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Concept and Performance of a Stripmap-F-STEC Mode to Image Wide Swaths at High Resolution with the Novel StriX Small Satellite
No full textPerspective Projection of an Ellipse and an Ellipsoid for Analytical View Factor Evaluation
Full text linkRadiative view factors are fundamental quantities for evaluating radiative heat transfer between different surfaces. While analytical expressions of view factors have been evaluated for various types of basic geometries, including circular disks and spheres, extending these solutions to more complex geometries, such as ellipses and ellipsoids has remained challenging due to mathematical complexity. This study evaluates the analytical view factor expressions of an ellipse and a triaxial ellipsoid from a plate element in an arbitrary position and orientation. The proposed analytical methods generalize the existing analytical solutions for disk and sphere related geometries, and extend their applicability to more complex geometrical configurations. For both cases, the perspective projection of the target geometry is analyzed, and the original view factor is transformed into an equivalent ellipse view factor, which has known analytical solutions from the previous study. Finally, the derived view factor expressions are validated by comparison with the numerical results
A Novel Deep-Learning-Based Approach for Estimating High-Resolution InSAR Parameters
No full textNowadays, SAR Interferometry (InSAR) represents one of the most powerful tools to perform complex tasks, such as retrieving Earth’s surface topography and monitoring its deformations. However, denoising strategies are crucial for the generation of reliable and high-quality InSAR products. In this framework, we propose a complete and generalized theoretical and statistical model to physically describe and simulate a noise-free interferogram, together with its corresponding noisy version, starting from the knowledge of the InSAR acquisition geometry and of the underlying topography. A deep-learning-based model is then trained in a fully-supervised manner to estimate high-resolution InSAR parameters, i.e. coherence and interferometric phase, leveraging the proposed statistical model. In particular, an accurate assessment of the network’s estimation performance is conducted by comparing it to state-of-the-art denoising filters, such as Boxcar and Phi-Net and showing the added value of the proposed theoretical modifications to the state-of-the-art literature
On Order Degree Problem for Moore Bound
No full textThe degree diameter problem is a quest to determine the largest graph in terms of vertices satisfying given degree and diameter constraints. The largest possible graphs that can exist and that are subject to degree and diameter constraints are called Moore graphs. Since Moore graphs are rare, researchers are eager to build graphs closer to Moore graphs. This paper discusses the possibility of constructing graphs closer to Moore graphs, keeping a fixed order and minimizing the number of vertex pairs that break the diameter constraint, and suggests a new general relative index that measures the closeness to optimality. Based on the proposed index, it is highlighted that some of the graphs constructed in this work are closer to Moore graphs than the existing best results in the degree diameter problem. Furthermore, a fitness landscape analysis is conducted to identify the nature and the difficulty of the problem. This new method can be considered a new approach to constructing graphs closer to Moore graphs
Performance Comparison of Cognitive SAR System Concepts for Ship Detection
No full textWe present a cognitive synthetic aperture radar concept for maritime ship detection and evaluate it on high-resolution TerraSAR-X SLC spotlight data. The concept consists of a leading satellite in a wide swath mode and a following satellite illuminating locations of interest with high resolution. We compare the ship detection performance of the concept with a concept operating a single SAR sensor in stripmap mode with medium resolution. Both the stripmap and the wide swath mode are simulated from the spotlight data with low-pass filters. The cognitive SAR concept surpasses the detection performance even with a sub-optimal greedy heuristic for the crucial beam positioning task
Rapid Web-Based Crisis Information through Automation of Processes: Enhancing First Responders' Access to Critical Geodata
No full textRapid and straightforward dissemination of information to emergency services is critical for informed decision-making during crises. Earth observation data is a valuable source for obtaining a widespread situational overview, e.g., by delineating the water extent during flood events. In this study, we present a prototype process chain for the rapid delivery of web-based crisis information derived from very high-resolution (VHR) optical imagery, introducing more automation across the stages of satellite-based emergency mapping. Initiated by a monitoring system of relevant warning sources, we leverage the time benefits of pre-tasking VHR satellites by employing a programmatic ordering of satellite data. The water extent is segmented based on a deep learning trained model from which further geodata are derived. The relevant information is disseminated via a web application that enables interactive exploration and rapid updates. Testing the process chain for a simulated flood event demonstrated that the crisis information could be provided within hours after the warned flood event and was positively evaluated by first responders. While automation improves the timeliness of crisis product delivery, we conclude that semi-automation is preferable to full automation, as each crisis is unique and requires expert decisions at critical stages
Exerimental validation of clock synchronisation and baseline determination approaches for multistatic SAR formations
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Dynamics of interstitial molecular-type double donor complexes in silicon
Full text linkComplementary time-resolved spectroscopies have been applied to study dynamics of molecular-type magnesium-related donors. Large interstate energy gaps of these donors prevent nonradiative decays through a first-order, one-phonon-assisted scattering – the main relaxation mechanism in shallow substitutional donors in low-doped silicon. Analysis reveals very short decay times of the deepest excited states of molecular donors: dephasing within less than 10 ps and relaxation rates above 30/ns. These decays are several times shorter than those observed in single-electron hydrogen-like substitutional donors, but longer than those in helium-like interstitial atomic magnesium centers in silicon. Spectral correlations of temporal dependences of particular transients to the lattice phonon overtones suggest that phonon-assisted electronic scattering contributes also to decoherence of states in these double donors. Such efficient second-order phonon-assisted processes were underestimated for dynamics of deep impurities in semiconductors
Thermo-Hydraulic Validation of a Molten Salt Test Receiver Model
No full textThis paper presents the validation of a detailed dynamic process model of a high performance molten salt test receiver located in the Multi-Focus-Tower in Jülich, Germany. The model was improved in several steps after comparison with the measurement data, and
lessons learned are derived from the results of the validation process. The model shows excellent accuracy, beating the expectations. Nevertheless, there are still some phenomena that are not yet fully understood, which makes further investigation necessary before the results can be transferred to other systems with full confidence. Despite the remaining uncertainties, the model can now serve as a digital twin for the testing system that can generate synthetic
training data for machine learning systems or functions as a basis for model predictive controls (MPC) or model based operational assistance systems (OAS)