1、Designation: G 197 08Standard Table forReference Solar Spectral Distributions: Direct and Diffuseon 20 Tilted and Vertical Surfaces1This standard is issued under the fixed designation G 197; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis table of solar spectral irradiance distributions has been developed to meet the need forweigh
3、ting functions to be used in evaluating the broadband transmittance of fenestration systems orthe performance of technologies such as building-integrated photovoltaic devices. To compare therelative optical performance of spectrally sensitive products by theoretical simulation, or to comparethe perf
4、ormance of products by actual testing under laboratory conditions, separate reference standardsolar spectral distributions for direct and diffuse irradiance are required. This table was prepared usingversion 2.9.2 of the Simple Model of the Atmospheric Radiative Transfer of Sunshine (SMARTS)atmosphe
5、ric transmission code (1, 2).2SMARTS uses parameterizations of version 4.0 of the AirForce Geophysical Laboratory (AFGL) Moderate Resolution Transmission model, MODTRAN (3, 4).An extraterrestrial spectrum differing only slightly from the extraterrestrial spectrum in ASTM E 490is used to calculate th
6、e resultant spectra. The directional beam and diffuse hemispherical (2p steradianacceptance angle) spectral irradiances on planes tilted 20 (representative of a pitched roof slope) and90 (tilt of a typical wall) to the horizontal are tabulated. The wavelength range for the spectra extendsfrom 280 nm
7、 to 4000 nm, covering the spectral range for which windows or solar collectors respondto shortwave energy. The input parameters used in conjunction with SMARTS for each set ofconditions are tabulated. The SMARTS model and documentation are available as an adjunct to thisstandard.1. Scope1.1 This tab
8、le provides terrestrial solar spectral irradiancedistributions that may be employed as weighting functions to(1) calculate the broadband solar or light transmittance offenestration from its spectral properties; or (2) evaluate theperformance of building-integrated technologies such as pho-tovoltaic
9、electricity generators. Most of these systems areinstalled on vertical walls, but some are also installed onpitched roofs or on other tilted structures, such as sunspaces.Glazing transmittance calculations or measurements requireinformation on both the direct and diffuse components ofirradiance. The
10、 table provides separate information for directand diffuse irradiance, and for two different tilt angles, 20 and90 relative to the horizontal. All distributions are provided at2002 wavelengths within the spectral range 2804000 nm. Thedata contained in this table reflect reference spectra withuniform
11、 wavelength interval (0.5 nanometer (nm) below 400nm, 1 nm between 400 and 1700 nm, an intermediate wave-length at 1702 nm, and 5 nm intervals from 1705 to 4000 nm).The data table represents reasonable cloudless atmosphericconditions favorable for the computerized simulation, com-parative rating, or
12、 experimental testing of fenestration systems.1.2 The data contained in this table were generated using theSMARTS version 2.9.2 atmospheric transmission model de-veloped by Gueymard (1, 2).1.3 The selection of the SMARTS radiative model togenerate the spectral distributions is chosen for compatibili
13、tywith previous standards (ASTM G 173 and G 177). Theatmospheric and climatic conditions are identical to those inASTM G 173. The environmental conditions are also identical,with only one exception (see sections 4.3 and X1.2).1.4 The table defines four solar spectral irradiance distribu-tions:1.4.1
14、Separate direct and diffuse solar spectral irradianceincident on a sun-facing, 20 tilted surface in the wavelengthregion from 2804000 nm for air mass 1.5, at sea level.1These tables are under the jurisdiction ofASTM Committee G03 on Weatheringand Durability and is the direct responsibility of Subcom
15、mittee G03.09 onRadiometry.Current edition approved June 1, 2008. Published July 2008.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1.4
16、.2 Separate direct and diffuse solar spectral irradianceincident on a sun-facing, 90 (vertical) tilted surface in thewavelength region from 2804000 nm for air mass 1.5, at sealevel.1.5 The diffuse spectral distribution on a vertical surfacefacing away from the sun (i.e., shaded), or at any prescribe
17、dazimuth away from the sun, may be computed using the modelto obtain representative results (i.e., results that fall within anacceptable range of variance).1.6 The climatic, atmospheric, and geometric parametersselected reflect the conditions to provide a realistic set ofspectral distributions appro
