In a recent post, I talked about observing an eddy in the Arabian Sea in L-band ALOS PALSAR SAR imagery. In this post, I want to talk briefly about the physical interaction between SAR signals and eddies.
Spiral eddies are often convergence zones and act as accumulators of surface slicks. These surface slicks (could be biogenic / natural oil seeps / mineral oil etc.) make a surface layer over the ocean and actually dampen the surface waves of the ocean through a phenomenon called Marangoni Damping (see this seminal paper by Alpers and Hühnerfuss).
However, sometimes it is also possible that an eddy may appear brighter in SAR imagery than the surrounding ocean, due to wave-current and shear interactions.
In my paper on ocean currents from sequential SAR imagery, I talk about this phenomenon in the introduction, and you can also find some good references therein.
For further interest, here are a few other seminal papers on the science of ocean wave damping by surface slicks:
- The damping of ocean waves by surface films
- SAR observations of small-scale eddies
- Three interesting 1998 papers by Martin Gade: JGR1, JGR2, RSE
- Svetlana Karimova’s paper on seeing spiral eddies through SAR