@article{TuWangWalteretal.2014, author = {Tu, Rui and Wang, Rongjiang and Walter, Thomas R. and Diao, FaQi}, title = {Adaptive recognition and correction of baseline shifts from collocated GPS and accelerometer using two phases Kalman filter}, series = {Advances in space research}, volume = {54}, journal = {Advances in space research}, number = {9}, publisher = {Elsevier}, address = {Oxford}, issn = {0273-1177}, doi = {10.1016/j.asr.2014.07.008}, pages = {1924 -- 1932}, year = {2014}, abstract = {The real-time recognition and precise correction of baseline shifts in strong-motion records is a critical issue for GPS and accelerometer combined processing. This paper proposes a method to adaptively recognize and correct baseline shifts in strong-motion records by utilizing GPS measurements using two phases Kalman filter. By defining four kinds of learning statistics and criteria, the time series of estimated baseline shifts can be divided into four time intervals: initialization, static, transient and permanent. During the time interval in which the transient baseline shift is recognized, the dynamic noise of the Kalman filter system and the length of the baseline shifts estimation window are adaptively adjusted to yield a robust integration solution. The validations from an experimental and real datasets show that acceleration baseline shifts can be precisely recognized and corrected, thus, the combined system adaptively adjusted the estimation strategy to get a more robust solution. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.}, language = {en} } @article{SocquetValdesJaraetal.2017, author = {Socquet, Anne and Valdes, Jesus Pina and Jara, Jorge and Cotton, Fabrice and Walpersdorf, Andrea and Cotte, Nathalie and von Specht, Sebastian and Ortega-Culaciati, Francisco and Carrizo, Daniel and Norabuena, Edmundo}, title = {An 8month slow slip event triggers progressive nucleation of the 2014 Chile megathrust}, series = {Geophysical research letters}, volume = {44}, journal = {Geophysical research letters}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0094-8276}, doi = {10.1002/2017GL073023}, pages = {4046 -- 4053}, year = {2017}, abstract = {The mechanisms leading to large earthquakes are poorly understood and documented. Here we characterize the long-term precursory phase of the 1 April 2014 M(w)8.1 North Chile megathrust. We show that a group of coastal GPS stations accelerated westward 8months before the main shock, corresponding to a M(w)6.5 slow slip event on the subduction interface, 80\% of which was aseismic. Concurrent interface foreshocks underwent a diminution of their radiation at high frequency, as shown by the temporal evolution of Fourier spectra and residuals with respect to ground motions predicted by recent subduction models. Such ground motions change suggests that in response to the slow sliding of the subduction interface, seismic ruptures are progressively becoming smoother and/or slower. The gradual propagation of seismic ruptures beyond seismic asperities into surrounding metastable areas could explain these observations and might be the precursory mechanism eventually leading to the main shock.}, language = {en} } @misc{HeringHauptfleischJagoetal.2022, author = {Hering, Robert and Hauptfleisch, Morgan and Jago, Mark and Smith, Taylor and Kramer-Schadt, Stephanie and Stiegler, Jonas and Blaum, Niels}, title = {Don't stop me now: Managed fence gaps could allow migratory ungulates to track dynamic resources and reduce fence related energy loss}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1278}, issn = {1866-8372}, doi = {10.25932/publishup-57008}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-570087}, pages = {18}, year = {2022}, abstract = {In semi-arid environments characterized by erratic rainfall and scattered primary production, migratory movements are a key survival strategy of large herbivores to track resources over vast areas. Veterinary Cordon Fences (VCFs), intended to reduce wildlife-livestock disease transmission, fragment large parts of southern Africa and have limited the movements of large wild mammals for over 60 years. Consequently, wildlife-fence interactions are frequent and often result in perforations of the fence, mainly caused by elephants. Yet, we lack knowledge about at which times fences act as barriers, how fences directly alter the energy expenditure of native herbivores, and what the consequences of impermeability are. We studied 2-year ungulate movements in three common antelopes (springbok, kudu, eland) across a perforated part of Namibia's VCF separating a wildlife reserve and Etosha National Park using GPS telemetry, accelerometer measurements, and satellite imagery. We identified 2905 fence interaction events which we used to evaluate critical times of encounters and direct fence effects on energy expenditure. Using vegetation type-specific greenness dynamics, we quantified what animals gained in terms of high quality food resources from crossing the VCF. Our results show that the perforation of the VCF sustains herbivore-vegetation interactions in the savanna with its scattered resources. Fence permeability led to peaks in crossing numbers during the first