Bayesian updating provides a powerful route for quantifying uncertainty in geophysical inverse problems, such as the Antarctic grounding lines (GLs), which demarcate grounded from floating ice. GLs are required to calculate ice mass loss and consequently sea-level rise. However, existing remote sensing based GL datasets do not provide explicit uncertainties. Hence, we employ the cross entropy based importance sampling for Bayesian updating (CEBU) algorithm to infer GLs from Sentinel-1 SAR range offsets over the Larsen C Ice Shelf by inverting a simple 1D elastic beam model. We explicitly propagate observational uncertainties through the likelihood and extend CEBU to incorporate empirical ice thickness information as a non-parametric prior. To diagnose convergence and parameter importance, we introduce the Kolmogorov-Smirnov (KS) distance, tracking information flow and enabling filtering of non-informative updates. We further developed a data extraction approach that produces spatially dense quasi-1D profiles from 2D range offsets. The resulting GL estimates include full posterior PDFs which were filtered based on thresholds derived using CEBU metrics, including the KS distance. Because range offsets are unaffected by interferometric decorrelation, the GLs are spatially and temporally dense. The most probable GLs agree well with DInSAR delineations, with mean and median distances of $371m$ and $290m$. Our data extraction method also yielded more physically plausible posteriors in shear margin regions than the established flowline-based paradigm. The expert knowledge of ice thicknesses was propagated to other weakly constrained model parameters. This framework enables future development, including model evidence-based comparison of physical formulations, application to other ice shelves with challenging tidal or decorrelation conditions, and integration with more comprehensive rheological models. Together, these results highlight the potential of Bayesian updating for large scale geophysical inversion.

Glaciers that flow into the ocean lose mass at different rates, even under the same climate, because their response depends on local conditions such as bedrock shape, floating ice, and sea ice. Here we analyze two neighboring glaciers on the western Antarctic Peninsula, Rusalka and Hoek, between 1990 and 2025, using satellite observations of grounding line and calving front positions, sea ice, velocity, and surface elevation. Rusalka Glacier retreated and accelerated rapidly after 2017, when warm deep ocean water reached a downward-sloping bed. In contrast, Hoek Glacier remained stable, grounded on an upward-sloping bed and abutting a small floating ice shelf. At Hoek, summers with more sea ice coincided with less forward movement of the glacier front, underscoring the stabilizing effect of sea ice. Our results highlight how ocean heat, bed topography, and sea ice interact to control glacier change and Antarctic ice loss. After 2017, Rusalka Glacier has thinned and retreated due to Circumpolar Deep Water upwelling, while Hoek Glacier remained stable due to frontal sea ice and a small ice shelf, revealing the heterogeneity of outlet glacier responses in the west Antarctic Peninsula, according to satellite data analysis.

