Tobias Ullmann

Tobias Ullmann
University of Wuerzburg | JMU · Division of Remote Sensing

Professor

About

74
Publications
27,884
Reads
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839
Citations
Citations since 2017
47 Research Items
659 Citations
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2017201820192020202120222023050100150
2017201820192020202120222023050100150

Publications

Publications (74)
Article
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Recent research indicates an inverse relation between Synthetic Aperture Radar (SAR) signal and near-surface soil moisture (SM) over very dry sediments, arid to hyper-arid soils resp., caused by subsurface scattering effects. This phenomenon can lead to large errors when it comes to modelling and remote sensing-based estimation of SM. While the eff...
Article
Full-text available
The fast and accurate yield estimates with the increasing availability and variety of global satellite products and the rapid development of new algorithms remain a goal for precision agriculture and food security. However, the consistency and reliability of suitable methodologies that provide accurate crop yield outcomes still need to be explored....
Article
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Agroforestry systems (AFS) offer viable solutions for climate change because of the above-ground biomass (AGB) that is maintained by the tree component. Therefore, spatially explicit estimation of their AGB is crucial for reporting emission reduction efforts, which can be enabled using remote sensing (RS) data and methods. However, multiple factors...
Article
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In this contribution we highlight as an example the application of a freely available tool for the Google Earth Engine. The software allows cloud-free satellite images to be processed. We show processing examples for the Nile Delta (Egypt) and how the remote sensing images are used to find hints of buried landforms, such as former river branches of...
Article
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Warming induced shifts in tundra vegetation composition and structure, including circumpolar expansion of shrubs, modifies ecosystem structure and functioning with potentially global consequences due to feedback mechanisms between vegetation and climate. Satellite-derived vegetation indices indicate widespread greening of the surface, often associa...
Article
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Cocoa growing is one of the main activities in humid West Africa, which is mainly grown in pure stands. It is the main driver of deforestation and encroachment in protected areas. Cocoa agroforestry systems which have been promoted to mitigate deforestation, needs to be accurately delineated to support a valid monitoring system. Therefore, the aim...
Article
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Arctic permafrost coasts become increasingly vulnerable due to environmental drivers such as the reduced sea-ice extent and duration as well as the thawing of permafrost itself. A continuous quantification of the erosion process on large to circum-Arctic scales is required to fully assess the extent and understand the consequences of eroding permaf...
Article
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The mountain pine (Pinus mugo ssp. Mugo Turra) is an important component of the alpine treeline ecotone and fulfills numerous ecosystem functions. To understand and quantify the impacts of increasing logging activities and climatic changes in the European Alps, accurate information on the occurrence and distribution of mountain pine stands is neede...
Presentation
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Roughly one quarter of exposed land on the Northern Hemisphere and more than 65% of terrestrial area above 60°N are underlain by permafrost. Permafrost, defined as ground material which remains frozen for at least two consecutive years, stores around 1460-1600 billion tonnes of organic carbon, roughly twice the amount of carbon in the atmosphere. T...
Conference Paper
Currently, more than 40 % of the world’s population lives in coastal regions, a quarter of which situated less than 10 meters above sea level. Floods, saltwater intrusion, tsunamis, subsidence and erosion are among the natural risks to which coastal zones are exposed. The coastal region of Vietnam is particularly vulnerable to these risks because u...
Article
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Vietnam’s 3260 km coastline is densely populated, experiences rapid urban and economic growth, and faces at the same time a high risk of coastal hazards. Satellite archives provide a free and powerful opportunity for long-term area-wide monitoring of the coastal zone. This paper presents an automated analysis of coastline dynamics from 1986 to 2021...
Article
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Grasslands cover one-third of the agricultural area in Germany and play an important economic role by providing fodder for livestock. In addition, they fulfill important ecosystem services, such as carbon storage, water purification, and the provision of habitats. These ecosystem services usually depend on the grassland management. In central Europ...
