Ground Based Sky Conditions Observation by Whole-Sky Camera for Incident PAR Estimation

Abstract

PAR (Photosynthetic Active Radiation) is one of the important environmental factors to understand the plant activities. However, the incident PAR on ground surface is affected by the weather especially caused by cloud existence. In this study, we focus on the sky conditions formed by cloud existence and its effects of incident PAR on the ground surfaces. The purpose of this study is to estimate the direct and diffuse PAR by considering the effects of sky conditions change in the short time period. For this purpose, this paper describes the method how to discriminate and classify sky conditions by the ground based observation using whole-sky camera and the properties of direct, diffuse and global PARs shown at various sky conditions. As the result, 14 sky conditions were classified by sun appearance/hiding, cloud cover and sky brightness using whole-sky images taken around noon time. We could clarify the properties of incident PAR at each sky conditions. Also, we tried to estimate the global and diffuse PAR from the relationship between the observed PAR and sky conditions. It was confirmed that the possibility of incident PAR estimation using whole-sky image.