Differential reflectivity calibration without using vertical incidence observations

Rain observations at vertical incidence provide an excellent opportunity for a differential reflectivity, Zdr, calibration. Unfortunately not all radars are capable of such measurements. In this study we have developed a new approach that uses dual-polarization spectral slant profile observations to estimate Zdr biases.

The spectral differential reflectivity, that is the ratio of hh and vv power spectra, recorded at a high elevation angle (30-60 deg) yields Zdr measurements of different diameter raindrops. Thus by observing the part of the spectral differential reflectivity that is due to smaller raindrops one can estimate a Zdr bias. In this work we have developed a methodology that allows for estimation of Zdr biases from such measurements.

The proposed calibration methodology is demonstrated on CSU-CHILL observations of stratiform precipitation measurements carried out on July 26 2006. It will be shown that the proposed procedure allows for Zdr calibration accuracy within 0.1 dB. And estimated Zdr biases are in good agreement with ones retrieved from observations at vertical incidence.