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  • 1
    Dissertations
    Dissertations
    Potsdam
    Call number: AWI G3-13-0150
    Description / Table of Contents: Table of Contents: Abstract. - Zusammenfassung. - 1 Introduction. - 2 Thermo-erosion along the Yedoma Coast of the Buor Khaya Peninsula, Laptev Sea, East Siberia. - 3 Short- and long-term thermo-erosion of ice-rich permafrost coasts in the Laptev Sea region. - 4 Observing Muostakh Island disappear: erosion of a ground-ice-rich coast in response to summer warming and sea ice reduction on the East Siberian shelf. - 5 Synthesis. - Bibliography. - Acknowledgements
    Type of Medium: Dissertations
    Pages: v, 125 S. : Ill., graph. Darst., Kt.
    Note: Potsdam, Univ., Diss., 2013
    Branch Library: AWI Library
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  • 2
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract This article describes a neural network model that addresses the acquisition of speaking skills by infants and subsequent motor equivalent production of speech sounds. The model learns two mappings during a babbling phase. A phonetic-to-orosensory mapping specifies a vocal tract target for each speech sound; these targets take the form of convex regions in orosensory coordinates defining the shape of the vocal tract. The babbling process wherein these convex region targets are formed explains how an infant can learn phoneme-specific and language-specific limits on acceptable variability of articulator movements. The model also learns an orosensory-to-articulatory mapping wherein cells coding desired movement directions in orosensory space learn articulator movements that achieve these orosensory movement directions. The resulting mapping provides a natural explanation for the formation of coordinative structures. This mapping also makes efficient use of redundancy in the articulator system, thereby providing the model with motor equivalent capabilities. Simulations verify the model's ability to compensate for constraints or perturbations applied to the articulators automatically and without new learning and to explain contextual variability seen in human speech production.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2018-10-08
    Type: Dataset
    Format: application/zip, 126.0 kBytes
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  • 4
    Publication Date: 2018-12-12
    Type: Dataset
    Format: text/tab-separated-values, 16 data points
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  • 5
    Publication Date: 2018-12-12
    Type: Dataset
    Format: application/zip, 316.0 kBytes
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  • 6
    Publication Date: 2018-09-27
    Type: Dataset
    Format: text/tab-separated-values, 792 data points
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  • 7
    Publication Date: 2018-09-27
    Description: Thawing-induced cliff top retreat in permafrost landscapes is mainly due to thermo-erosion. Ground-ice-rich permafrost landscapes are specifically vulnerable to thermo-erosion and may show high degradation rates. Within the HGF Alliance Remote Sensing and the FP7 PAGE21 permafrost programs we investigated how SAR and optical remote sensing can contribute to the monitoring of erosion rates of ice-rich cliffs in Arctic Siberia (Lena Delta, Russia). We produced two different vector products: i) Intra-annual cliff top retreat based on TerraSAR-X (TSX) satellite data (2012-2014): High-temporal resolution time series of TSX satellite data allow the inter-annual and intra-annual monitoring of the upper cliff-line retreat also under bad weather conditions and continuous cloud coverage. This published SAR product contains the retreating upper cliff lines of a 1.5 km long part of eroding ice-rich coast of Kurungnakh Island in the central Lena Delta. The upper cliff line was mapped using a thresholding approach for images acquired in the years 2012, 2013 and 2014 for the months June (2013, 2014), July (2013, 2014), August (2012, 2013, 2014) and September (2013, 2014). The cliff top retreat vector product is called 'upper_cliff_TerraSAR-X'. While the 2014 cliff lines show a clear retreat of 2 to 3 m/month, the cliff top lines for 2012 and 2013 are not chronologically ordered. However, lines from the end of the season of a year are always close to the lines from the beginning of the next summer season, indicating low cliff retreat in winter. ii) 4-year cliff top retreat based on optical satellite data (2010-2014): Long-term cliff top retreat could be assessed with two high-spatial resolution optical satellite images (GeoEye-1, 2010-08-05 and Worldview-1, 2014-08-19). The cliff top retreat vector product is called 'upper_cliff_optical'. Results: The long-term cliff top retreat derived from optical satellite data are 35 m cliff retreat within 4 years. The higher-temporal resolution SAR data equivalently show long-term rates of 18 m within 2 years and nearly now degradation activities in winter but maximum erosion rates in summer months.The Intra-seasonal cliff top retreat lines from 2014 show a rate of 2 to 3 m per month.
