ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Publication Date: 2016-10-05
    Description: Displacements of the Earth's surface can be estimated using differential interferometric synthetic aperture radar. The estimates are derived from the phase difference between two radar acquisitions. When at least three such acquisitions are available, one can compute the displacement between the first and the third acquisition and compare it with the sum of the two intermediate displacements. These two are expected to be equal for a piston-like spatially uniform deformation. However, this is not necessarily the case in measured data. Such lack of phase closure can be due to decorrelation noise alone. It has also been attributed to complex scattering processes such as soil moisture changes or multiple scattering sources. However, the nature of these nonrandom effects is only poorly understood in cold regions, as the role of snow and freeze/thaw processes has not been studied to date. To distinguish the noise-like and the systematic effects, an asymptotic Wald significance test is proposed. It detects situations when the observed closure error cannot solely be explained by noise. Such situations with p 〈; 0.05 are observed at the Ku-band during snow metamorphism and melt and following a summer precipitation event in Sodankylä, Finland. They can also be prevalent (〉 25%) in the X-band observations of ice-rich permafrost regions in the Lena Delta, Russia, indicating the presence of processes that can have systematic and deleterious impacts on the estimation of surface movements. Satellite-based monitoring of these displacements is thus possibly subject to complex error sources in high-latitude regions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Publication Date: 2017-01-21
    Description: Permafrost soils have been shown to respond rapidly to warming temperatures. When ice-rich permafrost soils thaw, the melting ground ice reduces the volume and stability of the soils, inducing changes in the topography. We monitor surface elevation changes in three test sites in Northern Eurasia using single-pass TanDEM-X Science Phase data with submetre vertical precision. The results indicate the suitability of single-pass InSAR data for monitoring thaw-induced topographic changes (e.g. coastal erosion) but they also reveal the spurious impact of late-lying snow packs and water bodies, both of which are common in lowland permafrost areas. Furthermore, the coherence and hence the precision with which elevation changes can be estimated is found to be limited by the noise level in certain cases. As some of these influences could be mitigated using appropriate mission and acquisition designs, we conclude that single-pass interferometry has considerable potential for monitoring thaw-induced surface elevation changes in permafrost areas, which in turn could contribute to assessing their vulnerability, fate, and climate system feedback in a warming climate.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 2018-04-05
    Description: Thermokarst is expected to drive major changes in ice-rich permafrost regions, but its current and future extent and rates of change remain only partially understood; in part due to limited broad-scale observations. Here we show that time-lapse digital elevation models from single-pass interferometry can provide important synoptic observations of thermokarst-induced terrain changes and novel insight into the drivers and controls of thermokarst. We focus on retrogressive thaw slumps, an important and dynamic form of thermokarst. On sub-seasonal time scales, sparse measurements indicate that mass wasting at active slumps is often limited by the energy available for melting ground ice, but other factors such as rainfall or the formation of an insulating veneer are also thought important. To study the sub-seasonal drivers, we use TanDEM-X observations (12 m resolution) acquired during the Science Phase in summer 2015 over two study regions. The high vertical precision (30 cm), frequent observations (11 days) and large coverage (5000 km2) allow us to track volume losses as drivers (e.g. available energy) vary through time. We find that thaw slumps in the Tuktoyaktuk coastlands, Canada, are not energy limited in June, as they undergo limited mass wasting (height loss of around 0 cm/day) despite the ample available energy, indicating the widespread presence of an insulating snow or debris veneer. Later in summer, height losses generally increase (around 3 cm/day), but they do so in distinct ways. For many slumps, mass wasting tracks the available energy, a temporal pattern that is also observed at coastal yedoma cliffs on the Bykovsky Peninsula, Russia. However, the other two common temporal trajectories are asynchronous with the available energy, as they track strong precipitation events or show a sudden speed-up in late August, respectively. The contrasting temporal behaviour of nearby thaw slumps highlights the importance of complex local and temporally varying controls on mass wasting. This complexity reinforces the need for circum-arctic monitoring efforts, for which remote sensing approaches such as single-pass interferometry are indispensable.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed , info:eu-repo/semantics/conferenceObject
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2015-11-19
