Acoustic propagations in the presence of a subsurface cold core eddy in the Bay of Bengal - A case study

Abstract

Acoustic characteristics of a cold core eddy, observed in the Bay of Bengal during southwest monsoon period is studied using CTD data along the western boundary. The presence of eddy brings about a reduction in the ambient sound speEd. by 10 m.s sup(-1). The depth of SOFAR channel axis, which should have shown a deepening trend in this region remains constant under the influence of eddy. Ray tracing using a range-independent ray trace program showed that the arrivals arc delayEd. by about 100-200 ms under the influence of the eddy. The acoustic intensity computed along the eigen ray passing through the eddy suffers an additional loss of the order of 20-25 dB. The simulated travel time perturbations associated with the eddy was inverted using singular value decomposition. From the numerical experiments it was found that inversion carried out using 18 eigen rays with 9 layers adequately resolve the eddy profile using 9 eigen modes