Preprocessing and Assessment of Rain Drop Size Distributions Measured With a K-Band Doppler Radar and an Optical Disdrometer

Rain attenuation in millimeter-wave links depends on the drop size distributions (DSDs) of the raindrops. Empirical models disregard this dependence and estimate the specific attenuation using only the integrated rainfall rate [$R$ (mm/h)]. This approach is valid for lower frequencies but it progressively losses accuracy as the frequency of interest becomes higher within the millimeter-wave range. Both the characterization of rainfall phenomena and the prediction of rain attenuation can be improved with the knowledge of DSD, which, in turn, depend on the type of rain event (stratiform or convective) and the $R$ . In this article, long-term DSD measurements from a vertical Doppler radar [Micro Rain Radar (MRR-2)] and a laser optical disdrometer (Thies laser disdrometer) are used to obtain, classify, and compare the statistics of DSD in Madrid in a period of more than ten years. The process to obtain the DSD from these advanced instruments is analyzed in detail, providing recommendations about the calibration of the radar data and the most appropriate particle filtering to apply on the laser disdrometer data.