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370 results on '"HANSSEN, Ramon"'

19. Exploring the use of Sentinel-1 to monitor spatial and temporal evolution of permafrost in the Swiss Alps.

Author

Reinders, Kristina Juliana, Verhoeven, Govert Frederik, Sartorelli, Luca, Hanssen, Ramon, and Manconi, Andrea

Subjects
PERMAFROST, SURFACE analysis, TIME series analysis, INTERFEROMETRY
Abstract

In this work, we assess the performance of Persistent Scatterer Interferometry (PSI) based on Sentinel-1 data in the Swiss Alps, focusing on the analysis of surface displacement in areas located in permafrost. To this end, we exploit a PSI dataset over Canton Wallis and the recently published permafrost and ground ice map of Switzerland (PGIM). First we evaluate the sensitivity to radar detection of the terrain, given a particular slope distribution and given satellite orbital geometries. We find that 92 % of the areas currently labeled as permafrost satisfy the geometric visibility criteria, which is a necessary but not sufficient condition for detection of ground movement by satellite radar. Second, we analyse the PSI surface velocity and displacement time series observed in Canton Wallis in the period 2015 to 2022. We find that the displacements rates appear to be correlated with the occurrence of permafrost and that there is a significant difference in displacement rates between ice-poor and ice-rich permafrost compared to no-permafrost zones. However, the difference between the surface velocities retrieved in ice-poor permafrost and no-permafrost zones are small and additional information would be needed to discriminate ice-poor permafrost zones. [ABSTRACT FROM AUTHOR]

Published
2023
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20. Exploring the use of Sentinel-1 to monitor spatial and temporal evolution of permafrost in the Swiss Alps.

Author

Reinders, Kristina, Verhoeven, Govert, Sartorelli, Luca, Hanssen, Ramon, and Manconi, Andrea

Abstract

In this work, we assess the performance of Persistent Scatterer Interferometry (PSI) based on Sentinel-1 data in the Swiss Alps, focusing on the analysis of surface displacement in areas located in permafrost. To this end, we exploit a PSI dataset over Canton Wallis and the recently published permafrost and ground ice map of Switzerland (PGIM). First we evaluate the sensitivity to radar detection of the terrain, given a particular slope distribution and given satellite orbital geometries. We find that 92% of the areas currently labeled as permafrost satisfy the geometric visibility criteria, which is a necessary but not sufficient condition for detection of ground movement by satellite radar. Second, we analyse the PSI surface velocity and displacement time series observed in Canton Wallis in the period 2015 to 2022. We find that the displacements rates appear to be correlated with the occurrence of permafrost and that there is a significant difference in displacement rates between ice-poor and ice-rich permafrost compared to no-permafrost zones. However, the difference between the surface velocities retrieved in ice-poor permafrost and no-permafrost zones are small and additional information would be needed to discriminate ice-poor permafrost zones. [ABSTRACT FROM AUTHOR]

Published
2023
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28. InSAR training - presentations - 1st GATHERS Summer School

Author

Van Leijen, Freek and Hanssen, Ramon

Subjects
InSAR, SBAS, lecture, PSI
Abstract

Lectures given in the InSAR training part by Dr Freek van Leijen contains: - SAR introduction and physical and geometrical foundations - Standard error sources and biases - Time dependent processing SBAS/PSI - Interpretation of InSAR data - Validation/Integration

Published
2022
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39. Inverting elastic dislocations using the Weakly-enforced Slip Method

Author

van Zwieten, Gertjan, van Brummelen, E. Harald, Hanssen, Ramon F., van Zwieten, Gertjan, van Brummelen, E. Harald, and Hanssen, Ramon F.

Abstract

Earthquakes cause lasting changes in static equilibrium, resulting in global deformation fields that can be observed. Consequently, deformation measurements such as those provided by satellite based InSAR monitoring can be used to infer an earthquake's faulting mechanism. This inverse problem requires a numerical forward model that is both accurate and fast, as typical inverse procedures require many evaluations. The Weakly-enforced Slip Method (WSM) was developed to meet these needs, but it was not before applied in an inverse problem setting. Consequently, it was unknown what affects particular properties of the WSM, notably its inherent continuity, have on the inversion process. Here we show that the WSM can accurately recover slip distributions in a Bayesian-inference setting, provided that data points in the vicinity of the fault are removed. In a representative scenario, an element size of 1 km was found to be sufficiently fine to generate a posterior probability distribution that is close to the theoretical optimum. For rupturing faults a masking zone of 10 km sufficed to avoid numerical disturbances that would otherwise be induced by the discretization error. These results demonstrate that the WSM is a viable forward method for earthquake inversion problems. While our synthesized scenario is basic for reasons of validation, our results are expected to generalize to the wider gamut of scenarios that finite element methods are able to capture. This has the potential to bring modeling flexibility to a field that is often forced to impose model restrictions in a concession to computability.

Published
2022

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