19 research outputs found
Dynamic changes on the Wilkins Ice Shelf during the 2006–2009 retreat derived from satellite observations
The vast ice shelves around Antarctica provide significant restraint to the outflow from adjacent tributary glaciers. This important buttressing effect became apparent in the last decades, when outlet glaciers accelerated considerably after several ice shelves were lost around the Antarctic Peninsula (AP). The present study aims to assess dynamic changes on the Wilkins Ice Shelf (WIS) during different stages of ice-front retreat and partial collapse between early 2008 and 2009. The total ice-shelf area lost in these events was 2135 ± 75 km2 ( ∼ 15 % of the ice-shelf area relative to 2007). Here, we use time series of synthetic aperture radar (SAR) satellite observations (1994–1996, 2006–2010) in order to derive variations in surface-flow speed from intensity-offset tracking. Spatial patterns of horizontal strain-rate, stress and stress-flow angle distributions are determined during different ice-front retreat stages. Prior to the final break up of an ice bridge in 2008, a strong speed up is observed, which is also discernible from other derived quantities. We identify areas that are important for buttressing and areas prone to fracturing using in-flow and first principal strain rates as well as principal stress components. Further propagation of fractures can be explained as the first principal components of strain rates and stresses exceed documented threshold values. Positive second principal stresses are another scale-free indicator for ice-shelf areas, where fractures preferentially open. Second principal strain rates are found to be insensitive to ice-front retreat or fracturing. Changes in stress-flow angles highlight similar areas as the in-flow strain rates but are difficult to interpret. Our study reveals the large potential of modern SAR satellite time series to better understand dynamic and structural changes during ice-shelf retreat but also points to uncertainties introduced by the methods applied
New sensors benchmark report on KOMPSAT-3A: Geometric benchmarking over Maussane test site for CAP purposes
Imagery collected by KOMPSAT-3A satellite can be potentially used in The Common Agricultural Policy (CAP) image acquisition Campaign. The qualification and certificate is conducted by performing benchmarking tests, i.e. it has to be checked whether the planimetric accuracy of the produced orthoimages does not exceed certain values regulated by JRC. Therefore, a benchmarking test was carried out based on two KOMPSAT-3A imagery collected in February 2017 and March 2018. The first part of the report (chapter 2-6) describes in detail how the tests were performed, i.e. the auxiliary data, methodology and workflow used as well as outcome from the Internal Quality Control (IQC). The second part (chapter 7-9) deals with External Quality Control (EQC) and conclusions made on the basis of this assessment with regards to the VHR Image technical specifications criteria [iii]. While the first part, i.e. production of ortho imagery, was carried out by external an contractor (European Space Imaging - EUSI) the second part, i.e EQC, was performed by Joint Research Centre (JRC). In this way an independent and objective test was assured.JRC.D.5-Food Securit
The glaciers climate change initiative: Methods for creating glacier area, elevation change and velocity products
Glaciers and their changes through time are increasingly obtained from a wide range of satellite sensors. Due to the often remote location of glaciers in inaccessible and high-mountain terrain, satellite observations frequently provide the only available measurements. Furthermore, satellite data provide observations of glacier character- istics that are difficult to monitor using ground-based measurements, thus complementing the latter. In the Glaciers_cci project of the European Space Agency (ESA), three of these characteristics are investigated in detail: glacier area, elevation change and surface velocity. We use (a) data from optical sensors to derive glacier outlines, (b) digital elevation models from at least two points in time, (c) repeat altimetry for determining elevation changes, and (d) data from repeat optical and microwave sensors for calculating surface velocity. For the latter, the two sensor types provide complementary information in terms of spatio-temporal coverage. While (c) and (d) can be generated mostly automatically, (a) and (b) require the intervention of an analyst. Largely based on the results of various round robin experiments (multi-analyst benchmark studies) for each of the products, we suggest and describe the most suitable algorithms for product creation and provide recommendations concerning their practical implementation and the required post-processing. For some of the products (area, velocity) post-processing can influence product quality more than the main-processing algorithm
Änderungen von Gletschern im Karakorum Gebirge und von Schelfeisen an der Antarktischen Halbinsel – Ergebnisse einer satellitengestützten Bildanalyse
The components of the cryosphere are sensitive indicators of past and present climate variability. They provide some of the most detectable evidence of global climate change. The contribution of ice sheets, glaciers and ice caps to global sea-level rise has considerably increased during recent decades. Hence, the monitoring of these components on a regular basis is of great importance.