flush of woody plants before the rain started. Kudu and eland often showed increased energy expenditure when crossing the fence. Energy expenditure was lowered during the frequent interactions of ungulates standing at the fence. We found no alteration of energy expenditure when springbok immediately found and crossed fence breaches. Our results indicate that constantly open gaps did not affect energy expenditure, while gaps with obstacles increased motion. Closing gaps may have confused ungulates and modified their intended movements. While browsing, sedentary kudu's use of space was less affected by the VCF; migratory, mixed-feeding springbok, and eland benefited from gaps by gaining forage quality and quantity after crossing. This highlights the importance of access to vast areas to allow ungulates to track vital vegetation patches.}, language = {en} } @article{HeringHauptfleischJagoetal.2022, author = {Hering, Robert and Hauptfleisch, Morgan and Jago, Mark and Smith, Taylor and Kramer-Schadt, Stephanie and Stiegler, Jonas and Blaum, Niels}, title = {Don't stop me now: Managed fence gaps could allow migratory ungulates to track dynamic resources and reduce fence related energy loss}, series = {Frontiers in Ecology and Evolution}, journal = {Frontiers in Ecology and Evolution}, publisher = {Frontiers}, address = {Lausanne, Schweiz}, issn = {2296-701X}, doi = {10.3389/fevo.2022.907079}, pages = {1 -- 18}, year = {2022}, abstract = {In semi-arid environments characterized by erratic rainfall and scattered primary production, migratory movements are a key survival strategy of large herbivores to track resources over vast areas. Veterinary Cordon Fences (VCFs), intended to reduce wildlife-livestock disease transmission, fragment large parts of southern Africa and have limited the movements of large wild mammals for over 60 years. Consequently, wildlife-fence interactions are frequent and often result in perforations of the fence, mainly caused by elephants. Yet, we lack knowledge about at which times fences act as barriers, how fences directly alter the energy expenditure of native herbivores, and what the consequences of impermeability are. We studied 2-year ungulate movements in three common antelopes (springbok, kudu, eland) across a perforated part of Namibia's VCF separating a wildlife reserve and Etosha National Park using GPS telemetry, accelerometer measurements, and satellite imagery. We identified 2905 fence interaction events which we used to evaluate critical times of encounters and direct fence effects on energy expenditure. Using vegetation type-specific greenness dynamics, we quantified what animals gained in terms of high quality food resources from crossing the VCF. Our results show that the perforation of the VCF sustains herbivore-vegetation interactions in the savanna with its scattered resources. Fence permeability led to peaks in crossing numbers during the first flush of woody plants before the rain started. Kudu and eland often showed increased energy expenditure when crossing the fence. Energy expenditure was lowered during the frequent interactions of ungulates standing at the fence. We found no alteration of energy expenditure when springbok immediately found and crossed fence breaches. Our results indicate that constantly open gaps did not affect energy expenditure, while gaps with obstacles increased motion. Closing gaps may have confused ungulates and modified their intended movements. While browsing, sedentary kudu's use of space was less affected by the VCF; migratory, mixed-feeding springbok, and eland benefited from gaps by gaining forage quality and quantity after crossing. This highlights the importance of access to vast areas to allow ungulates to track vital vegetation patches.}, language = {en} } @misc{HeringHauptfleischKramerSchadtetal.2022, author = {Hering, Robert and Hauptfleisch, Morgan and Kramer-Schadt, Stephanie and Stiegler, Jonas and Blaum, Niels}, title = {Effects of fences and fence gaps on the movement behavior of three southern African antelope species}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1308}, issn = {1866-8372}, doi = {10.25932/publishup-58267}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-582672}, pages = {19}, year = {2022}, abstract = {Globally, migratory ungulates are affected by fences. While field observational studies reveal the amount of animal-fence interactions across taxa, GPS tracking-based studies uncover fence effects on movement patterns and habitat selection. However, studies on the direct effects of fences and fence gaps on movement behavior, especially based on high-frequency tracking data, are scarce. We used GPS tracking on three common African antelopes (Tragelaphus strepsiceros, Antidorcas marsupialis, and T. oryx) with movement strategies ranging from range residency to nomadism in a semi-arid, Namibian savanna traversed by wildlife-proof fences that elephants have regularly breached. We classified major forms of ungulate-fence interaction types on a seasonal and a daily scale. Furthermore, we recorded the distances and times spent at fences regarding the total individual space use. Based on this, we analyzed the direct effects of