A comparison of cloud top heights computed from airborne lidar and MAS radiance data using CO2 slicing

Data from two instruments onboard the National Aeronautics and Space Admini stration (NASA) ER-2 high-altitude aircraft have been utilized in the large st validation study to date in assessing the accuracy of the CO2-slicing cl oud height algorithm. Infrared measurements of upwelling radiance from the MODIS (Moderate-Resolution Imaging Spectroradiometer) airborne simulator (M AS) were used to generate cloud top heights and then compared to those deri ved from the Cloud Lidar System (CLS), operating with dual polarization at 0.532 mu m. The comparisons were performed for 10 flight days during the Su bsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS) field ex periment during April and May 1996 which included various singlelayer and m ultilayer cloud conditions. Overall, the CO2-slicing method retrieved cloud heights to within +/-500 m and to within +/-1500 m of the lidar heights in 32 and 64% of the cases, respectively, From a simulation of cloud height e rrors as a function of various error sources in the CO2-slicing algorithm: it was concluded that the problem of multilayer clouds is secondary to that of proper specification of clear-sky radiances.