Application of a radiation model for small-scale complex terrain in a GIS environment

Abstract

To calculate the radiation balance of small-scale heterogeneous terrain well known approaches were combined with the vegetation-boundary layer model HIRVAC (HIgh Resolution Vegetation Atmosphere Coupler). These modified approaches were transferred in a GIS (ArcView) environment to consider both topographic influences (terrain geometry, sky view factor) and the influence of different land uses (e.g. pasture and forest) on radiation components. The GIS application is based on the digital elevation model of the Saxonian land surveying office (SLVA) with a resolution of 25 meters and on the land use classification from the Institute of Cartography of the Technical University Dresden. The model was applied to the Eastern Ore Mountains (Saxony/Germany). To illustrate the results the area of the "Tharandter Wald" near Dresden was selected. The results show that the influences of topography and land use on radiation balance are equally important on a terrain with complex land surface patterns and a strong domination of small-scale topography. The shortwave insolation on a clear Spring day is, e.g., over areas with northern aspect up to 10 times lower than over southward orientated areas. The spruce areas in the forest are characterised by 2 times higher daily sums of net radiation than the adjacent clearcuts. The model results are in adequate agreement with measurements of the "Anchor Station Tharandter Wald" for the investigated period. The results can be applied for water budget modelling, forest management and for downscaling of satellite information. Zusammenfassung Zur Berechnung der Strahlungsbilanz eines kleinräumig heterogenen Gebietes wurden Ansätze aus der Literatur mit Ergebnissen des Vegetations-Grenzschichtmodells HIRVAC (HIgh Resolution Vegetation Coupler) kombiniert. Die modifizierten Ansätze wurden in eine GIS-Umgebung (ArcView)übertragen, um sowohl topographische Einflüsse wie Geländegeometrie und Horizonteinschränkung (sky view faktor) als auch den Einfluss unterschiedlicher Landnutzung (z.B. Wiese und Wald) auf die Strahlungskomponenten zu berücksichtigen. Die Anwendung im GIS basiert auf dem digitalen Höhenmodell des Landesvermessungsamtes von Sachsen mit einer Auflösung von 25 m sowie der Landnutzungsklassifikation des Instituts für Kartographie der Technischen Universität Dresden. Das Modell wurde für das Osterzgebirge (Sachsen/BRD) angewendet. Zur Ergebnisdarstellung wurde ein Gebietsausschnitt im Tharandter Wald nahe Dresden ausgewählt. Die Ergebnisse zeigen, dass die Einflüsse von Topografie und Landnutzung auf die Strahlungsbilanz in einem Gebiet mit komplexen Landoberflächenstrukturen und stark vom Relief geprägten Gelände gleichbedeutend sind. An einem Strahlungstag im Frühjahr ist z.B. die kurzwellige Einstrahlung auf nördlich orientierten Flächen bis zu zehnmal niedriger als auf südlich orientierten Flächen. Die Fichtenareale haben zweimal höhere Tagessummen der Strahlungsbilanz als benachbarte Kahlschläge. Die Modellergebnisse zeigen eine guteÜbereinstimmung mit Messwerten der "Ankerstation...

A novel approach in model-based mapping of soil water conditions at forest sites

“…Thus, the distributed calculation of meteorological SD-SOWA input data is primarily based on a digital elevation model (DHM/M745: Landesvermessungsamt Sachsen, 1996) with a horizontal grid size of 25 m  25 m and a vertical precision of 1 m. From the digital elevation data the values for aspect and inclination were derived for each 25 m  25 m pixel. Much of the regionalization approaches have been adapted from Goldberg and Bernhofer (2000), Goldberg andHä ntzschel (2002), andHäntzschel et al (2005). The climate effect due to the topographical situation of a single pixel is considered relative to a reference site, sufficiently close to represent the ''background climate'' of the area.…”

“…Solar radiation. Solar radiation is derived via the spatially distributed radiation model GISRAD (Goldberg and Hä ntzschel, 2002;Hä ntzschel et al, 2005) for each pixel depending on slope, aspect, and shading of the opposite slope. Main inputs are, (i) the ratio between the potential horizontal solar radiation at the reference site and the potential radiation at each pixel with a daily resolution, as well as (ii) the measured solar radiation at the reference site for each day.…”

GIS‐based regionalisation of radiation, temperature and coupling measures in complex terrain for low mountain ranges

“…To obtain temperature values needed for the calculation of long-wave radiation components in complex terrain the radiation model GISRAD (Goldberg & Häntzschel 2002) was linked to the coupled vegetation atmosphere model HIRVAC. HIRVAC (High Resolution Vegetation Atmosphere Coupler) is a one-and-a-half dimensional atmospheric boundary layer model (HUB), which includes a vertical high resolved vegetation canopy (based on the boundary layer model, after Mix et al 1994).…”

“…The direct, diffuse and reflected part of the irradiance can be identified by their calculations and so the intensity of solar irradiance for each point is identifiable. The detailed equations of GISRAD are published in Goldberg (1999) and Goldberg & Häntzschel (2002).…”

“…The platform used to transfer the pointbased model HIRVAC in an area is the GIS-based version of HIRVAC -the HIRGIS model (Goldberg & Häntzschel 2002 …”