Time filter
Source Type

Rizzoli P.,German Aerospace Center | Martone M.,German Aerospace Center | Rott H.,ENVEO IT GmbH | Rott H.,University of Innsbruck | Moreira A.,German Aerospace Center
Remote Sensing | Year: 2017

This paper presents for the first time a detailed study on information content of X-band single-pass interferometric spaceborne SAR data with respect to snow facies characterization. An approach for classifying different snow facies of the Greenland Ice Sheet by exploiting X-band TanDEM-X interferometric synthetic aperture radar acquisitions is firstly detailed. Large-scale mosaics of radar backscatter and volume correlation factor, derived from quicklook images of the interferometric coherence, represent the starting point for applying an unsupervised classification method based on the c-means fuzzy clustering algorithm. The data was acquired during winter 2010/2011. A partition of four different snow facies was chosen and interpreted using reference melt data, snow density, and in situ measurements. The variations in the stratification and micro-structure of firn, such as the variations of density with depth and the presence of percolation features, are identified as relevant parameters for explaining the significant differences in the observed interferometric signatures among different snow facies. Moreover, a statistical analysis of backscatter and volume correlation factor provided useful parameters for characterizing the snow facies behavior and analyzing their dependency on the acquisition geometry. Finally, knowing the location and characterization of the different snow facies, the two-way X-band penetration depth over the whole Ice Sheet was estimated. The obtained mean values vary from 2.3 m for the outer snow facies up to 4.18 m for the inner one. The presented approach represents a starting point for a long-term monitoring of ice sheet dynamics, by acquiring time-series, and is of high relevance for the design of future SAR missions as well. © 2017 by the authors.

Wuite J.,ENVEO IT GmbH | Rott H.,ENVEO IT GmbH | Rott H.,University of Innsbruck | Hetzenecker M.,ENVEO IT GmbH | And 5 more authors.
Cryosphere | Year: 2015

We use repeat-pass SAR data to produce detailed maps of surface motion covering the glaciers draining into the former Larsen B Ice Shelf, Antarctic Peninsula, for different epochs between 1995 and 2013. We combine the velocity maps with estimates of ice thickness to analyze fluctuations of ice discharge. The collapse of the central and northern sections of the ice shelf in 2002 led to a near-immediate acceleration of tributary glaciers as well as of the remnant ice shelf in Scar Inlet. Velocities of most of the glaciers discharging directly into the ocean remain to date well above the velocities of the pre-collapse period. The response of individual glaciers differs and velocities show significant temporal fluctuations, implying major variations in ice discharge as well. Due to reduced velocity and ice thickness the ice discharge of Crane Glacier decreased from 5.02 Gt ag'1 in 2007 to 1.72 Gt ag'1 in 2013, whereas Hektoria and Green glaciers continue to show large temporal fluctuations in response to successive stages of frontal retreat. The velocity on Scar Inlet ice shelf increased 2-3-fold since 1995, with the largest increase in the first years after the break-up of the main section of Larsen B. Flask and Leppard glaciers, the largest tributaries to Scar Inlet ice shelf, accelerated. In 2013 their discharge was 38% and 46% higher than in 1995. © Author(s) 2015.

Nagler T.,ENVEO IT GmbH | Rott H.,ENVEO IT GmbH | Rott H.,University of Innsbruck | Hetzenecker M.,ENVEO IT GmbH | And 4 more authors.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012

Observations of the 3D ice velocity field are important for studies of glacier hydraulics and for modeling the dynamic response of glaciers to changing boundary conditions. A method for 3D ice velocity retrieval from repeat pass SAR data of crossing orbits applying offset tracking in amplitude images is presented. In contrast to the conventional technique for ice motion mapping which assumes surface-parallel flow, this method delivers the true velocity vector. The procedure is validated using in-situ GPS data on an outlet glacier of the Vatnajökull ice cap in Iceland. © 2012 IEEE.