The Wordie Ice Shelf (WIS) in the Antarctic Peninsula (AP) has continued to retreat since 1966, and it almost completely disintegrated in the late 1990s. Although the main supply glacier of the WIS, the Fleming Glacier (FG), did not respond immediately, increases in the glacier velocity and dynamic thinning have been observed over the past two decades, especially after 2008 when only a small ice shelf remained at the Fleming Glacier front. As FG is now the fastest flowing outlet glaciers in the west Antarctic Peninsula, ice dynamics is the primary cause of mass loss. Basal sliding is the key mechanism for glacier acceleration and as it responds to thinning and changes in basal conditions. Furthermore, changes in ice-ocean interaction, such as changes in buttressing of ice streams and outlet glaciers like Fleming Glacier, are also leading to acceleration.Here, we use the Shallow Shelf Approximation (SSA) implementation of the Ice-sheet and Sea-level System Model (ISSM) simulating the basal shear stress distribution of FG in the years 2008, 2011, 2014, 2017, 2019 and 2021 using inverse modelling. To better regularize the glaciological inverse problem, we adopt the latest published L-curve analysis to select the optimal regularization level. Considering Fleming Glacier has a relatively small drainage basin, high resolution geometric data is necessary to obtain better constrained information of the basal conditions. We use TanDEM-X DEMs acquired in austral winter of 2011, 2014, 2017, 2019, and 2021 to provide accurate glacier surface elevations. These DEMs were generated from bi-static InSAR data acquired by the TanDEM-X mission and are with the most complete time series and the best quality that can be obtained in this area at present. We evaluate the existing ice velocity products and performed a spatio-temporal interpolation to obtain the average velocity of the year corresponding to the elevation data. We use the higher Antarctic ice sheet surface mass balance data RACM2.3p2 at 2 km resolution as a boundary condition. Regarding the bedrock topography, one of the main factors restricting the inversion accuracy, we evaluated all the existing subglacial topography data products within our inversions. To more accurately represent friction at the bed, we also tested Budd’s, Weertman’s and Schoof’s sliding laws, with different friction exponents and variable geometric data.Comparison of simulated basal shear stresses for 2008 and 2021 suggests the migration of the grounding line 8~9 km upstream by 2021 from the 2008 ice front/grounding line positions. This migration is consistent with the change in floating areas deduced from the calculated height above buoyancy. Our results indicate that the reducing basal shear stress may be directly related to the subglacial hydrologic system and lead to rapid increases in basal sliding and ongoing ungrounding. It will further promote the dynamic loss of glaciers when coupled with ocean forcing and retrograde bedrock.

The regular and robust mapping of grounding lines is essential for various applications related to the mass balance of marine ice sheets and glaciers in Antarctica and Greenland. Differential Interferometric Synthetic Aperture Radar (DInSAR) enables precise detection of tide-induced ice shelf flexure at a continent-wide scale with temporal resolutions of just a few days. While automated pipelines for generating differential interferograms are well established, grounding line delineation remains largely a manual process, which is labor-intensive and increasingly impractical given the growing data streams from current and upcoming synthetic aperture radar (SAR) missions. To address this limitation, we developed an automated pipeline employing the holistically nested edge detection (HED) neural network to delineate grounding lines from DInSAR interferograms. The network was trained in a supervised manner using 421 manually annotated grounding lines of outlet glaciers and ice shelves of the Antarctic Ice Sheet. We also evaluated the utility of non-interferometric features such as surface elevation, ice velocity, and differential tide levels for enhancing delineation performance. Our recommended neural network, trained on the real and imaginary interferometric features, achieved a median offset of 265 m and a mean offset of 421 m from manual grounding line delineations, as well as a predictive uncertainty of 401 m. Furthermore, we demonstrated this network's capacity to generalize by generating grounding lines for previously undelineated interferograms, highlighting its potential for large-scale, high-resolution spatiotemporal mappings.

Digital elevation models (DEMs) from the spaceborne interferometric radar mission TanDEM-X hold a large potential for glacier elevation change assessments and monitoring. However, a bias is potentially introduced through the penetration of the X-band signal into snow and firn that can be substantial. The magnitude of this bias has been analysed in some glaciarized regions of the world; still, the knowledge about X-band penetration of TanDEM-X in the European Alps is limited.In this study, we investigated the unique situation of almost synchronous acquisition of TanDEM-X and Pléiades DEMs over the Grosser Aletschgletscher, complemented with in-situ observations (ground penetrating radar, snow cores, snow pits), all within a four-day period in late winter 2021. The comparison of the TanDEM-X and Pléiades DEM revealed an elevation bias due to radar penetration of up to 8 m above 3400 m. Further, the concurrent in-situ measurements reveal that the signal is not obstructed by the last summer horizon but reaches into perennial firn.Our study improves our understanding about the magnitude of X-band penetration of TanDEM-X in the Alps and the underlying process with a relevance for glaciology, snow science, remote sensing and the wider geoscience community.

