Högström, E. (2023). Assessment of soil moisture derived from radar satellite data in the Arctic for the purpose of permafrost studies [Dissertation, Technische Universität Wien]. reposiTUm. https://doi.org/10.34726/hss.2023.28127
The Arctic tundra lowlands are to a large extent underlain by permafrost, which counts as an essential climate variable. Observations show a nearly four-fold faster warming here than the rest of the world during the last decades. The remote nature of the Arctic means that collected ground data are scarce, which is why availability and applicability of satellite data are crucial here.Soil moisture data from the active layer are of high demand for permafrost applications, such as modeling and flux up-scaling studies. Data from the C-band active microwave remote sensing instrument Advanced Scatterometer (ASCAT) provides an operational global coarse scale (25 km) surface soil moisture (SSM) product in near real time since 2008. However, there are challenges to the radar retrieval, related to the specific character of the Arctic, such as frozen ground conditions, landscape heterogeneity and seasonal variations. Here, such typically expected influences were examined for C-band backscatter derived SSM. Comparisons with Permafrost Land Surface Model output and analysis of finer resolution C-band SAR data showed backscatter deviations originating from water body surface roughness rather than actual SSM variations. The influence of water surfaces together with investigations of in-situ soil moisture data and meteorological data formed the base for suggesting precautions to the use of the satellite product as well as improvements to it. A potential bias could be explained by the lake fraction and to a great extent be attributed to wind. Hence, a correction was suggested with meteorological data in lake rich areas. The usage of higher spatial resolution data than currently available for operational global SSM is required in lowland permafrost environments. Temporal variations of soil moisture across tundra are high, theoretically pointing to applicability of the temporal evolution of C-band backscatter soil moisture products. Soil temperature measurements indicate aninfluence of temperature variations during the first half of the summer.
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