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 radar to measure quantitatively raindrop size distributions and rainfall intensity. The wavelength of the radar is 12.5 mm (K band). To improve estimates 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 diameters invalid; exponential extrapolation of the spectrum below drop diameters of 0.7 mm decreased the rain intensity up to 20%. Proper Mie corrections to the particle backscatter cross sections decreased the rain intensity between 5% and 30%. Calibration of the radar against a Joss-Waldvogel disdrometer led to a decrease in rain intensity of 49%. The electronic noise, Mie scatter, and calibration corrections yielded a correlation coefficient of 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 height of 100 m above ground were on average 12% higher than measurements with a conventional Hellmann rain gauge.