18、priate for building applicationsunder very clear-sky conditions, representative of near-maximum solar heat gains in buildings.1.7 A wide variety of orientations or local environmentalconditions is possible for exposed surfaces. The availability ofthe SMARTS model (as an adjunct to this standard) use
19、d togenerate the standard spectra allows users to evaluate spectraldifferences relative to the spectra specified here.2. Referenced Documents2.1 ASTM Standards:3E 490 Standard Solar Constant and Zero Air Mass SolarSpectral Irradiance TablesE 772 Terminology Relating to Solar Energy ConversionG 173 T
20、ables for Reference Solar Spectral Irradiances:Direct Normal and Hemispherical on 37 Tilted SurfaceG 177 Tables for Reference Solar Ultraviolet Spectral Dis-tributions: Hemispherical on 37 Tilted Surface2.2 ASTM Adjuncts:ADJG173CDSMARTS, Simple Model of the Atmo-spheric Radiative Transfer of Sunshin
21、e, Terrestrial SolarSpectral Modeling Code43. Terminology3.1 DefinitionsDefinitions of terms used in this specifica-tion not otherwise described below may be found in Terminol-ogy E 772.3.2 Definitions of Terms Specific to This Standard:3.2.1 aerosol optical depth (AOD)the wavelength-dependent total
22、 extinction (scattering and absorption) by aero-sols in the atmosphere. This optical depth (also called “opticalthickness”) is defined here at 500 nm.3.2.2 air mass zero (AM0)describes solar radiation quan-tities outside the Earths atmosphere at the mean Earth-Sundistance (1 Astronomical Unit). See
23、ASTM E 490.3.2.3 albedoalso called reflectance, a measure of thereflective characteristics of a surface relative to incidentirradiance.3.2.3.1 DiscussionFor this standard, the albedo refers tothe spectral reflectance of the ground relative to hemisphericalirradiance. Two different albedos are consid
24、ered by the model,and both only affect diffuse irradiance. The first albedocorresponds to the average surface reflectance of the far-fieldarea around the site, within a radius of 550 km. The secondalbedo is that of the foreground (or near-field) immediatelyadjacent to the tilted surface, to a distan
25、ce of 10100 m. Thetwo albedos can be identical or different, but the foregroundalbedos effect significantly increases with tilt angle, whereasthe far-field albedos effect on diffuse irradiance decreases withtilt angle.3.2.4 integrated irradiance El1-l2spectral irradiance inte-grated over a specific
26、wavelength interval from l1to l2,measured in Wm-2; mathematically:El12l25l2*l1Eldl (1)3.2.5 shadingcondition that results in partial obscurationof the sky, including the sun or not.3.2.5.1 DiscussionFor this standard, no shading of the skyis considered. However, the standard also applies to caseswhe
27、n the 20 or 90 tilted surfaces are shaded from the sunonly, due to their relative geometry or other circumstances.This cancels the direct irradiance component, so that the totalhemispherical irradiance reduces to the diffuse component.3.2.6 solar irradiance, spectral Elsolar irradiance E perunit wav
28、elength interval at a given wavelength l (unit: Wattsper square meter per nanometer, Wm-2nm-1)El5dEdl(2)3.2.7 spectral intervalthe distance in wavelength unitsbetween adjacent spectral irradiance data points.3.2.8 spectral passbandthe effective wavelength intervalwithin which spectral irradiance is
29、allowed to pass, as througha filter or monochromator. The convolution integral of thespectral passband (normalized to unity at maximum) and theincident spectral irradiance produces the effective transmittedirradiance.3.2.8.1 DiscussionSpectral passband may also be referredto as the spectral bandwidt
30、h of a filter or device. Passbands areusually specified as the interval between wavelengths at whichone half of the maximum transmission of the filter or deviceoccurs, or as full-width at half-maximum, FWHM.3.2.9 spectral resolutionthe minimum wavelength differ-ence between two wavelengths that can
31、be identified unam-biguously.3.2.9.1 DiscussionIn the context of this standard, thespectral resolution is simply the interval, Dl, between spectraldata points, or the spectral interval.3.2.10 spectral solar irradiance, diffuse Edlon a givenplane, the solar radiant flux at wavelength l received fromw
32、ithin the 2p steradian field of view of a tilted plane from theportion of the sky dome and the foreground included in theplanes field of view, excluding direct solar radiation.3.2.11 spectral solar irradiance, direct EDlon a givenplane, the solar radiant flux at wavelength l received directlyfrom th
33、e sun, excluding diffuse solar radiation.3.2.11.1 DiscussionIn practice, instruments measuring di-rect solar irradiance have a larger acceptance angle than theapparent diameter of the sun. Consequently, it is virtually3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact AS
34、TM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available on CD-ROM from ASTM International Headquarters. Order AdjunctNo. ADJG173CD.G197082impossible to measure EDlwithout the contribution
