A Quantitative Graph-Based Approach to Monitoring Ice-Wedge Trough Dynamics in Polygonal Permafrost Landscapes

In response to increasing Arctic temperatures, ice-rich permafrost landscapes are undergoing rapid changes. In permafrost lowlands, polygonal ice wedges are especially prone to degradation. Melting of ice wedges results in deepening troughs and the transition from low-centered to high-centered ice-wedge polygons. This process has important implications for surface hydrology, as the connectivity of such troughs determines the rate of drainage for these lowland landscapes. In this study, we present a comprehensive, modular, and highly automated workflow to extract, to represent, and to analyze remotely sensed ice-wedge polygonal trough networks as a graph (i.e., network structure). With computer vision methods, we efficiently extract the trough locations as well as their geomorphometric information on trough depth and width from high-resolution digital elevation models and link these data within the graph. Further, we present and discuss the benefits of graph analysis algorithms for characterizing the erosional development of such thaw-affected landscapes. Based on our graph analysis, we show how thaw subsidence has progressed between 2009 and 2019 following burning at the Anaktuvuk River fire scar in northern Alaska, USA. We observed a considerable increase in the number of discernible troughs within the study area, while simultaneously the number of disconnected networks decreased from 54 small networks in 2009 to only six considerably larger disconnected networks in 2019. On average, the width of the troughs has increased by 13.86%, while the average depth has slightly decreased by 10.31%. Overall, our new automated approach allows for monitoring ice-wedge dynamics in unprecedented spatial detail, while simultaneously reducing the data to quantifiable geometric measures and spatial relationships.BMBF PermaRiskNational Science FoundationPeer Reviewe

Multiscale Integration of High-Resolution Spaceborne and Drone-Based Imagery for a High-Accuracy Digital Elevation Model Over Tristan da Cunha

Very high-resolution (VHR) optical Earth observation (EO) satellites as well as low-altitude and easy-to-use unmanned aerial systems (UAS/drones) provide ever-improving data sources for the generation of detailed 3-dimensional (3D) data using digital photogrammetric methods with dense image matching. Today both data sources represent cost-effective alternatives to dedicated airborne sensors, especially for remote regions. The latest generation of EO satellites can collect VHR imagery up to 0.30 m ground sample distance (GSD) of even the most remote location from different viewing angles many times per year. Consequently, well-chosen scenes from growing image archives enable the generation of high-resolution digital elevation models (DEMs). Furthermore, low-cost and easy to use drones can be quickly deployed in remote regions to capture blocks of images of local areas. Dense point clouds derived from these methods provide an invaluable data source to fill the gap between globally available low-resolution DEMs and highly accurate terrestrial surveys. Here we investigate the use of archived VHR satellite imagery with approx. 0.5 m GSD as well as low-altitude drone-based imagery with average GSD of better than 0.03 m to generate high-quality DEMs using photogrammetric tools over Tristan da Cunha, a remote island in the South Atlantic Ocean which lies beyond the reach of current commercial manned airborne mapping platforms. This study explores the potentials and limitations to combine this heterogeneous data sources to generate improved DEMs in terms of accuracy and resolution. A cross-validation between low-altitude airborne and spaceborne data sets describes the fit between both optical data sets. No co-registration error, scale difference or distortions were detected, and a quantitative cloud-to-cloud comparison showed an average distance of 0.26 m between both point clouds. Both point clouds were merged applying a conventional georeferenced approach. The merged DEM preserves the rich detail from the drone-based survey and provides an accurate 3D representation of the entire study area. It provides the most detailed model of the island to date, suitable to support practical and scientific applications. This study demonstrates that combination archived VHR satellite and low-altitude drone-based imagery provide inexpensive alternatives to generate high-quality DEMs

Entwicklung und Anwendung eines datenbasierten Multikomponenten-Küstenevolutionsmodells am Beispiel der deutschen Nordseeküste

