Volume Reverberation at Mid Frequencies in the Norwegian Sea

Abstract

During July 1991, the Naval Research Laboratory (NRL) conducted volume reverberation measurements at seven locations in the Norwegian Sea between 63°N and 68°N as part of a multi-laboratory experiment directed by the SACLANT Undersea Research Centre. NRL obtained volume scattering strength versus depth profiles at frequencies between about 1 kHz and 10 kHz. During the day, scatterers were generally found between depths of 150 m and 500 m. Even though nights were short and the northern horizon was always visible except when obscured by cloud, scatterers were nearer the surface at night, extending from about 100 m to 400 m. Scattering strengths were high, with strongest scattering at about 2 kHz during the day and between 1 kHz and 2 kHz at night. Some geographic variation was observed, with scattering at the northernmost station being the weakest. Comparisons of the measurements to scattering strengths predicted from bioacoustic modeling of fisheries data have been made and indicate that the principal scatterers were most likely blue whiting.