Antarctica has an active subglacial hydrological system, with interconnected subglacial lakes fed by subglacial melt water. Subglacial hydrology can influence basal sliding, inject freshwater into the sub ice cavity and impact sediment transport and deposition which can stabilise grounding lines (GL). We use ICESat, ICESat-2 and CryoSat-2 altimetry to document the latest drainage of Subglacial Lake Engelhardt (SLE), which began in July 2021 and discharged >1.2 km3 of subglacial water into the Ross Ice Shelf cavity. We use RADARSAT-2 and TerraSAR-X interferometry to show the GL has retreated by 13 km downstream of the lake since the previous drainage in 2003-06. We evaluate the mechanism triggering SLE drainage, the cause of the observed GL retreat, and the interplay between subglacial hydrology and GL dynamics, including the growth of a grounded promontory protruding >27 km seaward from the GL.

Observations of glacier mass changes are key to understanding the response of glaciers to climate change and related impacts, such as regional runoff, ecosystem changes, and global sea level rise. Spaceborne optical and radar sensors make it possible to quantify glacier elevation changes, and thus multi-annual mass changes, on a regional and global scale. However, estimates from a growing number of studies show a wide range of results with differences often beyond uncertainty bounds. Here, we present the outcome of a community-based inter-comparison experiment using spaceborne optical stereo (ASTER) and synthetic aperture radar interferometry (TanDEM-X) data to estimate elevation changes for defined glaciers and target periods that pose different assessment challenges. Using provided or self-processed digital elevation models (DEMs) for five test sites, 12 research groups provided a total of 97 spaceborne elevation-change datasets using various processing approaches. Validation with airborne data showed that using an ensemble estimate is promising to reduce random errors from different instruments and processing methods but still requires a more comprehensive investigation and correction of systematic errors. We found that scene selection, DEM processing, and co-registration have the biggest impact on the results. Other processing steps, such as treating spatial data voids, differences in survey periods, or radar penetration, can still be important for individual cases. Future research should focus on testing different implementations of individual processing steps (e.g. co-registration) and addressing issues related to temporal corrections, radar penetration, glacier area changes, and density conversion. Finally, there is a clear need for our community to develop best practices, use open, reproducible software, and assess overall uncertainty to enhance inter-comparison and empower physical process insights across glacier elevation-change studies.

Abstract. The regular and robust mapping of grounding lines is essential for various applications related to the mass balance of marine ice sheets and glaciers, especially in Antarctica and Greenland. With Differential Interferometric Synthetic Aperture Radar (DInSAR) interferograms, it is possible to accurately capture the tide-induced bending of the ice shelf at a continent-wide scale and a temporal resolution of a few days. While current processing chains typically automatically generate differential interferograms, grounding lines are still primarily identified and delineated on the interferograms by a human operator. This method is time-consuming and inefficient, considering the volume of data from current and future SAR missions. We developed a pipeline that utilizes the Holistically-Nested Edge Detection (HED) neural network to delineate DInSAR interferograms automatically. We trained HED in a supervised manner using 421 manually annotated grounding lines for outlet glaciers and ice shelves on the Antarctic Ice Sheet. We also assessed the contribution of non-interferometric features like elevation, ice velocity and differential tide levels towards the delineation task. Our best-performing network generated grounding lines with a median distance of 186 m from the manual delineations. Additionally, we applied the network to generate grounding lines for undelineated interferograms, demonstrating the network's generalization capabilities and potential to generate high-resolution temporal and spatial mappings.

We estimate the seasonal impact in the ice velocity of the entire South Patagonian Icefield (SPI), the velocity mosaics from 2016 (Winter/Autumn), 2017(Summer/Spring) and 2018(Summer/Spring) were combined to obtain acceleration and deceleration maps. Additionally, a more detailed study was made for seven glaciers in particular, the freshwater Upsala, Viedma, Moreno, O’Higgins and the tidal influenced Pio XI, Jorge Montt, Amalia.

