Application of Image Cross-Correlation to the Measurement of Glacier Velocity Using Satellite Image Data

ArticleinRemote Sensing of Environment 42(3):177-186 · December 1992with 1,517 Reads
Abstract
Image-to-image cross-correlation software is applied to pairs of digital satellite images to map the velocity field of moving ice. This technique uses small-scale glacial surface features, such as crevasse scars and snow dunes, as markers on the surface of the moving ice. Displacements of the surface features are mapped by selecting small image areas centered on distinct features, or by dividing a large area of densely featured glacial surface into a grid of areas, and searching a subsequent image for matching areas using a cross-correlation algorithm. Interpolation of the peak correlation values allows the displacements to be measured to subpixel accuracy, resulting in very precise velocity measurements. Cross-correlation is also applied to provide image coregistration in areas devoid of bedrock exposures. In such areas, subtle large-scale topographic undulations in the ice surface, related to underlying bedrock structure, may be correlated by using large image areas and low-pass filtered images. Both types of applications are demonstrated, using Ice Stream D and Ice Stream E in West Antarctica as test areas. A high-resolution map of the velocity field of the central portion of Ice Stream E, generated by the displacement-measuring technique, is presented. The use of cross-correlation software is a significant improvement over previous manually-based photogrammetric methods for velocity measurement, and is far more cost-effective than in situ methods in remote polar areas.

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  • ... Optical-satellite-image-based ice-velocity measurement using feature tracking is a well-established method. Feature tracking involves tracking identifiable features between pairs of optical satellite images using an image-matching algorithm such as normalized cross-correlation (NCC) [12][13][14][15][16][17], cross-correlation operated in the frequency domain on orientation images (CCF-O) [18][19][20], and co-registration of optically sensed images and correlation (COSI-Corr) [21]. The results of a comparison [22] indicate that COSI-Corr is the most robust matching method. ...
    ... Tracking features between pairs of images is a robust way to define regions of movement such as the ice flow in Antarctica [13,15]. This method can be used with both optical satellite images and also synthetic aperture radar satellite images [7,8,28], and has been proven to be effective for most glaciers. ...
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  • ... Unlike the InSAR basis of interferometric phases, the pixel offset tracking (OT) technique [15]- [17] measures surface deformations based on the amplitude information of SAR imagery. Consequently, the OT technique is insensitive to phase noise, allowing it to retrieve large surface deforma- tions (in the order of several or even dozens of meters) that InSAR cannot achieve. ...
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  • ... Unlike the InSAR basis of interferometric phases, the pixel offset tracking (OT) technique [15]- [17] measures surface deformations based on the amplitude information of SAR imagery. Consequently, the OT technique is insensitive to phase noise, allowing it to retrieve large surface deforma- tions (in the order of several or even dozens of meters) that InSAR cannot achieve. ...
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  • ... Earlier circum-Antarctic mappings of surface velocity have been based on synthetic aperture radar (SAR) data with incomplete coverage for 1996-2000 ( Jezek et al., 2003;Rignot, 2006) and near-complete coverage for 2007-2009 ( Rignot et al., 2011a). Applications of optical imagery for surface velocity mapping have heretofore been limited to more local scales (e.g., Bindschadler and Scambos, 1991;Scambos et al., 1992) due to limited sensor capabilities, cloudiness and too few repeat-image acquisitions. Improvements in sensor technology (particularly in radiometric resolution) and far higher image acquisition rates for Landsat 8, launched in 2013, largely overcome these limitations ( Fahnestock et al., 2015;Jeong and Howat, 2015;Mouginot et al., 2017) and provide the ability to generate near-complete yearly mappings of surface velocity with high accuracy (∼ 10 m yr −1 ). ...
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  • ... Those can then be used to determine the glacier movement by using image correlation software. In our case, we used IMCORR [43] to obtain surface displacement rates. The IMCORR software determines the surface displacement rates by using a reference block of the raster cell values of the first image and correlating the values within a determined search block. ...
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  • ... Using the feature tracking approach, various studies of Himalayan glacial ice motion are reported using different optical satellite data like ASTER, SPOT-5, Landsat-TM ( Copland et al. 2009;Leprince et al. 2008;Scambos et al. 1992;Schellenberger et al. 2015;Scherler, Leprince, and Strecker 2008). The results from these studies are limited to some part of glacier due to the presence of cloud cover or shadow in the optical data. ...
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  • ... One of the early techniques developed to quantify morphological changes using satellite imagery is the correlation of multi-temporal orthorectified imagery. By finding the point of maximum correlation between small corresponding image patches, it was shown that horizontal ground movements could be tracked (Scambos et al, 1992). Initially mostly used to track glaciers because of the large displacements involved, the technique has, over the years, been made more robust and accurate; it is currently able to detect and track horizontal changes as small as 1/10 to 1/20 of the image pixel size (Van Puymbroeck et al, , Leprince et al, 2007). ...
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  • ... Moreover, this technique can extract the deformation information in both the slant-range and flight directions. As a result, it has been widely used in glacier movement studies [24][25][26][27] and landslide monitoring [28,29]. Furthermore, the newly developed SAR amplitude pixel-offset SBAS technique has been applied to large displacements and has obtained a good monitoring accuracy [30,31]. ...
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  • ... While the feasibility of measuring ice-motion from space-borne optical and Synthetic Aperture Radar (SAR) imagery has long been established ( [1,2], and references therein), the routine generation of ice velocity maps of Greenland and Antarctica has become feasible only recently [3][4][5], due to several factors: the unprecedented availability of regularly acquired free and open access data, provided in particular by the European Space Agency (ESA) Sentinel-1a and 1b SARs and the U.S. Geological Survey (USGS)/National Aeronautics and Space Administration (NASA) Landsat-8 mission; the maturity of the data processing techniques; the increased performance and affordability of storage and computing resources; the establishment of long-term Earth Observations programs, such as the ESA Climate Change Initiative (CCI) and the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs). ...
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    Ice velocity is one of the products associated with the Ice Sheets Essential Climate Variable. This paper describes the intercomparison and validation of ice-velocity measurements carried out by several international research groups within the European Space Agency Greenland Ice Sheet Climate Change Initiative project, based on space-borne Synthetic Aperture Radar (SAR) data. The goal of this activity was to survey the best SAR-based measurement and error characterization approaches currently in practice. To this end, four experiments were carried out, related to different processing techniques and scenarios, namely differential SAR interferometry, multi aperture SAR interferometry and offset-tracking of incoherent as well as of partially-coherent data. For each task, participants were provided with common datasets covering areas located on the Greenland ice-sheet margin and asked to provide mean velocity maps, quality characterization and a description of processing algorithms and parameters. The results were then intercompared and validated against GPS data, revealing in several cases significant differences in terms of coverage and accuracy. The algorithmic steps and parameters influencing the coverage, accuracy and spatial resolution of the measurements are discussed in detail for each technique, as well as the consistency between quality parameters and validation results. This allows several recommendations to be formulated, in particular concerning procedures which can reduce the impact of analyst decisions, and which are often found to be the cause of sub-optimal algorithm performance.
