ASTM E816-05(2010)
(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
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.
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.
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:
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.
Any WMO-sanctioned intercomparison of self-calibrating absolute cavity pyrheliometers held in WMO Region IV (North and Central America).
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.
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.
Any of the absolute radiometers participating in the above intercomparisons and be...
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 proscribes 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.
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 to 10 μm wavelength. Both reference and field pyrheliometers covered by this test method shall be nonselective over a range from 0.3 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 calibrations are...
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E816 − 05(Reapproved 2010)
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.Anumber 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 calledAbsolute Cavity Radiometers, on which the WRR depends, is covered by
procedures adopted by WMO and by various U.S. Organizations who occasionally convene such
intercomparisonsforthepurposeoftransferringtheWRRtotheUnitedStates,andtomaintainingthe
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 to 10 µm
primarystandardpyrheliometer,andtheotheristhetransferof
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 0.3
pyrheliometers. This test method proscribes the calibration
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 Thistestmethodisrelevantprimarilyforthecalibration
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 Dec. 1, 2010. Published December 2010. Originally
approved in 1981. Last previous edition approved in 2005 as E816–05. DOI: Angstrom, A., and Rodhe, B., “Pyrheliometric Measurements with Special
10.1520/E0816-05R10. 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 − 05 (2010)
2. Referenced Documents 3.1.6 primary standard pyrheliometers—pyrheliometers,se-
3 lected from the group of absolute pyrheliometers (see self-
2.1 ASTM Standards:
calibrating absolute cavity pyrheliometer).
E772Terminology of Solar Energy Conversion
3.1.7 reference pyrheliometer—pyrheliometers of any cat-
E824Test Method for Transfer of Calibration From Refer-
ence to Field Radiometers egory serving as a reference in calibration transfer procedures.
They are selected and well-tested instruments (see Table2 of
G90Practice for Performing Accelerated Outdoor Weather-
ing of Nonmetallic Materials Using Concentrated Natural ISO 9060), that have a low rate of yearly change in respon-
sivity. The reference pyrheliometer may be of the same type,
Sunlight
G167Test Method for Calibration of a Pyranometer Using a class, and manufacturer as the field radiometers in which case
it is specially chosen for calibration transfer purposes and is
Pyrheliometer
termed a secondary standard pyrheliometer (see ISO 9060), or
2.2 ISO Standards:
it may be of the self-calibrating cavity type (see self-
ISO 9059Calibration of Field Pyrheliometers by Compari-
4 calibrating absolute cavity pyrheliometer).
son to a Reference Pyrheliometer
3.1.8 secondary standard pyrheliometer—pyrheliometers of
ISO9060SpecificationandClassificationofInstrumentsfor
Measuring Hemispherical Solar and Direct Solar Radia- high precision and stability whose calibration factors are
derived from primary standard pyrheliometers. This group
tion
ISOTR9673TheInstrumentalMeasurementofSunlightfor comprises absolute cavity pyrheliometers that do not fulfill the
requirements of a primary standard pyrheliometer as described
Determining Exposure Levels
ISO 9846Calibration of a Pyranometer Using a Pyrheliom- in 3.1.6.
eter
3.1.9 self-calibrating absolute cavity pyrheliometer—aradi-
ometer consisting of either a single- or dual-conical heated
2.3 WMO Standard:
Guide to Meteorological Instruments and Methods of cavity that, during the self-calibration mode, displays the
powerrequiredtoproduceathermopilereferencesignalthatis
Observation, Fifth ed., WMO-No. 8
identicaltothesamplingsignalobtainedwhenviewingthesun
with an open aperture.The reference signal is produced by the
3. Terminology
thermopile in response to the cavity irradiance resulting from
3.1 Definitions:
heat supplied by a cavity heater with the aperture closed.
3.1.1 TherelevantdefinitionsofTerminologyE772applyto
the calibration method described in this test method. 3.2 Acronyms:
3.1.2 absolute cavity pyrheliometer—see self-calibrating 3.2.1 ACR—Absolute Cavity Radiometer
absolute cavity pyrheliometer.
3.2.2 ANSI—American National Standards Institute
3.2.3 ARM—Atmospheric RadiationMeasurement Program
3.1.3 direct radiation, direct solar radiation, and direct
3.2.4 DOE—Department of Energy
(beam) radiation—radiation received from a small solid angle
centered on the sun’s disk, on a given plane (see ISO 9060). 3.2.5 GUM—(ISO) Guide to Uncertainty in Measurements
That component of sunlight is the beam between an observer, 3.2.6 IPC—International Pyrheliometer comparison
orinstrument,andthesunwithinasolidconicalanglecentered
3.2.7 ISO—International Standards Organization
on the sun’s disk and having a total included planar field angle
3.2.8 NCSL—National Council of Standards Laboratories
of, for the purposes of this test method, 5 to 6°.
