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Leclercq, Paul Willem; Kääb, Andreas; Altena, Bas & Bazilova, Varvara
(2021).
Detection of glacier surge activity using cloud computing of Sentinel-1 radar data.
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Altena, Bas
(2019).
Observing the ice of our planet with daily cubesat imagery.
I Rutzinger, Martin & Heinrich, Kati (Red.),
Close Range Sensing Techniques in Alpine Terrain. Proceedings of the Innsbruck Summer School of Alpine Research 2019, 16.–22.06.2019 in Obergurgl, Austria.
Verlag der Österreichischen Akademie der Wissenschaften.
ISSN 978-3-7001-8622-9.
s. 10–11.
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Altena, Bas
(2019).
Sensing surface shifts with high-repeat Sentinel-2 imagery.
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Altena, Bas & Kääb, Andreas
(2019).
Shifts in surface, speed, or shadows: What do we measure with different time-of-day overpasses of Sentinel-2.
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Altena, Bas & Kääb, Andreas
(2019).
Techniques to reveal inter-annual glacier flow from optical remote sensing.
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Altena, Bas & Kääb, Andreas
(2019).
River ice velocity from Sentinel-twogether and PROBA-VELOCITY.
Vis sammendrag
Most optical satellite systems are set in a sun-synchronous orbit. Because of such similar configurations, orbits-of-opportunity arise. These are combinations of satellites that sense near-simultaneously. Consequently, more information can be generated from a single satellite mission when it is orchestrated with another. Hence, one tactic is to let a small-satellite piggyback with a monitoring program.
In this study we demonstrate such a strategy where we make use of the PROBA-V small-satellite in combination with Sentinel-2. The inclination of both satellites are very similar, as well as, their overpass time. This makes large scale extraction of displacements possible. One such application that can make use of this recording sequence is the monitoring of river ice break-up. In spring the melting season sets in and Arctic rivers increase in flow discharge. Eventually the water is able to break the ice cover, which will then float along. However, congestion of this ice results in jamming, associated flooding and ice run, causing damage to infrastructure and river banks. The long stretch of rivers make monitoring difficult, thus satellite remote sensing can be a means for identifying bottlenecks.
The resolution of Proba-V is 100 meters, but the time separation results in drift of the floating ice in the order of 1 km. Hence, from data of this satellite pair we are able to generate a dense velocity field over the Lena River in Russia, which stretches more than 300 km. This study demonstrates the potential of the Sentinels as an umbrella for other smaller missions. This near-simultaneous configuration has not been envisioned as a mission objective, but is coincidence. However for a future small-satellite design through clever orbit configurations can easily enhance a satellites product portfolio.
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Altena, Bas; Schellenberger, Thomas & Kääb, Andreas
(2019).
Bringing together remote sensing data to produce region-wide glacier velocities.
Vis sammendrag
The recent increase of medium resolution satellite programs that consistently senses the Earth surface has brought great potential for glaciology. Satellites like the Sentinel-1&2 tandems, Landsat 7&8 duo and Rapideye constellation sense mountain ranges almost without missing a day. Consequently, high resolution time-series can be constructed, for snow-cover or crack propagation, or other single scene information. Properties derived from combinations of acquisitions, such as, glacier velocity is more challenging. Velocity estimation is based upon image matching, which can be hindered by coherence loss or cloud cover. Consequently, generated velocity data have gaps and have scattered coverage at different time intervals.
This steady data stream has resulted in several initiatives to use image matching techniques in batch processing mode. Resulting in glacier velocity services being set-up (e.g.: cryoportal, GoLIVE, Geodetic data portal), but these initiatives are satellite specific. If such products are merged it is possible to increase temporal and spatial coverage and increase the reliability of the velocity estimates. We developed such a workflow that merges glacier velocity products of different time spans and type. This combined dataset covers several mountain ranges and has a regular time step at a monthly pace. This consistent time-series make it possible to observe glacier dynamics that are of short nature. As the satellite recordings already span several years, the dynamics of tidewater glaciers or (partial) surges can be observed and analyzed. This study therefor shows the great potential of bringing together different satellite systems.
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Altena, Bas; Armstrong, William & Kääb, Andreas
(2019).