Article
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Snow cover (SC) and timing of snowmelt are key regulators of a wide range of Arctic ecosystem functions. Both are strongly influenced by the amplified Arctic warming and essential variables to understand environmental changes and their dynamics. This study evaluates the potential of Sentinel-1 (S-1) synthetic aperture radar (SAR) time series for moni...
Article
Full-text available
The increasing availability and variety of global satellite products provide a new level of data with different spatial, temporal, and spectral resolutions; however, identifying the most suited resolution for a specific application consumes increasingly more time and computation effort. The region's cloud coverage additionally influences the choice...
Presentation
The classification of agroforestry systems is subjected to prediction error in the forest Zone of West Africa. The source of the error is linked to the nature of agroforestry systems (trees and crop manage together) creating a very heterogenous landscape, which is difficult to map. To monitor cocoa expansion and encroachment in protected areas, we...
Article
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Geoarchaeological information presented here pertains to a subsidiary Nile channel that once flowed west of the main Sebennitic distributary and discharged its water and sediments at Egypt’s then north-central deltaic coast. Periodical paleoclimatic episodes during the later Middle and Upper Holocene included decreased rainfall and increased aridit...
Article
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This study presents results on the internal structure and recent dynamics of a thrust moraine complex in the Zay Valley (Italian Alps) by means of geophysical surveying and remote sensing time series. Results from electrical resistivity tomography, refraction seismic tomography, ground-penetrating radar as well as a four-phase modeling approach pro...
Article
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Sacred water canals or lakes, which provided water for all kinds of purification rites and other activities, were very specific and important features of temples in ancient Egypt. In addition to the longer-known textual record, preliminary geoarchaeological surveys have recently provided evidence of a sacred canal at the Temple of Bastet at Bubastis...
Article
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This study explores the potential of Sentinel-1 Synthetic Aperture Radar (SAR) to identify phenological phases of wheat, sugar beet, and canola. Breakpoint and extreme value analyses were applied to a dense time series of interferometric (InSAR) and polarimetric (PolSAR) features recorded during the growing season of 2017 at the JECAM site DEMMIN (...
Article
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How to cite: Meister, J., Lange-Athinodorou, E., and Ullmann, T.: Preface: Special issue "Geoarchaeology of the Nile Delta", E&G Quaternary Sci. J., 70, 187-190, https://doi.org/10.5194/egqsj-70-187-2021, 2021.
Preprint
Full-text available
Snow cover (SC) and timing of snowmelt are key regulators of a wide range of Arctic ecosystem functions. Both are strongly influenced by the amplified arctic warming and essential variables to understand environmental changes and their dynamics. This study evaluates the potential of Sentinel-1 (S-1) synthetic aperture radar (SAR) time series for mo...
Article
Full-text available
The area of the Inner Asian Mountain Corridor (IAMC) follows the foothills and piedmont zones around the northern limits of Asia’s interior mountains, connecting two important areas for human evolution: the Fergana valley and the Siberian Altai. Prior research has suggested the IAMC may have provided an area of connected refugia from harsh climates...
Article
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Numerous ephemeral rivers and thousands of natural pans characterize the transboundary Iishana-System of the Cuvelai Basin between Namibia and Angola. After the rainy season, surface water stored in pans is often the only affordable water source for many people in rural areas. High inter- and intra-annual rainfall variations in this semiarid enviro...
Article
Full-text available
The contribution highlights the use of Landsat spectral-temporal metrics (STMs) for the detection of surface anomalies that are potentially related to buried near-surface paleogeomorphological deposits in the Nile Delta (Egypt), in particular for a buried river branch close to Buto. The processing was completed in the Google Earth Engine (GEE) for...
Article
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This study demonstrates an application-oriented approach to estimate area-wide surface roughness from Sentinel-1 time series in the semi-arid environment of the Orog Nuur Basin (southern Mongolia) to support recent geomorphological mapping efforts. The relation of selected mono-and multi-temporal SAR features and roughness is investigated by using...
