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Water 2018, 10(4), 398; https://doi.org/10.3390/w10040398

Unstructured-Mesh Terrain Analysis and Incident Solar Radiation for Continuous Hydrologic Modeling in Mountain Watersheds

1
Department of Geography and Environmental Sustainability, University of Oklahoma, Norman, OK 73019, USA
2
Department of Civil and Architectural Engineering, University of Wyoming, Laramie, WY 82071, USA
3
Center for Automated Sensing and Sampling, School of Meteorology, University of Oklahoma, Norman, OK 73019, USA
Current address: 100 E. Boyd St, Norman, OK 73019, USA
*
Author to whom correspondence should be addressed.
Received: 26 February 2018 / Revised: 20 March 2018 / Accepted: 22 March 2018 / Published: 28 March 2018
(This article belongs to the Special Issue Applications of Remote Sensing and GIS in Hydrology)
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Abstract

This article presents a methodology for estimating total incoming solar radiation from Triangular Irregular Network (TIN) topographic meshes. The algorithm also computes terrain slope degree and aspect (slope orientation) and accounts for self shading and cast shadows, sky view fractions for diffuse radiation, remote albedo and atmospheric backscattering, by using a vectorial approach within a topocentric coordinate system establishing geometric relations between groups of TIN elements and the sun position. A normal vector to the surface of each TIN element describes its slope and aspect while spherical trigonometry allows computing a unit vector defining the position of the sun at each hour and day of the year. Sky view fraction, useful to determine diffuse and backscattered radiation, is computed for each TIN element at prescribed azimuth intervals targeting the steepest elevation gradient. A comparison between the sun zenith angle and the steepest gradient allows deciding whether or not the pivot element is shaded. Finally, remote albedo is computed from the sky view fraction complementary functions for observed albedo values of the surrounding terrain. The sensitivity of the different radiative components to seasonal changes in atmospheric transmissivitties and surrounding albedo is tested in a mountainous watershed in Wyoming. This methodology represents an improvement on the current algorithms to compute terrain and radiation values on unstructured-mesh terrain models. All terrain-related features (e.g., slope, aspect, sky view fraction) can be pre-computed and stored for easy access into a subsequent, progressive-in-time, numerical simulation. View Full-Text
Keywords: triangular irregular networks; insolation; unstructured mesh; shadow casting; sky-view fraction; remote albedo triangular irregular networks; insolation; unstructured mesh; shadow casting; sky-view fraction; remote albedo
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Moreno, H.A.; Ogden, F.L.; Alvarez, L.V. Unstructured-Mesh Terrain Analysis and Incident Solar Radiation for Continuous Hydrologic Modeling in Mountain Watersheds. Water 2018, 10, 398.

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