  • ... Using the feature tracking approach, various studies of Himalayan glacial ice motion are reported using different optical satellite data like ASTER, SPOT-5, Landsat-TM ( Copland et al. 2009;Leprince et al. 2008;Scambos et al. 1992;Schellenberger et al. 2015;Scherler, Leprince, and Strecker 2008). The results from these studies are limited to some part of glacier due to the presence of cloud cover or shadow in the optical data. ...
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  • ... Pixel-offset (PO) is a technique that attempts to find the same distinctive features within subscenes of two images relevant to the same target area. In remote sensing, this is usually performed by considering either the Fourier shift theorem [28], or normalized cross-correlation (NCC) algorithms [29]. In SAR applications, PO allows co-registering image pairs or, while already co-registered, identifying the residual shifts related to the motion of distinctive features with accuracies in the order of 1/20th of pixel. ...
  • ... This work was very time consuming and there were no possibilities for obtaining sub-pixel measurements. Scambos et al., (1992) was the first to perform image matching automatically on glaciers. They used image matching algorithms based on normalized cross- correlation (NCC). ...
    Article
    Glacier movement is a crucial factor for assessing cryospheric climate change. Traditional methods of field surveys for studying glacier movement and velocity are often not possible owing to inaccessibility and harsh terrains. Furthermore, as it is not feasible to physically monitor and survey many glaciers around the globe, these traditional methods are limited in their global coverage. Remote sensing is an ideal tool to study such phenomena on a global scale. Optical remote sensing employs techniques such as feature tracking and pixel tracking, whereas, microwave remote sensing uses intensity tracking, speckle tracking, Interferometric SAR and Differential InSAR (DInSAR). This study focuses on estimation of glacier velocity and its seasonal variations using the image-matching technique for optical images for the Fisher glacier, a tributary glacier of the Amery ice shelf in Antarctica. The tool used in this study is the COSI-Corr module embedded in ENVI which provides the velocity in both azimuth and range resolution. The principle of estimating velocity using this tool is pixel tracking wherein similar pixels on two images are tracked where one is the master image and the other is a slave. This technique correlates the master and slave images over a time period and generates three outputs: displacements in the East-West and North-South directions and signal-to-noise ratio (SNR) image. Landsat 8 image pairs were used for cross correlation over a time span of four years spanning 2013–2017. With a resolution of 15m, the panchromatic band (Band 8) was the ideal choice for pixel tracking as the resolution of other bands is coarser. The initial window size for correlation was 64 while the final window size was 16. The resolution of the displacement images produced is dependent on the value assigned for the step size, which was set to 8. The resultant velocity was derived using the result of the two displacement images. The SNR image was used to remove all the pixels from the velocity output having the value of SNR less than 0.9, in order to reduce the effect of noise. The annual velocity of the Fisher glacier was estimated to be around 600 to 650myr−1 near the tongue where it merges with the Amery Ice Shelf, which was reduced to 150myr−1 as it recedes. The resultant velocity images have a resolution of 120m. The seasonal variation in velocity for the year 2013–2014 is 1.8myr−1, while in the succeeding year 2014-2015 it subdued to 1.7myr−1. The seasonal variation for the year 2015–2016 was estimated to be 7.9myr−1. The seasonal variation for 2016–2017 was 17.4myr−1.
  • ... In this algorithm multiple il- lumination directions from the northern sectors are considered to optimize the interpretability of the shaded relief by omitting cast shadows and enhancing the contrast. Based on the shad- ed reliefs, landslide-induced changes are finally assessed using an image correlation technique (IMCORR; Scambos et al., 1992) implemented in SAGA GIS. ...
    Article
    Full-text available
    Terrestrial and airborne 3D imaging sensors are well-suited data acquisition systems for the area-wide monitoring of landslide activity. State-of-the-art surveying techniques, such as terrestrial laser scanning (TLS) and photogrammetry based on unmanned aerial vehicle (UAV) imagery or terrestrial acquisitions have advantages and limitations associated with their individual measurement principles. In this study we present an integration approach for 3D point clouds derived from these techniques, aiming at improving the topographic representation of landslide features while enabling a more accurate assessment of landslide-induced changes. Four expert-based rules involving local morphometric features computed from eigenvectors, elevation and the agreement of the individual point clouds, are used to choose within voxels of selectable size which sensor’s data to keep. Based on the integrated point clouds, digital surface models and shaded reliefs are computed. Using an image correlation technique, displacement vectors are finally derived from the multi-temporal shaded reliefs. All results show comparable patterns of landslide movement rates and directions. However, depending on the applied integration rule, differences in spatial coverage and correlation strength emerge.
  • ... Likewise, in this case DIC approaches can be used to quantify offsets caused by the deformation. This strategy was initially developed to study the rapid flow of large glaciers [19], but more and more often applied to slope instabilities and landslide events [20,21]. ...
    Article
    Full-text available
    We leverage on optical and radar remote sensing data acquired from the European Space Agency (ESA) Sentinels to monitor the surface deformation evolution on a large and very active instability located in the Swiss Alps, i.e., the Moosfluh rock slope. In the late summer 2016, a sudden acceleration was reported at this location, with surface velocity rates passing from maximum values of 0.2 cm/day to 80 cm/day. A dense pattern of uphill-facing scarps and tension cracks formed within the instability and rock fall activity started to become very pronounced. This evolution of the rock mass may suggest that the most active portion of the slope could fail catastrophically. Here we discuss advantages and limitations of the use of spaceborne methods for hazard analyses and early warning by using the ESA Sentinels, and show that in critical scenarios they are often not sufficient to reliably interpret the evolution of surface deformation. The insights obtained from this case study are relevant for similar scenarios in the Alps and elsewhere.
  • ... Afin de faciliter ce calcul, nous sommes généralement ramenés à réduire la dimensionnalité des images multispectrales. Par exemple, les bandes synthétiques telles que la première composante de l'Analyse en Composantes Principales (ACP) peuvent être utilisées (Scambos et al., 1992). Heid et Kääb (2012) ont pour leur part 12 Chapitre 2. Calcul et analyse de STCD à partir de STIS sélectionné simplement la bande panchromatique pour avoir une meilleure résolution par rapport aux autres bandes. ...
