Oceanographic and Topographic Interactions in Underwater Acoustic Propagation, with Regional Applications

• Main Author: Carman, Jessie C.
• Other Authors: HARVARD UNIV CAMBRIDGE MA DIV OF APPLIED SCIENCES
• Format: Text
• Language: English
• Published: 1991
• Subjects: Physical and Dynamic Oceanography; Acoustics; *PROPAGATION; GLOBAL; PREDICTIONS; MODELS; INTERACTIONS; PARAMETERS; PHYSICAL PROPERTIES; TOPOGRAPHY; DEPTH; REGIONS; VARIABLES; DRIFT; SOUND TRANSMISSION; PARABOLAS; PATTERNS; DIFFERENTIAL EQUATIONS; FLUIDS; OCEANS; UNDERWATER ACOUSTICS; ACOUSTIC VELOCITY; OCEAN MODELS; BOTTOM; SEDIMENTS; LOW FREQUENCY; OPEN WATER; OCEANOGRAPHY; HIGH SENSITIVITY; SOURCES; *UNDERWATER SOUND; *SOUND TRANSMISSION; *SEDIMENTS; *ACOUSTIC VELOCITY; MATHEMATICAL PREDICTION; GULF STREAM; FRONTS(OCEANOGRAPHY); WATER MASSES; NORTH ATLANTIC OCEAN; OCEAN CURRENTS; ICELAND; FAROE ISLANDS; THESES.; Faroe Islands; Iceland; North Atlantic
• Online Access: http://www.dtic.mil/docs/citations/ADA241317; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA241317

Accurate range dependent underwater acoustic propagation using a parabolic approximation to the Helmholtz equation, and including sediment interactions, can be calculated in any part of the world ocean using sound speed fields generated by the Harvard Open Ocean Modeling system. The resulting acoustic predictions can be valid at any time for which oceanographic mesoscale environmental fields can be forecast. A thorough study is conducted of the effects of inclusion of a fluid sediment model with variable topographic depth on underwater acoustic propagation at low frequencies (25-100 Hz). Source depth and frequency dependencies of propagation patterns in the presence of such a sediment model are delineated in two realistic Gulf Stream region sound speed profiles. Effects of source depth and frequency on sensitivity to values of model parameters are determined and fundamental physical reasons for these sediment interaction effects given. Unusual propagation regimes occurring when source sound speed exceeds bottom sound speed, and then extreme sensitivity of these propagation regimes to sediment parametrization, are documented. Propagation effects are separately determined for topographic variations such as monotonic increase or decrease of depth, and oceanographic variations. Interaction effects when both physical conditions vary are detailed . Acoustic propagation is also studied in two other Atlantic regions. Distinct oceanographic surface boundary layer effects at frequencies too low for duct trapping are documented in the North Atlantic Drift Current region. Shallow -to- deep water propagation with strong oceanographic variations is demonstrated in the Iceland-Faeros front.