Internal waves and acoustic variability

During October 1994 and 1996 acoustic experiments were conducted in the Western Mediterranean off Nice in a region characterised by strong near-surface stratification and deep water. Transmissions at a frequency around 2000 Hz were made over ranges of 2-50 km from a ship to a coastal receiving array. The sound speed fluctuations due to internal waves were estimated using the Garrett and Munk (GM) spectrum and compared with observations, the observed internal waves being found to have less energy than the GM spectrum. A simulated velocity field due to internal waves was then produced by summing over a selection of frequencies with random phases, solutions for the vertical structure of the internal modes being obtained by a shooting method. The vertical velocity field was used with a 2D advection model to simulate the motion of temperature surfaces and hence the associated acoustic variability