On the origin of ogives.
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Altena, Bas; Scambos, Ted A; Fahnestock, M & Kääb, Andreas
(2018).
Automatic extraction of velocity time-series at mountain range scale from Landsat 8.
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Altena, Bas & Kääb, Andreas
(2018).
High-resolution surface and upper fjord circulation of Greenland fjords from optical remote sensing .
Vis sammendrag
Water within Greenland's fjords functions as conduit between the ice sheet and the Atlantic ocean. Exchange of energy and mass in the proglacial fjords is mainly driven by tides, wind, density fluctuations, glacial discharge and calving. All these forces change or alternate at different time scales and/or places. Measuring related (sub)surface fluxes in these fjords is complicated as fjord-ice hampers logistics and iceberg migration is able to damage measurement installations. However, an increasing fleet of optical satellites are sensing the Earth surface and can in this way observe Greenland fjords at multiple times a day.
In this study we introduce a novel type of surface velocity extraction over even short time scales (minutes and hours apart), which exploits the multitude of satellites images taken daily over specific sites and is able to separate the surface velocities from the flows occurring lower in the water column. The resulting velocity fields are able to capture small scale features (±10m) over the full range of large fjords (±100km). Imagery from the Planet constellation, Sentinel-2 and Landsat 8 are used to extract the (sub)surface flow regime of Sermilik fjord. This can be estimated for several days within a week, making it possible to capture whole fjord variability and the mode of fjord circulation. Such detailed and complete circulation information will help to complement in-situ measurements and improve the modelling of ice-ocean interaction.
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Altena, Bas & Kääb, Andreas
(2018).
Doves & displacements.
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Altena, Bas & Kääb, Andreas
(2018).
Sensing a moving Arctic from space.
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Altena, Bas & Kääb, Andreas
(2018).
ICEFLOW: short-term movements in the cryosphere.
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Altena, Bas & Kääb, Andreas
(2018).
Kinematics in the Cryosphere from space.
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Altena, Bas
(2018).
From satellite snapshots towards snow and ice services.
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Altena, Bas
(2018).
Knowledge on the ground, through observed ice flow from space.
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Altena, Bas
(2018).
Should we send Hans Brinker to the Greenland Ice Sheet?
Tvergastein.
ISSN 1893-5605.
11,
s. 14–23.
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Altena, Bas
(2018).
Daily cubesat imagery to observe and assess processes in the cryosphere.
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Leclercq, Paul Willem; Aalstad, Kristoffer; Altena, Bas & Elvehøy, Hallgeir
(2017).
Modelling of glacier surface mass balance
with assimilation of glacier mass balance
and snow cover observations from remote
sensing.
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Altena, Bas & Kääb, Andreas
(2017).
Glacier ice loss monitored through the Planet cubesat constellation.
Vis sammendrag
The Planet cubesat constellation is a developing earth observation constellation, that is and will continue to sense the whole earth surface on a daily scale at high resolution. In this contribution, we exploit this datastream to estimate the iceberg production of an outlet glacier of the Southern Patagonian icefield, called Perito Moreno. We demonstrate an automatic pipeline that takes into account the displacement due to glacier motion and the ad-hoc coverage of the glacier, due to different observation angles and orbits. With such a robust and adaptive pipeline, constructing a high resolution and temporal dense dataset is possible to be obtained. Which is of great value to understand the complex behavior of calving.
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Altena, Bas & Dakka, Jumana
(2017).
Daily river ice monitoring from space.
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Altena, Bas
(2017).
Observing processes in the cryosphere through historical and modern optical data.
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Altena, Bas
(2017).
small cube-sats and big ice-cubes.
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Gong, Yongmei; Zwinger, Thomas; Åström, Jan A.; Altena, Bas; Schellenberger, Thomas & Gladstone, Rupert M
[Vis alle 7 forfattere av denne artikkelen]
(2017).
Basal friction evolution and crevasse distribution during the surge in Basin-3, Austfonna ice-cap - offline coupling between a continuum ice dynamic model and a discrete element model.
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Winsvold, Solveig Havstad; Kääb, Andreas; Nuth, Christopher & Altena, Bas
(2016).
Landsat time-series analysis opens new approaches for regional glacier mapping.
