ASTM E816-15(2023)
(Test Method)Standard Test Method for Calibration of Pyrheliometers by Comparison to Reference Pyrheliometers
Standard Test Method for Calibration of Pyrheliometers by Comparison to Reference Pyrheliometers
SIGNIFICANCE AND USE
4.1 Though the sun trackers employed, the number of instantaneous readings, and the data acquisition equipment used will vary from instrument to instrument and from laboratory to laboratory, this test method provides for the minimum acceptable conditions, procedures, and techniques required.
4.2 While the greatest accuracy will be obtained when calibrating pyrheliometers with a self-calibrating absolute cavity pyrheliometer that has been demonstrated by intercomparison to be within ±0.5 % of the mean irradiance of a family of similar absolute instruments, acceptable accuracy can be achieved by careful attention to the requirements of this test method when transferring calibration from a secondary reference to a field pyrheliometer.
4.3 By meeting the requirements of this test method, traceability of calibration to the World Radiometric Reference (WRR) can be achieved through one or more of the following recognized intercomparisons:
4.3.1 International Pyrheliometric Comparison (IPC) VII, Davos, Switzerland, held in 1990, and every five years thereafter, and the PMO-2 absolute cavity pyrheliometer that is the primary reference instrument of WMO.6
4.3.2 Any WMO-sanctioned intercomparison of self-calibrating absolute cavity pyrheliometers held in WMO Region IV (North and Central America).
4.3.3 Any sanctioned or non-sanctioned intercomparison held in the United States the purpose of which is to transfer the WRR from the primary reference absolute cavity pyrheliometer maintained as the primary reference standard of the United States by the National Oceanic and Atmospheric Administration's Solar Radiation Facility in Boulder, CO.7
4.3.4 Any future intercomparisons of comparable reference quality in which at least one self-calibrating absolute cavity pyrheliometer is present that participated in IPC VII or a subsequent IPC, and in which that pyrheliometer is treated as the intercomparison's reference instrument.
4.3.5 Any of the absolute radiometers p...
SCOPE
1.1 This test method has been harmonized with, and is technically equivalent to, ISO 9059.
1.2 Two types of calibrations are covered by this test method. One is the calibration of a secondary reference pyrheliometer using an absolute cavity pyrheliometer as the primary standard pyrheliometer, and the other is the transfer of calibration from a secondary reference to one or more field pyrheliometers. This test method prescribes the calibration procedures and the calibration hierarchy, or traceability, for transfer of the calibrations.
Note 1: It is not uncommon, and is indeed desirable, for both the reference and field pyrheliometers to be of the same manufacturer and model designation.
1.3 This test method is relevant primarily for the calibration of reference pyrheliometers with field angles of 5° to 6°, using as the primary reference instrument a self-calibrating absolute cavity pyrheliometer having field angles of about 5°. Pyrheliometers with field angles greater than 6.5° shall not be designated as reference pyrheliometers.
1.4 When this test method is used to transfer calibration to field pyrheliometers having field angles both less than 5° or greater than 6.5°, it will be necessary to employ the procedure defined by Angstrom and Rodhe.2
1.5 This test method requires that the spectral response of the absolute cavity chosen as the primary standard pyrheliometer be nonselective over the range from 0.3 μm to 10 μm wavelength. Both reference and field pyrheliometers covered by this test method shall be nonselective over a range from 0.3 μm to 4 μm wavelength.
1.6 The primary and secondary reference pyrheliometers shall not be field instruments and their exposure to sunlight shall be limited to calibration or intercomparisons. These reference instruments shall be stored in an isolated cabinet or room equipped with standard laboratory temperature and humidity control.
Note 2: At a laboratory where cali...
General Information
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Standards Content (Sample)
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.
Designation: E816 − 15 (Reapproved 2023)
Standard Test Method for
Calibration of Pyrheliometers by Comparison to Reference
Pyrheliometers
This standard is issued under the fixed designation E816; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Accurate and precise measurement of the direct (beam) radiation component of sunlight are
required in (1) the calibration of reference pyranometers by the shading disk or optical occluding
methods, (2) determination of the energy collected by concentrating solar collectors, including
exposure levels achieved in use of Practice G90 dealing with Fresnel-reflecting concentrator test
machines, and (3) the assessment of the direct beam for energy budget analyses, geographic mapping
of solar energy, and as an aid in the determination of the concentration of aerosol and particulate
pollution, and water vapor effects.