Single-pass Interferometric SAR satellite configurations offer unique opportunities for observing dynamic features of ice masses. Future cross-track interferometry constellations of satellite missions will produce interferometric DEMs over virtually all glaciers globally and will offer significant advancements for regular monitoring their surface elevation. In the present contribution we want to address some of the main issues encountered when mapping the topographic changes with multitemporal TanDEM-X InSAR DEMs over glaciers. We illustrate open questions for InSAR DEM data acquisition when targeting height change rate calculation for mountain and outlet glaciers at large scale.

Wilkes Land, East Antarctica, has been losing mass at an accelerating rate over recent decades in response to enhanced oceanic forcing. Overlying the Aurora Subglacial Basin, it has been referred to as the “weak underbelly” of the East Antarctic Ice Sheet and is drained by several major outlet glaciers. Despite their potential importance, few of these glaciers have been studied in detail. This includes the six outlet glaciers which drain into Vincennes Bay, a region recently discovered to have the warmest intrusions of modified Circumpolar Deep Water (mCDW) ever recorded in East Antarctica. Here, we use satellite imagery; differential synthetic aperture radar interferometry (DInSAR); and remotely sensed datasets of ice-surface velocity, ice-surface elevation and grounding line position to investigate ice dynamics between 1963 and 2022. Our results support previous observations of extensive grounding line retreat at Vanderford Glacier, measured at 18.6 km between 1996 and 2020. The persistent grounding line retreat, averaging 0.8 km yr−1, places Vanderford Glacier as the fastest retreating glacier in East Antarctica, and the third fastest in Antarctica, across decadal timescales. Such rapid retreat is consistent with the hypothesis that warm mCDW is able to access deep cavities formed below the Vanderford Ice Shelf, driving high rates of basal melting close to the grounding line. With a retrograde slope observed inland along the Vanderford Trench, such oceanic forcing may have significant implications for the future stability of Vanderford Glacier.

Glaciers distinct from the Greenland and Antarctic ice sheets are currently losing mass rapidly with direct and severe impacts on the habitability of some regions on Earth as glacier meltwater contributes to sea-level rise and alters regional water resources in arid regions. In this review, we present the different techniques developed during the last two decades to measure glacier mass change from space: digital elevation model (DEM) differencing from stereo-imagery and synthetic aperture radar interferometry, laser and radar altimetry and space gravimetry. We illustrate their respective strengths and weaknesses to survey the mass change of a large Arctic ice body, the Vatnajökull Ice Cap (Iceland) and for the steep glaciers of the Everest area (Himalaya). For entire regions, mass change estimates sometimes disagree when a similar technique is applied by different research groups. At global scale, these discrepancies result in mass change estimates varying by 20%–30%. Our review confirms the need for more thorough inter-comparison studies to understand the origin of these differences and to better constrain regional to global glacier mass changes and, ultimately, past and future glacier contribution to sea-level rise.

Accurate identification of grounding lines is of immense importance for estimating the mass budgets of ocean-terminating ice sheets and glaciers of Antarctica and Greenland. In Differential Interferometric SAR (DInSAR) interferograms, human experts still largely manually digitize grounding lines. The time-consuming nature of this task makes it infeasible to produce timely, continent-wide grounding line mappings. This study employed a Deep Neural Network (DNN) to automate delineation. The Holistically-Nested Edge Detection (HED) network was trained in a supervised manner on features derived from interferometric phase, elevation data, ice velocity, tidal amplitude, atmospheric pressure and corresponding manual delineations. HED-generated lines achieved a median deviation of 209 m with a median absolute deviation of 153 m from manual delineations. The developed automatic pipeline demonstrates the potential for generating spatially and temporally dense mappings of the grounding line.

