TanDEM-X:Deriving InSAR Height Changes and Velocity Dynamics of Great Aletsch Glacier

• Main Authors: Silvan Leinss, Philipp Bernhard
• Format: Article
• Language: English
• Published: IEEE 2021-01-01
• Series: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
• Subjects: Common-band filter; copolar phase difference (CPD); digital elevation model (DEM); DEM differencing; geocoding; Great Aletsch Glacier
• Online Access: https://ieeexplore.ieee.org/document/9424980/

Great Aletsch Glacier (Grosser Aletschgletscher), the largest glacier in the European Alps, contains 20&#x0025; of the entire Swiss ice mass. Therefore, it has been selected as a super-testsite for the TanDEM-X satellite mission. Dense time series with a repeat interval down to 11 d were acquired between 2011 and 2019 using two polarizations (HH and VV) and across-track baselines of 0&#x2013;1 km. To evaluate the use of interferometric single-pass synthetic aperture radar mission for glaciological applications, we implemented a processing pipeline in interactive data language (IDL) and computed 130 digital elevation models (DEMs) from bistatic radar interferograms. We present a method to circumvent a common pitfall during orthorectification of radar DEM differences. Regression analysis of DEM time series shows a height loss of up to 8 m a<inline-formula><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> on the tongue and 1.5 m a<inline-formula><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> when averaged over the whole glacier area. In spring 2013, we observed X-band penetration depths of 4<inline-formula><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula>2 m in the accumulation area. For strongly crevassed areas, the coherence drops already to 0.5 for across-track baselines <inline-formula><tex-math notation="LaTeX">$\mathbf {B_\perp }&gt;$</tex-math></inline-formula> 200 m. With patch-based incoherent offset tracking, we obtained an almost complete 200 m resolution velocity map. Velocities reach up to 0.8 m d<inline-formula><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula>, show a seasonal variability of <inline-formula><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula>0.05 m d<inline-formula><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula>, and agree within 0.04 m d<inline-formula><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula>(root mean square error) with field measurements. Copolar phase differences suggest an approximation of snow accumulation. We demonstrate orthorectification of the backscatter intensity using simultaneously acquired TanDEM-X interferograms, which allows for the decoupling of horizontal velocity estimates from phase-center height changes due to penetration and ice melt.