Donald R. Del Balzo
SACLANT Undersea Res. Ctr., Viale San Bartolomeo, 400, 19138 La Spezia, Italy
An experiment was conducted in October 1989 in shallow water (250-320 m) near Vestfjorden in support of sonar system research at SACLANTCEN. This talk describes some observations of acoustic variability and array performance at short range for one-way pulse propagation during a 46-min period. The signals were 0.5-s LFM pulses in the frequency band of 340--345 Hz. They were received at a range of 13 km on 59 elements of a towed array. Large variability in the received signal level across the array, by as much as 10--15 dB, was observed on some individual pulses. These acoustic variations appear to be related to depth variability along the array due to a small array tilt. Normal mode calculations in this environment indicate the existence of a deep acoustic null in the vicinity of the measured data. Average array signal gain degradation for all data with SNR>20 dB is only 0.6 dB, so the array beamforming performance is close to the theoretical maximum on this 27-wavelength aperture in shallow water.