    Thesis
    Ce travail de thèse traite de la découverte de connaissances à partir de Séries Temporelles de Champs de Déplacements (STCD) obtenues par imagerie satellitaire. De telles séries oc- cupent aujourd’hui une place centrale dans l’étude et la surveillance de phénomènes naturels tels que les tremblements de terre, les éruptions volcaniques ou bien encore le déplacement des glaciers. En effet, ces séries sont riches d’informations à la fois spatiales et temporelles et peuvent aujourd’hui être produites régulièrement à moindre coût grâce à des programmes spatiaux tels que le programme européen Copernicus et ses satellites phares Sentinel.Nos propositions s’appuient sur l’extraction de motifs Séquentiels Fréquents Groupés (SFG). Ces motifs, à l’origine définis pour l’extraction de connaissances à partir des Sé- ries Temporelles d’Images Satellitaires (STIS), ont montré leur potentiel dans de premiers travaux visant à dépouiller une STCD. Néanmoins, ils ne permettent pas d’utiliser les indices de confiance intrinsèques aux STCD et la méthode de swap randomisation employée pour sélectionner les motifs les plus prometteurs ne tient pas compte de leurs complémentarités spatiotemporelles, chaque motif étant évalué individuellement.Notre contribution est ainsi double. Une première proposition vise tout d’abord à asso- cier une mesure de fiabilité à chaque motif en utilisant les indices de confiance. Cette mesure permet de sélectionner les motifs portés par des données qui sont en moyenne suffisam- ment fiables. Nous proposons un algorithme correspondant pour réaliser les extractions sous contrainte de fiabilité. Celui-ci s’appuie notamment sur une recherche efficace des occurrences les plus fiables par programmation dynamique et sur un élagage de l’espace de recherche grâce à une stratégie de push partiel, ce qui permet de considérer des STCD conséquentes. Cette nouvelle méthode a été implémentée sur la base du prototype existant SITS-P2miner, déve- loppé au sein du LISTIC et du LIRIS pour extraire et classer des motifs SFG.Une deuxième contribution visant à sélectionner les motifs les plus prometteurs est égale- ment présentée. Celle-ci, basée sur un critère informationnel, permet de prendre en compte à la fois les indices de confiance et la façon dont les motifs se complètent spatialement et tem- porellement. Pour ce faire, les indices de confiance sont interprétés comme des probabilités, et les STCD comme des bases de données probabilistes dont les distributions ne sont que par- tielles. Le gain informationnel associé à un motif est alors défini en fonction de la capacité de ses occurrences à compléter/affiner les distributions caractérisant les données. Sur cette base, une heuristique est proposée afin de sélectionner des motifs informatifs et complémentaires. Cette méthode permet de fournir un ensemble de motifs faiblement redondants et donc plus faciles à interpréter que ceux fournis par swap randomisation. Elle a été implémentée au sein d’un prototype dédié.Les deux propositions sont évaluées à la fois quantitativement et qualitativement en uti- lisant une STCD de référence couvrant des glaciers du Groenland construite à partir de données optiques Landsat. Une autre STCD que nous avons construite à partir de données radar TerraSAR-X couvrant le massif du Mont-Blanc est également utilisée. Outre le fait d’être construites à partir de données et de techniques de télédétection différentes, ces séries se différencient drastiquement en termes d’indices de confiance, la série couvrant le massif du Mont-Blanc se situant à des niveaux de confiance très faibles. Pour les deux STCD, les méthodes proposées ont été mises en œuvre dans des conditions standards au niveau consom- mation de ressources (temps, espace), et les connaissances des experts sur les zones étudiées ont été confirmées et complétées.
  • ... The accuracy of the co-registration is assessed by the statistics of the error distribution (Table 2). In order to compute 3D displacements of the rock glacier between each pair of DEMs (2006DEMs ( -2005DEMs ( , 2011DEMs ( -2006DEMs ( , 2012DEMs ( -2011DEMs ( and 2015DEMs ( -2012 note that the 2013 DEM appeared as too noisy and unfavorable for image correlation), the elevation grids were processed in the IMCORRmodule within SAGA-GIS [28,29]. The algorithm retrieves pixels pattern between two georeferenced images and produces shapefiles (points and lines) containing the 2D and 3D displacements. ...
    Article
    Full-text available
    Rock glaciers result from the long-term creeping of ice-rich permafrost along mountain slopes. Under warming conditions, deformation is expected to increase, and potential destabilization of those landforms may lead to hazardous phenomena. Monitoring the kinematics of rock glaciers at fine spatial resolution is required to better understand at which rate, where and how they deform. We present here the results of several years of in situ surveys carried out between 2005 and 2015 on the Laurichard rock glacier, an active rock glacier located in the French Alps. Repeated terrestrial laser-scanning (TLS) together with aerial laser-scanning (ALS) and structure-from-motion-multi-view-stereophotogrammetry (SFM-MVS) were used to accurately quantify surface displacement of the Laurichard rock glacier at interannual and pluri-annual scales. Six very high-resolution digital elevation models (DEMs, pixel size <50 cm) of the rock glacier surface were generated, and their respective quality was assessed. The relative horizontal position accuracy (XY) of the individual DEMs is in general less than 2 cm with a co-registration error on stable areas ranging from 20–50 cm. The vertical accuracy is around 20 cm. The direction and amplitude of surface displacements computed between DEMs are very consistent with independent geodetic field measurements (e.g., DGPS). Using these datasets, local patterns of the Laurichard rock glacier kinematics were quantified, pointing out specific internal (rheological) and external (bed topography) controls. The evolution of the surface velocity shows few changes on the rock glacier’s snout for the first years of the observed period, followed by a major acceleration between 2012 and 2015 affecting the upper part of the tongue and the snout.
  • Article
    Full-text available
    In this study, rapid topographic changes and high creeping rates caused by the destabilisation of an active rock glacier in a steep mountain flank were investigated in detail with five unmanned aerial vehicle (UAV) surveys between June 2016 and September 2017. State-of-the-art photogrammetric techniques were employed to derived high-density point clouds and high-resolution orthophoto mosaics from the studied landform. The accuracy of the co-registration of subsequent point clouds was carefully examined and adjusted based on comparing stable areas outside the rock glacier, which minimised 3-D alignment errors to a mean of 0.12 m. Elevation and volumetric changes in the destabilised rock glacier were quantified over the study period. Surface kinematics were estimated with a combination of image correlation algorithms and visual inspection of the orthophoto mosaics. Between June 2016 and September 2017, the destabilised part of the rock glacier advanced up to 60–75 m and mobilised a volume of around 27 000 m3 of material which was dumped over the lower talus slope. This study has demonstrated a robust and customisable monitoring approach that allows a detailed study of rock glacier geometric changes during a crisis phase.
  • Article
    Three satellite images of the northern Larsen Ice Shelf arc used to derive velocity fields for the periods 1975–86 and 1986 89. Substantial increases in the speed of the ice between these periods are detected to a high degree of confidence. Ice which entered the ice shelf between Fothergill Point and Cape Worsley and ice from Drygalski Glacier has accelerated by approximately 15% over the measurement period. Ice from Bombardier and Dinsmoor Glaciers also exhibits acceleration but by a lesser amount. These accelerations may be the result of either significant retreat experienced by the ice shelf during this period or warming in the Antarctic Peninsula region. Velocities measured by surface survey over a 15 d period in 1991 indicate a slower velocity than the image-derived velocities in the limited region of overlap. These differences appear to be systematic and may be the result of uncontrolled errors in the surface survey. Limited control of one image could also contribute to some of these differences.
