A processing system to monitor Greenland outlet glacier velocity variations at decadal and seasonal time scales utilizing the Landsat imagery

Rosenau, Ralf; Scheinert, Mirko; Dietrich, Reinhard

doi:10.1016/j.rse.2015.07.012

Cited by 73 publications

(76 citation statements)

References 84 publications

(118 reference statements)

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“…Here we propose a value of 1.5 for regions where we expect little changes between the a-priori velocity field and the raw input velocities. The number of elements in a segment to be accepted, n min = 8, is already proposed in [9]. We can confirm this in Section 3.2, however, the result for n min between four and twelve seem to be very similar.…”

Section: Discussionsupporting

confidence: 70%

“…Our sensitivity analysis showed that a value between 0.2 and 0.4 removes most erroneous data points ( Figure A3). The factor w is designated to account for possible temporal changes between the a-priori velocity field and the satellite derived velocity field [9]. It is therefore highly dependent on the expected changes in the study region.…”

Section: Discussionmentioning

confidence: 99%

“…The first one divides the field into parts recursively, which are smooth within themselves, and was introduced by Rosenau et al [9]. In the second step, the remaining outliers are removed by a filter using the median of the field.…”

Section: Description Of the Filtermentioning

confidence: 99%

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A Combined Approach for Filtering Ice Surface Velocity Fields Derived from Remote Sensing Methods

2017

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Abstract:Various glaciological topics require observations of horizontal velocities over vast areas, e.g., detecting acceleration of glaciers, as well as for estimating basal parameters of ice sheets using inverse modelling approaches. The quality of the velocity is of high importance; hence, methods to remove noisy points in remote sensing derived data are required. We present a three-step filtering process and assess its performance for velocity fields in Greenland and Antarctica. The filtering uses the detection of smooth segments, removal of outliers using the median and constraints on the variability of the flow direction over short distances. The applied filter preserves the structures in the velocity fields well (e.g., shear margins) and removes noisy data points successfully, while keeping 72-96% of the data. In slow flowing regions, which are particularly challenging, the standard deviation is reduced by up to 96%, an improvement that affects vast areas of the ice sheets.

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Section: Discussionsupporting

confidence: 70%

Section: Discussionmentioning

confidence: 99%

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A Combined Approach for Filtering Ice Surface Velocity Fields Derived from Remote Sensing Methods

2017

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“…These processes of interest often occur in either inaccessible or dangerous locations (e.g., due to icefall) which favors remote sensing methods. In particular the Landsat-archive is a popular resource for worldwide glacier velocity estimation [4], due to its long history and free availability [5,6]. Nonetheless, for many applications, the matching of whiskbroom (up to Landsat 7) and pushbroom sensors (Landsat 8) is limited to acquisitions from the same relative orbit.…”

Section: Introductionmentioning

confidence: 99%

“…As such, the repeat data are acquired with similar looking angles, and differential displacements from orthorectification offsets in the different images are minimized due to vertical DEM errors. Alternatively, the orthoprojection discrepancy can be adjusted by remapping, for instance with the help of elevation data [6]. However, in many cases there will be a difference between the DEM used for orthorectification and the true elevation at acquisition time as glaciers are dynamic topographic features that may exhibit vertical changes of many meters per year.…”

Section: Introductionmentioning

confidence: 99%

Elevation Change and Improved Velocity Retrieval Using Orthorectified Optical Satellite Data from Different Orbits

Altena

Kääb

2017

Remote Sensing

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Abstract:Optical satellite products are available at different processing levels. Of these products, terrain corrected (i.e., orthorectified) products are the ones mostly used for glacier displacement estimation. For terrain correction, a digital elevation model (DEM) is used that typically stems from various data sources with variable qualities, from dispersed time instances, or with different spatial resolutions. Consequently, terrain representation used for orthorectifying satellite images is often in disagreement with reality at image acquisition. Normally, the lateral orthoprojection offsets resulting from vertical DEM errors are taken into account in the geolocation error budget of the corrected images, or may even be neglected. The largest offsets of this type are often found over glaciers, as these may show strong elevation changes over time and thus large elevation errors in the reference DEM with respect to image acquisition. The detection and correction of such orthorectification offsets is further complicated by ice flow which adds a second offset component to the displacement vectors between orthorectified data. Vice versa, measurement of glacier flow is complicated by the inherent superposition of ice movement vectors and orthorectification offset vectors. In this study, we try to estimate these orthorectification offsets in the presence of terrain movement and translate them to elevation biases in the reference surface. We demonstrate our method using three different sites which include very dynamic glaciers. For the Oriental Glacier, an outlet of the Southern Patagonian icefield, Landsat 7 and 8 data from different orbits enabled the identification of trends related to elevation change. For the Aletsch Glacier, Swiss Alps, we assess the terrain offsets of both Landsat 8 and Sentinel-2A: a superior DEM appears to be used for Landsat in comparison to Sentinel-2, however a systematic bias is observed in the snow covered areas. Lastly, we demonstrate our methodology in a pipeline structure; displacement estimates for the Helheim-glacier, in Greenland, are mapped and corrected for orthorectification offsets between data from different orbits, which enables a twice as dense a temporal resolution of velocity data, as compared to the standard method of measuring velocities from repeat-orbit data only. In addition, we introduce and implement a novel matching method which uses image triplets. By formulating the three image displacements as a convolution, a geometric constraint can be exploited. Such a constraint enhances the reliability of the displacement estimations. Furthermore the implementation is simple and computationally swift.

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Mass transport waves amplified by intense Greenland melt and detected in solid Earth deformation

Adhikari

Ivins

Larour

2017

Geophysical Research Letters

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The annual cycle and secular trend of Greenland mass loading are well recorded in measurements of solid Earth deformation. Horizontal crustal displacements can potentially track the spatiotemporal detail of mass changes with great fidelity. Our analysis of Greenland crustal motion data reveals that a significant excitation of horizontal amplitudes occurs during the intense melt years. We discover that solitary seasonal waves of substantial mass transport (1.67 ± 0.54 Gt/month) traveled at an average speed of 7.1 km/month through Rink Glacier in 2012. We deduce that intense surface melting enhanced either basal lubrication or softening of shear margins, or both, causing the glacier to thin dynamically in summer. The newly routed upstream subglacial water was likely to be both retarded and inefficient, thus providing a causal mechanism for the prolonged ice transport to continue well into the winter months. As the climate continues to produce increasingly warmer spring and summer, amplified seasonal waves of mass transport may become ever more present with important ramifications for the future sea level rise.

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A processing system to monitor Greenland outlet glacier velocity variations at decadal and seasonal time scales utilizing the Landsat imagery

Cited by 73 publications

References 84 publications

A Combined Approach for Filtering Ice Surface Velocity Fields Derived from Remote Sensing Methods

A Combined Approach for Filtering Ice Surface Velocity Fields Derived from Remote Sensing Methods

Elevation Change and Improved Velocity Retrieval Using Orthorectified Optical Satellite Data from Different Orbits

Mass transport waves amplified by intense Greenland melt and detected in solid Earth deformation

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