Toward the development of a diffuse horizontal shortwave irradiance working standard

Abstract

[1] The first intensive observation period (IOP) to simultaneously measure diffuse horizontal shortwave irradiance (scattered solar radiation that falls on a horizontal surface) with a wide array of shaded pyranometers suggested that a consensus might be reached that would permit the establishment of a standard with a smaller uncertainty than previously achieved. A second IOP has been held to refine the first IOP measurements using a uniform calibration protocol, offset corrections for all instruments and validation of those corrections, improvements in some of the instruments, and better data acquisition. The venue for both IOPs was the Department of Energy's Atmospheric Radiation Measurement central facility in northern Oklahoma. The 9 days of measurements in October 2003 included a better mixture of clear and overcast conditions than during the first IOP and revealed considerable differences among the instruments' responses for different cloud conditions. Four of the 15 instruments were eliminated as candidates to be included in the standard because of noisy signals, inadequate offset correction, or instability with respect to the majority of the measurements. Eight pyranometers agreed to within ±2% for clear-sky conditions. Three others have a high bias on clear days relative to these eight, but all 11 agree within ±2% on overcast days. The differences and causes of this behavior under clear and cloudy skies are examined.

Pyranometer Thermal Offset: Measurement and Analysis

“…This monitoring is performed until the detector has responded to the SW blocking but before the dome temperature changes significantly. This is a reliable procedure, since the dome temperature has a time constant that is distinguishably longer than the detector (several minutes vs a few seconds) (Bush et al 2000;Dutton et al 2001;Haeffelin et al 2001;Michalsky et al 2005;Carlund 2013). Its main drawback is the possible effect of the capping on the thermal balance due to the cap emission and the alteration of the circulation of the air (Ji and Tsay 2010).…”

Solar Resource for High-Concentrator Photovoltaic Applications

“…Various studies have been published to evaluate the comparative performance of various types of radiometers [4,24,36,62,64,101]. Such studies can help make sound decisions about the most appropriate type and brand of sensor to buy depending on the specificities of each project including budget.…”

Atmospheric Radiation Measurement Program Science Plan. Current Status and Future Directions of the ARM Science Program

“…Early studies demonstrated that broadband shortwave direct irradiance models and measurements were in agreement to better than 1%, but model calculations of the diffuse flux were typically high by 10s of percents, sometimes off by as much as 30 W m -2 (Halthore et al 1998;Kato et al 1997). Additional research results, primarily impacting the actual measurements of diffuse shortwave radiation, have reduced this difference to about 10% or 7-10 W m -2 (Cess et al 2000;Dutton et al 2001;Michalsky et al 1999Michalsky et al , 2004Philipona 2002;Younkin and Long, 2004).…”