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Winsvold, Solveig Havstad; Kääb, Andreas; Altena, Bas & Nuth, Christopher
(2016).
Using a new optical satellite for investigating glaciers and Jøkulhlaups.
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Winsvold, Solveig Havstad; Kääb, Andreas; Nuth, Christopher & Altena, Bas
(2016).
Fusion of Optical and SAR Time-series for Glacier Mapping Applications
.
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Winsvold, Solveig Havstad; Kääb, Andreas; Altena, Bas & Nuth, Christopher
(2016).
The potential of Sentinel-2 for investigating glaciers and glacier lakes.
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Altena, Bas
(2016).
Surges of St. Elias glaciers, recent and blasts from the past.
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Altena, Bas; Leclercq, Paul Willem & Kääb, Andreas
(2016).
Automatic monitoring of the transient snowline on mountain glaciers.
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Altena, Bas & Kääb, Andreas
(2016).
Estimating the seasonal glacier flow-field evolution of Kronebreen from the SPOT5-take5 campaign.
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Altena, Bas & Kääb, Andreas
(2016).
Why is my orthophoto distorted?
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Altena, Bas & Kääb, Andreas
(2016).
Glacier photogrammetry.
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Altena, Bas & Kääb, Andreas
(2016).
Exploiting orthorectification offsets in optical satellite data for glacier elevation change and velocity.
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Altena, Bas; Dunse, Thorben & Schellenberger, Thomas
(2016).
Crevasse evolution of Basin-3 during its speed-up.
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Leclercq, Paul Willem; Aalstad, Kristoffer; Elvehøy, Hallgeir & Altena, Bas
(2016).
Assimilation of glacier mass balance and snow cover fraction observations in a glacier surface mass balance model.
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Leclercq, Paul Willem; Aalstad, Kristoffer; Elvehøy, Hallgeir & Altena, Bas
(2016).
Assimilation of glacier mass balance and snow cover fraction observations in a glacier surface mass balance model.
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Kääb, Andreas & Altena, Bas
(2016).
An icy Planet.
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Kääb, Andreas & Altena, Bas
(2016).
Microsatellite constellations for monitoring cryospheric processes and related natural hazards.
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Kääb, Andreas; Winsvold, Solveig Havstad; Altena, Bas & Nuth, Christopher
(2016).
The potential of Sentinel-2 for investigating glaciers, permafrost and related natural hazards.
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Winsvold, Solveig Havstad; Kääb, Andreas; Altena, Bas & Nuth, Christopher
(2016).
Radiometrisk og geometrisk ytelse av Sentinel-2 relatert til brekartlegging.
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Altena, Bas & Kääb, Andreas
(2015).
Increasing information content of multi-spectral imagery for glacier mapping.
Vis sammendrag
Optical image matching is a powerful technique to extract glacier velocities. This technique is able to work in a highly automatic fashion, and is thus a valuable tool for large scale glacier analysis. Image matching relies on the principle of persistent surface features which can be identified in an image pair. For glacier velocity estimation, these features are typically crevasses, meltwater channels, debris, dust patterns, etc. Thus in order to successfully match two images, such features should be the most dominant objects in the image, in respect to other phenomena which are short lived. To reach such an optimum, several spectral bands can be chosen, or the higher resolution panchromatic band. However, every option has its pro and con’s, and this study aims at combining these aspects to come to an optimal image.
Our method drives on the linearity and cross-spectral correlation between spectral bands. The panchromatic band is the backbone of the image, and additional information is included from the near infrared (NIR) and short wave infrared (SWIR). Consequently, saturation is detected and adjusted. All this can be done in an automatic fashion, and is precluded against snow properties of which the SWIR is highly reactive to.
We assess our methodology qualitatively by looking at the top of the correlation score, but also the spread of this peak through Gaussian fitting. The correlation score is related to the reliability of a measurement, while the spread is a proxy for its precision. Matching is done over a large sample set of glaciers, which change in, season, glacier type, and lithology. Furthermore, from our theory we can explain why principle component analysis (PCA) is a powerful pre-processing step. Nevertheless our method seems to perform better, and from our theory we can identify weaknesses in PCA. Furthermore, our method is tested against a higher spatial- and radiometric-resolution acquisition. This gives more confidence in our claims, and justifies our methodological decisions.
