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Seasonal and Long-Term Vegetation Effects on Sentinel-1 Range Coregistration Shifts
Get PDFIn the SAR4Tectonics project, targeted at measuring ground deformation in tectonically active zones, we processed, with interferometric techniques, over 1500 stacks of Sentinel-1 SLCs, averaging 160 images per stack. During the InSAR processing, coregistration was performed between the stack reference image, located at the center of the time series, and all other images. This was achieved using patch-based incoherent cross-correlation for the range direction and the Enhanced Spectral Diversity technique for the azimuth direction. Several corrections were applied beforehand, including instrument timing correction, tropospheric and ionospheric path delays, and solid Earth tides. Tectonic plate motions were afterwards also removed from the coregistration shifts using GNSS data. The remaining shifts should primarily reflect residuals from the correction process, orbit-related errors, and random noise.
Unexpectedly, residual range coregistration shifts exhibit systematic trends and yearly oscillations in forested regions, with non-vegetated areas showing the expected zero-mean, uncorrelated, and flat residuals. These signals are consistent between ascending and descending stacks, with the trends always directed towards the satellite (shortening the radar range). Over vegetated temperate regions, trends average approximately 5 cm/year, increasing to around 10 cm/year in equatorial and tropical regions. Oscillations have amplitudes ranging from 10 to 80 cm, with the largest values in tropical and temperate areas, and minimal oscillations (<5 cm) in equatorial regions. The oscillation peaks (minimum delay) occur consistently within climatic zones, around June in temperate regions, September in tropical areas, and January in the southern Hemisphere.
The correlation of these signals with vegetation cover and climatic zones rules out significant correction errors, such as those linked to the ionospheric effects of the growing solar cycle or uncompensated tectonic motion. Instead, the signals seem to suggest that radar delay is influenced by seasonal vegetation dynamics and longer-term multiyear trends, possibly linked to variations in plant water content, as well as their slow growth over time. These signals contrast with results from persistent and distributed scatterers (PS/DS), which primarily capture well-known phenomena such as ground deformation from tectonic motion or subsidence due to groundwater extraction. However, PS/DS are generally absent over vegetated areas, meaning no PS/DS measurements are available to confirm the coregistration residual signals observed in these regions.
To our knowledge, this phenomenon represents a novel discovery. While the exact physical mechanisms driving these trends is still unclear, these findings seem to suggest that radar delays could be used in an innovative way to monitor vegetation growth and inter-annual variability, which could also provide insights into plant health or drought stress
Assessing Sand Deposit Dynamics at the Island of Langeoog, Germany by Means of Multi-Sensor Remote Sensing Data
No full textLangeoog is one of the East Frisian Islands located in the German Wadden Sea. The island's coastal morphodynamics are strongly influenced by environmental factors such as tides and currents. As natural sediment supplies cannot always compensate for coastal erosion of sand deposits, coastal protection measures are crucial for preserving the island. Langeoog is a special case in this context, as it is the only island in the barrier island chain that is mostly managed without the use of coastal protection structures such as groynes or revetments, due to its prevailing current and sedimentation processes. The island’s settlement and infrastructure are surrounded by a protective dune and adjacent sandy beach areas to the west and north. Conservation measures to preserve the dune are only necessary in the northern part, in front of the Pirolatal, where sand replenishments are carried out regularly to counteract ongoing beach erosion by restocking the sand deposits in front of the protective dune. To initiate necessary measures and estimate the required sediment volumes, knowledge about the development of this beach section is essential for local coastal protection authorities. In this study, we investigate the suitability of optical multi-sensor remote sensing data to analyse changes in the sand deposits and their effects on the condition of the protective dune in front of Pirolatal on Langeoog Island from 2018 to 2023. For this purpose, we processed high-resolution (HR) and medium-resolution (MR) optical satellite data, applying index-based threshold methods to estimate several proxies of coastal dynamics, such as the instantaneous waterline, the location and state of the protective dune, and the extent of permanently dry sand areas under regular tidal conditions. We compare the results to elevation data to assess the potential of 2D remote sensing data for monitoring this coastal section. The results show that the state of the beach and the height of the dune’s break-off are strongly influenced by accretion events (sand replenishments) and ongoing erosion, particularly during storm surges in the winter season. The condition of the sand deposit is also crucial for determining the position of the instantaneous waterline. This study demonstrates the benefit of a multi-sensor optical satellite data approach to support coastal monitoring and applied coastal protection efforts
Exciting families of passive gaits in an elastic quadruped via natural motion manifold control
