Continued Analysis of High-Frequency Broadband Acoustic Scattering from Non-Linear Internal Waves during SW06

Abstract

LONG-TERM GOALSTo understand high-frequency broadband acoustic backscattering from small-scale physical processes, such as internal waves, turbulence, and microstructure, in shallow, stratified waters. OBJECTIVESThe primary objective of the overall research program was to measure high-frequency broadband acoustic backscattering in highly stratified, energetic environments and to determine the contribution to scattering from temperature and salinity microstructure. Testing the validity of existing scattering models and the initial development of new, and/or extensions of existing, simple physics-based scattering models was a secondary objective of this work.To accomplish the stated objectives, high-frequency broadband (150-600 kHz) acoustic backscattering measurements were performed during the generation, propagation, and dissipation of non-linear internal waves in August 2006 as a part of the SW06/NLIWI experiment. Almost coincident microstructure measurements were collected by Jim Moum with a profiling microstructure instrument, Chameleon. The contribution to scattering from biological organisms was quantified using netsamples, from which the zooplankton taxa, size, and depth (in coarse vertical bins) can be determined.Analysis of these data to date has focused on (1) determining the dominant scattering mechanisms giving rise to enhanced backscattering often associated with the passage of non-linear internal waves, with particular attention given to elevated scattering associated to Kelvin-Helmholtz instabilities, and (2) inverting the broadband scattering data for meaningful biological and physical parameters and comparing the acoustically-inferred to directly measured parameters, thereby allowing the validity of the scattering models to be tested.The primary objectives of the effort described here are: 1) to understanding and quantifying the contribution to acoustic backscattering from the seasonal pycnocline, 2) to investigate the statistics