The ray compatations for different angles of emergence have been carried. From this analysis it was evident that the average travel time difference is +0.4s approximately amounting to a temperature fall by 0.0375℃ over the entire water column transgressed by the acoustic rays.
Summary of the results
･ Analysis of climatic temperature, salinity fields, sound speed and sound channel parameters enabled identification of regions of significant variations.
･ Analytical form of sound speed profile revealed wide deviations in the thermocline.
･ Reference sound speed profiles have been constructed region-wise and season-wise to examine the order of expected variabilityin the north Indian Ocean.
･ Seasonal sound profiles have been used to perform ray tracing considering both range independent and range dependent environments,.
･ The number of eigen rays increase with the source-receiver range. For an optimum range of 300km, 15 to 20 useful rays exist. Number of rays increase according to the ratio R/200.
･ For a propagation range of 300km, the arrivals spread over a time span of about 400ms in the Arabian Sea and much less (〜110ms) in the Bay of Bengal.
･ Eigen ray estimations revealed that for the case of an up slope (down slope) propagation higher number, '22' (lower number '3') of rays reach the receiver.
･ For a propagation range of 300km, the computed acoustic losses due to spreading, showed variations between 90dB and 120dB for different eigen rays while the chemical absorption losses for a source frequency of 400Hz (200Hz) account for about 15.25dB (4.25dB). At 400Hz, absorption takes place at the rate of 1.76 x 10-3dB/km over the ambient value.
･ Simulation of acoustic propagation over a range of 6000km (Cape Leeuwin - Madras) path revealed that acoustic pulse would take about 70 minutes to reach the receiver. It will undergo a transmission loss between 100 and 120dB.
Acknowledgement
The financial support granted to CSM by JAMSTEC, Japan to participate in this symposium is gratefully acknowleged. We thank the Director, NlO for according permission to present this material. The authors appreciate assistance rendered by S.N. Jakhi, M. Wahidulla and A. Y. Mahale in getting camera ready script with figures.
