Shallow Water Propagation and Surface Reverberation Modeling

• Main Author: Deane, Grant B
• Other Authors: SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB
• Format: Text
• Language: English
• Published: 2012
• Subjects: Hydrology; Limnology and Potamology; Acoustics; *REVERBERATION; *SHALLOW WATER; ACOUSTIC COMMUNICATIONS; BUBBLES; GRAVITY WAVES; SURFACE WAVES; UNDERWATER COMMUNICATIONS; BREAKING WAVES; ACOMS(UNDERWATER ACOUSTIC COMMUNICATIONS); Sea ice
• Online Access: http://www.dtic.mil/docs/citations/ADA574830; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA574830

The primary long-term goal is to measure and model high-frequency acoustic propagation in the presence of surface gravity waves and breaking waves to better understand the effects of surface reverberation on shallow water, underwater acoustic communications (ACOMS). Secondary long-term goals are to exploit measurements of breaking wave noise to infer bubble cloud populations at the sea surface and their effect on reverberation, and to model high-frequency, forward scattering from sea ice. These original goals have been augmented in 2012 to study the effects of bubbles on surface reverberation through the analysis of surface video footage of breaking waves. The overall program objectives are reproduced below for completeness. Program objectives specific to work in 2012 were to: (1) continue the work of Berry (1972) to deduce the form of surfaces from scattered sound and (2) study the physical and (inferred) acoustical properties of sub-surface bubble plumes from remote images of breaking waves. Berry's research focused on determining the structure of sea ice from scattered sound. He determined some of the basic physical constraints that would limit an inversion method based on reflected pulses interacting with a rough ice surface, but did not present any actual inversions for surface shape. Our objective has been to extend this work to actually determine surface shape from scattered acoustic pulses, and compare the results with experiment. This work will be used to help interpret field data of bistatic scattering from sea ice cover and calibrate approximate analytical and numerical acoustic models used to compute bistatic scattering. The clouds of bubbles entrained at the sea surface by breaking waves are an important topic in underwater acoustics. Waveguide reverberation (i.e. reverberation in shallow water or through a surface duct) typically includes a significant fraction of energy scattered from the sea surface. The original document contains color images.