Cloud cover estimation using multitemporal hemisphere imageries

The solar radiation is the origin of energy for the photosynthesis and forest productivities. On the other hand, clouds constantly appear, move and disappear all the time and influence atmospheric and radiation conditions at the same time. Therefore, to understand cloud parameters which consist of cloud covers, its distributions and types etc. for a short time interval can help us to estimate solar radiation or photosynthetically active radiation (PAR) with high accuracy. Authors have been observed and measured various parameters related with photosynthesis and carbon exchange for tropical rain forest in Borneo Malaysia so far. Concerning to the cloud conditions, we also monitor the whole sky using the commercial digital camera with the fisheye converter lens and can obtain hemisphere imageries about every two minutes interval. As the experimental study about cloud parameters, in this paper, we present 1) the observation system of whole sky conditions, 2) how to analyze the obtained hemisphere imageries and 3) the method to estimate cloud cover and understand cloud distribution with sun position. Here, we use Sky Index which is calculated using visible RGB image taken by digital camera. This index is useful to separate whole sky area to clouds and the blue sky areas. Then multi-temporal cloud covers can be estimated from the Sky Index generated by multi-temporal hemisphere imageries. Through this study, we also could recognize the efficiency to understand cloud cover, cloud distributions and types by using hemisphere imageries and Sky Index. As the continuous works, we examine the relationship between the solar radiation and cloud conditions such as cloud covers, distribution and types.