A comparative analysis of broadband global and diffuse irradiance methods to determine Ångström's turbidity coefficient

Abstract

SYNOPSIS Two methods to determine Ångström's Turbidity Coefficient, using horizontal global and diffuse irradiances in cloudless skies are compared. It is shown that the method referred to as “Global and diffuse” (GDIM), which does not require other measurements than irradiances, is preferable when horizontal global and diffuse broadband irradiance measurements are available by the side of temperature and relative humidity, necessary measurements to apply the second method. Global and diffuse irradiance measurements are often available, but they are less often accompanied by the other measurements. In these circumstances only GDIM can be applied. GDIM's advantage was taken to determine monthly mean values of Ångström's turbidity coefficient between 1989 and 1998, in Valencia, Spain. It was observed that the turbidity coefficient decreased throughout the period analysed.