This test method requires calibration to the World Radiometric Reference (WRR), maintained by
the World Meteorological Organization (WMO), Geneva. The Intercomparison of Absolute Cavity
Pyrheliometers, also called Absolute Cavity Radiometers, on which the WRR depends, is covered by
procedures adopted by WMO and by various U.S. Organizations who occasionally convene such
intercomparisons for the purpose of transferring the WRR to the United States, and to maintaining the
WRR in the United States. These procedures are not covered by this test method.
1. Scope 1.4 When this test method is used to transfer calibration to
field pyrheliometers having field angles both less than 5° or
1.1 This test method has been harmonized with, and is
greater than 6.5°, it will be necessary to employ the procedure
technically equivalent to, ISO 9059.
defined by Angstrom and Rodhe.
1.2 Two types of calibrations are covered by this test
1.5 This test method requires that the spectral response of
method. One is the calibration of a secondary reference
the absolute cavity chosen as the primary standard pyrheliom-
pyrheliometer using an absolute cavity pyrheliometer as the
eter be nonselective over the range from 0.3 μm to 10 μm
primary standard pyrheliometer, and the other is the transfer of
wavelength. Both reference and field pyrheliometers covered
calibration from a secondary reference to one or more field
by this test method shall be nonselective over a range from
pyrheliometers. This test method prescribes the calibration
0.3 μm to 4 μm wavelength.
procedures and the calibration hierarchy, or traceability, for
transfer of the calibrations. 1.6 The primary and secondary reference pyrheliometers
NOTE 1—It is not uncommon, and is indeed desirable, for both the
shall not be field instruments and their exposure to sunlight
reference and field pyrheliometers to be of the same manufacturer and
shall be limited to calibration or intercomparisons. These
model designation.
reference instruments shall be stored in an isolated cabinet or
1.3 This test method is relevant primarily for the calibration
room equipped with standard laboratory temperature and
of reference pyrheliometers with field angles of 5° to 6°, using
humidity control.
as the primary reference instrument a self-calibrating absolute
NOTE 2—At a laboratory where calibrations are performed regularly, it
is advisable to maintain a group of two or three secondary reference
cavity pyrheliometer having field angles of about 5°. Pyrheli-
pyrheliometers that are included in every calibration. These serve as
ometers with field angles greater than 6.5° shall not be
controls to detect any instability or irregularity in the standard reference
designated as reference pyrheliometers.
pyrheliometer.
1.7 This test method is applicable to calibration procedures
This test method is under the jurisdiction of ASTM Committee G03 on
using natural sunshine only.
Weathering and Durabilityand is the direct responsibility of Subcommittee G03.09
on Radiometry.
Current edition approved March 15, 2023. Published March 2023. Originally
approved in 1981. Last previous edition approved in 2015 as E816 – 15. DOI: Angstrom, A., and Rodhe, B., “Pyrheliometric Measurements with Special
10.1520/E0816-15R23. Regard to the Circumsolar Sky Radiation,” Tellus, Vol 18, 1966, pp. 25–33.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E816 − 15 (2023)
1.8 This standard does not purport to address all of the 3.1.4 field pyrheliometer, n—pyrheliometers that are de-
safety concerns, if any, associated with its use. It is the signed and used for long-term field measurements of direct
responsibility of the user of this standard to establish appro- solar radiation. These pyrheliometers are weatherproof and
priate safety, health, and environmental practices and deter- therefore possess windows, usually quartz, at the field aperture
mine the applicability of regulatory limitations prior to use. that pass all solar radiation in the range from 0.3 μm to 4 μm
1.9 This international standard was developed in accor- wavelength.
dance with internationally recognized principles on standard-
3.1.5 opening angle, n—with radius of field aperture de-
ization established in the Decision on Principles for the
noted by R and the distance between the field and receiver
Development of International Standards, Guides and Recom-
apertures denoted by l, the opening angle is defined for right
mendations issued by the World Trade Organization Technical
circular cones by the equation:
Barriers to Trade (TBT) Committee.
