Abstract. Incident solar radiation at the Earth's surface is the result of a complex interaction of energy between the atmosphere and the surface. Recently much progress has been made towards the creation of accurate, physically-based solar radiation formulations that can model this interaction over topographic and other surfaces (such as plant canopies) for a large range of spatial and temporal scales. In this paper we summarize our current work on solar radiation models and their implementation within both GIS and image processing systems. An overview of the effects of topography and plant canopies on solar radiation is presented along with a discussion of various options for obtaining the data necessary to drive specific solar radiation models. Examples are given from our own work using two models, ATM (Atmospheric and Topographic Model), a model based within an image processing framework, and SOLARFLUX, a GIS-based model. We consider issues of design, including CIS implementation and interface, computational problems, and error propagation.

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Author ContributionsENS is the lead writer for the manuscript, DS lead discussions and helped articulate the key points of discussion for the manuscript, RP provided HISUI and OCO3 information and subfigures associated with Figure 2 as well as with edits for the manuscript, SS helped edit the general text, developed Figure 2 and provided text for terrestrial biosphere models section, AS helped edit the general text and provided text for terrestrial biosphere models sections, LD provided the GEDI sub-figure in Figure 2 and text describing GEDI, JBF helped with general editing and provided the ECOSTRESS sub-figure in Figure 2, FF helped with general editing, SU helped develop the original manuscript outline, RD, AS and PW were key in contributing ideas for the manuscript.

This research analyzes the topographic distribution of clear‐sky incoming solar radiation over the tallgrass Konza Prairie, site of FIFE, the First ISLSCP (International Satellite Land Surface Climatology Program) Field Experiment. Using a two‐stream atmospheric radiation model and digital elevation grids of 25‐, 50‐, and 100‐m grid spacing, clear‐sky radiation is simulated throughout the day for three dates: December 15, March 15, and June 15. Geostatistical analysis is used to characterize the spatial and temporal variability in modeled radiation at each grid spacing. The variance and spatial autocorrelation of simulated incoming radiation depend on Sun angle and elevation grid spacing. The behavior of the variance as a function of Sun angle, optical depth, and mean terrain slope can be explained by considering direct radiation variability on a simplified terrain model of uniform albedo where slopes are equal and azimuths are distributed uniformly in all directions. For this constant‐slope model it can be shown analytically that the solar zenith angle at which variance is maximized is a function of optical depth only and is independent of elevation, slope, and aspect. Results from the two‐stream simulations support this conclusion and suggest its applicability to real terrain.

A radiative transfer algorithm is combined with digital elevation and satellite reflectance data to model spatial variability in net solar radiation at fine spatial resolution. The method is applied to the tall-grass prairie of the 16 x 16 kin2 FIFE site (First ISLSCP Field Experiment) of the International Satellite Land Surface Climatology Project. Spectral reflectances as measured by the Landsat thematic mapper (TM) are corrected for atmospheric and topographic effects using field measurements and accurate 30-m digital elevation data in a detailed model of atmosphere-surface interaction. The spect.ral reflectances are then integrated to pi'oduce estimates of surface albedo in the range 0.3-3.0/.•m. This map of albedo is used in an atmospheric and topographic radiative transfer model to produce a map of net solar radiation. A map of apparent net solar radiation is also derived using only the TM reflectance data, uncorrected for topography, and the average field-measured downwel!ing solar irradiance. Comparison with field measurements at 10 sites on the prairie shows that the topographically derived radiation map accurately' captures the spatial variability in net solar radiation, but the apparent map does not. The regional means for the entire site, as estimated from field measurements by themselves, from the topographic model, and from the apparent net solar radiation map are nearly equal, although the variance is an order of magnitude larger for the topographic model. INTRODUCTIONThe effects of local and regional variability of land surface characteristics such as soils, orography, and vegetation for regional and global climate are not well known. The possible feedbacks between the land surface and the atmosphere are significant enough that it is important we more fully understand land surface variability at spatial scales that are preferably below the scales we wish to model. A key component in the climatology of the Earth is net solar radiation. Net solar radiation is that amount of energy available at the ground surface to drive processes such as air and soil heating, evaporation and photosynthesis and is a fundamental quantity in the energy balance of the !and surface. However, its temporal and spatial variability is not well understood. Because uncertainty in estimates of net solar radiation can cause uncertainty in the outputs of general circulation model climate change scenarios, e.g., by changing potential evapotranspiration [Rind et al., 1990], it is important that we have accurate synoptic and seasonal regional estimates of net solar radiation for the Earth's surface. In addition, local variability per se is important for regional modeling studies, such as catchment scale models of water balance. Next to clouds and other variations inthe scattering and absorbing properties of the atmosphere, topography and surface albedo are the most important controls on the spatial distribution of radiation, where "albedo" refers to the global-hemispherical reflectance of the surface to solar shortwave and near-inf...