  • Article
    A combination of image-based velocity mapping techniques and finite-element modeling has been used to study a part of the southern shear margin of Ice Stream D, Antarctica. The study area is a region over which the margin shows considerable development morphologically, where a new southern margin is forming in response to an abrupt increase in ice-stream width just upstream of the study area. A series of ice-speed profiles perpendicular to the margin was determined by semiautomated displacement measurements of small ice features in sequential Landsat TM images. Transverse speed gradients ∂u/∂y of these profiles were determined by calculating the slope of a high-order polynomial fit to the speed profiles. Maximum ice speed and ∂u/∂y increase dramatically as the margin develops in the downstream direction, from 420 to 670 mal,and from 0.02 to 0.16 a, respectively. Finite-element modeling of the upstream and downstream profiles suggests that a considerable change occurs in the stiffness of the ice in the marginal zone between the two profiles, and in the stiHness or amount of sliding in the basal layer underlying the margin. Ice in the downstream profile appears to have marginal zones of softer ice in which shear strain is concentrated and uniformly low resistance to deformation in the bed. For the upstream profile, modeling suggests that the ice is not softened near the margin and that the bed is stiffer near the margin. Model-based calculations suggest that the bed shear is responsible for 69% of the resistance to flow in the upstream margin area;this value is 51 % in the downstream area.
  • Article
    The velocity field of the confluence area of two large ice stream tributaries forming Ice Stream D in West Antarctica is studied using sequential Landsat images. Sequential satellite image analysis allows for a very high density of velocity measurements, based on computer-measured displacements of features such as crevasses, crevasse scars, and ice mounds recognizable in both images. Automated displacement measurement of these features results in a detailed map of surface velocities from which surface-horizontal strain-rate fields can be calculated. Correlations between the surface morphology, the velocity field, and the strain-rate field of Ice Stream D reveal a number of important characteristics of ice stream flow: • the characteristic flowband appearance of streaming ice is present at velocities from below 100 m a−1 to above 350 m a−1; • in the upstream areas, there appears to be no sharp transition between “sheet” flow, typical of the surrounding ice sheet, and “streaming” flow; • the fastest moving portions of the ice stream are nearly devoid of surface topography undulations; • the confluence area is characterized by acceleration of the ice in the slower tributary as it impinges on faster-moving ice, and by highly convergent flow. Velocity in the faster-moving tributary changes little, and there is no persistent evidence of the shear margins of the joined tributaries downstream of the confluence. This study demonstrates that sequential satellite image analysis, coupled with computer-determined displacement measurements, can provide accurate velocity and strain-rate information on a regional scale rapidly and cost-effectively. Such data sets are required for modelling ice sheet evolution, and for monitoring any changes in ice flow within the ice streams.
  • Article
    In spite of their importance to global climate and sea level, the mass balance of the Antarctic ice sheet and the dynamics of the coast of Antarctica are largely unknown. In 1990, the U.S. Geological Survey, in cooperation with the Scott Polar Research Institute. U.K., began a long-term coastal mapping project in Antarctica that is based on analysis of Landsat images and ancillary sources. The project has live objectives: (1) to determine coastline changes that have occurred between the mid-1970s and the late 1980s/early 1990s; (2) to establish an accurate base-line series of 24 1: 1 000 000 scale maps that define the glaciological characteristics of the coastline: (3) to determine velocities of outlet glaciers, ice streams and ice shelves: (4) to compile a comprehensive inventory of outlet glaciers and ice streams: and (5) to compile a 1: 5 000 000 scale map of Antarctica derived from the 24 maps. Analysis of images used in producing the first five of the 24 maps has shown that ice fronts, iceberg tongues and glacier tongues are the most dynamic and changeable features in the coastal regions of Antarctica. Seaward of the grounding line of outlet glaciers, ice streams and ice shelves, the floating margin is subject to frequent, large calving events and rapid flow. Although calving does occur along ice walls, the magnitude of their change on an annual to decadal basis is generally not discernible on Landsat images; therefore, ice walls can be used as relatively stable reference features for measuring other changes along the coast. Velocities of outlet glaciers, ice streams and ice shelves range from 0.1 to several kilometers per year.
  • Article
    Full-text available
    A field of vectors showing the average velocity of the surging glacier Osbornebreen, Svalbard, was determined by comparing sequential SPOT (Système pour l’Observation de la Terre) and Landsat thematic mapper images. Crevasses which developed during the initial phase of the surge in the winter of 1986–87 were tracked using a fast Fourier chip cross-correlation technique. A digital elevation model (DEM) was developed using digital photogrammetry on aerial photographs from 1990. This new DEM was compared with a map drawn in 1966. The velocity field could be almost entirely determined with 1 month separation of the images, but only partly determined with images 1 year apart, due to changes of the crevasse pattern. The velocity field is similar to that found for Kronebreen, a continuously fast-moving tidewater glacier. No distinct zones of compressive flow were present and the data gave no evidence of a compression zone/surge front traveling downstream. The velocity field, the rapid advance of the terminus and the development of transverse crevasses in the upper accumulation area within a 6 month period may indicate that the surge developed as a zone of extension starting near the terminus and propagating quickly upstream. The crevasse pattern in the images is therefore interpreted to be the result of the extension zone traveling upstream, and, as the whole glacier starts to slide, the crevasse pattern alters according to the bedrock topography.
  • Article
    Advanced very high-resolution radiometer (AVHRR) images and a radar-altimetry-based digital elevation model (DEM) covering part of the northeast Greenland ice stream are combined to create an improved topographic map of the area using photoclinometry. In this application of photoclinometry, a DEM is used to establish the photometric relationship for two AVHRR images of a snow surface. Slopes from the DEM are compared with AVHRR data that are filtered (i.e. blurred) to the resolution of the DEM to give an empirical photometric determination. This is then used to convert unfiltered AVHRR data into quantitative slope measurements of the surface in the along-sun direction in each image, resolving features not present (or poorly represented) in the DEM. Co-registration of the images is based on the assumption that the two slope fields from the images describe one continuous smooth surface. The combined slopes are then converted to topography. In the test case, the technique adds topographic details with spatial scales of ~3 to ~20 km. A comparison of our results with airborne laser elevation profiles demonstrates that the new technique recovers most of the topography that is missed by the DEM. The improved topographic map reveals a ten-fold increase in local surface relief over the ice-stream feature, and shows the presence of shallow troughs over the shear margins of the feature.