Calving Front (CF) is an important parameter to analyse ice sheet dynamics and to measure glacier mass balance. DEM products covering polar regions are critical remote sensing data sources to provide fundamental terrain information for glaciological studies. It is necessary to provide accurate CFs for DEM specific applications, such as mass balance calculation or the substitution of water values with geoid values in the DEM editing process. However, much less attention is paid to automatically delineate CFs from DEM data. In this study, we propose a DEM-based Automatic CF Extraction method (DACE) to efficiently extract the CFs from DEM data. In DACE, a height-sensitive terrain feature is designed to enhance the contrast between the ice sheet and the ocean by combining elevation and roughness information. To improve the CF extraction performance, a two-category image classification based on game theory is proposed that considers the spatial consistency of the feature image created. For validation, DACE was applied to DEM products generated from the single-pass SAR interferometry mission TanDEM-X (TDM) at different posting sizes (12 and 90 m) and to the optical photogrammetry-based Reference Elevation Model of Antarctica (REMA) with a 2 m posting. The proposed algorithm can achieve a CF extraction accuracy of better than 14, 20, and 70 m for the 2-m REMA, 12- and 90-m TDM DEMs, respectively, when compared with the manually delineated CFs. The experimental results demonstrate that the proposed algorithm can effectively extract the CFs from DEM data. DACE can be used to replace water values and edit the DEMs themselves. The CFs extracted from the DEM data can also be used for glacier mass balance calculation with the DEM-based geodetic method and for the temporal analysis of CF changes when multi-temporal DEM data are available.

The drainage divides of ice sheets separate the overall glaciated area into multiple sectors and outlet glaciers. These catchments represent essential input data for partitioning glaciological measurements or modelling results to the individual glacier level. They specify the area over which basin specific measurements need to be integrated. The delineation of drainage basins on ice sheets is challenging due to their gentle slopes accompanied by local terrain disturbances and complex patterns of ice movement. Therefore, in Greenland the basins have been mostly delineated along the major ice divides, which results in large drainage sectors containing multiple outlet glaciers. In [1] we developed a methodology for delineating individual glaciers that was applied to the Northeast Greenland sector and proposed slightly changed separations between 79N and Zachariae basins driven by the ice flow lines. In the present study the method is extended to the entire Greenland Ice Sheet. We present a fully traceable approach that combines ice sheet wide velocity measurements by Sentinel-1 SAR and the 90 m TanDEM-X global DEM to derive individual glacier drainage basins for the entire Greenland Ice Sheet with a modified watershed algorithm. We delineate a total of 335 individual glacier catchments, a result triggered by the number and location of the selected seed points. The resulting dataset will be made publicly available online and is extensible by even more granular delineations of individual tributaries upon request. The proposed approach has the potential to produce catchment areas also for the entirety of the Antarctic Ice Sheet. [1] Krieger, L., D. Floricioiu, and N. Neckel (Feb. 1, 2020). “Drainage Basin Delineation for Outlet Glaciers of Northeast Greenland Based on Sentinel-1 Ice Velocities and TanDEM-X Elevations”. In:Remote Sensing of Environment 237, p. 111483.

Synthetic aperture radar interferometry (InSAR) is an efficient technique for mapping the surface elevation and its temporal change over glaciers and ice sheets. However, due to the penetration of the SAR signal into snow and ice, the apparent elevation in uncorrected InSAR digital elevation models (DEMs) is displaced versus the actual surface. We studied relations between interferometric radar signals and physical snow properties and tested procedures for correcting the elevation bias. The work is based on satellite and in situ data over Union Glacier in the Ellsworth Mountains, West Antarctica, including interferometric data of the TanDEM-X mission, topographic data from optical satellite sensors and field measurements on snow structure, and stratigraphy undertaken in December 2016. The study area comprises ice-free surfaces, bare ice, dry snow and firn with a variety of structural features related to local differences in wind exposure and snow accumulation. Time series of laser measurements of NASA's Ice, Cloud and land Elevation Satellite (ICESat) and ICESat-2 show steady-state surface topography. For area-wide elevation reference we use the Reference Elevation Model of Antarctica (REMA). The different elevation data are vertically co-registered on a blue ice area that is not affected by radar signal penetration. Backscatter simulations with a multilayer radiative transfer model show large variations for scattering of individual snow layers, but the vertical backscatter distribution can be approximated by an exponential function representing uniform absorption and scattering properties. We obtain estimates of the elevation bias by inverting the interferometric volume correlation coefficient (coherence), applying a uniform volume model for describing the vertical loss function. Whereas the mean values of the computed elevation bias and the elevation difference between the TanDEM-X DEMs and the REMA show good agreement, a trend towards overestimation of penetration is evident for heavily wind-exposed areas with low accumulation and towards underestimation for areas with higher accumulation rates. In both cases deviations from the uniform volume structure are the main reason. In the first case the dense sequence of horizontal structures related to internal wind crust, ice layers and density stratification causes increased scattering in near-surface layers. In the second case the small grain size of the top snow layers causes a downward shift in the scattering phase centre.

