Polarimetric Weather Radar Calibration - Engineering Challenges

The Tri-Agency NEXRAD program has deployed a polarimetric upgrade to the WSR-88D network radars. This modification provides new base variables to the operational community and has opened exciting new possibilities for improved forecasts and warnings. One variable in particular, differential reflectivity, is critically important to improved precipitation estimates and hydrometeor classification. However, the quality of the differential reflectivity estimate is highly dependent on the removal of biases induced by the radar system hardware. These biases must be measured to an uncertainty of 0.1 dB in order to obtain maximum benefit from the polarimetric capability.

This paper will review the engineering challenges being pursued in our efforts to further improve the calibration the WSR-88D to the required level of accuracy with a focus on the use of cross polarization power ratios and solar scans. Other potential methods will be reviewed and analyzed for their applicability to the WSR-88D system. Finally, we will present a status on development of improvements to operational maintenance processes.