Preprint
The area of the Inner Asian Mountain Corridor (IAMC) follows the foothills and piedmont zones around the northern limits of Asia’s interior mountains, connecting two important areas for human evolution: the Fergana valley and the Siberian Altai. Prior research has suggested the IAMC may have provided an area of connected refugia from harsh climates...
Article
Full-text available
This study compares the performance of the five widely used crop growth models (CGMs): World Food Studies (WOFOST), Coalition for Environmentally Responsible Economies (CERES)-Wheat, AquaCrop, cropping systems simulation model (CropSyst), and the semi-empiric light use efficiency approach (LUE) for the prediction of winter wheat biomass on the Dura...
Presentation
Full-text available
In this study, we investigated a retrogressive thaw slump at the edge of the Richardson Mountains (Northwest Territories, Canada) using high-resolution drone acquisitions, manual frost probing, 3D GPR and quasi-3D ERT to understand interactions and/or relationships between surface and subsurface conditions during the further development of the slum...
Article
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Illegal small-scale mining (galamsey) in South-Western Ghana has grown tremendously in the last decade and caused significant environmental degradation. Excessive cloud cover in the area has limited the use of optical remote sensing data to map and monitor the extent of these activities. This study investigated the use of annual time-series Sentine...
Article
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This study investigates synthetic aperture radar (SAR) time series of the Sentinel-1 mission acquired over the Atacama Desert, Chile, between March 2015 and December 2018. The contribution analyzes temporal and spatial variations of Sentinel-1 interferometric SAR (InSAR) coherence and exemplarily illustrates factors that are responsible for observe...
Article
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Air temperatures in the Arctic have increased substantially over the last decades, which has extensively altered the properties of the land surface. Capturing the state and dynamics of Land Surface Temperatures (LSTs) at high spatial detail is of high interest as LST is dependent on a variety of surficial properties and characterizes the land–atmos...
Article
The biomass of three agricultural crops, winter wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and canola (Brassica napus L.), was studied using multi-temporal dual-polarimetric TerraSAR-X data. The radar backscattering coefficient sigma nought of the two polarization channels HH and VV was extracted from the satellite images. Subsequen...
Article
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This contribution highlights recent findings of geomorphological and geophysical investigations that were un-dertaken at the excavation site of Bubastis (Eastern Nile Delta, Egypt) in order to find evidence of the existence and location of the sacred canals of Bubastis that were described by Herodotus in the 5th century BCE. None of the preceding a...
Article
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With the Sentinel-1 satellites of the Copernicus Mission of the European Space Agency a new C-Band Synthetic Aperture Radar (SAR) system operates and acquires data suited for continued earth observation. The so called Interferometric Wide Swath mode realizes a high spatial resolution of less than fifteen meters and offers a large swath width of abo...
Article
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The city of Bubastis (Tell Basta) is situated in the south-eastern Nile delta and was of great importance in Ancient Egypt. While the remains of the city have been the subject of archaeological investigations for more than one hundred years, little research has been carried out on the characterization of the former landscape in general and on the l...
Article
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Detailed information on the land cover types present and the horizontal position of the land–water interface is needed for sensitive coastal ecosystems throughout the Arctic, both to establish baselines against which the impacts of climate change can be assessed and to inform response operations in the event of environmental emergencies such as oil...
Article
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In this study, polarimetric Synthetic Aperture Radar (PolSAR) data at X-, C- and L-Bands, acquired by the satellites: TerraSAR-X (2011), Radarsat-2 (2011), ALOS (2010) and ALOS-2 (2016), were used to characterize the tundra land cover of a test site located close to the town of Tuktoyaktuk, NWT, Canada. Using available in situ ground data collected...
Conference Paper
Full-text available
Von der prädynastischen Zeit bis zur römischen Herrschaft in Ägypten war Bubastis (Tell Basta) eine bedeutende Metropole im südöstlichen Nildelta; bekannt durch teils einzigartige antike Bauwerke. Durch die Urbanisierung sind große Teile der Stätte jedoch im Laufe des letzten Jahrhunderts überbaut worden und es liegen für viele dieser Bereiche kein...
