Sodar for precipitation measurements

Abstract

A 6.4 kHz Doppler sodar has been used in a feasibility study to retrieve rain rate and drop size distribution from sodar Doppler spectra. For rain rates above about 0.5 mm/h raindrop and turbulence spectra can be separated, thus allowing a drop size distribution measurement in the Prandtl layer without assumptions on the size distribution type for drop diameters above 1 mm. The noise of the sodar used mostly forced us to 10 min averages for the rather light rain episodes (< mm/h rain rate) we have enountered in January 1993 at our experimental site in Northern Germany. In order to arrive at consistent rain parameter retrievals we have corrected both the mean vertical wind influence and the drop size dependent reaction to turbulent motion. The comparison to a drop counter at the site gives good results only for the periods with rain rates above 1 mm/h at the absence of drizzle. Assuming a height independent rain rate in the Prandtl layer even gives the possibility for a near surface temperature profile retrieval. For higher sodar frequencies above 15 kHz a clearer separation of turbulence and rainspectra would lower the threshold drop size and thus improve rain parameter retrievals but be more strongly dependent on the near surface temperature and humidity profiles. (orig.)Available from TIB Hannover: RR 1347(160) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman