On the performance of a low-cost K-band Doppler radar for quantitative rain measurements

This paper deals with the ability of a vertically pointing, FM-CW Doppler r adar to measure quantitatively raindrop size distributions and rainfall int ensity. The wavelength of the radar is 12.5 mm (K band). To improve estimat es of the rainfall intensity, radar-received noise, Mie scatter, and radar calibration corrections are applied to the radar data. The electronic noise correction rendered the radar particle size retrievals below 0.7-mm drop d iameters invalid; exponential extrapolation of the spectrum below drop diam eters of 0.7 mm decreased the rain intensity up to 20%. Proper Mie correcti ons to the particle backscatter cross sections decreased the rain intensity between 5% and 30%. Calibration of the radar against a Joss-Waldvogel disd rometer led to a decrease in rain intensity of 49%. The electronic noise, M ie scatter, and calibration corrections yielded a correlation coefficient o f 0.94 in a comparison of the radar and disdrometer data for a case study. The daily rain sums over half a year derived from radar measurements at a h eight of 100 m above ground were on average 12% higher than measurements wi th a conventional Hellmann rain gauge.