    Description: Icebergs are hazards to lives and goods during navigation in cold waters. In the context of iceberg detection with SAR images, an extensive work was carried out for the detection of large icebergs, but the identification of small bergs or target embedded in sea ice is till difficult. In this work, a new detector is propose to tackle this issue based on dual-polarimetric incoherent (i.e. detected) images. The algorithm is based on the principle that small icebergs are contained in a limited area and they are supposed to have a volume contribution that is higher compared to the sea or sea-ice background. The detector is tested on RADARSAT-2 quad-polarimetric data, where only the multi-looked intensities of the HH and HV channels are used.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2017-04-27
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2017-08-30
    Description: Predicting future thaw slump activity requires a sound understanding of the atmospheric drivers and geomorphic controls on mass wasting across a range of time scales. On sub-seasonal time scales, sparse measurements indicate that mass wasting at active slumps is often limited by the energy available for melting ground ice, but other factors such as rainfall or the formation of an insulating veneer may also be relevant. To study the sub-seasonal drivers, we derive topographic changes from single-pass radar interferometric data acquired by the TanDEM-X satellite (12 m resolution). The high vertical precision (around 30 cm), frequent observations (11 days) and large coverage (5000 km2) allow us to track volume losses as drivers such as the available energy change during summer in two study regions. We find that thaw slumps in the Tuktoyaktuk coastlands, Canada, are not energy limited in June, as they undergo limited mass wasting (height loss of around 0 cm/day) despite the ample available energy, indicating the widespread presence of an insulating snow or debris veneer. Later in summer, height losses generally increase (around 3 cm/day), but they do so in distinct ways. For many slumps, mass wasting tracks the available energy, a temporal pattern that is also observed at coastal yedoma cliffs on the Bykovsky Peninsula, Russia. However, the other two common temporal trajectories are asynchronous with the available energy, as they track strong precipitation events or show a sudden speed-up in late August, respectively. The observed temporal patterns are poorly related to slump characteristics like the slump area. The contrasting temporal behaviour of nearby thaw slumps highlights the importance of complex local and temporally varying controls on mass wasting.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2019-05-17
    Description: Predicting future thaw slump activity requires a sound understanding of the atmospheric drivers and geomorphic controls on mass wasting across a range of timescales. On sub-seasonal timescales, sparse measurements indicate that mass wasting at active slumps is often limited by the energy available for melting ground ice, but other factors such as rainfall or the formation of an insulating veneer may also be relevant. To study the sub-seasonal drivers, we derive topographic changes from single-pass radar interferometric data acquired by the TanDEM-X satellites. The estimated elevation changes at 12 m resolution complement the commonly observed planimetric retreat rates by providing information on volume losses. Their high vertical precision (around 30 cm), frequent observations (11 days) and large coverage (5000 km2) allow us to track mass wasting as drivers such as the available energy change during the summer of 2015 in two study regions. We find that thaw slumps in the Tuktoyaktuk coastlands, Canada, are not energy limited in June, as they undergo limited mass wasting (height loss of around 0 cm day−1) despite the ample available energy, suggesting the widespread presence of early season insulating snow or debris veneer. Later in summer, height losses generally increase (around 3 cm day−1), but they do so in distinct ways. For many slumps, mass wasting tracks the available energy, a temporal pattern that is also observed at coastal yedoma cliffs on the Bykovsky Peninsula, Russia. However, the other two common temporal trajectories are asynchronous with the available energy, as they track strong precipitation events or show a sudden speed-up in late August respectively. The observed temporal patterns are poorly related to slump characteristics like the headwall height. The contrasting temporal behaviour of nearby thaw slumps highlights the importance of complex local and temporally varying controls on mass wasting.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2019-07-17
    Description: Introduction: The observation of sea ice is a major topic in remote sensing due to the difficulty of performing frequent in situ expeditions [1, 2]. Monitoring of sea ice is important for many environmental issues [1]. First of all, it is a sensitive climate indicator and it plays an important role in global climate systems. It restricts the exchange of heat and chemical constituents between ocean and atmosphere acting as an insulator. Moreover, it influences global climate system for effects related with its elevated albedo, reducing the amount of solar radiation absorbed at the Earth’s surface. On the other hand, sea ice affects oceanic circulation directly by the rejection of salt to the underlying ocean during ice growth, that is responsible for deep water formation. Besides these, the possibility and safety of navigation in Polar Regions is severely influenced by the presence of sea ice. SAR: Microwave sensors and Synthetic Aperture Radar (SAR) are very valuable for monitoring of sea ice since they can acquire information in absence of solar illumination (i.e. during Polar nights) and with almost any weather conditions. Unfortunately, the description of the backscattering behaviour of sea ice