Application of an active layer monitoring scheme based on the MODIS-LST product at a polygonal tundra site in Siberia.

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Langer, M. , Westermann, S. and Boike, J. (2009): Application of an active layer monitoring scheme based on the MODIS-LST product at a polygonal tundra site in Siberia. , American Geophysical Union Fall Meeting, December 12-18, 2009, San Francisco, CA, USA. .
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A significant warming of the arctic has been reported, which is expected to continue within different scenarios of climate change. Permafrost is directly affected by this warming trend which emphasises the importance of a global permafrost monitoring scheme. Such monitoring projects can be realised by using remote sensing products, which provide continuous measurements on a global scale. Since permafrost is a ground temperature phenomenon, it is not directly accessible to remote sensing applications. Therefore, remote sensing products must be combined with models, facilitating access to the temperature dynamics of the deeper ground. A possible scheme makes use of land surface temperature (LST) products to drive permafrost models (e.g. Marchenko et al. 2009, Hachem et al. 2009).However, LST detection is problematic in heterogeneous landscapes, which can not be resolved by satellite sensors. This is especially true for permafrost areas, such as the polygonal tundra, which is highly fractionated and characterized by wet and dry surface patches. In this study we analyze the potential effects of spatial differences in summer surface temperature at a polygonal tundra site at the Lena-River Delta. For this reason we apply a high-resolution thermal imaging system mounted on a 12 m tower. The obtained results clearly show that spatial temperature variations are significantly reduced by temporal averaging. Hence, the accuracy of satellite based permafrost monitoring is rather affected by the temporal than by the spatial resolution of the LST-products. We than investigate the performance of an active layer monitoring scheme based on a MODIS-LST product.For this purpose, surface temperatures obtained by MODIS and the thermal imaging system are projected into the ground, using a numerical solution of the heat transfer equation. The applied soil model feature a freeze thaw algorithm and a three phase heat conductivity / capacity model. The results are compared to measurements of soil temperature profiles and the effects of varying soil characteristics are demonstrated.Some erroneous measurements of the MODIS product were identified, which are most likely associated with an incorrect cloud cover mask. The satellite data acquisition is frequently prevented by a cloud cover. Hence, gap filling procedures are found to be an essential issue for future work on satellite-based permafrost monitoring schemes. Marchenko S., Hachem S., Romanovsky V. and C. Duguay.: 2009, Permafrost and Active Layer Modeling in Northern Eurasia using MODIS Land Surface Temperatures as an input data. Geophysical Research Abstracts, Vol. 11, EGU2009-11077.Hachem S., Duguay C.R., and M. Allard.: 2009, Improving permafrost mapping from space with addition of snow cover information. Geophysical Research Abstracts, Vol. 11, EGU2009-701.

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