ATOC signal enhancement using adaptive filtering

Abstract

A moored, autonomous recording system deployed off the east coast of New Zealand in early 1996 acquired signals from the Pioneer seamount ATOC source. Unfortunately, the data were corrupted by a very strong, aliased interfering signal electrically coupled from a malfunctioning power supply which drifted in frequency by over 400 Hz, and also by a mechanically coupled vibration at the rotation frequency of the hard disk used to store the data. Pulse compression of the biphase modulated psuedorandom sequence used to encode the transmission spreads the energy in these signals across the desired signal’s spectral passband, degrading the signal-to-noise ratio of the receptions. Since both unwanted components are unstable in frequency, classical digital filters are unable to eliminate them. However, an adaptive LMS filter has been used to track and virtually remove the interfering signals before pulse compression, resulting in signal-to-noise ratio gains of up to 6 dB.