Malenovsky Z.,University of Zürich | Rott H.,ENVEO IT GmbH | Rott H.,University of Innsbruck | Cihlar J.,ZEMKON INC. | And 4 more authors.
Remote Sensing of Environment | Year: 2012

The Sentinel-1, -2, and -3 satellite missions can meet various observational needs for spatially explicit physical, biogeophysical, and biological variables of the ocean, cryosphere, and land research activities. The currently known observational requirements were extracted from documents produced by major international scientific projects and programs. The summarized observational needs were then cross-referenced with the capabilities of the planned sensors aboard of the first three Sentinels. A comparative analysis, also incorporating scientific challenges of the ESA Living Planet Programme and the Essential Climate Variables (ECVs), resulted in a preliminary scientific priority assessment of the reviewed environmental variables. Results of these activities, discussed and consolidated in March 2011 at the Sentinels for Science (SEN4SCI) scientific workshop, demonstrate the high potential of the Sentinel-1, -2, and -3 missions for systematic, long-term observations of the Earth system. © 2012 Elsevier Inc.

Rott H.,ENVEO IT GmbH | Rott H.,University of Innsbruck | Floricioiu D.,German Aerospace Center | Wuite J.,ENVEO IT GmbH | And 3 more authors.
Geophysical Research Letters | Year: 2014

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-1, with the largest contribution by Drygalski Glacier amounting to 2.2 ± 0.2 Gt a-1 . 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. © 2014. The Authors.

Nicholson L.I.,University of Innsbruck | Prinz R.,University of Innsbruck | Prinz R.,ENVEO IT GmbH | Molg T.,TU Berlin | Kaser G.,University of Innsbruck
Cryosphere | Year: 2013

The Lewis Glacier on Mt Kenya is one of the best-studied tropical glaciers, but full understanding of the interaction of the glacier mass balance and its climatic drivers has been hampered by a lack of long-term meteorological data. Here we present 2.5 yr of meteorological data collected from the glacier surface from October 2009 to February 2012. The location of measurements is in the upper portion of Lewis Glacier, but this location experiences negative annual mass balance, and the conditions are comparable to those experienced in the lower ablation zones of South American glaciers in the inner tropics. In the context of other glaciated mountains of equatorial East Africa, the summit zone of Mt Kenya shows strong diurnal cycles of convective cloud developme. © Author(s) 2013. CC Attribution 3.0 License.

Rott H.,University of Innsbruck | Rott H.,ENVEO IT GmbH | Muller F.,ENVEO IT GmbH | Nagler T.,ENVEO IT GmbH | Floricioiu D.,German Aerospace Center
Cryosphere | Year: 2011

The outlet glaciers to the embayment of the Larsen-B Ice Shelf started to accelerate soon after the ice shelf disintegrated in March 2002. We analyse high resolution radar images of the TerraSAR-X satellite, launched in June 2007, to map the motion of outlet glaciers in detail. The frontal velocities are used to estimate the calving fluxes for 2008/2009. As reference for pre-collapse conditions, when the glaciers were in balanced state, the ice fluxes through the same gates are computed using ice motion maps derived from interferometric data of the ERS-1/ERS-2 satellites in 1995 and 1999. Profiles of satellite laser altimetry from ICESat, crossing the terminus of several glaciers, indicate considerable glacier thinning between 2003 and 2007/2008. This is taken into account for defining the calving cross sections. The difference between the pre- and post-collapse fluxes provides an estimate on the mass imbalance. For the Larsen-B embayment the 2008 mass deficit is estimated at 4.34 ± 1.64 Gta-1, significantly lower than previously published values. The ice flow acceleration follows a similar pattern on the various glaciers, gradually decreasing in magnitude with distance upstream from the calving front. This suggests stress perturbation at the glacier front being the main factor for acceleration. So far there are no signs of slow-down indicating that dynamic thinning and frontal retreat will go on. © 2011 Author(s).

