SAR & GOM
The GOM is a dynamic marine basin; it encompasses important energy and fisheries resources; it hosts intense population centers and real state development, it is a crucial transportation corridor and it has been a nexus of hurricane activity. SAR satellite data contributes to scientific study and effective management in the region. The utility of SAR data is enhanced by high spatial resolution, independences from cloud cover and its ability to distinguish fine-scale processes.
Hurricane studies with SAR in the GOM.
The Radarsat-1, Envisat and ERS-1 and ERS-2 spacecraft have passed over several storms in the Gulf of Mexico. We used NOAA post-season track data, extracted from the Historical North Atlantic Tropical Cyclone Tracks dataset, from NOAA (available at the Coastal Services Centers website: http://maps.csc.noaa.gov/hurricanes/) to match hurricane tracks with our GA. This review shows that, of the 213 hurricanes and storms developed on the Atlantic Ocean since 1992, 73 of them entered the Gulf of Mexico area. Intersection of hurricane tracks in the corresponding time frame with Radarsat, Envisat and ERS footprints, indicate that at least 30 tropical depressions and hurricanes have been captured in more than 100 SAR images in the Gulf of Mexico.
Marine applications of SAR images also include utilization of algorithms that extract wind vector information as well as ocean waves feature analysis. Wind stress is one of the main forces driving ocean dynamic process, retrieval of wind information from SAR imagery provides a useful complement to support traditional wind observations and numerical modeling. Therefore the GOM SAR data set may be useful for future studies of tropical storm processes.
Estimation of wind intensity during hurricane is problematic due to the difficulty of instrument ing extreme conditions. SAR data can provide an alternative source for this information. The significance of these observations and their possible major effect on air-sea fluxes also improve the prediction of hurricane intensity change. It has been found that SAR images could provide valuable details about a storms’ structure when it is out of range of coastal radars. SAR images has been used to analyze roll vortices in regions between the rain bands of hurricanes where no other sensor has capability to monitor this phenomena.
Eddies, Oceanic Fronts and The Loop Current
Depending on the wind stress, SAR satellites can detect eddies in several beam modes. Evaluation of the potential of SAR for eddy detection and vertical motion in ocean has been tested with high accuracy. We examined records showing the extent of the loop current and detached eddies and compared these with our G.A. The results indicate that at least 6400 SAR images cover both the Loop Current and eddy activity areas.
Natural seepage of hydrocarbons.
SAR data can be used to detect layers of floating oil released by natural or accidental events. Interactions between the sea surface and microwaves are very sensitive to variations in sea surface roughness. Rough surfaces scatter large amounts of energy back to the antenna and have bright signatures, while smooth surfaces reflect the energy away from the antenna and have dark signatures. The high sea reflectivity is due to Bragg scattering from capillary and short gravity waves; therefore, the backscatter intensity in sea water is stronger than in surfactants. The detection of oil slicks with single-polarization signals from SAR sensors has been found to be optimal at small incidence angles and under moderate wind speeds, ranging from 3-10 m/s.
The distribution and relative density of SAR collection appears to be strongly correlated with areas of energy production and exploration. In the Southern GOM, the Cantarel area has been the focus of over 3000 SAR image collections. In the northern GOM SAR images cover the continental slope off Lousiana with a collection density of between 660 and 900 images per unit area. Therefore, although the applications intended by users of SAR data are not well documented, one can speculate that energy exploration and pollution monitoring are among the major reasons for the historical collection of SAR data in this region.