Article
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This study investigates a two component decomposition technique for HH/VV-polarized PolSAR (Polarimetric Synthetic Aperture Radar) data. The approach is a straight forward adaption of the Yamaguchi decomposition and decomposes the data into two scattering contributions: surface and double bounce under the assumption of a negligible vegetation scatt...
Article
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The Digital Elevation Model (DEM) of the TanDEM-X Mission (TDX) is the first InSAR derived elevation model that offers a pan-Arctic coverage: This data are likely to become the standard for applications that deal with the area-wide characterization and classification of periglacial – respectively Arctic – surface morphology, topography, or hydrogra...
Article
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The Sentinel-1 Satellite (S-1) of ESA’s Copernicus Mission delivers freely available C-Band Synthetic Aperture Radar (SAR) data that are suited for interferometric applications (InSAR). The high geometric resolution of less than fifteen meter and the large coverage offered by the Interferometric Wide Swath mode (IW) point to new perspectives on the...
Article
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The paper describes the latest results of geographic and geophysical investigations at the site of Tell Basta, the ancient city Bubastis, in the south-eastern Nile Delta. Given the obvious impact of the local geomorphology and hydrogeography on the evolution of the city, the addition of such methods to the ongoing archaeological studies at the site...
Article
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River deltas belong to the most densely settled places on earth. Although they only account for 5% of the global land surface, over 550 million people live in deltas. These preferred livelihood locations, which feature flat terrain, fertile alluvial soils, access to fluvial and marine resources, a rich wetland biodiversity and other advantages are,...
Conference Paper
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Zusammenfassung: Die im südöstlichen Nildelta gelegene antike Stadt Bubastis (Tell Basta) war seit prädynastischer Zeit eine Metropole mit überregionaler Bedeutung. Durch die unmittelbare Nähe zweier Nilarme und zum Eingang des Wadi Tumilats hielt die Stadt eine herausragende strategische Position. Ziel des Projekts ist die Rekonstruktion der antik...
Article
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In this work the potential of polarimetric Synthetic Aperture Radar (PolSAR) data of dual-polarized TerraSAR-X (HH/VV) and quad-polarized Radarsat-2 was examined in combination with multispectral Landsat 8 data for unsupervised and supervised classification of tundra land cover types of Richards Island, Canada. The classification accuracies as well...
Article
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Crop mapping in West Africa is challenging, due to the unavailability of adequate satellite images (as a result of excessive cloud cover), small agricultural fields and a heterogeneous landscape. To address this challenge, we integrated high spatial resolution multi-temporal optical (RapidEye) and dual polarized (VV/VH) SAR (TerraSAR-X) data to map...
Article
About 50 locations ('cold spots') where permafrost (Arctic and Antarctic) in situ monitoring has been taking place for many years or where field stations are currently established (through, for example the Canadian ADAPT program) have been identified. These sites have been proposed to WMO Polar Space Task Group as focus areas for future monitoring...
Conference Paper
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Increased rates of permafrost degradation and erosion along Arctic coastlines are anticipated, as a result of changing climatic conditions. To characterize and quantify rates of change, baselines in terms of the land cover types present and the physical location of the land-water interface, need to be established. Earth observation data provides a...
Article
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Arctic coastal regions are strongly endangered by changing climatic conditions and anthropo-genic utilization, for example due to permafrost degradation, or near-shore oil drilling. Since SAR systems are operating independently from external illumination or cloud shadowing, they are suitable for continuous area-wide monitoring of arctic environment...
Article
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The aim of this study is the contextualization of urban growth and sprawl experienced in the coastal conurbation of Mersin in southern Turkey. For this purpose, an interdisciplinary approach is developed by using methods of remote sensing and social sciences. The sample areas identified by using a series of satellite images available for the period...