fences and fence gaps on the animals' movement behavior for the previously defined types of animal-fence interactions. Antelope-fence interactions peaked during the early hours of the day and during seasonal transitions when the limiting resource changed between water and forage. Major types of ungulate-fence interactions were quick, trace-like, or marked by halts. We found that the amount of time spent at fences was highest for nomadic eland. Migratory springbok adjusted their space use concerning fence gap positions. If the small home ranges of sedentary kudu included a fence, they frequently interacted with this fence. For springbok and eland, distance traveled along a fence declined with increasing utilization of a fence gap. All species reduced their speed in the proximity of a fence but often increased their speed when encountering the fence. Crossing a fence led to increased speeds for all species. We demonstrate that fence effects mainly occur during crucial foraging times (seasonal scale) and during times of directed movements (daily scale). Importantly, we provide evidence that fences directly alter antelope movement behaviors with negative implications for energy budgets and that persistent fence gaps can reduce the intensity of such alterations. Our findings help to guide future animal-fence studies and provide insights for wildlife fencing and fence gap planning.}, language = {en} } @article{HeringHauptfleischKramerSchadtetal.2022, author = {Hering, Robert and Hauptfleisch, Morgan and Kramer-Schadt, Stephanie and Stiegler, Jonas and Blaum, Niels}, title = {Effects of fences and fence gaps on the movement behavior of three southern African antelope species}, series = {Frontiers in Conservation Science}, volume = {3}, journal = {Frontiers in Conservation Science}, publisher = {Frontiers}, address = {Lausanne, Schweiz}, issn = {2673-611X}, doi = {10.3389/fcosc.2022.959423}, pages = {1 -- 19}, year = {2022}, abstract = {Globally, migratory ungulates are affected by fences. While field observational studies reveal the amount of animal-fence interactions across taxa, GPS tracking-based studies uncover fence effects on movement patterns and habitat selection. However, studies on the direct effects of fences and fence gaps on movement behavior, especially based on high-frequency tracking data, are scarce. We used GPS tracking on three common African antelopes (Tragelaphus strepsiceros, Antidorcas marsupialis, and T. oryx) with movement strategies ranging from range residency to nomadism in a semi-arid, Namibian savanna traversed by wildlife-proof fences that elephants have regularly breached. We classified major forms of ungulate-fence interaction types on a seasonal and a daily scale. Furthermore, we recorded the distances and times spent at fences regarding the total individual space use. Based on this, we analyzed the direct effects of fences and fence gaps on the animals' movement behavior for the previously defined types of animal-fence interactions. Antelope-fence interactions peaked during the early hours of the day and during seasonal transitions when the limiting resource changed between water and forage. Major types of ungulate-fence interactions were quick, trace-like, or marked by halts. We found that the amount of time spent at fences was highest for nomadic eland. Migratory springbok adjusted their space use concerning fence gap positions. If the small home ranges of sedentary kudu included a fence, they frequently interacted with this fence. For springbok and eland, distance traveled along a fence declined with increasing utilization of a fence gap. All species reduced their speed in the proximity of a fence but often increased their speed when encountering the fence. Crossing a fence led to increased speeds for all species. We demonstrate that fence effects mainly occur during crucial foraging times (seasonal scale) and during times of directed movements (daily scale). Importantly, we provide evidence that fences directly alter antelope movement behaviors with negative implications for energy budgets and that persistent fence gaps can reduce the intensity of such alterations. Our findings help to guide future animal-fence studies and provide insights for wildlife fencing and fence gap planning.}, language = {en} } @phdthesis{Antonoglou2024, author = {Antonoglou, Nikolaos}, title = {GNSS-based remote sensing: Innovative observation of key hydrological parameters in the Central Andes}, doi = {10.25932/publishup-62825}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-628256}, school = {Universit{\"a}t Potsdam}, pages = {xxii, 116}, year = {2024}, abstract = {The Central Andean region is characterized by diverse climate zones with sharp transitions between them. In this work, the area of interest is the South-Central Andes in northwestern Argentina that borders with Bolivia and Chile. The focus is the observation of soil moisture and water vapour with Global Navigation Satellite System (GNSS) remote-sensing methodologies. Because of the rapid temporal and spatial variations of water vapour and moisture circulations, monitoring this part of the hydrological cycle is crucial for understanding the mechanisms that