Determination of Mixed Layer Depth from C-Band Synthetic Aperture Radar (SAR)

Abstract

Oceanic internal waves are frequently observed on the continental shelf during the summer season, when the ocean is stratified. The appearance of internal wave phenomena in remote sensing images has been increasing the curiosity to observe internal wave at specific area in the world. Studies reveal that Synthetic Aperture Radar has a capability to detect internal waves. In the present study, ENVISAT Advanced Synthetic Aperture Radar (ASAR) image acquired on October 4, 2003, was used to determine Mixed Layer Depth (MLD) off Bay of Bengal of Indian Ocean region. The image showed several prominent trains of internal waves, with several wave packets in each train. The ocean was assumed to be a two layer system, and that the local semidiurnal tide is the generating force for the internal waves. By assuming that the local semidiurnal tide period is the generating source for these waves, and by measuring the distance between the wave packets, it is possible to derive the group velocity of the internal waves from Synthetic Aperture Radar (SAR) images directly. The mixed –layer depth is then derived by assuming the ocean as a two-layer finite depth model. The group velocity measured from the SAR image and the simulated group velocity by the two layer finite depth model was matched to get the mixed layer depth. The estimated mixed layer depth was 21m. This value show reasonably good agreement with the actual depth of 19.5m of in-situ ARGO buoy.