High-frequency broadband matched field processing in the 8-16 kHz band

Abstract

We will show model-based localization results at 8-16 kHz using a single hydrophone in several shallow water environments, with successful tracking out to 3 km. It is very difficult to produce accurate replicas of the field at these high frequencies, due to sensitivity to small bathymetric features, surface motion (waves), and water column fluctuations. To reduce this sensitivity, we match the envelope of the field in the time domain, using the Bellhop ray-tracing model to calculate replicas. At these high frequencies, ray tracing is a viable approach. SignalEx tests have been conducted in a variety of shallow water coastal environments to relate acoustic communications performance to oceanographic conditions. A fixed receiver and a transmitter drifting out to minimum detectable ranges were used. Waveforms to probe the channel in the 8 to 16 kHz band were transmitted at regular intervals. These signals were initially used to study the channel and subsequently to test our source localization algorithms. Working in the time domain enables the fluctuations to be directly observed as changes in the times of arrival. After aligning a sequence of probe pulses on the stabler initial arrivals, the pattern of fluctuations in the amplitudes and arrival times of the later arrivals can be observed. These fluctuations cause mismatch between the data and the replicas with which the data is being correlated. We will present measurements of the time-varying channel response and source localization results from a shallow water site off the coast of La Jolla in San Diego, California.