Nijegorodov, N.; Carlsson, S.; Lekorwe, O. - In: Renewable Energy 5 (1994) 5, pp. 1514-1516
The paper presents a new formula for air mass, obtained theoretically and proved experimentally. It is in a good agreement with the known one upto θz = 70°, but for θz > 70° it gives smaller values of air mass, especially for θz = 90°.