  • Article
    We use surface velocity derived from sequential Landsat imagery and a control method to estimate the basal-friction distribution of a major West Antarctic ice stream. The area-averaged basal stress is approximately 1.4 × 104 Pa, or about 29% of the area-averaged driving stress of 4.9 × 104 Pa. Uncertainty of the derived area-averaged basal stress is difficult to assess and depends primarily on spatial variation of the flow-law rate factor in the constitutive law. Spatial variation associated with depth-averaged temperature variation gives an uncertainty of approximately ±103 Pa. Approximately 60% of the ice stream has a basal-stress magnitude less than 104 Pa, and approximately 30% has less than 103 Pa. These characteristics suggest the presence of a mechanically weak, water-charged subglacial till. Small-scale sticky spots where basal friction exceeds the area-averaged driving stress are scattered irregularly across the subglacial regime and comprise approximately 15% of the ice-stream area. Sticky spots cluster in regions where Landsat imagery suggests structural features in the underlying bedrock.
  • Article
    Landsat multispectral scanner and thematic mapper images were co-registered For the Kangerdlugssuaq Fjord region in East Greenland and were used to map glacier drainage-basin areas, changes in the positions of tide-water glacier termini and to estimate surface velocities of the larger tide-water glaciers. Statistics were compiled to document distance and area changes to glacier termini. The methodologies developed in this study are broadly applicable to the investigation of tide-water glaciers in other areas. The number of images available for consecutive years and the accuracy with which images are co-registered are key factors that influence the degree to which regional glacier dynamics can be characterized using remotely sensed data. Three domains of glacier state were interpreted: net increase in terminus area in the southern part of the study area, net loss of terminus area for glaciers in upper Kangerdlugssuaq Fjord and a slight loss of glacier terminus area northward from Ryberg Fjord. Local increases in the concentrations of drifting icebergs in the fjords coincide with the observed extension of glacier termini positions Ice-surface velocity estimates were derived for several glaciers using automated image cross-correlation techniques The velocity determined for Kangerdlugssuaq Gletscher is approximately 5.0 km a−1 and that for Kong Christian IV Gletscher is 0.9 km a−1. The continuous presence of icebergs and brash ice in front of these glaciers indicates sustained rates of ice-front calving.
  • Article
    The combined application of continuous GPS data (high temporal resolution) with spaceborne interferometric synthetic aperture radar (InSAR) data (high spatial resolution) can reveal much more about the complexity of large landslide movement than is possible with geodetic measurements tied to only a few specific measurement sites. This approach is applied to a ~4 km2 reactivated translational landslide in the Columbia River Gorge (Washington State), which moves mainly during the winter rainy season. Results reveal the complex three-dimensional shape of the landslide mass, how onset of sliding relates to cumulative rainfall, how surface velocity during sliding varies with location on the topographically complex landslide surface, and how the ground surface subsides slightly in weeks prior to downslope sliding.
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    Satellite observations have transformed our understanding of the Antarctic cryosphere. The continent holds the vast majority of Earth's fresh water, and blankets swathes of the Southern Hemisphere in ice. Reductions in the thickness and extent of floating ice shelves have disturbed inland ice, triggering retreat, acceleration and drawdown of marine-terminating glaciers. The waxing and waning of Antarctic sea ice is one of Earth's greatest seasonal habitat changes, and although the maximum extent of the sea ice has increased modestly since the 1970s, inter-annual variability is high, and there is evidence of longer-term decline in its extent.
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    In the present study we estimate the velocity and thickness of the Patseo glacier, Himachal Pradesh, India. The average velocity of the glacier was estimated as ~5.47 m/year using co-registration of optically sensed images and correlation (COSI-Corr) method. The glacier thickness was found to vary between 12 and 278 m, with an average value 59 m. The total glacier ice volume was estimated as ~15.8 × 10 7 m 3 , with equivalent water reservoir of ~14.5 × 10 7 m 3. Ground penetrating radar (GPR) surveys were conducted during 2004 and 2013 for validation of the estimated glacier thickness. The glacier thickness estimated using COSI-Corr method was found to be in agreement with GPR-retrieved glacier thickness (RMSE = 4.75 m; MAE = 3.74 m). The GPR profiles collected along the same geographic locations on the glacier during 2004 and 2013 showed a reduction in ice thickness of ~1.89 m, and thus resulting in an annual ice thickness decrease of ~0.21 m. The glacier area was estimated for 2004 and 2013 using LISS IV satellite data and found to be ~2.52 and ~2.30 sq. km respectively. This shows an annual reduction of ~0.024 sq. km in glacier area. The total annual loss in glacier ice volume was estimated as ~4.55 × 10 5 m 3. This loss in the glacier ice volume of the Patseo glacier is supported by the snow and meteorological observations collected at a nearby field observatory of Snow and Avalanche Study Establishment (SASE). The climate data collected at SASE meteorological observatory at Patseo (3800 m), between 1993-94 and 2014-15 showed an increasing trend in the mean annual temperature and a decreasing trend in winter precipitation .
  • Article
    This paper presents a novel method for modeling and robustly estimating the time-series 3-D mining-induced large displacements from a single imaging geometry (SIG) synthetic aperture radar (SAR) amplitude data set using the offset-tracking (OT) technique (hereafter referred to as the OT-SIG). It first generates multitemporal observations of 3-D mining-induced displacements from the single-geometry SAR amplitude data set with the assistance of a prior model. Then, a functional relationship between mining-induced time-series 3-D displacements and the multitemporal 3-D deformation observations generated is constructed. Finally, the time-series 3-D displacements are robustly estimated based on the constructed function model using the M-estimator. The proposed OT-SIG provides a robust and cost-effective tool for retrieving time-series 3-D mining-induced large displacements, relaxing the basic requirement of the traditional method that at least two different viewing geometries' SAR data are needed. Finally, we tested the proposed OT-SIG with descending TerraSAR-X SAR amplitude data set over the Daliuta coal mining area in China. The results show that the root-mean-square errors (RMSEs) of OT-SIG-estimated time-series displacements are about 0.22 and 0.11 m in the vertical and horizontal directions, respectively. These RMSEs are around 5.7% and 10.9% of the maximum in situ deformation measurements in the corresponding directions, which can meet the accuracy requirements of practical applications.
  • Article
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    Satellite images were analyzed to measure the frontal positions and ice speeds of 19 marine-terminating outlet glaciers along the coast of Prudhoe Land, northwestern Greenland from 1987 to 2014. All the studied glaciers retreated over the study period at a rate of between 12 and 200 m a ⁻¹ , with a median (mean) retreat rate of 30 (40) m a ⁻¹ . The glacier retreat began in the year ~2000, which coincided with an increase in summer mean air temperature from 1.4 to 5.5 °C between 1996 and 2000 in this region. Ice speed near the front of the studied glaciers ranged between 20 and 1740 m a ⁻¹ in 2014, and many of them accelerated in the early 2000s. In general, the faster retreat was observed at the glaciers that experienced greater acceleration, as represented by Tracy Glacier, which experienced a retreat of 200 m a ⁻¹ and a velocity increase of 930 m a ⁻¹ during the study period. A possible interpretation of this observation is that flow acceleration induced dynamic thinning near the termini, resulting in enhanced calving and rapid retreat of the studied glaciers. We hypothesize that atmospheric warming conditions in the late 1990s triggered glacier retreat in northwestern Greenland since 2000.
