Identification of Bed Forms Through ERS SAR Images in San Matías Gulf, Argentina

Abstract

The European Space Agency (ESA) funded two projects in 1991 and 1994 concerning the observation of the Argentine coastal environment with synthetic aperture radar (SAR). Studies were carried out for the periods 1992–1994 and 1994–1997. Several ERS-1/2 satellite SAR images were acquired over the San Matías Gulf in the Patagonian coast during these two periods. SAR is a side-looking imaging radar that operates from either a satellite or an aircraft. The instrument emits a series microwave pulses toward the earth in a direction perpendicular to the flight path. Imagery is constructed from the strength and time delay of the returned signals, which depend primarily on the roughness and dielectric properties of the surface under observation and the distance from the radar. Ocean surface roughness wave-like patterns, imaged as a series of bright and dark linear features by SAR, are persistently observed over the San Matías Gulf mouth region. A total of thirty-three (33) ERS-1/2 SAR images (100 km × 100 km) from 15 different orbits from 1992 to 2000 were analyzed. This series of observations has allowed for a detailed examination of the location, persistence, and the conditions involved in the imaging of the observed wave-like patterns. Very strong tidal currents of the order of 2 m/s characterize the gulf region. The characteristics of recurrent surface patterns in the SAR images indicate that they are caused by the interaction of the tidal currents with bed forms in the bottom topography of the gulf. The location of these bed forms is poorly documented in the available bathymetric charts of the region. The SAR images show the significant potential that satellite radar observations have as a tool for detecting unmapped coastal ocean bottom features, particularly, where bathymetric mapping activities can be extremely difficult, dangerous, or costly.