Investigation of clear-sky occurrence rate estimated from CALIOP and MODIS observations

We derived the global 6distribution of the clear-sky occurrence rate during the daytime using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Moderate-resolution Imaging Spectrometer (MODIS) data. Our goal was to estimate the frequency of likely successful CO₂ and CH₄ column concentration retrievals by the Greenhouse gases Observing Satellite (GOSAT). Clear-sky regions over land were frequently found around desert regions throughout the year, and at northern mid-latitudes in the winter hemisphere. Overall, clear-sky regions covered approximately 11% of the globe annually, on average. From a comparison of the CALIOP and MODIS cloud data for June 2007, we found that MODIS overestimated the clear-sky ratio by approximately 5%, except for in the tropics.