Remote sensing of Tyrrhenian shallow waters using the adjoint of a full-field acoustic propagation model

Over the past two years the capabilities of adjoint-based inversion have been explored for applications both in geoacoustic inversion and shallow-water acoustic tomography. Starting from case studies based on the principles of optimal control theory the performance of adjoint modeling has been constantly improved to more realistic scenarios ever since. In particular, the concept of semi-automatic adjoint generation has been introduced for inversion of satellite ocean colour imagery and geoacoustic characterization of seabed properties. In the framework of a Maritime Rapid Environmental Assessment sea trial (MREA/BP07) that was conducted in the same area south of the island of Elba as the earlier Yellow Shark experiment (YS94), this paper examines the original YS94 geoacoustic data and the recent MREA07 oceanographic data to demonstrate adjoint-based acoustic monitoring of environmental parameters in Mediterranean shallow waters. First, the adjoint-generated environmental gradients are validated for an application in geoacoustic inversion where the bottom geoacoustic parameters of the layered seabed are determined from long range acoustic propagation data in the water column. Then, for the application in ocean acoustic tomography, the temporal variability of MREA/BP07 sound-speed field data is analyzed in terms of empirical orthogonal functions and the adjoint-based approach is used to track the time-varying sound speed profile of the experimental transect.

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