    Type: Dataset
    Format: text/tab-separated-values, 6 data points
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  • 8
    Publication Date: 2015-02-04
    Description: Observations of coastline retreat using contemporary very high resolution satellite and historical aerial imagery were compared to measurements of open water fraction, summer air temperature, and wind. We analysed seasonal and interannual variations of thawing-induced cliff top retreat (thermo-denudation) and marine abrasion (thermo-abrasion) on Muostakh Island in the southern central Laptev Sea. Geomorphometric analysis revealed that total ground ice content on Muostakh is made up of equal amounts of intrasedimentary and macro ground ice and sums up to 87%, rendering the island particularly susceptible to erosion along the coast, resulting in land loss. Based on topographic reference measurements during field campaigns, we generated digital elevation models using stereophotogrammetry, in order to block-adjust and orthorectify aerial photographs from 1951 and GeoEye, QuickBird, WorldView-1, and WorldView-2 imagery from 2010 to 2013 for change detection. Using sea ice concentration data from the Special Sensor Microwave Imager (SSM/I) and air temperature time series from nearby Tiksi, we calculated the seasonal duration available for thermo-abrasion, expressed as open water days, and for thermo-denudation, based on the number of days with positive mean daily temperatures. Seasonal dynamics of cliff top retreat revealed rapid thermo-denudation rates of −10.2 ± 4.5 m a−1 in mid-summer and thermo-abrasion rates along the coastline of −3.4 ± 2.7 m a−1 on average during the 2010–2013 observation period, currently almost twice as rapid as the mean rate of −1.8 ± 1.3 m a−1 since 1951. Our results showed a close relationship between mean summer air temperature and coastal thermo-erosion rates, in agreement with observations made for various permafrost coastlines different to the East Siberian Ice Complex coasts elsewhere in the Arctic. Seasonality of coastline retreat and interannual variations of environmental factors suggest that an increasing length of thermo-denudation and thermo-abrasion process simultaneity favours greater coastal erosion. Coastal thermo-erosion has reduced the island's area by 0.9 km2 (24%) over the past 62 years but shrank its volume by 28 x 106 m3 (40%), not least because of permafrost thaw subsidence, with the most pronounced with rates of ≥− 11 cm a−1 on yedoma uplands near the island's rapidly eroding northern cape. Recent acceleration in both will halve Muostakh Island's lifetime to less than a century.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
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  • 9
    Publication Date: 2015-03-31
    Description: This study aims at understanding the patterns of thermo-erosional valleys and identifying the key drivers for their distribution in an ice-rich permafrost landscape in the central Lena Delta, Siberia. The spatial extent of thermo-erosional processes and related landforms (e.g. water tracks, gullies, valleys) and their impact on the degradation of permafrost is still not well quantified. Although degradation processes related to thermokarst and the resulting landscape features are well studied in ice-rich permafrost regions, only a few studies with detailed investigations of thermo-erosional processes and resulting features and their relevance for permafrost degradation exist. These processes and features are important indicators of climate change in the Arctic. The Arctic is a substantial and very sensitive element in earth’s climatic system that is undergoing extensive and rapid changes. Permafrost degradation affects the climatic system through carbon release and changes the living conditions for arctic communities. We use high resolution remote sensing data and digital elevation models (DEMs) to derive and analyse geomorphometric relief characteristics to understand periglacial landscape dynamics. However, geometric correction of remote sensing data, and generation of DEMs in arctic lowlands, is challenging due to low relief and surface contrast gradients and often scarce reference data. Therefore, high quality and high-resolution DEMs are rarely available, especially in Siberia. To address these difficulties, this study is using a multi-sensor and multi-temporal satellite data approach for a detailed inventory and 2D/3D morphometric analysis of thermo-erosional valleys on Kurungnakh Island. A high resolution DEM with 5m spatial resolution and a RMSE of 3.8 m was generated from ALOS PRISM stereo-datasets acquired in 2006 and 2009 and validated against extensive ground measurements taken during an expedition in July 2013. Mapping of 1214 stream segments related to thermo-erosional processes with a total length of 336 km was performed using a time-series of orthorectified GeoEye-1 and RapidEye datasets. We measured 32 longitudinal and transversal profiles of thermo-erosional valleys at three key sites, each representing different stages of valley evolution. We used additional profiles extracted from the DEM to characterize different valley types on Kurungnakh Island. We present a detailed inventory and characterization of thermo-erosional features on Kurungnakh Island. Our findings show a strong dependence of thermo-erosional processes to the prior degradation of ice-rich permafrost through thermokarst activity. Since the stream network of Kurungnakh Island is poorly developed, accelerated permafrost thawing due to an arctic warming could promote the degradation of ice-rich permafrost by thermo-erosional processes and alter the hydrologic regime as well as the sediment and carbon fluxes. Our dataset provides a new level of accuracy for the Lena Delta region.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 10
    Publication Date: 2015-05-06
    Description: Although a subsurface phenomenon, permafrost creates distinct features on the land surface which can be observed using remote sensing data. This is especially true for the East Siberian Arctic where ice-rich permafrost is abundant in the geological subsurface and only protected by a thin layer of organic soils. In the Lena River Delta, deeper seasonal thaw during increasingly frequent warm summers does not only result in irreversible loss of ground ice and subsequent land subsidence, but also in discharge of soil organic carbon that was previously fixed in permafrost. To characterize the dynamics of thawing permafrost and its impacts on landscapes, hydrology, and emission of methane and carbon dioxide we analyse optical remote sensing time series from various sensors. Local field measurements (meteorology, ground temperature, geodetic surveys) during several recent Russian-German Arctic expeditions complement our remote sensing studies and help differentiating factors causing relief and land cover changes. While previous studies concentrated on general inventory of thermokarst landforms, higher temporal resolution of contemporary image acquisitions provides unique information for the understanding of seasonal processes, such as ice-on and ice-off on thermokarst lakes, shore erosion on delta channels, water level changes and drainage events in lakes, and wettening/drying of thermokarst-affected areas. Ground truth data provides the basis for calibration and correction of 21 RapidEye scenes (level 1B) from 2014 using a bundle block adjustment procedure. Next steps will include extraction of seasonal variations of band metrics such as NDVI which we will compare to decadal Landsat time series of landcover change and multitemporal, photogrammetrically-derived digital elevation models in order to identify signatures and trends typical for permafrost thaw related processes on the surface. Our approach will allow assessment of rates and short-term changes in thermokarst dynamics and landscape evolution. In addition, the derived data will be valuable for permafrost-thaw model parameterization.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed , info:eu-repo/semantics/conferenceObject
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