Underwater acoustic communication has several applications for civilians and defence. It is a challenging engineering problem, where large variability of ambient noise and highly variable channel characteristics limits the performance of communication system. In addition horizontal transmissions in shallow water is considered very challenging due to time varying delay spread and significant Doppler spread. An experiment was conducted to study the diurnal variability of underwater acoustic communication channel properties of the south west coast of India. Time spread and bit error rate for different ranges and depths are compared in this paper. Influence of prevailing sound speed profile on acoustic communication link is also discussed.
During November 2017, an active source seismic survey was performed in Andaman sea to study the acoustic propagation characteristics. High power low frequency acoustic signals generated by 20-air gun array onboard ORV Samudra Ratnagar were recorded from INS Sagardhwani at four different depths within 8 km ranges in shallow and deep waters. Low frequency sound levels were estimated using root mean square and power spectral values. Amplitude levels were analysed with respect to arrival time variation with frequency and is presented.
South Eastern Arabian Sea is well known for its prolonged and warmer sea surface temperature (>30 °C) events generally known as Arabian Sea mini warm pool occurring during the pre-monsoon periods (March-May). To study the intensity and spatial extent of the warm pool, ten years (2007-2016) of satellite-derived weekly averaged SST and in-situ data measured from INS Sagardhwani are used. The analysis is done based on the precondition ‘sea surface temperature > 30 °C’ and lasts more than a week. These analysis demonstrate the existence of a strong inter-annual variability. It is also identified that the sea surface temperature in the year 2016 is the hottest over the decade with maximum spatial coverage and prolonged period of occurrence. These anomalous events are also explained in terms of variabilities of the atmospheric water vapour and wind at the sea surface.
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