Jean O. Nam
J. Robert Fricke
Dept. Ocean Eng., Cambridge, MA 02139
Propagation of high-frequency signals, O(10 kHz), in a shallow-water channel, O(10 m), is complicated by multipath effects associated with the surface and bottom. The goal of this research is to dereverberate the time spread and dispersed received signal into a processed signal with a temporal duration comparable to that of the outgoing pulse. Given the impulse response of the channel and the received signal, an inverse filtering method utilizing minimum-phase components can be effective. However, because of channel dynamics caused by turbulence, internal waves, and thermal stratification, calculation of the exact impulse response is impossible. A more robust signal recovery method, known as cepstral smoothing, has been developed to separate the signal from the channel impulse response in the cepstral domain. Using this method, the recovery is independent of the channel impulse response and is robust in the presence of additive noise. The cepstral smoothing method dereverberates the original signal, but absolute time delay information is lost. A moving rms window applied to the original received signal recovers the lost time delay.