Results of environment inversion using modes extracted from vertical line array data

Abstract

The results are presented for geoacoustic inversion using the depth-dependent normal modes extracted from vertical line array (VLA) data. The normal modes for multiple frequencies are obtained by performing a singular value decomposition (SVD) on VLA data recorded as a source moves outward in range. The data-extracted mode functions are then used to invert for the environmental parameters. The Levenberg–Marquardt nonlinear optimization method is used to adjust the environmental parameters to find the best fit between the data-extracted modes and modes modeled by the ORCA normal mode model. The method is useful for determining the sound speed profile and the characteristics of the uppermost bottom layers [T. B. Neilsen and E. K. Westwood, J. Acoust. Soc. Am. 104, 1741 (1998)]. Mode extraction and geoacoustic inversion results for a range-independent track during the ACTII experiment will be presented. Extension of the theory for mode extraction (and preliminary results for inversion using simulated data) in a range-dependent environment using the adiabatic approximation will also be presented. [Work supported by ONR.]