We analyzed volume change and mass balance of outlet glaciers of the northern Antarctic Peninsula over the period 2011 to 2013, using topographic data of high vertical accuracy and great spatial detail, acquired by bistatic radar interferometry of the TanDEM-X/TerraSAR-X satellite formation. The study area includes glaciers draining into the Larsen-A, Larsen Inlet, and Prince-Gustav-Channel embayments. After collapse of buttressing ice shelves in 1995 the glaciers became tidewater calving glaciers and accelerated, resulting in increased ice export. Downwasting of most glaciers is going on, but at reduced rates compared to previous years in accordance with deceleration of ice flow. The rate of mass depletion is 4.2 ± 0.4 Gt a À1 , with the largest contribution by Drygalski Glacier amounting to 2.2 ± 0.2 Gt a À1 .On the technological side, the investigations demonstrate the capability of satellite-borne single-pass radar interferometry as a new tool for accurate and detailed monitoring of glacier volume change.

Abstract. We analysed volume change and mass balance of outlet glaciers on the northern Antarctic Peninsula over the periods 2011 to 2013 and 2013 to 2016, using high-resolution topographic data from the bistatic interferometric radar satellite mission TanDEM-X. Complementary to the geodetic method that applies DEM differencing, we computed the net mass balance of the main outlet glaciers using the mass budget method, accounting for the difference between the surface mass balance (SMB) and the discharge of ice into an ocean or ice shelf. The SMB values are based on output of the regional climate model RACMO version 2.3p2. To study glacier flow and retrieve ice discharge we generated time series of ice velocity from data from different satellite radar sensors, with radar images of the satellites TerraSAR-X and TanDEM-X as the main source. The study area comprises tributaries to the Larsen A, Larsen Inlet and Prince Gustav Channel embayments (region A), the glaciers calving into the Larsen B embayment (region B) and the glaciers draining into the remnant part of the Larsen B ice shelf in Scar Inlet (region C). The glaciers of region A, where the buttressing ice shelf disintegrated in 1995, and of region B (ice shelf break-up in 2002) show continuing losses in ice mass, with significant reduction of losses after 2013. The mass balance numbers for the grounded glacier area of region A are −3.98 ± 0.33 Gt a−1 from 2011 to 2013 and −2.38 ± 0.18 Gt a−1 from 2013 to 2016. The corresponding numbers for region B are −5.75 ± 0.45 and −2.32 ± 0.25 Gt a−1. The mass balance in region C during the two periods was slightly negative, at −0.54 ± 0.38 Gt a−1 and −0.58 ± 0.25 Gt a−1. The main share in the overall mass losses of the region was contributed by two glaciers: Drygalski Glacier contributing 61 % to the mass deficit of region A, and Hektoria and Green glaciers accounting for 67 % to the mass deficit of region B. Hektoria and Green glaciers accelerated significantly in 2010–2011, triggering elevation losses up to 19.5 m a−1 on the lower terminus during the period 2011 to 2013 and resulting in a mass balance of −3.88 Gt a−1. Slowdown of calving velocities and reduced calving fluxes in 2013 to 2016 coincided with years in which ice mélange and sea ice cover persisted in proglacial fjords and bays during summer.

Abstract. We analyzed volume change and mass balance of outlet glaciers on the northern Antarctic Peninsula over the periods 2011 to 2013 and 2013 to 2016, using high resolution topographic data of the bistatic interferometric radar satellite mission TanDEM-X. Complementary to the geodetic method applying DEM differencing, we computed the net mass balance of the main outlet glaciers by the input/output method, accounting for the difference between the surface mass balance (SMB) and the discharge of ice into an ocean or ice shelf. The SMB values are based on output of the regional climate model RACMO Version 2.3p2. For studying glacier flow and retrieving ice discharge we generated time series of ice velocity from data of different satellite radar sensor, with radar images of the satellites TerraSAR-X and TanDEM-X as main source. The study area comprises tributaries to the Larsen-A, Larsen Inlet, and Prince-Gustav-Channel embayments (region A), the glaciers calving into Larsen B embayment (region B), and the glaciers draining into the remnant part of Larsen B ice shelf in SCAR Inlet (region C). The glaciers of region A, where the buttressing ice shelf disintegrated in 1995, and of region B (ice shelf break-up in 2002) show continuing losses in ice mass, with significant reduction of losses after 2013. The mass balance numbers for grounded glacier area of the region A are Bn = −3.98 ± 0.33 Gt a-1 during 2011 to 2013 and Bn = −2.38 ± 0.18 Gt a-1 during 2013 to 2016. The corresponding numbers for region B are Bn = −5.75 ± 0.45 Gt a-1 and Bn = −2.32 ± 0.25 Gt a-1. The mass losses in region C during the two periods were modest, Bn = −0.54 ± 0.38 Gt a-1, respectively Bn = −0.58 ± 0.25 Gt a-1. The main share in the overall mass losses of the region were contributed by two glaciers: Drygalski Glacier contributing 61 % to the mass deficit of region A, and Hektoria and Green glaciers accounting for 67 % to the mass deficit of region B. Hektoria and Green glaciers accelerated significantly in 2010/2011, triggering elevation losses up to 19.5 m a-1 on the lower terminus and a rate of mass depletion of 3.88 Gt a-1 during the period 2011 to 2013. Slowdown of calving velocities and reduced calving fluxes in 2013 to 2016 coincided with years when the sea ice cover in front of the glaciers persisted during summer.

Abstract. 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.

Abstract. 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 and an ice-free slope, surfaces not affected by radar signal penetration. The backscatter simulations with a multi-layer radiative transfer model show large variations for scattering of individual snow layers due to different size and structure of the scattering elements. The average depth-dependent backscatter contributions can be approximated by an exponential function. 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 TDM DEMs and the REMA show good agreement, a trend towards overestimation of penetration is evident for heavily wind-exposed areas and towards underestimation for areas with higher accumulation rates. The angular gradients of the backscatter intensity show also distinct differences between these two domains. This behaviour can be attributed to the anisotropy of the snow/firn volume structure showing differences in the size and shape of the scattering elements and in stratification related to snow accumulation and wind-driven erosion and deposition.