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Observations of Oceanic Internal Waves in Bay of Bengal using Synthetic Aperture Radar

K.V.S.R Prasad(1) and M. Rajasekhar(1)

(1) Andhra University, Waltair, Visakhapatnam - 530 003, India

Abstract

Oceanic internal waves are essentially a subsurface phenomenon, but do have strong surface manifestations that lend themselves particularly well to remote observation. Internal waves can exist in stratified waters of deep oceans as well as in marginal areas at all times and these can be significant participants in many physical processes in a stratified ocean. The generated mechanisms of internal waves are believed to be tidal flow over underwater obstacles (Seamounts, shelf brakes, and troughs) and other proposed generation mechanisms are frontal boundaries, varying winds with disturbed weather and seasonal wind conditions, etc., Amongst the variety of internal waves very energetic waves are created by reversing tidal flow over topography in a stratified environment (Bains, 1982). In the coastal environments, the generation region is expected to be the shelf edge. It is well known that satellite Synthetic Aperture Radar (SAR) is a very efficient at imaging surface manifestations of oceanic internal waves in all weather conditions. Vertical oscillations, or internal waves, by convergence and divergence water below, generate surface currents that modulate the spectral density of Bragg Waves, causing the large-scale wave like pattern signatures in SAR images. Sea surface manifestations of internal waves in the shallow continental shelf waters as well as in deep waters of north Bay of Bengal (15N to 21N and 82E to 86E) have been observed almost all seasons imaged by Synthetic Aperture Radar (SAR) images of ERS1/2 and Envisat ASAR missions during the period 1993 to 2004. Especially tidal generated shoreward propagating groups of internal wave packets are frequently fancied in shallow waters during summer months and as well as in September and October. Deep water propagating tidal generated long crest length internal wave packet on 18th February 2004 of Envisat Wide swath Advanced Synthetic Aperture Radar (ASAR) image profile is studied. Large number of short period, shoreward propagating rank ordered internal waves packets are revealed on continental shelf slope by Envisat ASAR image mode images on 4th October 2003. Wave packets have been modeled by KdV type equation and linked to Satellite image observations for internal wave parameters like characteristic half width (Zheng et.al., 2001), amplitudes and phase speeds. Also the authors made an attempt to identify the hot spots of internal waves in the north Bay of Bengal by SAR quick looks.

 

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