Simultaneous radar and lidar cloud measurements at Geesthacht (53.5°N, 10.5°E)

Abstract Comparisons have been made of the cloud profiles obtained from the backscatter signals of a 95-GHz radar and a 720-nm lidar system between 23 May and 4 November 1997 at Geesthacht (53°24′ N, 10°26′ E). Although the wavelengths of the two systems differ by a factor of 4 000, remarkably similar data have been obtained in many cases. There are differences, though. Small droplets do not interact significantly with the radar pulses, and hence can only be seen by the lidar due to their strong scattering in the UV/VIS. On the other hand, attenuation of the lidar pulses by underlying clouds and gas absorbers makes upper cloud regions and especially cloud top heights better detectable for the radar. Rain and snow falling out of a cloud and evaporating on the way down cannot be distinguished from the cloud region by the radar, but a fast downward component in the Doppler spectrum is indicative of precipitation in or under a cloud. For quantitative cloud studies collocated radar-lidar systems considerably add to the experimental capabilities of each of the two systems alone.