ESTIMATION OF OCEAN-BOTTOM PROPERTIES BY MATCHED-FIELD INVERSION OF ACOUSTIC FIELD DATA

Properties of the ocean bottom, including bathymetry and geoacoustic parameters such as sound speed, density and attenuation, are required for reliable acoustic propagation modeling and matched-field source localization. Bottom properties can be difficult to measure directly; however, inversion procedures hold much promise for estimating their values from acoustic field measurements. The inversion can be formulated as an optimization problem by assuming a discrete model of unknown parameters and a bounded search space for each parameter. The optimization then involves finding the set of parameter values which minimizes the mismatch between the measured acoustic field and modeled replica fields. Since the number of possible models can be extremely large, we have employed the method of simulated annealing which provides an efficient optimization that avoids becoming trapped in suboptimal solutions. The matching fields are computed using a normal mode model. In inversions for range-dependent parameters, the adiabatic approximation is employed: this allows mode values to be pre-computed for a grid of parameter values and stored in ''look-up'' tables for fast reference, which greatly improves computational efficiency. Synthetic inversion examples are presented for realistic range-independent and range-dependent environments.