Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Advancing the understanding of active microwave remote sensing of soil moisture and vegetation

Auteur : Greimeister-Pfeil, Isabella

Université de soutenance : Technische Universität Wien

Grade : Doktorin der technischen Wissenschaften (Dr.techn.) 2022

Résumé partiel
Active microwave remote sensing techniques provide a means for the monitoring of biogeophysical variables over land, independent of weather and cloud conditions and daylight. Several missions are in place nowadays which provide regular observations of the entire Earth surface. Observations provided by these sensors have for example been used for the retrieval of soil moisture (SM) and vegetation optical depth, a measure of canopy water content, density and structure. Some of these datasets are available publicly and on an operational basis. Despite the long history of active microwave remote sensing research, going back into the 1960s, there is a constant need to extend the understanding of how active microwave sensors perceive the land surface on the respective spatial scale of the satellite observations.The aim of this thesis was to study the multi-angular backscatter signal (σo) observed by the Advanced Scatterometer (ASCAT) sensor over the land surface. The focus was on the backscatter dependence on the incidence angle (σ’), as this relationship is crucial for the separation of SM and vegetation effects on the observed signal. Thereby, I aimed at advancing the understanding of how SM and vegetation dynamics influence σo and σ’ on the relatively coarse spatial scale of the ASCAT footprint. The main objectives can be summed up as follows : i) increase the understanding of the ASCAT back scatterincidence-angle relationship, in particular the first derivative σ’, ii) investigate the potential of a regional adjustment of parameter values for SM and vegetation optical depth retrieval, iii) improve theunderstanding of structural effects of vegetation canopies on σ’, and iv) reassess the assumption that σ’ is not or only weakly affected by SM.The conducted research highlighted the great potential of the coarse-scale ASCAT sensor for the retrieval of biogeophysical variables such as SM and vegetation dynamics.

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