Cloud boundary height measurements using lidar and radar

Using only lidar or radar an accurate cloud boundary height estimate is oft en not possible. The combination of lidar and radar can give a reliable clo ud boundary estimate in a much broader range of cases. However, also this c ombination with standard methods still can not measure the cloud boundaries in all cases. This will be illustrated with data from the Clouds and Radia tion measurement campaigns, CLARA. Rain is a problem: the radar has problem s to measure the small cloud droplets in the presence of raindrops. Similar ly, few large particles below cloud base can obscure the cloud base in rada r measurements. And the radar reflectivity can be very low at the cloud bas e of water clouds or in large regions of ice clouds, due to small particles . Multiple cloud layers and clouds with specular reflections can pose probl ems for lidar. More advanced measurement techniques are suggested to solve these problems. An angle scanning lidar can, for example, detect specular r eflections, while using information from the radars Doppler velocity spectr um may help to detect clouds during rain. (C) 2000 Elsevier Science Ltd. Al l rights reserved.