Spatial and temporal variability of the sound speed field in the water column can have a significant impact on acoustic propagation. It is difficult or sometimes impractical to measure fine scale variations in water column properties over an acoustic propagation path. When measurements are not available, water column properties must be approximated. In past work, inverse methods based on acoustic tomography and matched-field processing have been used to estimate mean water column sound speed profiles. In this work, a perturbative scheme using modal wave numbers is used to obtain range-dependent features of the water column. Based on the work of Rajan et al. (1987), a technique has been developed to estimate water column sound speed profiles using historical data to constrain the inversion. This constraint allows for a robust inversion; the result is accurate both when the inputs are noisy and when the bottom is poorly known. The new technique is demonstrated using data from the Shallow Water 2006 (SW06) experiment. Inversion results are compared to in situ measurements from the towed CTD chain.

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