found to compare well with model predictions, demonstrating the accuracy of first-order perturbation theory (for the ripple heights used in those experiments) for frequencies up to 30 kHz. By taking advantage of the backscattered data and the transmitted data, comparisons more stringent than in previous work were made between predicted and measured buried target backscatter levels. Results of a second series of measurements using larger ripple heights to investigate the impact of higher-order scattering effects on buried target detection are presented. (1 table, 9 figures, 10 refs.)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2003
- Accession Number
- ADA420050
Entities
People
- C. L. Nesbitt
- E. I. Thorsos
- J. L. Lopes
- Kevin L. Williams
- R. Lim
Organizations
- University of Washington