Abstract
Abstract. 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.
Highlights
Clouds control energy budget on both local and global scales
We proposed the simple ground-based observation method to discriminate clouds on whole sky image and one of extensions to the satellite-based observation by overlaying both ground and satellite-based images
We confirmed that our developed groundbased cloud observation method is useful to discriminate cloud existence and area of cloud coverage, and to overlay with satellite-based cloud image
Summary
Clouds control energy budget on both local and global scales. Generally, it is well known that lower clouds cool the surface and upper clouds have the effects to warm the surface (Clement et al, 2009). The efficient ground-based cloud observation is necessary to validate satellite-based observation such existing Terra & Aqua/ Moderate Resolution Imaging Spectroradiometer (MODIS) and under planning Global Change Observation Mission - Climate (GCOM-C) / Second generation GLobal Imager (SGLI) etc. The purpose of this study is to discriminate the cloud and overlay the cloud areas with satellite-based images by the efficient and simple ground-based cloud observation using commercial based digital camera and fish eye lens in order to validate the satellite-based observation. We mainly describe how to discriminate the cloud area on whole sky images, how to overlay the cloud areas to the satellite-based images and the test experiment. Through this experiment, the utilities of ground-based cloud observation are discussed
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