Die deutsche Nordseeküste ist ein komplexes System aus Wattflächen, Ästuaren und Barriereinseln. Innerhalb dieses Systems finden hydro- und morphodynamische Prozesse statt, die durch den Klimawandel beeinflusst werden. Um diese Prozesse und deren Veränderungen im Kontext von Küsten-und Naturschutz sowie wirtschaftlichen Interessen zu untersuchen, werden von staatlichen und wissenschaftlichen Akteuren Modellsysteme verwendet, die diese Prozesse auf der Basis mathematischer Regeln beschreiben und simulieren können. Sie werden daher als prozessbasierte Modellsysteme bezeichnet. Die morphologische Entwicklung und damit auch der Einfluss auf hydrodynamische Eigenschaften hängt stark von der sedimentologischen Zusammensetzung der Gewässerbodenoberfläche und des Untergrundes ab. Informationen hierüber werden in Naturmessungen erhoben und müssen mit speziellen Modellsystemen verarbeitet und in räumlich kontinuierliche Informationen überführt werden. Sie werden als datenbasierte Modellsysteme bezeichnet. Mangels geeigneter datenbasierter Modellierungsansätze bestand in der Berücksichtigung sedimentologischer Basisdaten zur Verwendung in prozessbasierten Modellsystemen bisher jedoch ein Defizit. Diese Lücke wird mit dem in dieser Arbeit entwickelten datenbasierten Multikomponenten-Küstenevolutionsmodell geschlossen. Hierzu werden in der Modellierung von bathymetrischen Daten übliche Approximations- und Interpolationsvorschriften generalisiert und auf funktionale Informationen der Korngrößenverteilung übertragen. In einer neuartigen Kopplung von bestehenden daten- und prozessbasierten Ansätzen werden punktuelle Entwicklungsgleichungen für skalare Eigenschaften einer Kornverteilung auf volle Summenlinien erweitert und in die Fläche übertragen. Hiermit ermöglicht das Küstenevolutionsmodell es, an der gesamten deutschen Nordseeküste zeitvariante sedimentologische Informationen sowohl der Oberfläche als auch des Untergrunds für prozessbasierte Modellsysteme nutzbar zu machen und so die Qualität ihrer Ergebnisse zu verbessern. Neben der Verwendung als Assistenzwerkzeug für prozessbasierte Modellsysteme können aus den einzelnen Komponenten des Küstenevolutionsmodells darüber hinaus küstengeologische Erkenntnisse abgeleitet werden, die so bisher entweder gar nicht beziehungsweise nicht in dem Ausmaß oder Detailgrad möglich waren. Durch einen außergewöhnlich langen Auswertungszeitraum von bis zu sieben Dekaden in Kombination mit einer verhältnismäßig hohen jährlichen Auflösung ist in der bathymetrischen Komponente eine regionale Trendumkehr in der Entwicklung der Höhen der Wattflächen im 21. Jahrhundert erkennbar, die bisher nicht identifiziert wurde und möglicherweise bereits auf Auswirkungen des Klimawandels hindeutet. Erstmals werden darüber hinaus mit der oberflächensedimentologischen Komponente die Auswirkungen starker anthropogener Eingriffe wie dem Bau des Eidersperrwerks auf die Oberflächensedimentologie in der Fläche und im zeitlichen Verlauf quantifizierbar. Die Modellierung des Gewässergrundaufbaus als dritte Komponente ermöglicht non-destruktive Analysen unter Anderem des Ablagerungsalters und schafft so neue Optionen zur zeitlichen Einordnung von Erosionsereignissen in flachseismischen Untersuchungen, die hierdurch auch in geschützten Habitaten ohne Ground-Truthing-Bohrkerne auskommen. Mit der Auswertung dieser Komponente wird zudem die hohe Relevanz der zeitvarianten Analyse des Untergrunds der Nordseeküste verdeutlicht, der genau wie die Bathymetrie und die Oberflächensedimentologie stets im zeitlichen Kontext betrachtet werden muss

Neolithic land-use in the Dutch wetlands: estimating the land-use implications of resource exploitation strategies in the Middle Swifterbant Culture (4600-3900 BCE)

