Quantification of Acoustic Variability from Thermohaline Fields in the Arabian Sea

Acoustic waves, when they propagate in water, exhibit fluctuations in their spectral characteristics due to multi-path and ocean medium variability, especially in coastal waters. Quantitative knowledge of these received signal fluctuations is essential to understand the randomness of acoustic wave propagation. Acoustic variability in the ocean can be attributed to various oceanographic processes such as fronts, eddies and internal waves.Internal waves are ubiquitous in the ocean and cause acoustic fluctuation due to perturbations in sound speed. Fluctuation of an acoustic pulse travelling in the presence of internal wave can be quantified using parameters such as travel time variance and frequency spread. Quantification of travel time variance using the thermohaline data is the focus of this paper.Here, we have quantified an acoustic fluctuation parameter as a function of sound speed variance. The buoyancy frequency, which is the upper frequency bound, is estimated to characterize the internal wave field. These two quantities are estimated using temperature and salinity profiles at a particular location in the Arabian Sea. We have estimated the coherence length for different grazing angles of acoustic waves from buoyancy frequencies for various source - receiver geometry. In this paper, attempts have been made to compute the travel time variance with range using sound speed variance and coherence length. This parameter describes the coherent nature of the received acoustic signals which would be required for the performance analysis of underwater sensors. The travel time variance is found to be dependent on the launch angle(upto8°), with maximum variability for higher angles.