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Traditionally oceanographic features such as fronts and eddies have been monitored using satellites equipped with optical sensors such as the Advanced Very High Resolution Radiometer (AVHRR). The disadvantage of using AVHRR, however, is that it requires cloud free conditions to view the Earth's surface. Synthetic Aperture Radar (SAR) provides all weather, day/night image acquisition capabilities. Currently little is known about the effects of sea surface temperature variations on the returned SAR signal, though it is known that some variation in surface roughness is present where oceanographic features occur. Research into these phenomena is being undertaken at the Defence Research Agency (DRA) in Farnborough, U.K.. To investigate the capabilities of SAR, for ocean front detection, the Ocean Fronts Feature Analysis System (OFFAS) has been developed by Earth Observation Sciences Limited under contract to DRA. Using OFFAS, AVHRR data is used to verify and validate the SAR responses to oceanographic features. This paper is an update to that presented at Oceanology International '94, in Brighton which discussed the research and development work into the use of SAR data from the ERS-1 satellite to identify oceanographic features. Since then the modifications to the software, mentioned in that paper, have been made. OFFAS II now provides the capability to geometrically rectify the images to a regular map projection prior to the simultaneous display and manipulation of both image types. Thus allowing faster location of features of interest identified within a reference image (e.g. AVHRR), delineation of them using a tracing procedure, then the automatic redrawing of the trace on the corresponding target image (e.g. SAR). In addition the geometrically rectified SAR images can be mosaiced together, this is particularly useful where large oceanographic features span more than one image. To date, trials performed using OFFAS have indicated its value in aiding interpretation of SAR image patterns by comparison and verification with AVHRR imagery.
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