ASTM G207-11(2019)e1

5.1 The methods described represent a means for calibration of field radiometers employing standard reference radiometers indoors. Other methods involve the natural sunlight outdoors under clear skies, and various combinations of reference radiometers. Outdoors, these methods are useful for cosine and azimuth correction analyses but may suffer from a lack of available clear skies, foreground view factor and directionality problems. Outdoor transfer of calibrations is covered by standards G167, E816, and E824.

5.2 Several configurations of artificial sources are possible, including:

5.3 Traceability of calibration for pyranometers is accomplished when employing the method using a reference global pyranometer that has been calibrated and is traceable to the World Radiometric Reference (WRR).4 For the purposes of this test method, traceability shall have been established if a parent instrument in the calibration chain can be traced to a reference pyrheliometer which has participated in an International Pyrheliometric Comparison (IPC) conducted at the World Radiation Center, (WRC), Davos, Switzerland.

5.4 Traceability of calibration of narrow band (for example, Ultraviolet) radiometers is accomplished when employing the method using a reference narrow band radiometer that has been calibrated and is traceable to the National Institute of Standards and Technology (NIST), or other national standards organizations.

5.5 The calibration method employed assumes that the accuracy of the values obtained with respect to the calibration source used are applicable to the deployed environment, with additional sources of uncertainty due to logging equipment and environmental effects above and beyond the calibration uncertainty.

5.6 The principal advantages of indoor calibration of radiometers are user convenience, lack of dependence on weather, and user control of test conditions.

5.7 The principal disadvantages of the indoor calibrations are the possible differences between natural environmental influences and the laboratory calibration conditions with respect to the spectral and spatial distribution of the source radiation (sun and sky versus lamps or enclosure walls).

5.8 It is recommended that the reference radiometer be of the same type as the test radiometer, since any difference in spectral sensitivity between instruments will result in erroneous calibrations. However, the calibration of sufficiently broadband detectors (approximately 700 nm or more), such as a silicon photodiode detector with respect to extremely broadband (more than 2000 nm) thermopile radiometers is acceptable, as long as the additional increased uncertainty in the field measurements, due to spectral response and spectral mismatch limitations, is acceptable. The reader is referred to ISO TR 96737 and ISO TR 99011.1 The method described in this standard applies to the indoor transfer of calibration from reference to field radiometers to be used for measuring and monitoring outdoor radiant exposure levels.

1.2 This test method is applicable to field radiometers regardless of the radiation receptor employed but is limited to radiometers having approximately 180° (2π Steradian), field angles.

1.3 The calibration covered by this test method employs the use of artificial light sources (lamps).

1.4 Calibrations of field radiometers are performed with sensors horizontal (at 0° tilt from the horizontal to the earth). The essential requirement is that the reference radiometer shall have been calibrated at horizontal tilt as employed in the transfer of calibration.

1.5 The primary reference instrument shall not be used as a field instrument and its exposure to sunlight shall be limited to outdoor calibration or intercomparisons.

1.6 Reference standard instruments shall be stored in a manner as to not degrade their calibration.

1.7 The method of calibration specified for total solar pyranometers shall be traceable to the World Radiometric Reference (WRR) through the calibration methods of the reference standard instruments (Method G167 and Test Method E816), and the method of calibration specified for narrow- and broad-band ultraviolet radiometers shall be traceable to the National Institute of Standards and Technology (NIST), or other internationally recognized national standards laboratories (Standard G138).

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.