Stability and influence evaluation of calibrating pyrgeometers outdoors with different pyrgeometer coefficients

Pyrgeometer is an instrument used for measuring longwave radiation from the Earth's atmosphere and surface. In this article, four pyrgeometers calibrated with a standard pyrgeometer in 2015 and 2016 are analyzed, the net longwave radiation and sensitivities are calculated, we set the sensitivities of these four pyrgeometers retrieved in the calibration of 2013 as the reference, then stabilities of these pyrgeometers are evaluated, only the non-stability of one CGR4 pyrgeometer is up to 1.9%, while the rest are all within 1%. Then the pyrgeometer coefficients k
₁
=0.058 and k
₂
=0.9993 obtained from low-temperature blackbody and approximate values of k
₁
=0 and k
₂
=1 are used to calculate the net longwave radiation for a CG4 pyrgeometer using the data collected in 2016 calibration, different k
₁
and k
₂
lead to different net longwave radiations, the corresponding sensitivities are compared and show a non-negligible bias of 7.1%.