Get PDFMotivated by the need for efficiency and robustness in repetitive robotic tasks such as locomotion, this study introduces the concept of Natural Motion Manifolds (NMMs) and presents a control method to stabilize and excite motions based on these structures. By considering the intersection of a Poincaré section with a surface comprising a continuum of autonomous evolutions, the proposed controller extends the linearized Poincaré map control from a single orbit to a family of orbits. This allows us to derive simple controllers to excite intrinsic nonlinear resonances and exploit the natural dynamics when varying the energy target (or the running velocity). We validated the method through simulations and experiments on a serial elastic quadruped. Relying on natural dynamics and minimal motor commands, we could implement a bounding gait at desired velocities without needing dynamic compensations. The experiments provide a thorough validation of the feasibility and the benefits of controlled, predictable, and purposeful oscillatory behavior via explicit excitation of a quadruped's natural dynamics
The Modular Earth Submodel System (MESSy): Long Lasting Interface Concept on Its Way into the Future
No full textOverview of the Modular Earth Submodel System (MESSy) integrated framework in light of setting up a long lasting software interface
Entwicklung und Validierung eines Wasserstoffzug-Antriebsstrangmodells zur Untersuchung von Energieeffizienzmaßnahmen
No full textIm europaischen Schienennetz kommen immer häufiger Wasserstoffzüge zum Einsatz. Sie bieten eine vielversprechende Alternative zu batteriebetriebenen ZÜgen, da sie dank der Nutzung von Wasserstoff nicht auf lange Ladezeiten angewiesen sind. Dennoch ist die Effizienz solcher Systeme aufgrund der Brennstoffzelle begrenzt. Zudem ist Wasserstoff als Energietrager teuer. Daher ist es entscheidend, zu untersuchen, wie Brennstoffzellenzuge betrieben werden mÜssen, um die bestmögliche Effizienz zu erzielen. Hierbei können Modellierungen in Python unterstutzen, indem sie Fahrweisen und Energiemanagement-Strategien analysieren. Solche Modellierungen ermoglichen es, Optimierungspotenziale aufzudecken und Betriebsstrategien zu entwickeln.
Im Rahmen dieser Arbeit wurde aufgezeigt, dass durch gezielte Nutzung von Leerlaufphasen des Zuges und reduzierte Hochstgeschwindigkeiten der Wasserstoffverbrauch um 8,2% bzw. 7,9%. gesenkt werden kann. Die Untersuchung von Energiemanagement-Strategien zeigt außerdem, dass der Betrieb der Brennstoffzelle an einem optimalen Betriebspunkt entscheidend fur die Effizienz des Systems ist. Mit einer Energiemanagement-Strategie, bei der die Batterie bewusst mit geringerer Leistung geladen wurde, konnten 28,8% Wasserstoff eingespart werden. Eine weitere Energiemanagement-Strategie, bei der zusatzlich verschiedene Ladebereiche-Bereiche der Batterie betrachtet wurden, um die Leistung der Brennstoffzelle zu regulieren, führte sogar zu einer Reduktion des Verbrauchs um 38,6%. Zudem wurde in beiden Fallenüberschüssige Energie besser vom System genutzt. Insgesamt konnte damit gezeigt werden, dass ein optimiertes Energiemanagement, welches die Brennstoffzelle in einem effizienten Betriebspunkt halt und überschüssige Energie besser nutzt, wesentlich zur Steigerung der Energieeffizienz beiträgt
Investigation of CH4 emissions from boreal wetlands by remote sensing during the airborne CoMet 2.0 campaign
Get PDFMethane (CH4) is a potent greenhouse gas, and its atmospheric concentration has been rising due to emissions from both anthropogenic and natural sources. Recognizing its significant impact on climate change, several international treaties, such as the Global Methane Pledge, have identified CH4 reduction as a key mitigation target. Accurately quantifying its emissions is essential for understanding their respective contributions to climate change and improving global CH4 budgets. In particular, natural sources such as wetlands play a crucial role but remain highly uncertain, making it difficult to predict future CH4 dynamics. Wetlands are recognised as the largest natural CH4 source. Nevertheless, they also represent the most significant source of uncertainty in CH4 emissions estimates. In August/September 2022, the German Aerospace Center conducted an airborne campaign over Canada. The objective of the mission was to measure the weighted column-integrated dry-air molar mixing ratios of CH4. These were measured below the aircraft along its flight
track over boreal wetlands. The measurements were taken using an IPDA lidar, which was mounted on board the research aircraft. Several flights over the Hudson Bay Lowlands, which is one of the largest Arctic-boreal wetlands in the world with significant contribution to the global CH4 budget were conducted as part of the campaign. The objective of this study was to quantify regional and large scale (between 36 km and 889 km) gradients in CH4 concentration using lidar. These gradients are used in a mass balance approach to calculate CH4 fluxes. In this approach, a desig-
nated upwind and downwind region is established within the area of interest. Inside these regions, the difference between the inflow and outflow of methane concentration is measured to assess the increase in methane concentration. As this method requires, next to the methane concentration, also information about the transport, wind information is taken from a numerical weather prediction model.
Data from three individual flights were analysed in detail. Not all of the three flights show a general accumulation of CH4 along the wind direction. Furthermore, the circumstances for calculating emissions vary between the three flights. The flights differ in their flight pattern, the wind speed, the homogeneity of the wind, and the CH4 distribution. Nevertheless, it was possible to calculate fluxes that differed for the various flights. Backward trajectories from HYSPLIT showed the history of air parcels along the wind. In order to explain the results, the backward trajectories and emission estimates from WetCHARTs are used.
