Estimation of net short-wave radiation by the use of remote sensing and a digital elevation model-a case study of a high arctic mountainous area

Abstract

A fast method for estimating the net short-wave radiation in high arctic mountainous areas is developed by combining Landsat-5 Thematic Mapper (TM) satellite data and a digital elevation model (DEM). Methods to: (1) correct remote sensing data for the atmospheric e V ect; (2) perform a thorough and extensive topographic correction via the DEM; and (3) model the irradiance from a radiation model are described. By combining the above-mentioned methods, a model with great applicability-e.g. creation of albedo maps, terrain modelled short wave radiation and correction of satellite images for both topographic and atmospheric e V ects, is developed. A great advantage of this model is that it combines atmospheric and topographic correction. Most models only correct for one of the two. Another great advantage is that it has a limited number of inputs. Beside the satellite data and the DEM, the only inputs are visibility, latitude, longitude, atmospheric pressure and time of day and day of year (DOY). Furthermore the model can be implemented in any image processing software. The model was tested and validated on satellite data from April to September in the period 1995 to 1998 with a total of nine TM-images. To validate the model, the results were compared with ground measurements. The result of the validation showed that: (1) the modelled results show very good agreement with the measured data; (2) atmospheric and topographic correction of images is possible without using expensive software; and (3) the topographic correction is of great importance. Even a small change in the topography has a greater e V ect on the net short wave radiation than a lack of atmospheric correction. The future use of the model is to produce input to other models that estimate snowmelt, energy balance, biomass production and CO 2 -uxes and to determine regional and seasonal variation.

Scale effect and scale correction of land-surface albedo in rugged terrain

“…Much work has shown that the effect of topography on albedo estimation should be taken into account in fine-scale remote sensing data. These include Landsat-5 Thematic Mapper (TM) (Proy et al 1989, Dubayah 1992, Hansen et al 2002, SPOT high resolution visible (HRV) (Bishop andColby 2002, Shepherd andDymond 2003) and QuickBird (Wu et al 2008). Theoretically, the effect of topography in coarse-scale data such as the advanced very high resolution radiometer (AVHRR) (Burgess et al 1995, Cihlar et al 2004) and the moderate resolution imaging spectroradiometer (MODIS) should also be considered.…”

Further evaluation of the Sim-ReSET model for ET estimation driven by only satellite inputs

“…Since we have no ground observational data for slopes in mountainous areas, we cannot evaluate the effect of topography on solar radiation and thus ET estimates in this study. However, based on prior studies (Hansen et al 2002, Allen et al 2006), a topographic correction will be combined in Sim-ReSET to improve the accuracies of R n and ET estimates in our future study.…”

Improved calibration of Landsat-5 TM applicable for high-latitude and dark areas

“…The TOA reflectance is thus not a valid measure for the reflective characteristics of these areas. The radiation distribution in these areas was found from the radiative transfer method from Hansen et al (2002) and Modtran (Modtran 1997). As mentioned earlier, a bright and highly reflective area as found in A1 and A2 is better suited for this purpose since high radiance and DC decrease the impact of the calibration offset.…”

“…Instead, equation (1) is used to calculate the surface reflectance for R1 and R2 while taking into account the altitude variation between the two sites. For a more detailed description of the calculation of the surface reflectance see Hansen et al (2002). The final calibration target is also divided into two locations (A1 and A2).…”