3.2.9 NIST—NationalInstituteofStandardsandTechnology
3.2.10 NREL—National Renewable Energy Laboratory
3.1.4 field pyrheliometer—pyrheliometers that are designed
and used for long-term field measurements of direct solar 3.2.11 PMOD—Physical Meteorological Observatory Da-
vos
radiation.Thesepyrheliometersareweatherproofandtherefore
possess windows, usually quartz, at the field aperture that pass 3.2.12 SAC—Singapore Accreditation Council
all solar radiation in the range from 0.3 to 4 µm wavelength. 3.2.13 SINGLAS—Singapore LaboratoryAccreditation Ser-
vice
3.1.5 opening angle—with radius of field aperture denoted
3.2.14 UKAS—United Kingdom Accrediation Service
by R and the distance between the field and receiver apertures
3.2.15 WRC—World Radiation Center
denoted by l, the opening angle is defined for right circular
3.2.16 WRR—World Radiometric Reference
cones by the equation:
3.2.17 WMO—World Meteorological Organization
Z 5 tan R/l (1)
o
The field angle is double the opening angle.
4. Significance and Use
4.1 Though the sun trackers employed, the number of
instantaneous readings, and the data acquisition equipment
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
used will vary from instrument to instrument and from labo-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ratorytolaboratory,thistestmethodprovidesfortheminimum
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. acceptable conditions, procedures, and techniques required.
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4.2 While the greatest accuracy will be obtained when
4th Floor, New York, NY 10036, http://www.ansi.org.
Available from World Meterological Organization, Geneva, Switzerland. calibrating pyrheliometers with a self-calibrating absolute
E816 − 05 (2010)
cavity pyrheliometer that has been demonstrated by intercom- nometer aligned with its axis vertical and calibrated in accor-
parisontobewithin 60.5%ofthemeanirradianceofafamily 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-
ring calibration from a secondary reference pyrheliometer to
4.3 By meeting the requirements of this test method, trace-
field pyrheliometers. Generally, good calibration conditions
ability of calibration to the World Radiometric Reference
exist when the cloud cover is less than 12.5%.
(WRR) can be achieved through one or more of the following
recognized intercomparisons:
NOTE 3—Contrails of airplanes that are within 15° of the sun can be
tolerated providing the ratio of so affected measurements to unaffected
4.3.1 International Pyrheliometric Comparison (IPC) VII,
measurements is small in any series.
Davos, Switzerland, held in 1990, and every five years
NOTE 4—Atmospheric water vapor in the pre-condensation phase
thereafter,andthePMO-2absolutecavitypyrheliometerthatis
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
heldintheUnitedStatesthepurposeofwhichistotransferthe
conditions with Linke turbidity factors lower than six (see ISO
WRR from the primary reference absolute cavity pyrheliom-
9059 and ISO 9060).
etermaintainedastheprimaryreferencestandardoftheUnited
5.2.2 The circumsolar radiation (aureole) originates from
States by the National Oceanic and Atmospheric Administra-
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 distance of about 15° by
4.3.4 Any future intercomparisons of comparable reference
several orders of magnitude, depending on the type and
2,8,9
quality in which at least one self-calibrating absolute cavity
concentrationoftheaerosol. Thetypicalamountofcircum-
pyrheliometer is present that participated in IPC VII or a
solar radiation within an angular distance of 5° of the sun
subsequent IPC, and in which that pyrheliometer is treated as
represents only a few percent of the direct solar radiation. If
the intercomparison’s reference instrument.
standard and field pyrheliometers have different field-of-view
4.3.5 Any of the absolute radiometers participating in the
angles, the aerosol may strongly influence the accuracy of the
above intercomparisons and being within 60.5% of the mean
transfer of calibration. Calculated percentages of circumsolar
of all similar instruments compared in any of those intercom-
contained in direct solar radiation, for different aerosol types
parisons.
and solar elevation angles, are given for information in
Appendix X1.
4.4 The calibration transfer method employed assumes that
the accuracy of the values obtained are independent of time of
5.3 Differences in Geometry—If the pyrheliometers being
year and, within the constraints imposed, time of day of
compared do not have similar opening angles, atmospheric
measurements. With respect to time of year, the requirement
turbidity will introduce errors into the calibration.
for normal incidence dictates a tile angle from the horizontal
5.4 Wind Conditions—Wind conditions are known to affect
that is dependent on the sun’s zenith angle and, thus, the air
instrumentsdifferently,particularlysomeself-calibratingabso-
mass limits for that time of year and time of day.
lute cavity pyrheliometers, particularly when the wind is
blowing from the direction of the sun’s azimuth (630°).
5. Interferences
Measurements affected by wind conditions should be rejected.
5.1 Radiation Source—Transfer of calibration from refer-
A tolerable maximum wind speed for unprotected measure-
ence to secondary standard or field pyrheliometers is accom-
ment conditions cannot be specified.
plished by exposing the two instruments to the same radiation
field and comparing their corresponding measurands. The NOTE5—Pyrheliometerswithopenapertureswillyieldlowermea
...
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