control the local climate. Moreover, GNSS-based techniques have previously shown high potential and are appropriate for further investigation. This study includes both logistic-organization effort and data analysis. As for the prior, three GNSS ground stations were installed in remote locations in northwestern Argentina to acquire observations, where there was no availability of third-party data. The methodological development for the observation of the climate variables of soil moisture and water vapour is independent and relies on different approaches. The soil-moisture estimation with GNSS reflectometry is an approximation that has demonstrated promising results, but it has yet to be operationally employed. Thus, a more advanced algorithm that exploits more observations from multiple satellite constellations was developed using data from two pilot stations in Germany. Additionally, this algorithm was slightly modified and used in a sea-level measurement campaign. Although the objective of this application is not related to monitoring hydrological parameters, its methodology is based on the same principles and helps to evaluate the core algorithm. On the other hand, water-vapour monitoring with GNSS observations is a well-established technique that is utilized operationally. Hence, the scope of this study is conducting a meteorological analysis by examining the along-the-zenith air-moisture levels and introducing indices related to the azimuthal gradient. The results of the experiments indicate higher-quality soil moisture observations with the new algorithm. Furthermore, the analysis using the stations in northwestern Argentina illustrates the limits of this technology because of varying soil conditions and shows future research directions. The water-vapour analysis points out the strong influence of the topography on atmospheric moisture circulation and rainfall generation. Moreover, the GNSS time series allows for the identification of seasonal signatures, and the azimuthal-gradient indices permit the detection of main circulation pathways.}, language = {en} } @phdthesis{Hoechner2010, author = {H{\"o}chner, Andreas}, title = {GPS based analysis of earthquake induced phenomena at the Sunda Arc}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-53166}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Indonesia is one of the countries most prone to natural hazards. Complex interaction of several tectonic plates with high relative velocities leads to approximately two earthquakes with magnitude Mw>7 every year, being more than 15\% of the events worldwide. Earthquakes with magnitude above 9 happen far more infrequently, but with catastrophic effects. The most severe consequences thereby arise from tsunamis triggered by these subduction-related earthquakes, as the Sumatra-Andaman event in 2004 showed. In order to enable efficient tsunami early warning, which includes the estimation of wave heights and arrival times, it is necessary to combine different types of real-time sensor data with numerical models of earthquake sources and tsunami propagation. This thesis was created as a result of the GITEWS project (German Indonesian Tsunami Early Warning System). It is based on five research papers and manuscripts. Main project-related task was the development of a database containing realistic earthquake scenarios for the Sunda Arc. This database provides initial conditions for tsunami propagation modeling used by the simulation system at the early warning center. An accurate discretization of the subduction geometry, consisting of 25x150 subfaults was constructed based on seismic data. Green's functions, representing the deformational response to unit dip- and strike slip at the subfaults, were computed using a layered half-space approach. Different scaling relations for earthquake dimensions and slip distribution were implemented. Another project-related task was the further development of the 'GPS-shield' concept. It consists of a constellation of near field GPS-receivers, which are shown to be very valuable for tsunami early warning. The major part of this thesis is related to the geophysical interpretation of GPS data. Coseismic surface displacements caused by the 2004 Sumatra earthquake are inverted for slip at the fault. The effect of different Earth layer models is tested, favoring continental structure. The possibility of splay faulting is considered and shown to be a secondary order effect in respect to tsunamigenity for this event. Tsunami models based on source inversions are compared to satellite radar altimetry observations. Postseismic GPS time series are used to test a wide parameter range of uni- and biviscous rheological models of the asthenosphere. Steady-state Maxwell rheology is shown to be incompatible with near-field GPS data, unless large afterslip, amounting to more than 10\% of the coseismic moment is assumed. In contrast, transient Burgers rheology is in agreement with data without the need for large aseismic afterslip. Comparison to postseismic geoid observation by the GRACE satellites reveals that even with afterslip, the model implementing Maxwell rheology results in amplitudes being too small, and thus supports a biviscous asthenosphere. A simple approach based on the assumption of quasi-static deformation propagation is introduced and proposed for inversion of coseismic near-field GPS time series. Application of this approach to observations from the 2004 Sumatra event fails to quantitatively reconstruct the rupture propagation, since a priori conditions are not fulfilled in this case. However, synthetic tests reveal the feasibility of such an approach for fast estimation of rupturing properties.