Speaker
Dr
Stefano Tebaldini
(Politecnico di Milano)
Description
The main objective of the AlpTomoSAR experiment was then to assess the added value of L-Band TomoSAR for glacier and icecap applications, by discussing:
o The level of analogy/complementarity/synergy of TomoSAR w.r.t. Nadir looking systems.
o The added value w.r.t. single baseline inversion.
o The information content of SAOCOM-CS TomoSAR over glaciers, icecaps and ice sheets.
The campaign has encompassed coincident in-situ data, GPR, and SAR surveys, gathered in about two weeks from the end of February to the beginning of March 2014. Field works have also included deployment, maintenance, and dismantlement of 8 corner reflectors. SAR data were acquired by repeatedly flying over the Mittelbergferner along an oval-like racetrack configuration, so as to illuminate the scene from two opposite view points.
The analysis of TomoSAR cubes immediately shows the complexity of the glacier sub-surface scattering. Most areas are characterized by surface scattering in proximity of the Lidar surface, plus a complex pattern of in-depth volumetric scattering beneath. A significant backscatter signal is observed in the top 10 to 20 m. In other areas, instead, a gap on the order of 10-20 m is observed between surface and in-depth scattering. These results show that modelling scattering from the ice layer in terms of an exponential decay due to uniform wave extinction is definitely insufficient for characterizing glaciers.
The availability of a dense in-situ information allowed to further analyse TomoSAR cubes, and associate the observed features with physical interpretation.
Corner reflectors, deployed on the snow surface, were observed in TomoSAR cubes to float about 2-3 m above surface scattering. This observation implies that the observed surface in TomoSAR cubes corresponds to the snow/glacier ice interface, whereas the winter snow volume does not appear to contribute to the signal. This result is also consistent with field measurements of the winter snowpack depth.
Various subsurface features observed in GPR transects at 600 MHz and 200 MHz can be clearly identified in TomoSAR sections as like firn bodies, crevasses, and even the bedrock down to 50 m below the ice surface.
Accordingly, the AlpTomoSAR experiment has provided evidence that, for a temperate glacier, L-Band waves can penetrate down to tens of meters, and that Tomographic SAR imaging can successfully be employed to derive information on the subsurface structure which is in well agreement with low frequency GPR profiles.
Primary author
Dr
Stefano Tebaldini
(Politecnico di Milano)
Co-authors
Dr
Achim Heilig
(University of Heidelberg)
Prof.
Helmut Rott
(ENVEO)
Dr
Thomas Nagler
(ENVEO)
