7 December 1998 Evaluation of the different irradiance components on a rugged terrain
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An algorithm based on the Monte Carlo principle is developed to solve the radiative transfer problem in the reflective domain of the solar spectrum and is used to precisely evaluate ground irradiance on a rugged terrain. This method allows to simulate paths of photons inside the earth- atmosphere system without any assumption and calculate the different identified irradiance components and particularly those coming from environment. To establish the relative contribution of each of these terms, several typical relief and atmosphere configurations are considered. In a first step, two ground types simulations assuming lambertian reflectances are computed. Over vegetation-covered hills in the near IR, in the portion badly exposed to the direct solar beam, the environment irradiance contributes more than 20 percent of the total signal received at ground level. When severe slopes and higher reflectance values are considered, this contribution can exceed 60 percent in shadowed areas. These simulations demonstrate the necessity to take into account the high order terms when the region of interest presents important slopes and/or high reflectance ground. the case of non-lambertian reflectances is also dealt and it is shown that in the present configuration lambertian reflectances can be assumed to calculate the environment terms without significant errors on total irradiance, even in the shadow.
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Christophe Miesch, Christophe Miesch, Xavier Briottet, Xavier Briottet, Yann H. Kerr, Yann H. Kerr, Francois Cabot, Francois Cabot, "Evaluation of the different irradiance components on a rugged terrain", Proc. SPIE 3494, Atmospheric Propagation, Adaptive Systems, and Lidar Techniques for Remote Sensing II, (7 December 1998); doi: 10.1117/12.332434; https://doi.org/10.1117/12.332434

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