An Estimation of Distribution of Solar Radiation Using Data from 17 Agricultural Meteorological Stations in Hyogo Prefecture

In order to observe solar radiation, we set up Agricultural Meteorological Stations (AMS) at 17 sites in Hyogo Prefecture in 1994 and 1995. An AMS was equipped with a thermometer, a rain gauge, a pyranometer and a data-logger. Using the observed solar radiation data at the AMS sites, daily solar radiation (DSR) in each non-AMS site in both July and August 1995 was calculated.The estimating method was as follows: in the first step, DSR of an average year was calculated by the harmonic method from monthly solar radiation as standardized by the National Institute Agro-Environmental Science of Japan. In the second step, the estimated DSR in the non-AMS site was caluculated from: DSR e, t=DSR a, t+Σ[(DSR e, i-DSR a, i)/Li]/Σ(1/Li), where DSR e, t and DSR a, t are respectively the estimated and an average year's DSR of the target non-AMS site, DSR e, i and DSR a, i are respectively the estimated and an average year's DSR of i-th selected AMS site, and Li is the distance between the target non-AMS site and i-th selected AMS site. Errors between estimated DSR and observed DSR at each AMS site were shown by the Root Mean Square Error. Daily RMSEs in July and August ranged from 1.0 to 3.1MJ/m2/day, and this estimation method is useful in obtaining accurate solar radiation for all non-AMS sites.