Overall this study showed that a maximum gradient of up to 11 ppb (across a distance of approximately 600 km) could be observed, epresenting a relative increase of 0.55 %. The mass balance approach typically works best for ideal conditions: well mixed boundary layer, homogeneous wind perpendicular to upwind and downwind region, uniform methane source distribution and therefore lower upwind concentration than downwind concentrations
Thermische Analyse der Temperaturverteilung im additiven High-Speed Sintering Verfahren zur lokalen Optimierung von PA12-Bauteileigenschaften
Get PDFDiese Studie untersuchte die inhomogene Temperaturverteilung im Pulverbett beim
High-Speed-Sintering (HSS)-Verfahren. Der Fokus lag auf der Analyse des thermischen Verhaltens mithilfe von Infrarot-(IR)-Thermographie, um die Temperaturverteilung innerhalb einzelner Schichten besser zu verstehen und zu homogenisieren. Zur
gezielten Homogenisierung der Temperaturverteilung wurden sieben verschiedene
Graustufen (GS1-GS7) als Werkzeug zur lokalen Steuerung des Energieeintrags
eingesetzt. Thermische Analysen zeigten positions- und schichtabhängige Gradienten innerhalb der Baukammer, wobei zentrale Bereiche höhere Temperaturen als die
Ränder aufwiesen. Mechanische Tests zeigten eine Abhängigkeit zwischen den GS
und den Materialeigenschaften: GS3-Proben zeigten höhere Zugfestigkeit und geringere Streuung. Obwohl andere GS teilweise ähnliche Temperaturen erreichten, blieb
dieses Ergebnis aus. Dunklere GS und höhere Temperaturen führten zu einer Vergrößerung der Bauteilabmessungen. Durch die gezielte Einbringung von GS, angepasst an die ermittelten Temperaturgradienten, konnten die Temperaturverteilung erfolgreich homogenisiert und die Bauteileigenschaften optimiert werden. Die Ergebnisse dienen als Grundlage für die Entwicklung einer Methode zur Homogenisierung
thermischer Inhomogenitäten im HSS-Prozess
Reparaturprozess eines Winglets: Problemvisualisierung mittels Virtual Reality
No full textIn der Luftfahrtbranche stellen effiziente und zuverlässige Maintenance-, Repair- and Overhaul-Prozesse einen essenziellen Bestandteil des sicheren Flugbetriebs dar. Insbesondere bei der Reparatur komplexer Faserverbundbauteile wie Winglets treten in der Praxis häufig Ineffizienzen auf, etwa durch verschiedene Dokumentationsformen oder durch viele zu treffende Absprachen vieler beteiligter Akteure. Ziel dieser Arbeit war es, eine Virtual-Reality-Anwendung zu entwickeln, welche exemplarisch zwei zentrale Problemfelder im Reparaturprozess eines Winglets visualisiert. Durch eine immersive, interaktive Darstellung sollen Nutzer ein besseres Verständnis für Prozessineffizienzen erlangen. Die Anwendung wurde mit der Open-Source-Game-Engine Godot realisiert und anschließend mithilfe qualitativer und quantitativer Methoden evaluiert. Die Ergebnisse zeigen, dass VR ein geeignetes Werkzeug zur Vermittlung komplexer Prozessstrukturen sein kann und insbesondere in der Schulung und Sensibilisierung von Personal Potenzial bietet. Abschließend werden Verbesserungsvorschläge sowie mögliche Einsatzszenarien in der industriellen Praxis diskutiert
Conceptual Study on DC-DC Converter Topologies in Battery-Fuel Cell Electric Aircraft Propulsion
No full textThe propulsion system architectures of all-electric aircraft often rely on multiple energy sources, in particular hydrogen-based fuel cells and batteries, to accommodate varying power demands throughout a mission profile. In this study, the source-side architecture for electric aircraft propulsion was investigated, focusing on the integration with power management and distribution systems. A two-port configuration with dual active bridge converters and a multi-port topology utilizing a triple active bridge converter were compared. Through the analysis of a hydrogen-based regional aircraft mission profile, the performance of each converter was assessed for the relevant mission phases. The topologies were evaluated in terms of efficiency, power density and control complexity. Semiconductor and transformer losses were calculated to assess system efficiency, utilizing thermal models and analytical methods. An existing sizing approach was extended to include transformer design, enabling the evaluation of volumetric and gravimetric power density. The preliminary design results in 22.7 kW/ kg for the three-port architecture, which is slightly higher than the 21.9 kW/ kg for the two-port architecture. Depending on the mission phase, either the dual active bridge or the triple active bridge would be more advantageous. Additionally, complexity and control considerations for the evaluated converter systems were addressed in this paper, offering insights into the key characteristics and trade-offs for electric aircraft propulsion concepts