The SESAME I Experiment, Acoustic Data Processing and Catalog

The first Shelf Edge Study Acoustic Measurement Experiment, SESAME I, was conducted August/September, 1995. The experiment took place at the Malin Shelf (56 deg 33' N, 9 deg 0' W) with the objective of determining the effects of solitary internal waves on acoustic fluctuations at the shelf edge. This paper describes the preliminary analysis of the narrow band continuous wave (CW) acoustic data from the three acoustic legs of the experiment. The acoustic data sets were collected using two Data Acquisition Buoy Systems (DABS), the first deployed in shallow water (170 m) at the shelf edge and the second deployed approximately 6100 m down slope in 500 m of water. Acoustic measurements were made over a frequency band of 100 to 2100 Hz with CW tonals broadcast at 150, 400, 800, and 1600 Hz. The signals were transmitted at source depths of 20, 50, and 100 m at multiple ranges from the array. System calibration analysis revealed both systems had low system noise floors and a flat amplitude response from approximately 125 Hz to 2000 Hz for all channels. The shallow-water DABS system had two hydrophones with an amplitude offset; calibration values applied to the data correct for these offsets. System calibrations have been applied to the acoustic results to produce transmission loss values versus source receiver range. Received levels were highest from the 500 m source depth at all frequencies and at both array locations. Both the 20 m and 100 m source depths often had very low signal to noise ratios, limiting the amount of reliable TL data. The deep-water DABS system had a lower dynamic range that resulted in the loss of acoustic data on the top three phones of the array. This was due to high noise levels during all events, probably associated with flow noise past the phones (the mean current speed was 10 to 40 cm/s) i*H9,G(3Æ*I-*G*)H(>GD,Æ[read more]