Simulation of Acoustic Backscatter from Bubble Plumes Using a Finite-Element Model and a CW Full-Field Backscatter Method

• Main Authors: Chin-Bing, Stanley A., Murphy, Joseph E.
• Other Authors: NAVAL OCEANOGRAPHIC AND ATMOSPHERIC RESEARCH LAB STENNIS SPACE CENTER MS
• Format: Text
• Language: English
• Published: 1990
• Subjects: Acoustic Detection and Detectors; Acoustics; *SIMULATION; ENVIRONMENTS; OCEAN SURFACE; MODELS; FINITE ELEMENT ANALYSIS; NUMERICAL ANALYSIS; BACKSCATTERING; MONOSTATIC RADAR; FULL WAVE RECTIFIERS; MATHEMATICAL ANALYSIS; BUBBLES; PRESSURE; PLUMES; ACOUSTIC EQUIPMENT; PACIFIC OCEAN; ACOUSTIC SCATTERING; REVERBERATION; ACOUSTIC VELOCITY; NORWEGIAN SEA; WAVES; ACOUSTIC FIELDS; INTERNAL WAVES; FOAM; BISTATIC RADAR; CONVERGENCE ZONES; ANOMALIES; FOAM COMPUTER PROGRAM; PEFFRAME COMPUTER PROGRAM; PE61153N; WUDN257033; Norwegian Sea; Pacific
• Online Access: http://www.dtic.mil/docs/citations/ADA230146; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA230146

Backscatter from large bubble plumes has been suggested as a possible cause of anomalous reverberation. This possibility has been examined using a finite-element full-wave acoustic model, FOAM and PE-FFRAME, a hybrid marching version of FOAM, applied to a large sea-surface plume having sound speed and density representative of a 30% volume fraction. A cw differencing technique was applied to isolate the backscatter. The technique involves calculating the total full-wave acoustic field with and without the object (plume) present; taking the difference of the two complex pressure fields in the backscattered direction gives a measure of the backscattered acoustic field caused by the object. The cw full-field backscatter method (cw FFBM) has been benchmarked by an analytic calculation of the backscattered field from a rigid plate. This and other benchmark examples will be presented that validate the cw FFBM. Plume backscatter using the cw FFBM was examined for environments in the Norwegian Sea and the Pacific. Intenal wave fields were also introduced into both the Norwegian Sea and Pacific environments via an internal wave model. Numerical simulations using PEFFRAME and the cw FFBM will be presented that show the combined effects of Long-range (one convergence zone) monostatic and bistatic backscatter from a Large bubble plume in the presence of an internal wave field and the sea-surface boundary.