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    We evaluate the capability of three different digital image correlation (DIC) algorithms to measure long-term surface displacement caused by a large slope instability in the Swiss Alps. DIC was applied to high-resolution optical imagery taken by airborne sensors, and the accuracy of the displacements assessed against global navigation satellite system measurements. A dynamic radiometric correction of the input images prior to DIC application was shown to enhance both the correlation success and accuracy. Moreover, a newly developed spatial filter considering the displacement direction and magnitude proved to be an effective tool to enhance DIC performance and accuracy. Our results show that all algorithms are capable of quantifying slope instability displacements, with average errors ranging from 8–12% of the observed maximum displacement, depending on the DIC processing parameters, and the pre- and postprocessing of the in- and output. Among the tested approaches, the results based on a fast Fourier transform correlation approach provide a considerably better spatial coverage of the displacement field of the slope instability. The findings of this study are relevant for slope instability detection and monitoring via DIC, especially in the context of an ever-increasing availability of high-resolution air- and spaceborne imagery. The FFT-based DIC algorithm as well as all described pre- and postprocessing routines are available under the MIT license at: https://github.com/bickelmps/DIC_FFT_ETHZ and https://de.mathworks.com/matlabcentral/fileexchange/67273-dic-fft-ethz
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    Terrestrial time-lapse photogrammetry is a rapidly growing method for deriving measurements from glacial environments because it provides high spatio-temporal resolution records of change. However, glacial photogrammetry toolboxes are limited currently. Without prior knowledge in photogrammetry and computer coding, they are used primarily to calculate ice flow velocities or to serve as qualitative records. PyTrx (available at https://github.com/PennyHow/PyTrx) is presented here as a Python-alternative toolbox to widen the range of photogrammetry toolboxes on offer to the glaciology community. The toolbox holds core photogrammetric functions for point seeding, feature-tracking, image registration, and georectification (using a planar projective transformation model). In addition, PyTrx facilitates areal and line measurements, which can be detected from imagery using either an automated or manual approach. Examples of PyTrx's applications are demonstrated using time-lapse imagery from Kronebreen and Tunabreen, two tidewater glaciers in Svalbard. Products from these applications include ice flow velocities, surface areas of supraglacial lakes and meltwater plumes, and glacier terminus profiles.
  • Book
    Cambridge Core - Climatology and Climate Change - Polar Environments and Global Change - by Roger G. Barry
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    Ice shelves play an important role in buttressing land ice from reaching the sea, thus restraining the rate of grounded ice loss. Long-period gravity-wave impacts excite vibrations in ice shelves that can expand pre-existing fractures and trigger iceberg calving. To investigate the spatial amplitude variability and propagation characteristics of these vibrations, a 34-station broadband seismic array was deployed on the Ross Ice Shelf (RIS) from November 2014 to November 2016. Two types of ice-shelf plate waves were identified with beamforming: flexural-gravity waves and extensional Lamb waves. Below 20 mHz, flexural-gravity waves dominate coherent signals across the array and propagate landward from the ice front at close to shallow-water gravity-wave speeds (~70 m s ⁻¹ ). In the 20–100 mHz band, extensional Lamb waves dominate and propagate at phase speeds ~3 km s ⁻¹ . Flexural-gravity and extensional Lamb waves were also observed by a 5-station broadband seismic array deployed on the Pine Island Glacier (PIG) ice shelf from January 2012 to December 2013, with flexural wave energy, also detected at the PIG in the 20–100 mHz band. Considering the ubiquitous presence of storm activity in the Southern Ocean and the similar observations at both the RIS and the PIG ice shelves, it is likely that most, if not all, West Antarctic ice shelves are subjected to similar gravity-wave excitation.
  • Article
    Full-text available
    Deep-seated gravitational slope deformations (DSGSDs) endanger settlements and infrastructure in mountain areas all over the world. To prevent disastrous events, their activity needs to be continuously monitored. In this paper, the movement of the Reissenschuh DSGSD in the Schmirn valley (Tyrol, Austria) is quantified based on point clouds acquired with a Riegl VZ®-6000 long-range laser scanner in 2016 and 2017. Geomorphological features (e.g., block edges, terrain ridges, scarps) travelling on top of the landslide are extracted from the acquired point clouds using morphometric attributes based on locally computed eigenvectors and -values. The corresponding representations of the extracted features in the multi-temporal data are exploited to derive 3D displacement vectors based on a workflow exploiting the iterative closest point (ICP) algorithm. The subsequent analysis reveals spatial patterns of landslide movement with mean displacements in the order of 0.62 ma − 1 , corresponding well with measurements at characteristic points using a differential global navigation satellite system (DGNSS). The results are also compared to those derived from a modified version of the well-known image correlation (IMCORR) method using shaded reliefs of the derived digital terrain models. The applied extended ICP algorithm outperforms the raster-based method particularly in areas with predominantly vertical movement.
  • Thesis
    Full-text available
    In high mountain environment, changing boundary conditions from climate change such as melting glaciers and permafrost retreat influence the stability of alpine soil and rock slopes. Slope deformation processes are complex and a sound understanding is a prerequisite to investigate the impact of changing climatic conditions and to predict the future behaviour as well as to develop safety measures. The thesis aims to exploit all information about landslide deformation behaviour and processes from imagery and laser scanning data which are required to understand past and present landslide evolution. Already existing and new deformation analyses methods are applied, improved and developed with the aim to i) analyse the retrospective landslide development over a longer time period and ii) to analyse the current landslide behaviour by appropriate and ongoing monitoring methods. Laser scanning and imagery data are well suited for this task because the data is available in national, federal and local archives of most Alpine countries and the sensors are applicable for the monitoring campaigns in rough mountain environment with no direct access to infrastructure. In the frame of this study, two active high alpine deep-seated rock compound slides and an active rock glacier were investigated. The three study sites are located in the Eastern Alps, Austria, and differ in their topography as well as process characteristics. For process and deformation analyses, the data from airborne and imaging campaigns was collected and field campaigns with terrestrial laser scanning and UAV were performed. The data from different sources were pre-processed to a geo-referenced point cloud, respectively to a geo-referenced ortho-image and then compiled into a common coordinate reference system. Slope deformation processes with a destruction of the surface, e.g. due to rock fall, were analysed by means of a robust 3D distance measurement approach for point cloud data. Slope processes with en-block displacements (e.g. slides) were analysed by applying an image correlation and breakline tracking technique. The derived distance change and displacement maps, together with information from field surveys and terrestrial photographs, were used for interpretation. This includes i) the identification of different landslide processes (i.e. rock and soil slide displacements, rock fall, rock avalanches, rock glacier creep, debris slides etc., ii) the delineation of different slabs (rock slide) or zones (rock glacier) and analyses of their activity, geometry and kinematics and iii) the interpretation of the failure mechanism (e.g. toppling or rotational sliding behaviour). The extracted information was used to develop a geological model of the slope deformation. The analyses show that both rock slides are composed of different slabs with different spatial and temporal deformation behaviour. For the ice contacted rock slide, the glacier retreat was reconstructed since the 1950s based on imagery, laser scanning data and historic topographic maps. The results show a correlation between glacier retreat and rock slide activity. The rock glacier deformation behaviour was reconstructed since the 1970s and showed an increase in creep velocity since the end of the last century. The results derived with the methods and workflows developed in this thesis focusing on the kinematics and the geometry of the landsides could serve as input to study the impact of permafrost degradation and glacier retreat on landslides e.g., by numerical modelling. The results are further an essential contribution to assess the risk in the context of infrastructure, to design safety measures, and to predict the future deformation development.
