Sufficient plant-available water is one of the most important requirements for vital, stable, and... more Sufficient plant-available water is one of the most important requirements for vital, stable, and well-growing forest stands. In the face of climate change, there are various approaches to derive recommendations considering tree species selection based on plant-available water provided by measurements or simulations. Owing to the small-parcel management of Central European forests as well as small-spatial variation of soil and stand properties, in situ data collection for individual forest stands of large areas is not feasible, considering time and cost effort. This problem can be addressed using physically based modeling, aiming to numerically simulate the water balance. In this study, we parameterized, calibrated, and verified the hydrological multidimensional WaSiM-ETH model to assess the water balance at a spatial resolution of 30 m in a German forested catchment area (136.4 km2) for the period 2000–2021 using selected in situ data, remote sensing products, and total runoff. Bas...
Drylands cover approximately 40% of the Earth’s land surface and are home to over a quarter of th... more Drylands cover approximately 40% of the Earth’s land surface and are home to over a quarter of the global population. Despite the deficit of surface water, rare but strong precipitation events are the fundamental driver for geomorphic activity in arid regions. A quantification of the frequency and magnitude of episodic river discharge is essential for a robust characterization of flood hazards and, thus, better understanding of the poorly studied hydromorphodynamics in deserts. However, observation data from gauges are sparsely distributed and, if existent, often do not cover a sufficiently long seamless time series or feature extensive gaps. This applies, for instance, to the remote Northwest Namibia, where more than a dozen ephemeral rivers drain the Kunene Highlands towards the Skeleton Coast, yet daily river flow data for a period of several decades is only available from the Hoanib.Hence, we propose a workflow based on the Landsat multispectral satellite imagery archive to dete...
This study demonstrates a circum-Arctic monitoring framework for quantifying annual change of per... more This study demonstrates a circum-Arctic monitoring framework for quantifying annual change of permafrost-affected coasts at a spatial resolution of 10 m. Frequent cloud coverage and challenging lighting conditions, including polar night, limit the usability of optical data in Arctic regions. For this reason, Synthetic Aperture RADAR (SAR) data in the form of annual median and standard deviation (sd) Sentinel-1 (S1) backscatter images covering the months June–September for the years 2017–2021 were computed. Annual composites for the year 2020 were hereby utilized as input for the generation of a high-quality coastline product via a Deep Learning (DL) workflow, covering 161,600 km of the Arctic coastline. The previously computed annual S1 composites for the years 2017 and 2021 were employed as input data for the Change Vector Analysis (CVA)-based coastal change investigation. The generated DL coastline product served hereby as a reference. Maximum erosion rates of up to 67 m per year ...
Arctic permafrost coasts become increasingly vulnerable due to environmental drivers such as the ... more 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 permafrost coastlines. This study presents a novel approach to quantify annual Arctic coastal erosion and build-up rates based on Sentinel-1 (S1) Synthetic Aperture RADAR (SAR) backscatter data, in combination with Deep Learning (DL) and Change Vector Analysis (CVA). The methodology includes the generation of a high-quality Arctic coastline product via DL, which acted as a reference for quantifying coastal erosion and build-up rates from annual median and standard deviation (sd) backscatter images via CVA. The analysis was applied on ten test sites distributed across the Arctic and covering about 1038 km of coastline. Results revealed maximum er...
Grasslands cover one-third of the agricultural area in Germany and play an important economic rol... more 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 Europe, grasslands are grazed and/or mown, whereby the management type and intensity vary in space and time. Spatial information on the mowing timing and frequency on larger scales are usually not available but would be required in order to assess the ecosystem services, species composition, and grassland yields. Time series of high-resolution satellite remote sensing data can be used to analyze the temporal and spatial dynamics of grasslands. Within this study, we aim to overcome the drawbacks identified by previous studies, such as optical data availability and the lack of comprehensive reference data, by testing the time series of various Se...
Agroforestry systems (AFS) offer viable solutions for climate change because of the aboveground b... more Agroforestry systems (AFS) offer viable solutions for climate change because of the aboveground 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 including the spatial distributions within the AFS, their structure, their composition, and their variable extents hinder an accurate RS-assisted estimation of the AGB across AFS. The aim of this study is to (i) evaluate the potential of spaceborne optical, SAR and LiDAR data for AGB estimations in AFS and (ii) estimate the AGB of different AFS in various climatic regions. The study was carried out in three climatic regions covering Côte d’Ivoire and Burkina Faso. Two AGB reference data sources were assessed: (i) AGB estimations derived from field measurements using allometric equations and (ii) AGB predictions from the GEDI level 4A (L4A)...
Vietnam’s 3260 km coastline is densely populated, experiences rapid urban and economic growth, an... more 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 for Vietnam’s entire coastal zone using the Landsat archive. The proposed method is implemented within the cloud-computing platform Google Earth Engine to only involve publicly and globally available datasets and tools. We generated annual coastline composites representing the mean-high water level and extracted sub-pixel coastlines. We further quantified coastline change rates along shore-perpendicular transects, revealing that half of Vietnam’s coast did not experience significant change, while the remaining half is classified as erosional (27.7%) and accretional (27.1%). A hotspot analysis shows that coastal segments with the highest c...
