Conventional Doppler radar sends out a horizontal energy pulse providing a one‐dimensional view of precipitation. Dual pol radar sends both horizontal and vertical pulses, providing a two‐dimensional view. Thus, it provides much better information about the size, shape, and estimated amount of precipitation, distinguishing between rain, snow, and hail. Basic dual pol products include correlation coefficient (CC), differential reflectivity (ZDR), and specific differential phase (KDP). More information is available on our Dual Pol webpage.
Above, a linear area of high reflectivity values (pink/purple) were present within a supercell (left 2 images). CC data (upper right) showed a zone of reduced values (about 0.8-0.9; green within white oval) coincident with the high reflectivity values. ZDR (lower right) showed very low values (0-1.5; blue/green within white oval) indicating spherical shapes suggestive of very large hailstones and hail mixed with rain. Surrounding red colors in ZDR indicated large rain drops which are more hamburger bun-shaped in the cloud. Dual pol clearly identified large hail in this storm which produced softball size hail just prior to the images above. Reflectivity alone (left) suggested large hail, but could not confirm it as high reflectivity values can result from a combination of precipitation sizes, types, and densities.