Low-frequency ambient noise variation in the Beaufort Sea

Abstract

NRL/SSC conducted Arctic acoustics experiments in the Beaufort Sea as part of ICEX-92 in March and April of 1992. One objective was to collect a long-term time series of low-frequency (less than 50-Hz) acoustic ambient noise with a volumetric array to investigate environmental forcing functions and 3-D noise characteristics. A total of 191 nearly continuous hours of acoustic ambient noise was collected with a vertical array and three horizontal line arrays that were separated approximately 60° in azimuth. A geophone array was also deployed coincident with one of the horizontal line arrays. Meterological data collected included wind speed, wind direction, temperature, and barometric pressure. Oceanographic data included CTD’s and current velocities. Local environmental conditions varied widely during the data collection period. In addition, both ridging and an opening of the ice occurred within 500 ft of the vertical array during data collection. The focus of this presentation is the first step in the analysis of this data set and examines the relationship between ambient noise level fluctuations observed on an individual hydrophone and changes in local air temperature for different time scales. Gradual surface temperature increases and decreases over 10-h time segments occur simultaneous with an increase in the noise fluctuation. Temperature changes during time periods less than 5 h show minimal effect on noise fluctuations. Geophone data agree well with acoustic data in both level and fluctuation. Comparisons of ambient noise with other local forcing functions will be discussed. [This research was supported by ASW Environmental Acoustics Support Program (AEAS).]