Comparison of in-situ measured ground heat fluxes within a heteorogeneous urban ballast layer |
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Authors: | S Weber |
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Institution: | (1) Department of Applied Climatology and Landscape Ecology, Institute of Geography, University of Duisburg-Essen, Campus Essen, Essen, Germany |
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Abstract: | Summary This study concentrates on measurements of ground heat fluxes within a porous urban ballast layer that were conducted from
June to September 2002 at the goods station in Osnabrück, Germany. To account for the limitation of accurately installing
sensors within the heterogeneous and porous ballast bulk, the heat fluxes were calculated from four different methods to compare
their variability, dynamics and shortcomings. Ground heat fluxes were gathered from 1) a heat flux plate with the inclusion
of heat storage between the soil surface and the heat flux plate, 2) temperature gradient measurements with correction for
heat storage, 3) temperature gradient measurements with a modelled surface temperature and a laboratory derived thermal conductivity,
4) as residual from the surface energy balance equation. The results show a distinct deviation of the four methods for absolute
values of the ground heat flux as well as for temporal dynamics on the diurnal cycle. As indicated by the temporal dynamics
of the ground heat flux times series and a simple error analysis of the four methods, the most plausible estimates for an
urban application in a heterogeneous ballast layer were obtained by temperature gradient measurements between the surface
and −0.05 m. Overall, the results indicate that accurate ground heat flux measurements in urban applications still prove difficult
to acquire. |
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