How does dual pol do at differentiating the size of the debris? If the updraft is pulling in some leaf, twig, or grass debris it seems to me there could be some false positives. On the other hand, weak tornadoes detected on the radar in a forested area that are pulling in light material, may not be apparent at all to damage survey crews.
I'm not sure. In my experience, CC (rho_hv) is *extremely* sensitive to size/shape variability, particularly when there is a large variance in dielectric factor, and debris often has such variability. I suppose that smooth, nearly-uniform small debris may not lead to as much of a decrease in rho_hv, but we know that's not what tornado debris typically "is". The Canton Lake tornado from 5/24/11 was sampled by some mobile, polarimetric radars (NOXP and DOWs), and, if I recall those data correctly, the "debris" signature became much less apparent when the tornado moved over the lake compared to what it was on land. In that case, though, unless one considers lake water to be "debris", the transition from land to water resulted in a significant decrease in debris loading and content.
There is a brand new paper paper (it's not in print yet) that addresses some of these issues, however:
Bodine, D., M. Kumjian, R. Palmer, P. Heinselman, and A. Ryzhkov, 2013:
Tornado damage estimation using polarimetric radar. Wea. Forecasting, in press.
I haven't had time to read this paper yet, though. If you have access to Early Online Release papers for WAF, however, you should check it out.