Z 5 tan R/l (1)
o
2. Referenced Documents
The field angle is double the opening angle.
2.1 ASTM Standards:
3.1.6 primary standard pyrheliometers, n—pyrheliometers,
E772 Terminology of Solar Energy Conversion
selected from the group of absolute pyrheliometers (see self-
E824 Test Method for Transfer of Calibration From Refer-
calibrating absolute cavity pyrheliometer).
ence to Field Radiometers
3.1.7 reference pyrheliometer, n—pyrheliometers of any
G90 Practice for Performing Accelerated Outdoor Weather-
category serving as a reference in calibration transfer proce-
ing of Materials Using Concentrated Natural Sunlight
dures. They are selected and well-tested instruments (see
G167 Test Method for Calibration of a Pyranometer Using a
Table 2 of ISO 9060), that have a low rate of yearly change in
Pyrheliometer
responsivity. The reference pyrheliometer may be of the same
2.2 ISO Standards:
type, class, and manufacturer as the field radiometers in which
ISO 9059 Calibration of Field Pyrheliometers by Compari-
case it is specially chosen for calibration transfer purposes and
son to a Reference Pyrheliometer
is termed a secondary standard pyrheliometer (see ISO 9060),
ISO 9060 Specification and Classification of Instruments for
or it may be of the self-calibrating cavity type (see self-
Measuring Hemispherical Solar and Direct Solar Radia-
calibrating absolute cavity pyrheliometer).
tion
3.1.8 secondary standard pyrheliometer, n—pyrheliometers
ISO TR 9673 The Instrumental Measurement of Sunlight for
of high precision and stability whose calibration factors are
Determining Exposure Levels
derived from primary standard pyrheliometers. This group
ISO 9846 Calibration of a Pyranometer Using a Pyrheliom-
comprises absolute cavity pyrheliometers that do not fulfill the
eter
requirements of a primary standard pyrheliometer as described
2.3 WMO Standard:
in 3.1.6.
Guide to Meteorological Instruments and Methods of
Observation, Seventh ed., WMO-No. 8 3.1.9 self-calibrating absolute cavity pyrheliometer, n—a
radiometer consisting of either a single- or dual-conical heated
3. Terminology
cavity that, during the self-calibration mode, displays the
power required to produce a thermopile reference signal that is
3.1 Definitions:
identical to the sampling signal obtained when viewing the sun
3.1.1 The relevant definitions of Terminology E772 apply to
with an open aperture. The reference signal is produced by the
the calibration method described in this test method.
thermopile in response to the cavity irradiance resulting from
3.1.2 absolute cavity pyrheliometer, n—see self-calibrating
heat supplied by a cavity heater with the aperture closed.
absolute cavity pyrheliometer.
3.1.10 slope angle, n—with radius of the sensor denoted by
3.1.3 direct radiation, direct solar radiation, and direct
r, the radius of the limiting aperture is denoted by R, and the
(beam) radiation, n—radiation received from a small solid
distance between aperture and sensor denoted by l, the slope
angle centered on the sun’s disk, on a given plane whose
angle equation is defined as:
normal (perpendicular to the plane) points to the center of the
sun’s disk (see ISO 9060). That component of sunlight is the
S 5 arcTan ~R 2 r!⁄l (2)
beam between an observer, or instrument, and the sun within a
3.2 Acronyms:
solid conical angle centered on the sun’s disk and having a total
3.2.1 ACR—Absolute Cavity Radiometer
included planar field angle of, for the purposes of this test
3.2.2 ANSI—American National Standards Institute
method, 5° to 6°.
3.2.3 ARM—Atmospheric RadiationMeasurement Program
3.2.4 DOE—Department of Energy
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.2.5 GUM—(ISO) Guide to Uncertainty in Measurements
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.2.6 IPC—International Pyrheliometer comparison
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 3.2.7 ISO—International Standards Organization
Available from International Organization for Standardization (ISO), 1, ch. de
3.2.8 NCSL—National Council of Standards Laboratories
la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org.
5 3.2.9 NIST—National Institute of Standards and Technology
Available from World Meterological Organization, 7bis, avenue de la Paix, CP.
