Detecting Targets above the Earth's Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1

: Global Navigation Satellite System (GNSS) reflected signals can be used to remotely sense the Earth’s surface, known as GNSS reflectometry (GNSS-R). The GNSS-R technique has been applied to numerous areas, such as the retrieval of wind speed, and the detection of Earth surface objects. This work proposes a new application of GNSS-R, namely to detect objects above the Earth’s surface, such as low Earth orbit (LEO) satellites. To discuss its feasibility, 14 delay Doppler maps (DDMs) are first presented which contain unusually bright reflected signals as delays shorter than the specular reflection point over the Earth’s surface. Then, seven possible causes of these anomalies are analysed, reaching the conclusion that the anomalies are likely due to the signals being reflected from objects above the Earth’s surface. Next, the positions of the objects are calculated using the delay and Doppler information, and an appropriate geometry assumption. After that, suspect satellite objects are searched in the satellite database from Union of Concerned Scientists (UCS). Finally, three objects have been found to match the delay and Doppler conditions. In the absence of other reasons for these anomalies, GNSS-R could potentially be used to detect some objects above the Earth’s surface.Peer ReviewedPostprint (published version

PTV-Stream: A simplified particle tracking velocimetry framework for stream surface flow monitoring

Abstract Particle tracking velocimetry (PTV) is a promising image-based approach for remote streamflow measurements in natural environments. However, most PTV approaches require highly-defined round-shaped tracers, which are often difficult to observe outdoors. PTV-Stream offers a versatile alternative to cross-correlation-based PTV by affording the identification and tracking of features of any shape transiting in the field of view. This nearest-neighbor algorithm is inherently thought for estimating surface flow velocity of streams in outdoor conditions. The procedure allows for reconstructing and filtering the trajectories of features that are more likely to pertain to actual objects transiting in the field of view rather than to water reflections. The procedure is computationally efficient and is demonstrated to yield accurate measurements even in case of downsampled image sequences

2020 NASA Technology Taxonomy

This document is an update (new photos used) of the PDF version of the 2020 NASA Technology Taxonomy that will be available to download on the OCT Public Website. The updated 2020 NASA Technology Taxonomy, or "technology dictionary", uses a technology discipline based approach that realigns like-technologies independent of their application within the NASA mission portfolio. This tool is meant to serve as a common technology discipline-based communication tool across the agency and with its partners in other government agencies, academia, industry, and across the world

Beurteilung der Gefährdung durch Treibgut bei extremen Überschwemmungsereignissen