  • Conference Paper
    Full-text available
    The monitoring of inland water and continental ice sheets is very important from water management and global climate related studies. The current study utilizes the SGDR data from Saral-Altika during 2013-2017 to estimate and monitor water level in 24 major reservoirs of India. The R2 value for majority of reservoirs was more than 0.99 and RMSE error value also was less than 0.40 m. In addition, wide rivers of India such as Mahanadi River, was also monitored using Altika data covering part of Mahanadi River from Khairmal to Naraj gauging sites during 2013-2016 time period. One dimensional hydro-dynamic (1D-HD) model was setup for this part of river to generate river Discharge at virtual gauge. The part of Antarctic ice sheet South of Indian research station Maitri, East Antarctica, was studied for ice sheet elevation changes using ground based stake network as well as space based altimeter/LIDAR datasets during 2003-2017 time period. 2003-2009 time was used for getting elevation changes using Icesat-1 level 2 altimetry product, and Geophysical Data Record (GDR) data from Altika was used with slope correction from 2013-2016 time period. An extensive network of ground based stake networks were used for validating the derived elevation changes. The ice sheet and glacier line of site velocity was estimated using Sentinel-1 based InSAR data with 6 to 12 day time interval data sets for year 2016 and 2017. The derived glacier velocity was comparable with optical image (Landsat-8) based glacier velocity for same year and also with historical Radarsat-1 based glacier velocity results.
  • Article
    Mountain glacier is one of the extremely sensitive indicators for climate change, and its surface motion distribution and corresponding variation are valuable information for understanding ice mass exchange and glacier dynamics. This paper presents the long-term ice velocity distributions of Inylchek Glacier in the Tianshan region by pixel-tracking algorithm with time-series Landsat imagery acquired during 2006–2016. Then the monitored ice motion fields of Inylchek Glacier were carefully analyzed and revealed a generally similar spatial distribution characteristic. Most of the ice of the North Inylchek Glacier remains in a stagnant state except for the upstream part, but a relatively high velocity of 20–40 cm/day with an RMSE of 3 cm/day was observed on most part of the South Inylchek Glacier, except for the slow-moving glacier terminus. We also state the glacier dynamics around Lake Merzbacher and their possible effect on its glacier lake outburst flood (GLOF) risk. Besides, the surface velocity distribution on South Inylchek Glacier surface during the ablation period from 2014 to 2016 was also established and also compared with annual velocity. The corresponding difference yields that there is a positive relation between ice motion and temperature variation. Therefore, the time-series ice surface motion yielded by the Landsat imagery thus could provide us an efficient and low-cost way to analyze the current state and changes in glaciers, thanks to the continuous and regular spaceborne observations provided by the Landsat satellites.
  • Chapter
    Proglacial areas represent transitional zones between glacial and periglacial landscapes. Non-glacial processes in the proglacial zone might evolve under periglacial conditions, and vice versa periglacial processes often occur in proglacial zones. Hence, periglacial morphodynamics constitute an inherent part of proglacial studies and are therefore presented here in the context of the research project PROSA. To get an overview of periglacial morphodynamics in the Upper Kaunertal, we (i) established a permafrost model based on BTS measurements, (ii) analysed meteorological data in order to verify ground indications for thermal-contraction cracking and (iii) analysed both geophysical and remote sensing data for the identification of permafrost creep and thermokarst phenomena. In addition, this chapter includes a case study on the morphodynamics of a complex rock glacier in the Riffltal, a tributary valley to the Upper Kaunertal. Results show a diverse genesis and development of different rock glacier parts and lobes, which are mainly related to glacial advances during the Egesen and LIA stadials. More recent developments are largely dependent on (i) sediment sources and pathways constituting diverse states of activity, (i) dynamic interactions between the tongues and (iii) the topographic surrounding, that is already causing dynamic inactivity of parts of the rock glacier.
  • Chapter
    This chapter presents the sediment budget of the Upper Kaunertal (Kauner valley, Ötztal Alps, Austria) for the years 2012–2014 as obtained in the framework of the PROSA (high-resolution measurements of morphodynamics in rapidly changing PROglacial Systems of the Alps) research project. An important methodological basis of this high-mountain sediment budget is the usage of study area-wide LiDAR data (TLS and ALS) of comparatively high temporal and spatial resolution to measure rates of erosion and deposition, and to regionalize/upscale rates at the local scale. After several billion measurement points and data from fieldwork, mapping, and modeling efforts had been processed and evaluated, it was possible to identify and quantify sediment transfer by all relevant processes at the scale of the 62 km² study area. These processes include rockfall of three different magnitude classes, debris flows, avalanches, creep on talus, fluvial processes (hillslopes and main fluvial system), rock glaciers, and glaciers. After a short presentation of the process-specific methods to obtain catchment-wide rates, we discuss process-specific results and the budget. The sediment budget does not only show the relative importance of the mentioned processes and spatial subunits (proglacial vs. non-proglacial) in the Upper Kaunertal. It also gives insight into the importance of high-magnitude events and the configuration of the sediment transport system.
  • Article
    The methodical bases and some results of using satellite radiothermovision to study global atmospheric latent heat circulation according to the data of regular satellite radiothermal monitoring are described. This approach does not use an a priori model of circulation; it implements an objective procedure for the analysis of the dynamics of periodically measured fields of total precipitable water. The reconstructed directions and the values of the mean-zonal transport velocity, the average position of the thermal equator at ~5° N, and the positions of the axis of the intertropical convergence zone over individual oceans are very consistent with the known results of independent observations and numerical modeling. Some problematic aspects of the analysis procedure are discussed.
  • Article
    Radar interferometry, ice-penetrating radar profiles and an elevation model are used to determine the velocity fields, rates of ice discharge, approximate states of balance and catchment area for three large outlet glaciers in northeast Greenland. Discharge through flux gates is calculated for Humboldt and Petermann Gletscher, which are found to be in balance (at the level that the accumulation is known). A large difference between the measured and estimated fluxes for Ryder Gletscher may be a reflection of unsteady flow behavior for this glacier. The patterns of ice flow for the three glaciers considered are each unique, showing that the nature of ice discharge varies substantially from basin to basin, controlled by bed conditions and the presence of subglacial troughs and obstructions.
