Underwater acoustic propagation experiments during ARMEX

Two-ship acoustic propagation experiments were conducted in deep waters of the Arabian Sea between 22-25 July and 7-8 August 2002 from onboard INS Sagardhwani ORV Sagarkanya during ARMEX-I phase. The aim this experiment was to understand spatial (up 30 km) temporal 24 hr) fluctuations intensities within surface duct. transmissions made 15m depth at 2.4 KHz 620 Hz frequencies one ship signals received 40m depths on second ship. data recorded for 10 min duration each transmission sec averages taken computing intensities. Simultaneous oceanographic temperature (CTD XBT), currents (ADCP) waves (SBWR) also recorded. Steady homogeneous mixed layer 50-60m offered an ideal environmental condition duct propagation. sea-state moderate with significant wave height ranging 1.5 2.3m. sub-surface upper 125m water column revealed predominance tides change current direction 6 hr intervals. speeds ~ 50 cm/s. analysis highlighted importance variations compared variations. Around 20 dB intensity noticed variability where as only 7 fluctuation observed variability.