Thursday, September 10, 2009

Fusing information - when means don't cut it look at variance

Interpreting what you see can be a challenging task for the brain. We have a lot of mental resource dedicated to processing visual information but still a lot of illusions get past us, mostly due to lack concentration or presumptions which prevent us from paying attention to certain details.

The standard assumption for detecting an oil spill/slick in SAR is that the oil reduces surface tension and dampens capillary waves, flattening the sea surface and reducing backscatter. Other natural means may have the same impact, mainly doldrums and calm sea conditions. The power spectral densities in both of these sea surface anomalies can be very similar. The slicks however differ in textural infomation since the oil does not heavily dampen the natural wind driven waves, causing the oil to form streaks. Instead of the slow to compute but detailed texture filter banks or occurrence/co-occurrence measure, simple kernel based variance measures may help distingish streaky oil slicks from just plain old calm sea.

The West Atlas rig leak becoming a long drawn out affair and claims and counter claims everywhere with no material evidence, observing the dynamics of the slick can be important. Sometimes not only does the wind play a part, the bathymetry takes a role as well. The Timor Sea has resources worth billions shared by Australia and East Timor. The Envisat images show a lot of dark areas in the sea which can only be differentiated by texture. The oil seems to be dispersing at a bathymetric feature and right at the dispersion point is a QuickBird image, in the middle of the ocean, taken quite a while ago in May. I wonder what is so interesting there.
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