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Altena, Bas; Kääb, Andreas & Nuth, Christopher
(2015).
Robust glacier displacements using knowledge-based image matching.
Vis sammendrag
Matching of repeat optical satellite images is a powerful tool for the analysis of glacier movement. Due to the rapid growth of earth observation data archives there is an increasing potential for regional glacier flow studies on a decadal scale. However, exploitation of these image collections is hindered by the currently manual pre- and post-processing steps required. Automating these steps, and using content from all available imagery will help tap the wealth of information present within the data. In this study we explore this possibility with the aim to extract velocity fields that are both accurate and reliable. We propose a bottom-up approach in which simple image matching estimates from three images are pierced together, to give rise to the far more complex time-dependent glacier flow. Taking advantage of our knowledge of glacier behavior, rather then crude statistical inferences. We first loosen the threshold of the matching, estimating dispersions for every candidate match. Then by implementing the procedure for multiple time periods we constrain the solution making it possible to apply probabilistic testing. Our approach is alternative to common top-down implementations and instead derives from first principles. In summary, we introduce the concept of precision and reliability of image matching which enhances the analysis of velocity fields with hypothesis model testing to investigate its driving forces.
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Nuth, Christopher; Kohler, Jack; Köhler, Andreas; Schuler, Thomas; Chapuis, Anne & Altena, Bas
(2012).
Observing the Kronebreen glacier system from the ground, by air and space, and through seismic waves.
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Kääb, Andreas Max; Altena, Bas; Karstensen, Jonas & Narama, Chiyuki
(2009).
Spaceborne remote sensing of glacier mass changes and dynamics.
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Kääb, Andreas Max; Altena, Bas; Karstensen, Jonas; Nuth, Christopher & Narama, Chiyuki
(2009).
Spaceborne remote sensing of glacier mass changes and dynamics.
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Altena, Bas; Kääb, Andreas; Leclercq, Paul Willem & Nuth, Christopher
(2018).
Optiske satellitter observerer endringer i isbevegelse.
Universitetet i Oslo.
ISSN 1501-7710.
Vis sammendrag
Komplekse sytemer er ofte målt med indikatorer. Isbreer endrer seg i takt med klimaet, og er derfor viktige klimaindikatorer. En bres massebalanse er relatert til klima og dens dynamikk er relatert til lokale egenskaper og systemets tilstand. Når vi vil ha en bedre oversikt over klimaet så må dynamikken på mange breer observeres.
I denne doktorgradsavhandlingen brukes optiske satellitt systemer til å observere mange breer og registrere bredynamikk på kort og lang tidsskala. Fokuset i denne avhandlingen er å observere brebevegelse fra forskjellige optiske satellitt systemer for å registrere mest mulig pålitelig informasjon fra fire tiår med data fra satellittarkiver. Det introduseres en ny metode for å estimere brebevegelse fra forskjellige satellittbaner. Innfallsvinkelen er å estimere høydeforandringer og brebevegelse samtidig. I tillegg introduserer vi en bildesammenlikning basert på “triangle closure” som gjør metoden robust, men fortsatt pålitelig.
Det er mulig å observere brebevegelse med korte tidsintervall med en ny metode basert på “optical flow”. Små perioder med økt brehastighet på grunn av økt vannmengde i det subglasiale systemet under en bre, kan bli observert nøyaktig både romlig og i tid. Dette er kun mulig på grunn av den økte tilgangen de siste årene på gratis og fritt tilgjengelige satellittbilder. Metoden gjør det mulig å raskt undersøke og identifisere om en bre er ustabil.
For å bedre forstå bredynamikk kan man transformere data fra brebevegelse til strukturert informasjon. Jo mer brehastighetdata man har tilgjengelig, jo vanskeligere blir det å tolke hastighetssignalet til breen. Men ved å introdusere etterprosessering basert på votering så kan man filtrere ville observasjoner. Dette ble anvendt på et stort datasett av brehastigheter til å konstruere månedlige tidsserier over flere fjellkjeder i Alaska. Både årlige og sesongbaserte observasjoner var mulig å finne, også for mindre brearmer.