Improvement of Cirrus Cloud-Top Height Estimation Using Geostationary Satellite Split-Window Measurements Trained with CALIPSO Data

抄録

We developed a method for the estimation of cloud-top height using only split-window channels of infrared observations from geostationary satellites. Lookup tables (LUTs) were constructed based on regression of them with direct observations of cloud top height from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Cloud Profiling Radar onboard the CALIPSO and CloudSat satellites, respectively. Our previous estimation scheme using cloud radar underestimated the top heights of cirriform cloud. In this study, using CALIOP data, we succeeded in reducing the underestimation of the height of cirriform clouds. Although CALIOP can detect optically thin clouds around the tropopause, their top heights cannot be estimated well using split-window observations. By defining the altitude at which the optical depth from the top had a specified value τ_min (= 0.2) as the cloud-top height, we could create a practical LUT. In the LUT, the underestimation of the heights of cirriform cloud was corrected substantially, while reducing the effect of the low sensitivity of split-window observations to thin tropopause cloud.