92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Monday, 23 January 2012
Data Processing of the VU C-Band Polarimetric Radar Data
Hall E (New Orleans Convention Center )
Raquel Evaristo, Valparaiso University, Valparaiso, IN; and T. M. Bals-Elsholz, A. Stepanek, K. H. Goebbert, and B. J. Wolf
Manuscript (784.1 kB)

Radar measurements may be affected by errors such as calibrations errors (in reflectivity (Zh) and differential reflectivity (Zdr) ), attenuation and differential attenuation. Any type of study that involves these measurements should be sure that these errors have been properly corrected.

Zdr is easy to calibrate by pointing the radar at the vertical during a rain event, preferably with weak winds. If raindrops fall steadily, their dimensions seen from below should all be similar, producing a 0dB Zdr. Reflectivity may be calibrated through a method that uses the redundancy of the polarimetric variables in rain. The specific differential phase (Kdp), defined as the range derivative of the differential phase shift PhiDP, is immune to calibration errors. Combined, the three variables Zh, Zdr and Kdp provide redundant information in rain, and this characteristic is used to calibrate Zh (provided that Zdr was previously calibrated). We will also attempt to calibrate using a more classical approach: using a metal sphere attached to a tethered balloon. Knowing the size of the sphere, and the distance from the radar we can calculate the theoretical value for reflectivity and compare with the measured reflectivity.

Attenuation and differential attenuation are corrected using PhiDP, which has been shown to be proportional to the attenuation and differential attenuation coefficients (ah and ad respectively). We calculate ah and ad for each radial, instead of using the same coefficients for the whole domain. This should produce a more realistic correction, especially in cases of convective rain, since attenuation is stronger along the radial where rainfall is heavier.

Examples and results from each of these methods will be presented

Supplementary URL: