Techniques will be developed to identify the boundaries of surface slicks from satellite scatterometers and to better model the transport of surface oil. Satellite observations alone are often too sparse in time and irregular in space to determine the location of surface oil with the fine resolution in both space and time desired for many applications; and models of surface transport have substantial errors. These approaches, which are interconnected through physics of air/sea interaction, will be combined to improve our ability to properly locate evolving oil spills.
These goals will be achieved by:
1. Modeling how oil modifies the momentum and energy exchange through the air/sea interface and to include this physical model in a coupled atmosphere/wave/ocean model that is used to model oil transport
2. Using the model output as a first guess at the slick position in an automated analysis of satellite data.
All of these activities are closely related. They are tied together with two physical models; one model of how oil modified the surface waves, and one of how surface waves modify air/sea exchange and satellite observations. An additional benefit of this research will be better modeling of ocean mixing, dynamics and thermodynamics below the surface slick. Understanding how oil modifies waves, and how waves modify air/sea interaction and remote sensing are the keys to this proposed work.
Oil slicks strongly dampen surface waves that are generated by the local winds (called wind waves), and much more weakly dampen waves generated by distant winds (called swell). Satellite sensors that use active techniques respond to the surface roughness generated by wind waves. For the vast majority of conditions in the Gulf of Mexico, oil slicks appear as an area of very low wind speeds (less than about 1.5 m/s). The first guess on the location(s) of the oil spill will be used to distinguish the slick locations from areas that really do have such low wind speeds.
For those times when there are broad areas of low wind speed, or broad areas of winds that are strong enough to generate wind waves despite the oil (both of which have been observed to occur), the improved model of surface transport will help estimate the location of the surface slick. These improvements in the model will be made by applying an existing model of air/sea interaction that separates the impacts of wind waves and swell to change the air/sea transfer (e.g., modifies the drag coefficient).
The existing atmosphere/wave/ocean model will be modified to use this air/sea interaction model. This approach takes advantage of the atmosphere/wave/ocean model already making physically sound use of the air/sea interaction in many processes (e.g., surface energy exchange, surface momentum exchange, Ekman transport, ocean mixing, sediment transport, and deeper ocean transport), and simply improves the modeled air/sea interaction that does not account for how oil modified surface waves and other aspects of air/sea interaction. The result will be a more self consistent and improved automated system for tracking oil.