  • Article
    Ten Landsat Thematic Mapper images together show Ice Streams E, D and most of Ice Stream C on Siple Coast, West Antarctica. The images are interpreted to reveal aspects of both spatial and temporal evolution of the ice streams. Onset of ice-stream flow appears to occur at distributed sites within the ice-stream catchment, and the apparent enhanced flow continues in channels until they join, forming the main ice stream. Most crevassing on these ice streams is associated with features of horizontal dimensions between 5 and 20 km. We suggest these features are caused by bed structures which may be an important source of restraint to ice flow, similar to ice rumples on ice shelves. A pattern of features near the grounding line of the now-stagnant Ice Stream C are interpreted as having formed because there was a period of reduced flux before the ice stream stopped.
  • Article
    A description of digital image corrections and the techniques for performing such corrections is introduced. A brief description of optical and electro-optical image processing is provided. Finally, a detailed discussion of the need to correct or process the data, the sources of image errors, techniques for image correction and a definition of the equations used to correct the data are given.-M.Alam
  • Article
    A simple method for the cosmetic removal of scan-line noise from geometrically corrected Landsat Thematic Mapper data is presented. The method used only standard spatial filters and arithmetic routines that are already present on most image processing systems. Examples are provided, and the possible effects upon image signal are discussed. -Author
  • Article
    Digitally enhanced Landsat Thematic Mapper (TM) images of Antarctica reveal snow and ice features to a detail never seen before in satellite images. The six TM reflective spectral bands have a nominal spatial resolution of 30 m, compared to 80 m for the Multispectral Scanner (MSS). TM bands 2–4 are similar to the MSS bands. TM infra-red bands 5 and 7 discriminate better between clouds and snow than MSS or the lower TM bands. They also reveal snow features related to grain-size and possibly other snow properties. These features are not observed in the visible wavelengths. Large features such as flow lines show best in the MSS and lower TM bands. Their visibility is due to photometric effects on slopes. TM thermal band 6 has a resolution of 120 m. It shows ground radiation temperatures and may serve to detect liquid water and to discriminate between features having similar reflectivities in the other bands, such as blue ice. Repeated Landsat images can be used for sophisticated glaciological studies. By comparing images from 1975 and 1985, flow rates averaging 0.72 km a ⁻¹ , and mean longitudinal and transverse strains of respectively 1.3 × 10 ⁻⁴ a ⁻¹ and 130 × 10 ⁻⁴ a ⁻¹ have been measured for Jutulstraumen, Dronning Maud Land.
  • Article
    Apparent ice-surface topography is observed at several scales on Landsat multi-spectral scanner (MSS) imagery. Digitally enhanced MSS scenes from Antarctica and Nordaustlandet, Svalbard, are compared with ice-surface elevations from aircraft altimetry (relative accuracy 2-3 m) to show that this apparent topography is real. Apparent ice divides on Landsat images fit closely with divides on alti­ metric records. Ice-surface irregularities within drainage basins are also shown to be real. On Byrd Glacier, Antarctica, apparent "flow lines" coincide with ridges on altimetric records. Synoptic Landsat data, calibrated by information from aircraft altimetric flight lines, are used to classify the surface roughness of the ice caps on Nordaustlandet and 40% of the Antarctic ice sheet. On Nordaustlandet, the roughest ice is of amplitude 15-25 m and wavelength 3-4.5 km. Drainage basins with such rough surface cha racteristics may be associated with ice streams or possibly past surge activity. The most rough Antarctic terrain is up to 60 m in amplitude, with wavelengths of
  • Article
    Results art, presented of spectral analyses of the surface and bedrock profiles along a flow line of the Wilkes ice cap and the surface along the Greenland E.G.I.G. profile. Although the bedrock appears irregular over all was velengths studied, the ice-cap surface is typically characterized by a smooth curve with small-scale surface undulations superimposed on it. The following relations of Budd (1969, 19701 are confirmed. The “damping factor" or ratio of the bedrock amplitude to the surface amplitude is a minimum for wavelengths λ about 3.3 times the ice thickness. The surface lags the bed in the direction of motion by λ/4. The magnitude of the minimum damping factor φ m is typically least near the coast, and increases inland depending on the ice thickness Z , the velocity V , and the mean ice viscosity η (which is a function of stress and temperature) according to where p is the mean ice density and g is the gravitational acceleration. Thus the determination of the damping factors provides a valuable means of estimating the ice flow parameter η .
  • Article
    Satellite images showing the disintegration of the Wordie Ice Shelf, which lies off the west coast of the Antarctic Peninsula, are presented. Fracture, either in the form of surface crevasses or rifts extending to the bottom of the ice shelf, has been responsible for iceberg calving and weakening the central region of the ice shelf. These fracture processes, which led to retreat of the ice front, were apparently enhanced by the presence of increased amounts of melt water, resulting from a warming trend recorded in mean annual air temperatures in Marguerite Bay. If this warming trend continues, other nearby ice shelves on the Antarctic Peninsula may be at risk. But substantial additional warming would be required before similar processes could initiate breakup of the Ross and Filchner-Ronne ice shelves, which help stabilize the West Antarctic ice sheet.
  • Article
    A portion of AVHRR data taken on December 5, 1987 at 06:15 GMT over a part of Antarctica is used here to show that many of the most significant dynamic features of ice sheets can be identified by a careful examination of AVHRR imagery. The relatively low resolution of this instrument makes it ideal for obtaining a broad view of the ice sheets, while its wide swath allows coverage of areas beyond the reach of high-resolution imagers either currently in orbit or planned. An interpretation is given of the present data, which cover the area of ice streams that drain the interior of the West Antarctic ice sheet into the Ross Ice Shelf.
  • Article
    Full-text available
    The surface velocity of a rapidly moving ice stream has been determined to high accuracy and spatial density with the use of sequential satellite imagery. Variations of ice velocity are spatially related to surface undulations, and transverse velocity variations of up to 30 percent occur. Such large variations negate the concept of plug flow and call into question earlier mass-balance calculations for this and other ice streams where sparse velocity data were used. The coregistration of images with the use of the topographic undulations of the ice stream and the measurement of feature displacement with cross-correlation of image windows provide significant improvements in the use of satellite imagery for ice-flow determination.
  • Article
    Many Landsat images of Antarctica show distinctive flow and crevasse features in the floating part of ice streams and outlet glaciers immediately below their grounding zones. Some of the features, which move with the glacier or ice stream, remain visible over many years and thus allow time-lapse measurements of ice velocities. Measurements taken from Landsat images of features on Byrd Glacier agree well with detailed ground and aerial observations. The satellite-image technique thus offers a rapid and cost-effective method of obtaining average velocities, to a first order of accuracy, of many ice streams and outlet glaciers near their termini.
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