General Introduction

Radar images acquired over the ocean by the synthetic aperture radar (SAR) aboard the European Remote Sensing satellites ERS-1 and ERS-2 contain a wealth of information on small scale and mesoscale phenomena in the ocean and the marine boundary layer. Oceanic phenomena that can be delineated on SAR images of the sea surface include ocean surface waves, internal waves, eddies, oceanic fronts, underwater bottom topography, ship wakes, oceanic wakes behind islands, oil slicks, river plumes and upwelling areas; atmospheric phenomena include katabatic wind fields, land-sea breeze, atmospheric wakes behind islands and coastal mountains, gap winds, boundary layer rolls, convective cells, atmospheric gravity (or internal) waves, and rain cells. Since the launch of the ERS-1 satellite on July 17, 1991, and the launch of the ERS-2 satellite on April 20, 1995, a large number of oceanographic and meteorological investigations have been carried out in which ERS SAR images have been used. These images, especially when used in combination with other remote sensing and situ data and with model calculations, have led to significant new results in oceanography and marine meteorology. However, most of these investigations concern ocean areas located at mid or high latitudes. But ERS SAR images acquired over tropical or subtropical ocean areas are even more suited for extracting oceanographic and meteorological information because here, on the average, the wind speed is lower, which, in general, gives rise to stronger radar signatures of oceanic and the atmospheric phenomena on ERS SAR images.

The purpose of this website is to attract the attention of a broad readership in countries lying in the tropical and subtropical zones to ERS SAR imagery acquired over the ocean and to motivate scientists from these countries to use them for their oceanographic and meteorological investigations. For this purpose we have assembled some 180 sample ERS SAR images acquired over tropical and subtropical ocean areas which show typical sea surface manifestations of several oceanic and atmospheric phenomena. Before presenting the ERS SAR images in each category, a short introduction to the phenomena is given and a reference list added. In some cases we have included SPOT images and added ancillary information to the images.

In a certain sense, this website can be considered as a follow-on publication of the NASA-JPL publication entitled "Seasat views oceans and sea ice with synthetic aperture radar" by Fu and Holt (1982) and of the ESA publication entitled "SAR feature catalogue" by Johannessen et al. (1994). The latter publication contains ERS-1 SAR images that were acquired mainly over the Norwegian Sea. Here we present ERS SAR images which were acquired over different parts of the tropical and subtropical ocean and which show typical radar signatures of oceanic and atmospheric phenomena. Most of the ERS SAR images shown in this website were received and processed at the ERS receiving stations in Singapore and Taiwan.

We hope that this publication will contribute to enhance the awareness about the potential that lies in ERS SAR imagery for oceanographic and meteorological research.

References

• Fu, L.-L. & Holt, Seasat views oceans and sea ice with synthetic aperture radar, NASA-JPL publication 81-120, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA (1982).
• Johannessen, J.A., Digranes, G., Espedal, H., Johannessen, O.M. & Samuel, P., Brown, D. & Vachon, P., SAR ocean feature catalogue, ESA SP-1174 (October 1994).