The repeat observations and measurements of cryospheric variables have become available with the launch of Earth Observation satellites. These instruments are very suitable to monitor large-scale changes on repeat intervals due to wide footprints and both high spatial and temporal resolution. Above all, active remote sensing systems operating in the microwave domain of the electromagnetic spectrum were most useful. These systems work independently from daylight since they provide their own source of radiation and are able to penetrate through clouds or dust. Modern twin satellite missions, such as the TanDEM-X mission, offer new possibilities for interferometric processing due to very short temporal baselines between image acquisitions.
The goal of this study was to investigate the potential of new satellite mission data in conjunction with archived data for the quantification of changes of the cryosphere. For this purpose, glaciers in a high mountain area and floating ice shelves on the margin of the Antarctic ice sheet were selected. The respective cryospheric variables showed highly dynamic behavior during the last decades and were hence, chosen for this study. Several remote-sensing based methods were used and adapted to specific requirements of the satellite data or the studied objects. The applied methods include: the use of multi-spectral satellite data for mapping glacier outlines and termini position changes, the monitoring of changes in glacier surface flow by means of ‘intensity offset tracking’ algorithms and the quantification of glacier elevation and mass changes using SAR interferometry. In order to monitor ice shelves in a recession stage, comparable techniques were used: the calculation of changes in surface flow and ice thickness, the detection of fractures on the ice surface as well as the influence of tidal effects on the ice shelf.
In the first part of this study, results are presented for glaciers in the Karakoram Region. Previous results showed anomalous behavior of some glaciers expressed in stable and advancing glacier termini or in balanced glacier mass budgets during recent decades. In contrast, glaciers in adjacent mountain ranges are often affected by thinning and frontal recession. Additionally, numerous surge-type glaciers are found in the Karakoram. These glaciers are characterized by cyclic speed up of flow accompanied by considerable terminus advances. In the following longer-lasting quiescent period, ice flow remains nearly stagnant and glacier tongues retreat or stay stable. Results of this study show a comprehensive inventory of glaciers in the Karakoram including the monitoring of termini position changes over several decades. The majority of glaciers showed stable termini and only few were retreating. An additional achievement of this study was a comprehensive mosaic of SAR based glacier surface flow. Nearly stable glacier elevation and mass changes during 2000-2012 confirm previous findings, yet small-scale patterns of elevation changes were quantified. Thanks to the high spatial resolution of modern SAR missions, comparably small and fast flowing surge-type glaciers could be identified. The glacier surge cycle was investigated in detail and small-scale spatial patterns of glacier elevation change were quantified, which might point to subsequent advance and speed up of the respective surge-type glaciers.
In the second part, the floating ice shelves along the margins of the Antarctic continent were investigated. These ice shelves are significantly affected by atmospheric and oceanic warming. As a consequence, ice shelf recession and thinning has been observed and is most pronounced on the Antarctic Peninsula. Ice shelf collapse leads to speed up and surface lowering of upstream grounded ice and hence, an additional contribution to sea-level rise. In this study, the Antarctic ice shelf extent was partitioned into areas that do or do not restrain the upstream ice flow. The latter ice shelf areas are referred to as passive shelf ice. If this fraction is small at present, the respective ice shelf is considered susceptible to further ice loss. Most susceptible ice shelves are located in the Bellingshausen and Amundsen Sea sectors. One of these ice shelves is Wilkins Ice Shelf, located on the Antarctic Peninsula. It was used as a case study to show the loss of ice shelf restraint during ice front recession. The retreat stages were surveyed by means of multi-temporal surface velocities and deduced products such as strain rate and stress regimes. The latter two helped to assess the ice-shelf stability during ice front break-up. A comprehensive, very detailed picture on ice thickness changes over the last decade as well as the formation of fractures on the ice shelf’s surface, points to a weakening ice shelf stability.Die Elemente der Kryosphäre reagieren empfindlich auf Änderungen des globalen Klimas. Steigende Temperaturen hinterlassen deutliche Spuren, die in der Kryosphäre ablesbar sind. So ist der Beitrag von Gletschern, Eiskappen und der großen Eisschilde zum globalen Meeresspiegelanstieg in den letzten Jahrzehnten deutlich gewachsen. Die flächendeckende Beobachtung der Kryosphäre in regelmäßigen Abständen ist daher von besonderer Bedeutung. Dies wurde erstmals durch den Start verschiedener ziviler Erdbeobachtungsmissionen in den 1970er Jahren möglich. Sie stellen ein wertvolles Instrument für die flächendeckende Beobachtung von Veränderungen der Kryosphäre dar und bieten sowohl zeitlich als auch räumlich hoch auflösende Aufnahmen. Vor allem aktive Mikrowellensysteme sind besonders wertvoll, da sie selbstständig elektromagnetische Wellen aussenden und damit unabhängig von der Solarstrahlung agieren. Bedingt durch die vergleichsweise langen Mikrowellen, durchdringen diese Systeme außerdem Wolken- oder Staubschichten in der Atmosphäre.