}, language = {en} } @misc{MayerUllmannSundeetal.2018, author = {Mayer, Martin and Ullmann, Wiebke and Sunde, Peter and Fischer, Christina and Blaum, Niels}, title = {Habitat selection by the European hare in arable landscapes}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1076}, issn = {1866-8372}, doi = {10.25932/publishup-46789}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-467891}, pages = {17}, year = {2018}, abstract = {Agricultural land-use practices have intensified over the last decades, leading to population declines of various farmland species, including the European hare (Lepus europaeus). In many European countries, arable fields dominate agricultural landscapes. Compared to pastures, arable land is highly variable, resulting in a large spatial variation of food and cover for wildlife over the course of the year, which potentially affects habitat selection by hares. Here, we investigated within-home-range habitat selection by hares in arable areas in Denmark and Germany to identify habitat requirements for their conservation. We hypothesized that hare habitat selection would depend on local habitat structure, that is, vegetation height, but also on agricultural field size, vegetation type, and proximity to field edges. Active hares generally selected for short vegetation (1-25 cm) and avoided higher vegetation and bare ground, especially when fields were comparatively larger. Vegetation >50 cm potentially restricts hares from entering parts of their home range and does not provide good forage, the latter also being the case on bare ground. The vegetation type was important for habitat selection by inactive hares, with fabaceae, fallow, and maize being selected for, potentially providing both cover and forage. Our results indicate that patches of shorter vegetation could improve the forage quality and habitat accessibility for hares, especially in areas with large monocultures. Thus, policymakers should aim to increase areas with short vegetation throughout the year. Further, permanent set-asides, like fallow and wildflower areas, would provide year-round cover for inactive hares. Finally, the reduction in field sizes would increase the density of field margins, and farming different crop types within small areas could improve the habitat for hares and other farmland species.}, language = {en} } @article{MayerUllmannSundeetal.2018, author = {Mayer, Martin and Ullmann, Wiebke and Sunde, Peter and Fischer, Christina and Blaum, Niels}, title = {Habitat selection by the European hare in arable landscapes}, series = {Ecology and Evolution}, volume = {8}, journal = {Ecology and Evolution}, number = {23}, publisher = {Wiley}, address = {Hoboken}, issn = {2045-7758}, doi = {10.1002/ece3.4613}, pages = {11619 -- 11633}, year = {2018}, abstract = {Agricultural land-use practices have intensified over the last decades, leading to population declines of various farmland species, including the European hare (Lepus europaeus). In many European countries, arable fields dominate agricultural landscapes. Compared to pastures, arable land is highly variable, resulting in a large spatial variation of food and cover for wildlife over the course of the year, which potentially affects habitat selection by hares. Here, we investigated within-home-range habitat selection by hares in arable areas in Denmark and Germany to identify habitat requirements for their conservation. We hypothesized that hare habitat selection would depend on local habitat structure, that is, vegetation height, but also on agricultural field size, vegetation type, and proximity to field edges. Active hares generally selected for short vegetation (1-25 cm) and avoided higher vegetation and bare ground, especially when fields were comparatively larger. Vegetation >50 cm potentially restricts hares from entering parts of their home range and does not provide good forage, the latter also being the case on bare ground. The vegetation type was important for habitat selection by inactive hares, with fabaceae, fallow, and maize being selected for, potentially providing both cover and forage. Our results indicate that patches of shorter vegetation could improve the forage quality and habitat accessibility for hares, especially in areas with large monocultures. Thus, policymakers should aim to increase areas with short vegetation throughout the year. Further, permanent set-asides, like fallow and wildflower areas, would provide year-round cover for inactive hares. Finally, the reduction in field sizes would increase the density of field margins, and farming different crop types within small areas could improve the habitat for hares and other farmland species.}, language = {en} }