Field-calibrated source tracking using channel measurements from high-frequency mobile platform transmissions

Abstract

Modern signal processing methods for acoustic arrays in a waveguide use acoustic propagation models to construct signal replicas that capture channel effects such as multipath and refraction. However, such model-based techniques require a detailed map of the propagation environment (often unavailable) and impose the significant computational burden of modeling the channel. We propose an alternative approach to this problem, in which mobile platforms such as AUV’s and gliders act as acoustic beacons for calibrating the field, replacing modeled signal replicas with directly measured channel impulse response functions. Key issues are whether channel estimates made in a (typically) high-frequency communications band and at a limited set of points can be extrapolated to lower frequency and to the entire field. Furthermore, the channel response may change with time, depending on the variability in the ocean waveguide, requiring periodic refresh of the calilbration. We will demonstrate this approach in simulation and with experiment data from two high-frequency experiments, KauaiEx and the Makai Experiment, in which a variety of acoustic communications waveforms were transmitted from towed and fixed systems.