Purposes of this research are to observe the vertical profile of the rain drop size distribution, and to utilize the results into formulating a new method of estimating rainfall intensity and/or amount by making use of information detected by operational radar observations. Firstly, observations were carried out by the MU Radar, which can detect vertical profiles of the Doppler spectrum that are composed of both the rain drop itself and air movements. Secondly, formulations to correlate the ground surface-based rainfall intensity with the radar reflectivity by taking into account both i) the difference in rainfall intensities between radar beam and rain gage height as well as ii) the width of Doppler spectrum were completed. Finally, the formulation was applied into two case studies using Miyama Radar and NEXRAD.