The angular distribution and interception of diffuse solar radiation below overcast skies

The angular distribution of diffuse radiation was measured from May 1976 to May 1977 with a set of purpose‐built actinometers. Radiance distributions for 98 overcast hours were fitted well by an expression similar to the conventional function for a ‘standard overcast sky’ (SOC). However, values of the coefficient b averaged 1.23, significantly smaller than for the SOC (b = 2). Expressions for the interception of diffuse irradiance by sloping planes are discussed.