[1] The Department of Energy's Atmospheric Radiation Measurement (ARM) program sponsored a large aerosol intensive observation period (AIOP) to study aerosol during the month of May 2003 around the Southern Great Plains (SGP) Climate Research Facility (CRF) in north central Oklahoma. Redundant measurements of aerosol optical properties were made using different techniques at the surface as well as in vertical profile with sensors aboard two aircraft. One of the principal motivations for this experiment was to resolve the disagreement between models and measurements of diffuse horizontal broadband shortwave irradiance at the surface, especially for modest aerosol loading. This paper focuses on using the redundant aerosol and radiation measurements during this AIOP to compare direct beam and diffuse horizontal broadband shortwave irradiance measurements and models at the surface for a wide range of aerosol cases that occurred during 30 clear-sky periods on 13 days of May 2003. Models and measurements are compared over a large range of solar-zenith angles. Six different models are used to assess the relative agreement among them and the measurements. Better agreement than previously achieved appears to be the result of better specification of input parameters and better measurements of irradiances than in prior studies. Biases between modeled and measured direct irradiances are in the worst case 1%, and biases between modeled and measured diffuse irradiances are less than 1.9%.

[1] The first intensive observation period (IOP) to simultaneously measure diffuse horizontal shortwave irradiance (scattered solar radiation that falls on a horizontal surface) with a wide array of shaded pyranometers suggested that a consensus might be reached that would permit the establishment of a standard with a smaller uncertainty than previously achieved. A second IOP has been held to refine the first IOP measurements using a uniform calibration protocol, offset corrections for all instruments and validation of those corrections, improvements in some of the instruments, and better data acquisition. The venue for both IOPs was the Department of Energy's Atmospheric Radiation Measurement central facility in northern Oklahoma. The 9 days of measurements in October 2003 included a better mixture of clear and overcast conditions than during the first IOP and revealed considerable differences among the instruments' responses for different cloud conditions. Four of the 15 instruments were eliminated as candidates to be included in the standard because of noisy signals, inadequate offset correction, or instability with respect to the majority of the measurements. Eight pyranometers agreed to within ±2% for clear-sky conditions. Three others have a high bias on clear days relative to these eight, but all 11 agree within ±2% on overcast days. The differences and causes of this behavior under clear and cloudy skies are examined.

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In 1982, the American Society for Testing and Materials (ASTM) adopted consensus standards for direct-normal and hemispherical (“global”) tilted solar terrestrial spectra (ASTM E891/E892/G159). These standard spectra were intended to evaluate photovoltaic (PV) device performance and other solar-related applications. The International Standards Organization (ISO) and International Electrotechnical Commission (IEC) adopted these spectra as spectral standards ISO 9845-1 and IEC 60904-3. Additional information and more accurately representative spectra are needed by today’s PV community. Modern terrestrial spectral radiation models, knowledge of atmospheric physics, and measured radiometric quantities are applied to develop new reference spectra under consideration by ASTM.

Abstract. In this work we explore the effect of the contribution of the solar spectrum to the recorded signal in wavelengths outside the typical 940-nm filter's bandwidth. We employ gaussian-shaped filters as well as actual filter transmission curves, mainly AERONET data, to study the implications imposed by the non-zero out-of-band contribution to the coefficients used to derive precipitable water from the measured water vapour band transmittance. Published parameterized transmittance functions are applied to the data to determine the filter coefficients. We also introduce an improved, three-parameter, fitting function that can describe the theoretical data accurately, with significantly less residual effects than with the existing functions. The moderateresolution SMARTS radiative transfer code is used to predict the incident spectrum outside the filter bandpass for different atmospheres, solar geometries and aerosol optical depths. The high-resolution LBLRTM radiative transfer code is used to calculate the water vapour transmittance in the 940-nm band. The absolute level of the out-of-band transmittance has been chosen to range from 10 −6 to 10 −4 , and typical response curves of commercially available silicon photodiodes are included into the calculations.It is shown that if the out-of-band transmittance effect is neglected, as is generally the case, then the derived columnar water vapour is mainly underestimated by a few percents. The actual error depends on the specific out-of-band transmittance, optical air mass of observation and water vapour amount. Further investigations will use experimental data from field campaigns to validate these findings.

Despite the existence of several possible pyrometric methodologies, temperature monitoring and control of samples heated at the focus of solar concentrators have still not received a universal and perfect solution. Here we present an analysis of solar-blind conditions and experimental measurements that have been carried out at the Odeillo Solar Furnace (IMP-CNRS). The aim here is to test different experimental configurations that can conceptually eliminate the reflected part of the concentrated solar flux. These configurations would allow near solar-blind measurements within the atmospheric absorption bands centered at 1.4 μm and 1.9 μm, and true solar-blind measurements within similar bands centered at 2.7 μm, 4.3 μm, and 6 μm. The parasitic reflected solar flux can be evaluated for each of these bands. In the case of alumina in particular, true solar-blind measurements can also be performed under blackbody conditions over the 8–12 μm band, and this is taken here as a convenient example of application. It is also demonstrated that solar-blind measurements are possible outside of these absorption bands, either by adding an appropriate radiation cutting filter (e.g., a quartz window) or by using an infrared narrow filter centered in a spectral region where the incident flux is negligible due to reflection losses (e.g., at 3.9 μm). The Solar Performance Factor is introduced to characterize the potential of any spectral region vis-a`-vis solar blindness.

[1] Atmospheric radiative transfer model estimates of diffuse horizontal broadband shortwave (solar) irradiance have historically been larger than measurements from a shaded pyranometer. A reference standard for the diffuse horizontal shortwave irradiance does not exist. There are no current efforts to develop an absolute standard that are known to the authors. This paper presents the case for a working standard for this measurement. Four well-behaved pyranometers from two previous intensive observation periods (IOP) were chosen for this study. The instruments were characterized for spectral and angular response before the IOP and calibrated during the IOP using a shade/unshade technique with reference direct irradiance from an absolute cavity radiometer. The results of the comparison and detailed analyses to explain the differences suggest selecting three of the four for the working standard. The 95% confidence uncertainty in this standard is estimated at 2.2% of reading + 0.2 W/m 2 . In lieu of a comparison to this trio, a procedure for obtaining low-uncertainty diffuse horizontal shortwave irradiance is suggested.

Variations in terrestrial spectral irradiance on photovoltaic devices can be an important consideration in photovoltaic device design and performance. This paper describes three available atmospheric transmission models, MODTRAN, SMARTS2, and SPCTRAL2. We describe the basics of their operation and performance, and applications in the photovoltaic community. Examples of model input and output data and comparisons between the model results for each under similar conditions are presented. The SMARTS2 model is shown to be much easier to use, as accurate as the complex MODTRAN model, and more accurate than the historical NREL SPCTRAL2 model.