It is not just these bodies of water that are in constant flux; the surrounding land is also subject to changes, and some of these are expected to become more pronounced as the climate continues to warm. The soil contains ice – and with increasing temperatures – more and more of this ice is likely to melt. The thawing permafrost soils can become unstable, leading to slope failures and coastal erosion, as well as posing a risk to human infrastructure.
These are among the many questions undertaken within the Helmholtz research alliance 'Remote Sensing and Earth System Dynamics', whose members include Sonya Antonova (AWI) and Simon Zwieback (ETH Zürich). Specifically, their research addresses the question of whether TanDEM-X data can be processed to show every summer's seasonal ground subsidence due to the melting of ice within the uppermost soil layer. "The magnitude of the subsidence can be used to derive the ice content within the active layer," explains Antonova. "This quantity is of the greatest interest for permafrost modelling." The subsidence can be assessed using the Differential SAR Interferometry (DInSAR) method, which requires acquiring at least two SAR images at different times over the same location. According to Zwieback: "This estimation is – in many regions, such as the Lena delta – hampered by the impact of additional surface processes, such as changes in the moss moisture content or vegetation growth, and it will be important to characterise the uncertainties that these processes cause. Subsidence measurements obtained on site help us to validate the interferometry results."