Impact of internal waves on the acoustic field at a coastal station off Paradeep, east coast of India

Internal Wave (IW) characteristics and the impact of IW on acoustic field have been studied utilizing the hourly time series of temperature and salinity data collected at a coastal site off Paradeep (north Bay of Bengal) during 24–25 October 2008. The IW characteristics, viz. period (tper), velocity (Cvel), wavelength (L), and wave numbers (k), are found to be 2.133–34.72 h, 0.135 km h−1, 0.37–6.2 km and 2.70–0.16 cycles km−1, respectively. The semi-diurnal tidal forces are predominant than diurnal as well as at other frequencies and its contribution is about 64% towards the total potential energy (E0 = 3.34 J m−2). Sound velocity perturbations with space and time in the presence of IW field are examined from Garrettt-Munk (GM) model. Transmission loss anomaly for optimized source-receiver configuration at the depth of 53 m and range of 9 km has been computed from acoustic modelling. The loss in the acoustic transmission is found to be 38.4 dB in the presence of low-frequency IW field.