Pacific Northwest National Laboratory
The DIFFCORR1DUTT VAP uses two techniques to correct shortwave (SW) data during daytime hours, using information from a collocated pyrgeometer. First, the detector-only correction technique uses data in the form of irradiance loss from the pyrgeometer detector. Second, the full-correction technique uses information from collocated pyrgeometer detector data, plus the difference between the case and dome temperatures. Both techniques collect nighttime data with corresponding pyranometer infrared-loss data. The fitting routine for detection and correction consists of two modes: dry and moist. Each mode is detected separately in the nighttime data and applied separately during the daytime. The correction to the SW daylight data is applied only if the data pass quality analysis checks. The DiffCorr1Dutt VAP output files contain a best estimate of the downwelling SW, and a best estimate of the diffuse SW. In addition, the output files contain other useful values, such as an estimate of the clear-sky Rayleigh diffuse SW amount, and standard surface meteorological measurements.
For more details, see Improved Correction of IR Loss in Diffuse Shortwave Measurements: An ARM Value-Added Product technical report.