GROUND-BASED CLOUD OBSERVATION FOR SATELLITE-BASED CLOUD DISCRIMINATION AND ITS VALIDATION

Solar radiation is a source of energy for ground surfaces. Clouds control energy budget on both local and global scales. We propose the simple ground-based observation method for various sky conditions instead of the existing visual observation. In the paper, we mainly describe how to discriminate clouds area on whole sky images, how to overlay the cloud areas to the satellite-based images and the test experiment. As for the discrimination of sky conditions, we use Sky Index (SI) and Brightness Index (BI) calculated from whole sky imageries. SI shows the extent of the blueness and grayscale and BI indicates the extent of the brightness. Sun, cloud and blue sky areas are divided by SI and BI threshold. As an extension of ground-based observation to satellite-based observation, clouds area discriminated by ground-based observation overlay to satellite images. Through this experiment, the utilities of ground-based cloud observation are discussed. The proposed ground-based cloud observation method and its satellite-based extension should be connected to satellite products with high quality by implementation of sky and clouds observation covering a wide area.