Comparing 94GHz radar cloud and precipitation drop spectra measurements with aircraft observations

In 1987 development began on a 94GHz radar at Penn State that, along with other instruments such as a ceilometer and microwave radiometer, is part of a cloud observing system (Albrecht et al., 1991). Preliminary experimental results indicate that the Doppler spectra measured by the radar are in agreement with drop size spectra collected by the aircraft. This agreement is best seen when a bimodal spectrum exists. In the case presented, the velocities for which the Doppler spectrum are local maxima correspond well to the peaks in the drop size spectra. There is confidence that the radar is able to accurately detect particles, such as cloud drops, which have negligible fall velocities and essentially act as tracers of vertical wind.