2300, CH-1211 Geneva 2, Switzerland, www.wmo.int. 3.2.10 NREL—National Renewable Energy Laboratory
E816 − 15 (2023)
3.2.11 PMOD—Physical Meteorological Observatory Da- measurements. With respect to time of year, the requirement
vos for normal incidence dictates a tile angle from the horizontal
3.2.12 SAC—Singapore Accreditation Council that is dependent on the sun’s zenith angle and, thus, the air
3.2.13 SINGLAS—Singapore Laboratory Accreditation Ser- mass limits for that time of year and time of day.
vice
3.2.14 UKAS—United Kingdom Accrediation Service 5. Interferences
3.2.15 WRC—World Radiation Center
5.1 Radiation Source—Transfer of calibration from refer-
3.2.16 WRR—World Radiometric Reference
ence to secondary standard or field pyrheliometers is accom-
3.2.17 WMO—World Meteorological Organization
plished by exposing the two instruments to the same radiation
field and comparing their corresponding measurands. The
4. Significance and Use
−2
direct irradiance should not be less than 300 W·m , but
4.1 Though the sun trackers employed, the number of −2
irradiance values exceeding 700 W·m is preferred.
instantaneous readings, and the data acquisition equipment
5.2 Sky Conditions—The measurements made in determin-
used will vary from instrument to instrument and from labo-
ing the instrument constant shall be performed only under
ratory to laboratory, this test method provides for the minimum
conditions when the sun is unobstructed by clouds for an
acceptable conditions, procedures, and techniques required.
incremental data-taking period. The most acceptable sky con-
4.2 While the greatest accuracy will be obtained when
ditions should be such that the direct irradiance is not less than
calibrating pyrheliometers with a self-calibrating absolute
80 % of the hemispherical irradiance measured with a pyra-
cavity pyrheliometer that has been demonstrated by intercom-
nometer aligned with its axis vertical and calibrated in accor-
parison to be within 60.5 % of the mean irradiance of a family
dance with Test Method G167. Also, no cloud formation may
of similar absolute instruments, acceptable accuracy can be
be within 15° of the sun during the period data are taken for
achieved by careful attention to the requirements of this test
record when either transferring calibration to a secondary
method when transferring calibration from a secondary refer-
standard pyrheliometer (to be used as a reference pyrheliom-
ence to a field pyrheliometer.
eter) from an absolute cavity pyrheliometer, or when transfer-
4.3 By meeting the requirements of this test method, trace- ring calibration from a secondary reference pyrheliometer to
field pyrheliometers. Generally, good calibration conditions
ability of calibration to the World Radiometric Reference
(WRR) can be achieved through one or more of the following exist when the cloud cover is less than 12.5 %.
recognized intercomparisons:
NOTE 3—Contrails of airplanes that are within 15° of the sun can be
4.3.1 International Pyrheliometric Comparison (IPC) VII,
tolerated providing the ratio of so affected measurements to unaffected
Davos, Switzerland, held in 1990, and every five years measurements is small in any series.
NOTE 4—Atmospheric water vapor in the pre-condensation phase
thereafter, and the PMO-2 absolute cavity pyrheliometer that is
occasionally causes variable atmospheric transmission. Generally, the
the primary reference instrument of WMO.
scattering of measuring data that is produced by these clusters is
4.3.2 Any WMO-sanctioned intercomparison of self-
acceptable.
calibrating absolute cavity pyrheliometers held in WMO Re-
5.2.1 The atmospheric turbidity during transfer of calibra-
gion IV (North and Central America).
tion should be close to values typical for the field measuring
4.3.3 Any sanctioned or non-sanctioned intercomparison
conditions. Generally, the turbidity should be confined to
held in the United States the purpose of which is to transfer the
conditions with Linke turbidity factors lower than six (see ISO
WRR from the primary reference absolute cavity pyrheliom-
9059 and ISO 9060).
eter maintained as the primary reference standard of the United
5.2.2 The circumsolar radiation (aureole) originates from
States by the National Oceanic and Atmospheric Administra-
7 forward scattering of direct solar radiation. It decreases from
tion’s Solar Radiation Facility in Boulder, CO.
the limb of the sun to an angular dist
...
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