is particularly challenging. For this reason, many scientists moved toward systems able to increase the amount of information acquired. In this context, polarimetry plays a key role, because it is able to enhance the discrimination capability of the observed target, solving many ambiguities revealed in single polarisation images [3]. Specifically, sea-ice could be modelled as a layered media showing several interfaces: air-snow, snow-ice and (eventually) ice-water [4, 2]. SAR polarimetry: A scattering (Sinclair) matrix [S] can be used to characterise the polarimetric behaviour of deterministic targets [3]. A scattering vector k can be obtained rearranging the elements of the scattering matrix. The Pauli basis was widely exploited to rearrange the scattering matrix in what is defined as the Pauli scattering vector k = [HH +VV, HH-VV, 2HV], where H stands for linear horizontal and V for linear vertical and the repeated letter is for transmitter-receiver. A target that pixel per pixel changes its polarimetric behaviour (i.e. scattering matrix) is defined ”partial” and can be characterised with the second order statistics of the scattering vector. The latter are generally arranged in a covariance matrix [C]. Sea-Ice classification with SAR polarimetry: This paper will compare three different classification methodologies that make advantage of polarimetric SAR data. 1) The first considers the estimation of “polarimetric observables” (ratios and coherences between polarimetric channels) to build a feature vector able to separate the different ice types (and open water) on a multidimensional space. This approach was largely adopted in the literature and its value is a consequence of the choice of observables that physically should capture the different behaviour of ice types and open water [2,5,6]. 2) The Wishart classifier for the covariance matrix [C]. This approach is based on the statistical distance (in the covariance matrix space) of the pixel from the different classes. The supervised version makes use of a first step where a Cloude-Pottier decomposition is performed [3]. The latter was already exploited in some occasions for sea ice classification [7]. 3) The classifier based on the perturbation analysis [8]. This recent classifier will be tested here since in some conditions showed improvements on the Wishart classifier. Specifically, the overall intensity of the backscattering is neglected and this is beneficial in situations where a modulation of the intensity may not be related to physical but rather geometrical phenomena. The three methodologies will be carefully compared in order to understand which the best methodology for the different situations is. Dataset used: The dataset exploited in this study was acquired during the ICESAR campaign in 2007 by the E-SAR airborne system of DLR (German Aerospace Agency). The sea ice acquisitions were carried out in Svalbard over three different locations: Fram Strait, Storfjord and Barents Sea. In this analysis only L-band acquisitions are used, since they are the only one presenting quad-polarimetric data. The resolution of the system is 2.12m in slant-range and about 1m in azimuth with a pixels spacing of 1.5m in range and 0.5m in azimuth. The NESZ goes from -30dB to -35dB, while the incidence angle from 26 to 65 degrees. Aerial photographs of the area during the acquisition show that first year ice is present, with areas of brash ice. Few small leads are also visible. Discussion: As a final remark, the results that will be presented show that polarimetry could help the data analysis solving eventual ambiguities. However, in many instances, the refrain in exploiting polarimetric modes is the impossibility to achieve very large swath (as ScanSAR images) that in many sea-ice applications are needed to cover vast areas in short time. Fortunately, in the next generations of SAR satellites this inconvenient may be bypassed by the possibility to use compact polarimetry (as for the RADARSAT constellation) or dual polarimetry (as for the Sentinel constellation) with ScanSAR modes. In particular, compact polarimetry somehow allows reconstructing quad-polarimetric data, although part of the information will be clearly lost. References: [1] S. Sandven, Johannessen, O.M., and K Kloster, Sea Ice Monitoring by Remote Sensing, John Wiley & Sons, 2006. [2] C.R. Jackson and J.R. Apel, Synthetic Aperture Radar Marine User’s Manual: National Oceanic and Athmospheric Administration (NOAA), NOAA, 2004. [3] S. R. Cloude, Polarisation: Applications in Remote Sensing, Oxford University Press, 2009. [4] S.V. Nghiem, R. Kwok, S.H. Yueh, and M.R. Drinkwater, “Polarimetric signatures of sea ice 1. theoretical model,” Journal of Geophysical Research, vol. 100(13), pp. 665–679, 1995. [5] Drinkwater, M., Kwok, R., Rignot, R., Israelsson, H., Onstott, R.G., & Winebrenner, D.P. (1992). Chapter 24. Potential Applications of Polarimetry to the Classification of Sea Ice. Geophysical Monograph Series, 68, 419 – 430. [6] H. Wakabayashi, T. Matsuoka, K. Nakamura, and F. Nishio, “Polarimetric characteristics of sea ice in the sea of Okhotsk observed by airborne L-Band SAR,” IEEE Transaction on Geoscience and Remote Sensing, vol. 42, 2004. [7] Scheuchl, B., Hajnsek, I., & Cumming, I.G. (2003). Classification Strategies for Polarimetric SAR Sea Ice Data. Proceedings on POLinSAR. [8] Armando Marino, Shane R. Cloude & Iain H. Woodhouse (2012), Detecting Depolarizing Targets using a New Geometrical Perturbation Filter, IEEE Transaction on Geoscience and Remote Sensing, 50(10), 2012.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 10 data points
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...