CHARACTERIZATION OF PYRGEOMETERS AND THE ACCURACY OF ATMOSPHERIC LONG-WAVE-RADIATION MEASUREMENTS

A detailed characterization is performed to calibrate pyrgeometers, us ing a newly developed apparatus that contains a blackbody radiation so urce and the means to vary the temperatures of the pyrgeometer under t esting. Calibration measurements cover the parameter space of radiatio n and instrument temperatures that prevail during field measurements. Dome-temperature measurements, normally provided on pyrgeometers, ate inadequate for accurate corrections of the dome emission. A new temper ature measurement with three sensors inside the dome at 45 degrees ele vation is proposed and has been implemented on several test instrument s. This modification and the detailed characterization measurements pe rmit an improved evaluation, based on thorough analysis of the thermal balance of the instrument, leading to a sensitivity factor C and thre e correction factors, k(1,2,3). Test measurements demonstrate the subs tantial improvement achieved on the accuracy of atmospheric and terres trial long-wave radiation measurements, down to +/-2 W m(-2).