A practical pyrgeometer using the representative angle

A simple directional pyrgeometer is tested and compared with a conventional standard pyrgeometer. The system presented in this article has a narrow directional response and points to the representative zenith angle of 52.5°. Because of its directional response, it can be used in a street canyon or in a forest provided that a small part of the sky is visible at the representative angle. The system can be assembled using inexpensive parts that are widely used in household appliances. As this system does not have a flat spectral sensitivity, a spectral correction method is also presented. The results show that the output of the new system agrees well with that from a conventional pyrgeometer (Kipp & Zonen CG3). The correlation coefficient is 0.995 and the standard deviation is 5.6 W m^-2 for 1-h averaged values.