Calibration support for the GML baseline observatories and the BSRN sites at Kwajalein, Bermuda, and BAO is carried out by the GML Solar Radiation Calibration Facility (SRCF). Calibrations and characterizations of pyranometers and pyrheliometers are performed as well as field exchanges of recalibrated instruments.
The GML reference cavity radiometers were compared with reference cavities from other organizations during 1994 and 1995. A cavity intercomparison was held at the National Renewable Energy Laboratory in Golden, Colorado, October 8- 10, 1994. In 1995 the GML references were taken to the World Radiation Center in Davos, Switzerland, for participation in the WMO sponsored eighth International Pyrheliometer Comparison (IPCVIII). These comparisons are typically conducted every 5 years and allow reference instruments from all of the WMO regions to document their performance relative to a standard group of instruments maintained at the World Radiation Center. Participation of the GML reference cavities (TM167502 and AHF28553) in IPCVIII maintains the historical traceability of the NOAA standards to the World Radiometric Reference maintained in Davos and the World Radiation Center. All solar radiation measurements made by GML are thus traceable to the world reference. SRCF was designated as the WMO/CIMO Region IV National Radiometric Calibration Center for the US in the late 1970s and has carried out the related tasks since that time.
Solar tracking accuracy at field sites has been improved by implemention of a more accurate solar position algorithm in the tracker control program, precision leveling of the solar tracker during installation and setup, and the addition of a solar position detector designed and built by GML to the solar tracker. Tracking accuracies of better than 0.1 degrees are achievable with these improvements. In addition, software was added to the tracker control computer that allows remote access to the tracker control program via modem. This capability, together with the solar position detector data, will allow monitoring of tracker performance at the remote sites and tracker control from Boulder if necessary. Installation of a new Eppley automated self-calibrating cavity radiometer system in the refurbished MLO solar dome was also completed during the latter part of 1995. Continuous direct-solar- beam data is now available in addition to the NIP data that have been collected since 1958.
In addition to the routine GML monitoring support for the four baseline observatories. The SRCF provides support, resources, training, and logistics assistance in other areas such as the World Meteorological Organization/Global Environmental Fund/ Global Atmospheric Watch (WMO/GEF/GAW) baseline station network.