Estimating net solar radiation using Landsat Thematic Mapper and digital elevation data

Abstract

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...

Topographic effects on solar radiation distribution in mountainous watersheds and their influence on reference evapotranspiration estimates at watershed scale

“…The local horizon information from the gridded data allows us to ascertain whether a given location at a certain sun position is shaded from direct sunlight by surrounding terrain and determines, at any location, the portion of the overlying hemisphere which is obscured by the terrain (Dozier et al, 1981;Dubayah, 1992). Thus, each hourly component, beam, diffuse and reflected radiation has been calculated separately to account for the topographic effects (González-Dugo et al, 2003) from the daily global radiation data measured at weather stations.…”

“…Despite the availability of topographically corrected models for the estimation of solar radiation fields as Dozier and Frew (1990), Dubayah (1992Dubayah ( , 1994, etc., these approaches are not commonly included in GIS-based hydrological models, which usually adopt simple approaches to estimate the incident radiation throughout the watershed, as explained next. In AnnAGNPS, a distributed-parameter, physically-based, continuous-simulation, watershed-scale, nonpoint-source pollutant model (Cronshey and Theurer, 1998), correction factors to take account of the effect of dust, water vapor, path length, and reflection and rescattering are applied to the extraterrestrial radiation in order to obtain the short wave radiation received at the ground surface.…”

“…At a global scale, latitudinal gradients caused by the earth's rotation and translation movements are well-known. However, at a smaller scale, apart from cloudiness and other atmospheric heterogeneities, topography determines the distribution of the incoming solar radiation; variability in slope angle and slope orientation, as well as the shadows cast by topographic agents, can lead to strong local gradients in solar radiation (Dozier, 1980;Dubayah, 1992;Dubayah and van Katwijk, 1992), with the corresponding influence on the energy-mass balance of the snow cover and its evolution (Dubayah and van Katwijk, 1992;Li et al, 2002;Herrero et al, 2009), the vegetation canopy (Dubayah, 1994), the surface soil layer, surface water bodies (Annear and Wells, 2007), etc.…”

Estimation of Daily Solar Radiation Budget at Kilometer Resolution over the Tibetan Plateau by Integrating MODIS Data Products and a DEM

“…The use of satellite remote sensing data allows us to monitor land surface solar radiative fluxes over large areas at a satisfying spatial and temporal resolution, which meets the requirements of current studies on climate and land surface processes. Numerous algorithms have been developed to estimate solar radiative fluxes using satellite radiometric measurements [6][7][8][9][10][11][12][13][14] and some have led to the production of regional or global datasets [15]. To the knowledge of the authors, among the best known are the Surface Radiation Budget project (SRB) [16], the Clouds and the Earth's Radiant Energy System (CERES) [17], the International Satellite 2 of 24 Cloud Climatology Project (ISCCP) [18], and the Global LAnd Surface Satellite (GLASS) radiation products [19].…”

A New Method for the Estimation of Broadband Apparent Albedo Using Hyperspectral Airborne Hemispherical Directional Reflectance Factor Values

“…This procedure has already been used for Landsat TM bands [13], considering the width of each band to spread from and to the midpoints between the said band and the two neighboring bands, i.e., the region between two bands was divided equally between the bands. The spectral region between channels 20 and 21 was divided, taking into account the typical spectral signature of vegetation as previously performed by other authors [43,44] (Figure 4). If the spectral region between these channels had been divided equally, channel 21 would have spanned from 1214 nm up to 1798 nm.…”