35、of diffuseradiation emanating from the suns aureole. This contributionis referred to as “circumsolar radiation.” Contrarily to ASTMG 173, the data in Table 3 use the ideal definition of directirradiance, and therefore ignore the circumsolar contribution.The sum of direct and diffuse irradiance is th
36、e hemisphericalsolar irradiance, EHl.3.2.12 total ozonethe depth of a column of pure ozoneequivalent to the total of the ozone in a vertical column fromthe ground to the top of the atmosphere. (unit: atmosphere-cm)3.2.13 total precipitable waterthe depth of a column ofwater (with a section of 1 cm2)
37、 equivalent to the condensedwater vapor in a vertical column from the ground to the top ofthe atmosphere. (unit: cm or g/cm2)3.2.14 wavenumbera unit of frequency, , in units ofreciprocal centimeters (symbol cm-1) commonly used in placeof wavelength, l (units of length, typically nanometers). Toconve
38、rt wavenumbers to nanometers, l nm = 1107/ cm-1.4. Technical Bases for the Tables4.1 These tables are modeled data generated using an airmass zero (AM0) spectrum based on the extraterrestrial spec-trum of Gueymard (1, 2) derived from Kurucz (5), the UnitedStates Standard Atmosphere of 1976 (USSA) re
39、ference Atmo-sphere (6), the Shettle and Fenn rural aerosol profile (7), andthe SMARTS version 2.9.2 radiative transfer code. Furtherdetails are provided in ASTM G 173.4.2 The 20 tilted surface closely represents the geometry ofpitched roofs or tilted glazed structures, which are commonelements of b
40、uildings. The 90 (vertical) surface represents thenorm for building walls.4.3 The tabulated diffuse irradiance is a combination ofscattered irradiance from the sky and reflected irradiance fromfar-field and near-field ground surfaces. Dry soil conditionshave been chosen for both surfaces. This is a
41、darker, lessreflective surface than what was used in ASTM G 173 orG 177.4.4 The documented USSA atmospheric profiles utilized inthe MODTRAN spectral transmission model (6) have beenused to provide atmospheric properties and concentrations ofabsorbers.4.5 To provide spectral data with a uniform spect
42、ral stepsize, the AM0 spectrum used in conjunction with SMARTS togenerate the terrestrial spectrum is slightly different from theASTM extraterrestrial spectrum, ASTM E 490. BecauseASTM E 490 and SMARTS both use the data of Kurucz (5),the SMARTS and E 490 spectra are in excellent agreementalthough th
43、ey do not have the same spectral resolution.4.6 The current spectra reflect improved knowledge ofatmospheric aerosol optical properties, transmission properties,and radiative transfer modeling (8).4.7 The terrestrial solar spectral in the tables have beencomputed with a spectral bandwidth equivalent
44、 to the spectralresolution of the tables, namely 0.5 nm to 5 nm (see 1.1).4.8 The SMARTS model code and documentation is avail-able as an adjunct standard. Request ASTM Stock numberADJG173CD.5. Significance and Use5.1 This standard does not purport to address the meanspectral irradiance incident on
45、tilted or vertical fenestration orbuilding-integrated systems over a day, a season, or a year. Thespectral irradiance distributions have been chosen to representa reasonable near-upper limit for solar radiation when thesesystems are exposed to clear-sky conditions similar to thoseused to calculate s
46、olar heat loads of buildings. The diffusespectral irradiance distributions can also be used to representconditions when these systems are shaded from the direct sun.5.2 Absorptance, reflectance, and transmittance of solarradiation are important factors in studies of light transmissionthrough semi-tr
47、ansparent plates. These properties are normallyfunctions of wavelength, which require that the spectral distri-bution of the solar flux be known before the solar-weightedproperty can be calculated.5.3 To compare the relative performance of competitiveproducts by computerized simulations, or to compa
48、re theperformance of products subjected to experimental tests inlaboratory conditions, a reference standard solar spectral dis-tribution for both direct and diffuse irradiance is desirable.5.4 The table provides appropriate standard spectral irradi-ance distributions for determining the relative opt
49、ical perfor-mance of semi-transparent materials and other systems. Thetable may be used to evaluate components and materials for thepurpose of solar simulation where the direct and the diffusespectral solar irradiances are needed separately.5.5 The selected air mass value of 1.5 for a plane-parallelatmosphere above a flat earth corresponds to a zenith angle of48.19. The SMARTS2 computation of air mass accounts foratmospheric curvature and the vertical density profile ofmolecules, which results in a solar zenith angle of 48.236, oran e
