A Comparison of Bathymetric Signatures Observed on ERS SAR and LANDSAT TM Images Over the Timor Sea

Abstract

Modulation of surface capillary waves by tidal current flow over submarine relief features causes roughness variations on the ocean surface that are detected by Synthetic Aperture Radar (SAR). Previous studies have demonstrated the presence of features in SAR images that correspond with submarine topography under appropriate sea-state and imaging conditions. In this study, bathymetric signatures observed on two European Remote Sensing Satellite (ERS) SAR images and a near-coincident Landsat Thematic Mapper (TM) image over an area west of Melville Island in the Timor Sea were investigated. Bathymetric features visible on the SAR and optical satellite images correspond well with isobaths of the study area. Submarine relief features seen on the satellite images of the study area were analysed in conjunction with wind and sea-state data. Based on the analysis, we highlight some factors governing the expression of submarine relief features seen in satellite images of the study area. Submarine relief signatures are sensed by optical and SAR sensors through different mechanisms, however similarities in signatures observed in the near-coincident optical and SAR images indicate that the underlying mechanism is common to optical and SAR imaging. Sun glint resulting from specular reflection and modulated by ocean surface roughness is the predominant mechanism producing features on the Landsat TM image that correspond with bathymetric signatures seen on the ERS SAR images. This study demonstrates the potential to extract information on sea bottom topography from sun glint in optical images under specific sun-sensor-target geometries and sea-state conditions, to complement similar information derived from SAR.