Meet our scientists: Thorben Döhne
We are pleased today to speak with Thorben Döhne (subproject 6), who works on his PhD together with Dr.-Ing. Mirko Scheinert at the Institut für Planetare Geodäsie of the Technische Universität Dresden. He's telling us about what led him to to study Greenland, in particular how changes in the Greenland ice mass can be estimated from satellite, and what are the caveat to this techniques.
How did you come about doing research on Greenland?
I remember watching nature documentaries as a child and seeing the enormous extent of ice masses of Greenland and Antarctica. I was impressed to see animals and humans living (and doing research!) under these hard conditions. I did not start studying geodesy with Greenland in mind but during the last semesters of my bachelor studies I learned more about geodesy in polar regions. Seeing that these unique regions whose nature already fascinated me as a child are also very interesting topics in science sparked my fascination again. One thing that also impressed me was hearing about Greenland in multiple fields of my studies. From satellite measurements spanning the whole ice sheet to GPS-measurements on the bedrock to photogrammetric measurements focusing on individual glaciers. During my masters studies I learned more about the processes of the ice sheets and developed skills working with real satellite measurements.
What is your contribution to the research on Greenland?
In GROCE I focus on the mass balance of the Greenland Ice Sheet. A great method to estimate the mass balance of the Greenland Ice Sheet is to use measurements of the GRACE (Gravity Recovery And Climate Experiment) and GRACE-FO (GRACE-Follow-On) satellite missions. To get a more detailed view on the different processes involved in the mass changes, our group combines GRACE data with data from satellite altimetry, satellite remote sensing and GNSS (Global Navigation Satellite System) measurements. In my work so far I focused on differences in mass estimations from GRACE data by different estimation methods. Although using the same GRACE data, different estimation methods show different mass change results. To compare and visualize the differences between the estimation methods, I described them with so called sensitivity kernels. These are weight distributions, different for each estimation method, which are used to integrate the GRACE measurements for the region of interest. When the estimation methods are expressed as their sensitivity kernel, it becomes straight-forward to quantify biasing effects affecting each method, like leakage: this is when mass changes of the region of interest are not fully captured by the estimation or when mass changes of adjacent regions leak inside the estimation. In my future work I will investigate how much external information is needed to get a robust estimation with reduced leakage
What are you most passionate about in your work?
I really like working with the GRACE data. The nature of satellite gravimetry is unique for its direct sensitivity to mass and its integrative nature. There is no danger of 'missing' something with these measurements and so it is quite reassuring to have these measurements as a starting point! But of course it is still a challenge to get a robust estimate with reduced leakage and to separate different processes. I enjoy working with experts in neighbouring fields to tackle this challenge!