Ziel dieser Arbeit war die Verwendung von Zeitreihen verschiedener Satellitendaten, um Änderungen von Gebirgsgletschern sowie von schwimmenden Schelfeisen am Rande des Antarktischen Kontinents zu detektieren und in einen globalen Kontext einzuordnen. Die jeweiligen Komponenten der Kryosphäre zeigten sich während der letzten Jahrzehnte hochdynamisch und wurden daher für diese Studie ausgewählt. Verschiedene Methoden der Fernerkundung wurden angewandt und sowohl an die Spezifikationen der jeweiligen Satellitendaten als auch an die heterogenen Untersuchungsobjekte angepasst. Die verwendete Methodik umfasst: das Detektieren von Änderungen der Gletscherfläche anhand multispektraler Satellitendaten, das Monitoring des Fließverhaltens eines Gletschers mit Hilfe von sog. ‚intensity offset tracking‘ Algorithmen, die Quantifizierung von Gletscherhöhen- und Gletschermassenänderungen auf Basis interferometrischer Techniken. Für das Monitoring von Schelfeisen in einem Rückzugsstadium wurden mit Hilfe ähnlicher Methoden diese Ziele verfolgt: die Erstellung multi-temporaler Fließgeschwindigkeiten und Eisdickenänderungen, das Detektieren von Rissen auf der Eisoberfläche sowie der Einfluss des Tidenhubs auf das frei schwimmende Schelfeis.
Die erzielten Ergebnisse werden zuerst für Gletscher im Karakorum Gebirge vorgestellt. Bisherige Untersuchungen einzelner Gletscher dort zeigten stabile oder sogar vorstoßende Gletscherfronten. Auch die Gletschermassen weisen eine ausgeglichene Bilanz aus. Im Gegensatz dazu sind Gletscher in angrenzenden Gebirgen häufig von Gletscherrückzug und –schmelze betroffen. Im Karakorum sind außerdem viele ‚galoppierende‘ (‚surge-type‘) Gletscher zu finden. Diese Gletschertypen sind durch eine kurze Periode schneller Fließgeschwindigkeiten und beträchtlich vorstoßender Gletscherstirne charakterisiert. Darauf folgend verringern sich die Fließgeschwindigkeiten wiederum und die Gletscherzunge bleibt unverändert oder zieht sich sogar zurück. In dieser Arbeit wurde erstmals ein flächendeckendes Gletscherinventar für den Karakorum erstellt. Darin enthalten sind Gletscherflächenänderungen für einen Zeitraum mehrerer Dekaden. Hieraus ergibt sich, dass die Mehrzahl der Gletscherflächen konstant blieb und nur sehr wenige Gletscher von Rückzug betroffen waren. Zudem zeigt die vorliegende Arbeit erstmals flächendeckende Fließgeschwindigkeiten für Gletscher im Karakorum. Moderne SAR Satellitendaten halfen bei der Quantifizierung von Höhenänderungen der Gletscher. Die Ergebnisse stützen vorhergehende Analysen, zeichnen sich jedoch durch die Quantifizierung sehr kleinräumiger Muster aus. Dank der hohen räumlichen Auflösung der modernen Satellitenmissionen konnten vergleichsweise kleine und schnell fließende ‚surge-type‘ Gletscher erstmalig identifiziert werden. Die zyklischen Veränderungen in Fläche, Fließverhalten und Gletscherhöhen konnten detailliert beobachtet und zukünftige aktive Phasen prognostiziert werden.