The migration of the glacier grounding line, the boundary between grounded ice and floating ice, is an important indicator of tice sheet stability in a warming climate. Ice-shelf thinning induces grounding line retreat, and potentially leads to the collapse of the inland catchment areas in centennial time periods. Therefore, a continuous observation of the grounding line position is of interest for ice sheet modelling also to predict future sea level rise. However, grounding line in nature is not static in position and it is subject to short-term fluctuations which are influenced by changes in ocean tide level and atmospheric pressure. Investigating tidal influence to the grounding line helps separating the tidal signal from the long-term migration because of ice shelf thinning. Also, it helps quantifying ice discharge and ice flow, as well as potential melting underneath the ice, due to intrusion of sea water. In this study, the correlation between the time series of grounding line, derived from Sentinel-1 double difference interferograms and the ocean tide level computed from CATS2008 tide model and air pressure corrected with NCEP reanalysis data are investigated. Study regions are chosen at the Filchner-Ronne Ice Shelf, the Amery Ice Shelf and Dronning Maud Land based on the availability of coherent interferograms and the large tidal amplitude at these locations. The result is expected to be presented as qualitative description of changes in the fringe belt pattern in double difference interferograms and statistical analysis of the derived changes in grounding line position, depending on the complexity of the grounding line structure and the topography of the bed rock.

The Getz region of West Antarctica is losing ice at an increasing rate; however, the forcing mechanisms remain unclear. Here we use satellite observations and an ice sheet model to measure the change in ice speed and mass balance of the drainage basin over the last 25-years. Our results show a mean increase in speed of 23.8 % between 1994 and 2018, with three glaciers accelerating by over 44 %. Speedup across the Getz basin is linear, with speedup and thinning directly correlated confirming the presence of dynamic imbalance. Since 1994, 315 Gt of ice has been lost contributing 0.9 ± 0.6 mm global mean sea level, with increased loss since 2010 caused by a snowfall reduction. Overall, dynamic imbalance accounts for two thirds of the mass loss from this region of West Antarctica over the past 25-years, with a longer-term response to ocean forcing the likely driving mechanism.

Surface crevasses covered by snow bridges can be mapped remotely on ice sheets and glaciers using active microwave synthetic aperture radar. They are highlighted against the surrounding snow due to increased scattering from the side-walls and base of snow bridges and usually appear as linear features. The contrast between crevasses and crevasse-free regions depends on the design of the sensor, the image acquisition parameters and the properties of the snow. Here we quantify how crevassed regions are represented at X-band for different polarizations, look directions and incidence angles, and discuss whether additional information about their physical properties can be gained from their radar signature. Snow bridge thicknesses and crevasse widths are measured on the ground in the McMurdo Shear Zone and Brunt Ice Shelf by ground-penetrating radar and excavation. TerraSAR-X is shown to reliably distinguish crevasse location, balancing penetration into the snow and horizontal resolution. We provide recommendations for radar imaging parameters that optimize the identification of individual crevasses and crevassed regions.