Friday, 8 August 2003
Validation of Snow Parameters as Derived from Dual-Wavelength Airborne Radar
Use of dual-wavelength radar, with properly chosen wavelengths, will significantly lessen the ambiguities for the retrieval of the microphysical properties of hydrometeors as compared with the use of the single wavelength radar such as the TRMM PR. A spaceborne radar operating at Ku and Ka bands has been proposed as one of the core instruments for the Global Precipitation Measurements (GPM) and will serve as a calibrator for other instruments aboard the GPM satellite in mapping precipitation globally. In an effort to examine the validity and accuracy of the dual-wavelength radar algorithms we will analyze the data taken from the Convective and Precipitation-Electrification Experiment (CaPE) in 1991, in which the dual-wavelength airborne radar was coordinated with in situ aircraft particle measurements. Our focus in this study will be on the retrieval of snow particle size distribution above the radar bright band during a stratiform storm. During CaPE, the airborne radar, built by Japan, was mounted on NASA T-39 aircraft while the in-situ particle measurements were made using a PMS 2D-P probe mounted on the T-28 aircraft of the South Dakota School of Mines & Technology. Neglecting the attenuation, a 2 parameter snow size distribution can be estimated directly from the difference of the reflectivities at two wavelengths and reflectivity at either wavelength. Having carefully registered the particle information obtained from the in-situ measurements on the T-39°¯s coordinates, the radar-derived size distributions are then compared with the in-situ measurements. In addition to the aircraft in situ measurements, the NCAR ground-based CP-2 radar that operates at S and X bands is also used in our study for the cases where the closely-collocated measurements with the airborne radar were made. Our preliminary results indicate that reasonable agreement is found for these comparisons despite the uncertainties resulting from possible mismatches of the sample volumes among the different sensors as well as the spatial and temporal offsets.