Anschließend befasst sich diese Arbeit mit den schwimmenden Schelfeisen des Antarktischen Kontinents. Durch die Erwärmung der Luft- und Ozeantemperatur dort haben sich die Schelfeise besonders an der Antarktischen Halbinsel stark verkleinert oder verdünnt. Das Verschwinden eines Schelfeises führt zu einem Anstieg der Fließgeschwindigkeiten der Eismassen flussaufwärts und trägt zum globalen Meeresspiegelanstieg bei. In dieser Arbeit werden Schelfeisbereiche quantifiziert, die eine Stützfunktion gegenüber gegründetem Eis ausüben oder aber keinerlei Funktion haben. Letztere werden hier als passives Schelfeis bezeichnet. Sobald die Fläche des passiven Schelfeises einen gewissen Schwellenwert unterschreitet, kann mit einem enormen Stabilitätsverlust und dem Verschwinden des betroffenen Schelfeises gerechnet werden. Am häufigsten betroffen sind Schelfeise in der Amundsen und Bellingshausen See. Dort liegt auch das Wilkins Schelfeis, welches in den vergangenen Jahren große Flächen verloren hat und zur Prüfung der aufgestellten Thesen herangezogen wurde. Zudem zeigt die Auswertung multi-temporaler Satellitendaten einen Anstieg der Fließgeschwindigkeiten im Zuge der Flächenverkleinerung sowie eine Änderung der Dehnungs- und Spannungsraten im Eis. Dadurch konnte die Stabilität des Eises während der Rückzugsstadien beurteilt werden. Schließlich zeigen flächendeckende Eisdickenänderungen im letzten Jahrzehnt sowie die Kartierung von Rissbildungen eine insgesamt geringe Stabilität des Wilkins Schelfeises
Surface velocities at Wilkins Ice Shelf, Antarctic Peninsula, link to shapefiles and GeoTIFFs
Glacier elevation changes in the Karakoram Range derived from TanDEM-X and SRTM/X-SAR digital elevation models, 2000-2012, link to GeoTIFF
Snow cover and glaciers in the Karakoram region are important freshwater resources for many down-river communities as they provide water for irrigation and hydropower. A better understanding of current glacier changes is hence an important informational baseline. We present glacier elevation changes in the central Karakoram region using TanDEM-X and SRTM/X-SAR DEM differences between 2000 and 2012. We calculated elevation differences for glaciers with advancing and stable termini or surge-type glaciers separately using an inventory from a previous study. Glaciers with stable and advancing termini since the 1970s showed nearly balanced elevation changes of -0.09 ± 0.12 m/a on average or mass budgets of -0.01 ± 0.02 Gt/a (using a density of 850 kg/m**3). Our findings are in accordance with previous studies indicating stable or only slightly negative glacier mass balances during recent years in the Karakoram. The high-resolution elevation changes revealed distinct patterns of mass relocation at glacier surfaces during active surge cycles. The formation of kinematic waves at quiescent surge-type glaciers could be observed and points towards future active surge behaviour. Our study reveals the potential of the TanDEM-X mission to estimate geodetic glacier mass balances, but also points to still existing uncertainties induced by the geodetic method
Surface velocities of Wilkins Ice Shelf between 2006 and 2009, link to GeoTIFFs
Ice shelves serve as important buttresses for upstream areas. Several large ice shelves on the Antarctic Peninsula have disintegrated or retreated, which implied dynamic consequences for upstream ice. The present study aims to assess dynamic changes on Wilkins Ice Shelf during multi-stage ice-front retreat in the last decade. A total area of 2135 ± 75 km² was lost in the period 2008-2009. The present study uses time-series of SAR satellite observations (2006-2009) in order to derive variations in multi-temporal surface flow from intensity offset tracking methods. From these velocity field, spatial patterns of horizontal strain rate and stress components were inferred during different ice-front retreat stages (not part of the data publication). These fields are used to explain the different break-up stages and to evaluate the ice-shelf stability (see related publication Rankl et al. 2017). For this purpose, we apply criteria which were forwarded to explain and assess past ice-shelf retreat