Quantitative Cross Validation of Space-Based and Ground-Based Radar Observations

Abstract

Simultaneous comparison of data collected from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR), and the S-band polarimetric radar, operated by the National Center for Atmospheric Research, is made to cross validate the calibration of the PR instrument and to quantify the effects of precipitation attenuation on PR measurements. Data collected during the Texas and Florida Underflights experiment were used in the cross validation. Quantitatively comparing radar reflectivities from two separate platforms that have widely different view angles, beamwidths, and frequencies is a challenging task. Nevertheless, it is extremely important for cross validation. An analysis procedure to implement such cross validation is presented. Theoretical simulation of S-band and Ku-band reflectivities of the rain medium is also presented to characterize the theoretical difference in reflectivities between S band and Ku band in the absence of attenuation. Analysis indicates that, when the attenuation is not significant, TRMM PR measurements agree to within about 1 dB of ground radar observations. It was also found that, in the presence of significant path-integrated attenuation, the attenuation-corrected reflectivities at altitudes less than 2 km agree to within about 1 dB with ground radar observations.