The Dutch wetlands witness the gradual adoption of Neolithic novelties by foraging societies during the Swifterbant period. Recent analyses provide new insights into the subsistence palette of Middle Swifterbant societies. Small-scale livestock herding and cultivation are in evidence at this time, but their importance if unclear. Within the framework of PAGES Land-use at 6000BP project, we aim to translate the information on resource exploitation into information on land-use that can be incorporated into global climate modelling efforts, with attention for the importance of agriculture. A reconstruction of patterns of resource exploitation and their land-use dimensions is complicated by methodological issues in comparing the results of varied recent investigations. Analyses of organic residues in ceramics have attested to the cooking of aquatic foods, ruminant meat, porcine meat, as well as rare cases of dairy. In terms of vegetative matter, some ceramics exclusively yielded evidence of wild plants, while others preserve cereal remains. Elevated δ15N values of human were interpreted as demonstrating an important aquatic component of the diet well into the 4th millennium BC. Yet recent assays on livestock remains suggest grazing on salt marshes partly accounts for the human values. Finally, renewed archaeozoological investigations have shown the early presence of domestic animals to be more limited than previously thought. We discuss the relative importance of exploited resources to produce a best-fit interpretation of changing patterns of land-use during the Middle Swifterbant phase. Our review combines recent archaeological data with wider data on anthropogenic influence on the landscape. Combining the results of plant macroremains, information from pollen cores about vegetation development, the structure of faunal assemblages, and finds of arable fields and dairy residue, we suggest the most parsimonious interpretation is one of a limited land-use footprint of cultivation and livestock keeping in Dutch wetlands between 4600 and 3900 BCE.NWOVidi 276-60-004Human Origin

Ways and Capacity in Archaeological Data Management in Serbia

Over the past year and due to the COVID-19 pandemic, the entire world has witnessed inequalities across borders and societies. They also include access to archaeological resources, both physical and digital. Both archaeological data creators and users spent a lot of time working from their homes, away from artefact collections and research data. However, this was the perfect moment to understand the importance of making data freely and openly available, both nationally and internationally. This is why the authors of this paper chose to make a selection of data bases from various institutions responsible for preservation and protection of cultural heritage, in order to understand their policies regarding accessibility and usage of the data they keep. This will be done by simple visits to various web-sites or data bases. They intend to check on the volume and content, but also importance of the offered archaeological heritage. In addition, the authors will estimate whether the heritage has adequately been classified and described and also check whether data is available in foreign languages. It needs to be seen whether it is possible to access digital objects (documents and the accompanying metadata), whether access is opened for all users or it requires a certain hierarchy access, what is the policy of usage, reusage and distribution etc. It remains to be seen whether there are public API or whether it is possible to collect data through API. In case that there is a public API, one needs to check whether datasets are interoperable or messy, requiring data cleaning. After having visited a certain number of web-sites, the authors expect to collect enough data to make a satisfactory conclusion about accessibility and usage of Serbian archaeological data web bases

Taphonomy, environment or human plant exploitation strategies?: Deciphering changes in Pleistocene-Holocene plant representation at Umhlatuzana rockshelter, South Africa

The period between ~40 and 20 ka BP encompassing the Middle Stone Age (MSA) and Later Stone Age (LSA) transition has long been of interest because of the associated technological change. Understanding this transition in southern Africa is complicated by the paucity of archaeological sites that span this period. With its occupation sequence spanning the last ~70,000 years, Umhlatuzana Rock Shelter is one of the few sites that record this transition. Umhlatuzana thus offers a great opportunity to study past environmental dynamics from the Late Pleistocene (MIS 4) to the Late Holocene, and past human subsistence strategies, their social organisation, technological and symbolic innovations. Although organic preservation is poor (bones, seeds, and charcoal) at the site, silica phytoliths preserve generally well throughout the sequence. These microscopic silica particles can identify different plant types that are no longer visible at the site because of decomposition or burning to a reliable taxonomical level. Thus, to trace site occupation, plant resource use, and in turn reconstruct past vegetation, we applied phytolith analyses to sediment samples of the newly excavated Umhlatuzana sequence. We present results of the phytolith assemblage variability to determine change in plant use from the Pleistocene to the Holocene and discuss them in relation to taphonomical processes and human plant gathering strategies and activities. This study ultimately seeks to provide a palaeoenvironmental context for modes of occupation and will shed light on past human-environmental interactions in eastern South Africa.NWOVidi 276-60-004Human Origin