Calculation of potential broadband biologically active and thermal solar radiation above vegetation canopies
- Connecticut Univ., Storrs, CT (United States)
A spectral model was assembled and used to compute the potential solar irradiance in five broad bands, that is, ultraviolet-B (280 - 320 nm in wavelength), ultraviolet-A (320 - 400 nm), photosynthetically active (400 - 700 nm), near infrared (700 - 1500 nm), and far infrared (1500 - 4000 nm), above a green vegetation canopy defined by ground albedo. Starting from the spectral solar irradiance above the atmosphere, the spectral model calculates unweighted potential (clear-sky) direct, diffuse, and global irradiance over the total solar spectrum at the ground-level by considering molecular scattering, scattering and absorption by aerosols, and absorption by ozone, uniformly distributed gases, and water vapor. Broadband irradiances and atmospheric transmittances were determined by spectral integration of the predictions from the spectral model over the five spectral regions. The effects of solar position, altitude, column ozone, column water vapor, and turbidity in the lower atmosphere on the broadband atmospheric transmittance were examined and quantified. Based on the analysis, a set of simple regression equations was developed for estimating the broadband values of the potential atmospheric transmittance in the five spectral regions. The regression model predicts global irradiance in any of the five broad bands at sea level for a fixed solar position, and then extends the predictions with multipliers of altitude and solar zenith angle. The major advantage of the regression model lies in the convenience of using easy-to-obtain, wavelength independent, parameters as input variables in predicting potential broadband irradiances for ecological studies in engineering units (W/sq m) for any given location and time.
- OSTI ID:
- 57435
- Journal Information:
- Journal of Applied Meteorology, Vol. 34, Issue 4; Other Information: PBD: Apr 1995
- Country of Publication:
- United States
- Language:
- English
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