Wavelet analysis comparing spectral characteristics of high frequency acoustics and hydrographic properties on Georges Bank

Abstract

Acoustic surveys of Georges Bank were carried out during the GLOBEC Broadscale program in January, March, and June of 1998 and 1999. The Greene Bomber towfish collected temperature, salinity, and fluorescence as well as the acoustics data at 120 and 420 kHz, from approximately 3 meters depth on all six cruises. With over 1200 kilometers of acoustic trackline on each cruise, covering well mixed, frontal, and well stratified water columns, a method is needed to characterize patch structures encountered. Wavelet analysis offers a computationally effective approach that can be applied to all the data obtained along the trackline. Variance analysis of the wavelet transform provides both spatial and spectral resolution simultaneously, allowing distinct consideration of spectra obtained in any spatial subset of the entire dataset. Temporal and spatial variations in the characteristic slopes and length scales of temperature, salinity, and fluorescence indicate that distinct spectral signatures exist that can be exploited to sort out physical and biological contributions. The extent to which physical and biological spectral signatures influence the wavelet variance spectra of the acoustic data is examined in each hydrographic regime.