Cocoa growing is one of the main activities in humid West Africa, which is mainly grown in pure s... more 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 of this research is to model the spatial distribution of uncertainties in the classification cocoa agroforestry. The study was carried out in Côte d’Ivoire, close to the Taï National Park. The analysis followed three steps (i) image classification based on texture parameters and vegetation indices from Sentinel-1 and -2 data respectively, to train a random forest algorithm. A classified map with the associated probability maps was generated. (ii) Shannon entropy was calculated from the probability maps, to get the error maps at different thresholds (0.2, 0.3, 0.4 and 0.5). Then, (iii) the generated error maps were analysed using a Geograph...
<p>The temple areas in ancient Egypt were most sacred and characterized by ... more <p>The temple areas in ancient Egypt were most sacred and characterized by a multitude of elements that emphasized their importance and enabled daily cultic activities. Very specific and important features of such temples were sacred water canals or lakes, the so-called <em>Isheru</em>, which provided water for all kinds of purification rites and activities. In addition to textual records, preliminary sedimentological analyses of core drillings and geophysical surveys provided geoarchaeological evidence of a sacred water body at the Temple of Bastet in the ancient city of Bubastis. To further explore the location, shape, or course of the already detected canal and to find evidence on the existence of a second waterway described by Herodotus in the 5th century BCE, 34 drillings and five 2D geoelectrical measurements were carried. Drilling and sediment analyses revealed loamy to clayey deposits with a thickness of up to five meters near the northern and southern enclosures of the Temple of Bastet. 2D electrical surveying confirmed the drilling results, indicating trench-formed layers of low resistivity values. The recovered deposits were interpreted as fluvial sediments, most likely deposited in a very low energy system, e.g. a canal or lake. Evidence of these fluvial sediments in numerous boreholes allows the reconstruction of two separate sacred canals both north and south of the Temple of Bastet. In addition to the course, the width of the canals of about 30 m can also be confirmed according to Herodotus' writings. The presence of numerous artefacts in the fluvial deposits, such as ceramic and limestone fragments, proves the anthropogenic use of the ancient canals. Presumably, these waterways were connected to the Nile via a tributary or canal located west or northwest of Bubastis.</p>
Collection of conference abstracts presented at the vDEUQUA2021 (2021-09-30 to 2021-09-01), the v... more Collection of conference abstracts presented at the vDEUQUA2021 (2021-09-30 to 2021-09-01), the virtual meeting of the German Quaternary Association (DEUQUA).
Sufficient plant-available water is one of the most important requirements for vital, stable, and... more Sufficient plant-available water is one of the most important requirements for vital, stable, and well-growing forest stands. In the face of climate change, there are various approaches to derive recommendations considering tree species selection based on plant-available water provided by measurements or simulations. Owing to the small-parcel management of Central European forests as well as small-spatial variation of soil and stand properties, in situ data collection for individual forest stands of large areas is not feasible, considering time and cost effort. This problem can be addressed using physically based modeling, aiming to numerically simulate the water balance. In this study, we parameterized, calibrated, and verified the hydrological multidimensional WaSiM-ETH model to assess the water balance at a spatial resolution of 30 m in a German forested catchment area (136.4 km2) for the period 2000–2021 using selected in situ data, remote sensing products, and total runoff. Bas...
Drylands cover approximately 40% of the Earth’s land surface and are home to over a quarter of th... more Drylands cover approximately 40% of the Earth’s land surface and are home to over a quarter of the global population. Despite the deficit of surface water, rare but strong precipitation events are the fundamental driver for geomorphic activity in arid regions. A quantification of the frequency and magnitude of episodic river discharge is essential for a robust characterization of flood hazards and, thus, better understanding of the poorly studied hydromorphodynamics in deserts. However, observation data from gauges are sparsely distributed and, if existent, often do not cover a sufficiently long seamless time series or feature extensive gaps. This applies, for instance, to the remote Northwest Namibia, where more than a dozen ephemeral rivers drain the Kunene Highlands towards the Skeleton Coast, yet daily river flow data for a period of several decades is only available from the Hoanib.Hence, we propose a workflow based on the Landsat multispectral satellite imagery archive to dete...
This study demonstrates a circum-Arctic monitoring framework for quantifying annual change of per... more This study demonstrates a circum-Arctic monitoring framework for quantifying annual change of permafrost-affected coasts at a spatial resolution of 10 m. Frequent cloud coverage and challenging lighting conditions, including polar night, limit the usability of optical data in Arctic regions. For this reason, Synthetic Aperture RADAR (SAR) data in the form of annual median and standard deviation (sd) Sentinel-1 (S1) backscatter images covering the months June–September for the years 2017–2021 were computed. Annual composites for the year 2020 were hereby utilized as input for the generation of a high-quality coastline product via a Deep Learning (DL) workflow, covering 161,600 km of the Arctic coastline. The previously computed annual S1 composites for the years 2017 and 2021 were employed as input data for the Change Vector Analysis (CVA)-based coastal change investigation. The generated DL coastline product served hereby as a reference. Maximum erosion rates of up to 67 m per year ...
