Wave and Surf Generated Ambient Noise Measurements


Investigator

Josette Paquin Fabre, James H. Wilson, Marshall D. Earle

Funding Source

Naval Research Laboratory, Washington, D.C.

Objectives

The objective was to obtain ambient noise data at offshore positions from outside of the surf zone (2 km from shore) to 7 km offshore for investigations of nearshore acoustic noise generated by waves and surf. The goal after data collection is development of predictive models for nearshore acoustic noise for application to Navy littoral operations.

Approach

Four Navy AN/SSQ-53D DIFAR sonobuoys were deployed approximately 2 km, 3 km, 5 km and 7 km from shore during 5 separate high wave height events during October. Deployments were made by leased commercial helicopter in positions away from immediate proximity to other sensors to avoid physical interference. Buoys were moored using a Norwegian type float and a Danforth anchor with extra weight. Transmitted ambient noise data for 0 to 7500 Hz was recorded using a Navy standard sonobuoy reciever inter- faced using an analog to digital (A to D) converter connected to a SUN Workstation. Data was recorded onto 8 mm data tapes. Several hours of analog data were also recorded. Data will be analyzed in conjunction with wave and surf measurements in addition to any environmental information from other experiments to develop and improve theoretical nearshore acoustic noise models.



Results

A total of 720 hours of acoustic data was recorded during DUCK94. A subset of the data was chosen for the first round of analysis. This subset represents 2 different wave events (Oct 13 and Oct 17) and 4 distances from shore. This data is currently being calibrated and analyzed using various data processing techniques in order to determine data quality, statistical properties, optimum processing methods, etc. Some results will be presented in May, 1996 at the Acoustical Society of America Meeting in Indianapolis. For a list of addresses of the investigators involved in Duck 94 click here.