Array performance and variability at short range near Vestfjorden

Abstract

An experiment was conducted in October 1989 in shallow water near Vestfjorden in support of low frequency active sonar system research at SACLANTCEN. This report addresses some acoustic measurement results from that test related to array performance and variability at short range. The received signal level varied by as much as 10-15 dB across the array on a single ping, as well as from ping to ping. This variability and changes in the multimode arrival structure are shown to be caused by small (1 m) changes in array depth. Average array signal gain degradation is less than 1 dB, so the array performance is nearly perfect, despite moderate tow-ship course variations and an unexpected "hole" in the acoustic field.