Modeling Solar Radiation at the Earth’s Surface

Radiometer Uncertainty Sources

Sensitivity Functions

Combined uncertainties depend on the product of the sensitivity functions (par­tial derivatives of the response with respect to the measurement equation variables) and error source magnitudes, et. The largest contributions to shade-unshade uncer­tainty are from the evg and evd which must include estimates of the thermal offset (10-70 jiV) described below, and data acquisition measurement uncertainty (typi­cally <10 |iV). For example, for an all-black sensor pyranometer with a responsiv- ity of 7.0 mV per 1000Wm-2, a 70-pV offset corresponds to an irradiance error of -10Wm-2.

For the shade-unshade technique, with fixed direct beam error eB « 4.0Wm-2, zenith angle error ez « 0.06°, and diffuse irradiance error eD « 2.0Wm-2 (black - and-white sensor), the uncertainty in RS for a pyranometer is a function of: zenith angle, uncertainty in the pyranometer voltages, and magnitude of the beam; it ranges from about 1.0% at small zenith angles to >10% for zenith angles greater than 85°. The component-summation technique normally has lower total uncertainties, since the uncertainty in the direct beam is essentially the same as in the shade - unshade calibration, the uncertainty contribution from the diffuse measurement is rather low, and only one voltage measurement is involved for the instruments un­der test, as opposed to two voltage measurements in the shade-unshade technique (Myers et al. 2004).

Modeling Solar Radiation at the Earth’s Surface

Quality Assessment Based Upon Comparison with Models

Many models based on the physics of radiation transfer through the clear atmo­sphere have been developed (Lacis and Hansen 1974; Atwater and Ball 1978; Hoyt 1978; Bird and Hulstrom 1981a, …

Solar Horizontal Diffuse and Beam Irradiation on Clear Days

There exist a number of models to determine the solar horizontal diffuse irradia­tion on a clear day (Kondratyev 1969) but they are complex and have very stringent conditions. Similarly, there …

Foreword

Reading the twenty chapters of this book caused me mixed reactions, though all were positive. My responses were shaped by several factors. Although I have main­tained a “watching brief’ on …

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