Nagler T.,ENVEO IT GmbH | Rott H.,ENVEO IT GmbH | Rott H.,University of Innsbruck | Hetzenecker M.,ENVEO IT GmbH | And 2 more authors.
Remote Sensing | Year: 2015

The Sentinel satellite constellation series, developed by the European Space Agency, represents the dedicated space component of the European Copernicus program, committed to long-term operational services in a wide range of application domains. Here, we address the potential of the Sentinel-1 mission for mapping and monitoring the surface velocity of glaciers and ice sheets. We present an ice velocity map of Greenland, derived from synthetic aperture radar (SAR) data acquired in winter 2015 by Sentinel-1A, the first satellite of the Copernicus program in orbit. The map is assembled from about 900 SAR scenes acquired in Interferometric Wide swath (IW) mode, applying the offset tracking technique. We discuss special features of IW mode data, describe the procedures for producing ice velocity maps, and assess the uncertainty of the ice motion product. We compare the Sentinel-1 ice motion product with velocity maps derived from high resolution SAR data of the TerraSAR-X mission and from PALSAR data. Beyond supporting operational services, the Sentinel-1 mission offers enhanced capabilities for comprehensive and long-term observation of key climate variables, such as the motion of ice masses. © 2015 by the authors.

De Rydt J.,British Antarctic Survey | Gudmundsson G.H.,British Antarctic Survey | Rott H.,ENVEO IT GmbH | Rott H.,University of Innsbruck | Bamber J.L.,University of Bristol
Geophysical Research Letters | Year: 2015

Following the disintegration of the Larsen B Ice Shelf, Antarctic Peninsula, in 2002, regular surveillance of its â20 tributary glaciers has revealed a response which is varied and complex in both space and time. The major outlets have accelerated and thinned, smaller glaciers have shown little or no change, and glaciers flowing into the remnant Scar Inlet Ice Shelf have responded with delay. In this study we present the first areawide numerical analysis of glacier dynamics before and immediately after the collapse of the ice shelf, combining new data sets and a state-of-the-art numerical ice flow model. We simulate the loss of buttressing at the grounding line and find a good qualitative agreement between modeled changes in glacier flow and observations. Through this study, we seek to improve confidence in our numerical models and their ability to capture the complex mechanical coupling between floating ice shelves and grounded ice. Key Points Ice shelf collapse reduces back pressure by up to 30% at the grounding line Ice shelf collapse causes instantaneous speedup that extends 15km inland Hektoria, Green, and Crane speed up >100m/yr, Flask and Leppard remain unaffected. © 2015. American Geophysical Union. All Rights Reserved.

Metsamaki S.,Finnish Environment Institute | Pulliainen J.,Finnish Meteorological Institute | Salminen M.,Finnish Environment Institute | Salminen M.,Finnish Meteorological Institute | And 6 more authors.
Remote Sensing of Environment | Year: 2015

The European Space Agency's Data User Element (DUE) project GlobSnow was established to create a global database of Snow Extent and Snow Water Equivalent. The Snow Extent (SE) product portfolio provided within ESA DUE GlobSnow (2008-2014) is introduced and described, with a special focus on the Daily Fractional Snow Cover (DFSC) of the SE version 2.0 and its successor 2.1 released in 2013-2014. The fractional snow retrieval uses the SCAmod method designed ecpecially to enable accurate snow mapping including forests. The basics of the methodology are presented, as well as the cloud screening method applied in SE production. Considerations for future validations together with discussion on some current issues and potential inaccuracies are presented. One focus of the investigation is on the representativeness of reference FSC generated from Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM. +) data, with a particular interest in forested areas. Two methods for reference data generation are investigated. When comparing the GlobSnow Daily Fractional Snow Cover to these reference data, we try to identify how the comparison reflects the possible inaccuracies of the DFSC and to define the conditions where the reference data are not representative. It is obvious that the evaluation result strongly depends on the quality of the reference data, and that the two methods investigated cannot provide representative reference data for dense forests. For fully snow-covered dense conifer forest area in Finland, a Root Mean Squared Error of 20-30% was obtained from comparisons although DFSC indicated full snow cover correctly. These first evaluations would indicate a good performance of GlobSnow SE products in forests; however, this does not necessarily show up in validations due to the non-representativeness of the reference data. It is also concluded that GlobSnow SE products are sensitive to the representativeness of the applied SCAmod parameters and that FSC overestimations may occur in dense forests. GlobSnow SE products are available at www.globsnow.info/se/. © 2014 Elsevier Inc.

Loading ENVEO IT GmbH collaborators
Loading ENVEO IT GmbH collaborators