Comparison of calculation methods for drop size distribution with a ground based dual-wavelength, dual-polarization radar

To know the drop size distribution (DSD) of rainfall is important for understanding rainfall mechanisms and estimation of rainfall amount. Also it is desired to use remote sensing instruments in order to survey large area (volume) in a short time. Radar is the best method if it has the ability to observe several parameters such as dual-wavelength and/or dual-polarization capability. The DSD estimation method with dual-wavelength (X-band and Ka-band) radar (dual-wavelength method) using airborne radar data has been previously shown. ZDR value of polarimetric radar is also utilized for estimation of DSD (ZDR method), under an assumption of an exponential type DSD. The authors first explain these calculation methods for the ground based system and also a method to estimate DSD by using four-parameter radar (dual-wavelength and dual polarization). Radar data used in this study is dual-wavelength; dual-polarization radar owned by Communications Research Laboratory (CRL), Japan, which is located at NASA/GSFC. Frequencies of this radar are 10 GHz and 34.5 GHz. This radar uses a lens horn antenna with the beam width of 5 degrees. The data sampling rate is 0.2 /spl mu/sec (range resolution is 30m).