Arctic permafrost coasts become increasingly vulnerable due to environmental drivers such as the ... more 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 permafrost coastlines. This study presents a novel approach to quantify annual Arctic coastal erosion and build-up rates based on Sentinel-1 (S1) Synthetic Aperture RADAR (SAR) backscatter data, in combination with Deep Learning (DL) and Change Vector Analysis (CVA). The methodology includes the generation of a high-quality Arctic coastline product via DL, which acted as a reference for quantifying coastal erosion and build-up rates from annual median and standard deviation (sd) backscatter images via CVA. The analysis was applied on ten test sites distributed across the Arctic and covering about 1038 km of coastline. Results revealed maximum er...
Grasslands cover one-third of the agricultural area in Germany and play an important economic rol... more 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 Europe, grasslands are grazed and/or mown, whereby the management type and intensity vary in space and time. Spatial information on the mowing timing and frequency on larger scales are usually not available but would be required in order to assess the ecosystem services, species composition, and grassland yields. Time series of high-resolution satellite remote sensing data can be used to analyze the temporal and spatial dynamics of grasslands. Within this study, we aim to overcome the drawbacks identified by previous studies, such as optical data availability and the lack of comprehensive reference data, by testing the time series of various Se...
Agroforestry systems (AFS) offer viable solutions for climate change because of the aboveground b... more Agroforestry systems (AFS) offer viable solutions for climate change because of the aboveground 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 including the spatial distributions within the AFS, their structure, their composition, and their variable extents hinder an accurate RS-assisted estimation of the AGB across AFS. The aim of this study is to (i) evaluate the potential of spaceborne optical, SAR and LiDAR data for AGB estimations in AFS and (ii) estimate the AGB of different AFS in various climatic regions. The study was carried out in three climatic regions covering Côte d’Ivoire and Burkina Faso. Two AGB reference data sources were assessed: (i) AGB estimations derived from field measurements using allometric equations and (ii) AGB predictions from the GEDI level 4A (L4A)...
Vietnam’s 3260 km coastline is densely populated, experiences rapid urban and economic growth, an... more 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 for Vietnam’s entire coastal zone using the Landsat archive. The proposed method is implemented within the cloud-computing platform Google Earth Engine to only involve publicly and globally available datasets and tools. We generated annual coastline composites representing the mean-high water level and extracted sub-pixel coastlines. We further quantified coastline change rates along shore-perpendicular transects, revealing that half of Vietnam’s coast did not experience significant change, while the remaining half is classified as erosional (27.7%) and accretional (27.1%). A hotspot analysis shows that coastal segments with the highest c...
Cocoa growing is one of the main activities in humid West Africa, which is mainly grown in pure s... more 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 of this research is to model the spatial distribution of uncertainties in the classification cocoa agroforestry. The study was carried out in Côte d’Ivoire, close to the Taï National Park. The analysis followed three steps (i) image classification based on texture parameters and vegetation indices from Sentinel-1 and -2 data respectively, to train a random forest algorithm. A classified map with the associated probability maps was generated. (ii) Shannon entropy was calculated from the probability maps, to get the error maps at different thresholds (0.2, 0.3, 0.4 and 0.5). Then, (iii) the generated error maps were analysed using a Geograph...
<p>The temple areas in ancient Egypt were most sacred and characterized by ... more <p>The temple areas in ancient Egypt were most sacred and characterized by a multitude of elements that emphasized their importance and enabled daily cultic activities. Very specific and important features of such temples were sacred water canals or lakes, the so-called <em>Isheru</em>, which provided water for all kinds of purification rites and activities. In addition to textual records, preliminary sedimentological analyses of core drillings and geophysical surveys provided geoarchaeological evidence of a sacred water body at the Temple of Bastet in the ancient city of Bubastis. To further explore the location, shape, or course of the already detected canal and to find evidence on the existence of a second waterway described by Herodotus in the 5th century BCE, 34 drillings and five 2D geoelectrical measurements were carried. Drilling and sediment analyses revealed loamy to clayey deposits with a thickness of up to five meters near the northern and southern enclosures of the Temple of Bastet. 2D electrical surveying confirmed the drilling results, indicating trench-formed layers of low resistivity values. The recovered deposits were interpreted as fluvial sediments, most likely deposited in a very low energy system, e.g. a canal or lake. Evidence of these fluvial sediments in numerous boreholes allows the reconstruction of two separate sacred canals both north and south of the Temple of Bastet. In addition to the course, the width of the canals of about 30 m can also be confirmed according to Herodotus' writings. The presence of numerous artefacts in the fluvial deposits, such as ceramic and limestone fragments, proves the anthropogenic use of the ancient canals. Presumably, these waterways were connected to the Nile via a tributary or canal located west or northwest of Bubastis.</p>
Collection of conference abstracts presented at the vDEUQUA2021 (2021-09-30 to 2021-09-01), the v... more Collection of conference abstracts presented at the vDEUQUA2021 (2021-09-30 to 2021-09-01), the virtual meeting of the German Quaternary Association (DEUQUA).
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Papers by Tobias Ullmann