Coastal areas are often important to economic, social, and environmental processes throughout the world. With changing climate and growing populations in these areas, coastal communities have become increasingly vulnerable to extreme flooding events, such as tsunami, storm surges, and flash floods. Within this new paradigm, there has been an effort to improve upon current methods of hazard assessment, particularly for tsunami. Recently, the American Society of Civil Engineers (ASCE) released the ASCE 7 Chapter 6 which was the world’s first standard, written in mandatory language, that addressed tsunami resilient design in a probabilistic manner for several of its prescriptions. While often the focus tends to be on mapping the hazards related to hydraulic loading conditions, post-tsunami field surveys from disaster-stricken coastal communities have also shown the importance of also considering the loads exerted by solid objects entrained within the inundating flows, commonly referred to as debris loading. Limited research has addressed debris hazard assessment in a comprehensive manner. Debris loading can be generally divided into two categories: impact and damming. Debris impact loads are caused by the rapid strike of solid objects against a structure. Debris damming loads are the result of the accumulation of debris at the face of or around a structure, causing thus an obstruction to the flow. The primary difference between these loads is the time period over which they act. The rapid loading due to debris impacts requires structural properties be considered in assessing the associated loads whereas debris damming loads are generally considered in a quasi-static manner. In assessing the hazard associated with both impact and damming loading conditions, methodologies must be developed to consider the likelihood of the load occurring and the magnitude of that load. The primary objective of this thesis was to develop a probabilistic framework for assessing debris hazards in extreme coastal flooding events. To achieve this objective, the components of the framework were split into three general categories: debris transport, debris damming, and debris impact. Several physical experimental studies were performed to address each of these components, representing the most comprehensive assessment of debris hazards in extreme flooding events to date.Küstengebiete auf der ganzen Welt sind oftmals wichtig für wirtschaftliche, soziale und ökologische Prozesse. Aufgrund des sich ändernden Klimas und der wachsenden Bevölkerung in diesen Gebieten sind Küstengemeinden zunehmend anfällig für extreme Überschwemmungen durch Tsunami, Sturmfluten und Sturzfluten. Innerhalb dieses neuen Paradigmas wurden Anstrengungen unternommen, um die derzeitigen Methoden zur Gefährdungsbeurteilung, insbesondere für Tsunami, zu verbessern. Die American Society of Civil Engineers (ASCE) veröffentlichte das ASCE 7 Chapter 6, den weltweit ersten verbindlichen Standard, der sich in mehreren seiner Vorschriften mit einem probabilistischen Ansatz mit tsunami-beständiger Konstruktion befasst. Während der Schwerpunkt häufig auf der Erfassung der Gefahren im Zusammenhang mit hydraulischen Belastungszuständen liegt, haben Felduntersuchungen in von Tsunami getroffenen Küstengebieten gezeigt, dass es wichtig ist, auch die Belastungen zu berücksichtigen, die von festen Gegenständen ausgehen, die im einströmenden Wasser als Treibgut mitgeführt werden. Umfassende Forschung zur Gefährdungsbeurteilung von Treibgut ist nur begrenzt vorhanden. Die Belastung durch Treibgut kann im Allgemeinen in zwei Kategorien unterteilt werden: Aufprall und Aufstau. Lasten aus dem Aufprall des Treibgutes werden durch das schnelle Auftreffen fester Gegenstände auf eine Struktur verursacht. Lasten aus dem Aufstauen sind das Ergebnis der Akkumulation von Treibgut an der Oberfläche oder um eine Struktur herum, was zu einer Behinderung der Strömung führt. Der Hauptunterschied zwischen diesen Lasten ist der Zeitraum, über den sie wirken. Die schnelle Belastung durch den Aufprall von Treibgut erfordert, dass bei der Beurteilung der damit verbundenen Belastungen strukturelle Eigenschaften berücksichtigt werden, wohingegen Lasten aus dem Aufstauen von Treibgut im Allgemeinen quasi-statisch berücksichtigt werden. Für die Bewertung der Gefährdung, die sowohl mit dem Aufprall als auch mit dem Aufstauen verbunden ist, müssen Methoden entwickelt werden, um die Wahrscheinlichkeit des Auftretens der Last und die Größe dieser Last zu berücksichtigen. Das Hauptziel der Dissertation war die Entwicklung eines probabilistischen Ansatzes zur Bewertung der Gefährdung durch Treibgut bei extremen Überflutungsereignissen an der Küste. Um dieses Ziel zu erreichen, wurden die Komponenten des Rahmens in drei allgemeine Kategorien unterteilt: Transport, Aufstau und Aufprall von Treibgut. Um jede dieser Komponenten zu untersuchen, wurden mehrere physikalisch-experimentelle Studien durchgeführt, die die bislang umfassendste Beurteilung der Gefährdung durch Treibgut bei extremen Überschwemmungen darstellen

The use of unmanned aerial vehicles (UAVs) for engineering geology applications

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Advanced laser applications in space safety

This thesis presents instrumentation models and mission simulations for three novel use cases of lasers in space. Firstly, the use of laser ranging in a gravimetry experiment to estimate the masses of near-Earth asteroids and other small solar system objects is presented in the context of a dual-flyby CubeSat mission. The technique is shown to be capable of estimating the mass of small bodies to better accuracy and lower mass than has previously been demonstrated using traditional radioscience. Secondly, a new method of laser ranging relevant to the above mission scenario is proposed and simulated, which utilises a CCD array as its primary sensor, along with a long-pulse or modulated CW laser. Despite the simple hardware, the new technique is shown to have great potential for precise range measurement which is sufficient for the application of asteroid mass estimation. Finally, a mission concept for the removal of space debris using a small constellation of satellites carrying high-power lasers is proposed and simulated in detail to determine its impact on a debris population designed to represent a post-collision debris shell. A high-fidelity model of the reaction forces due to photon pressure and laser ablation is developed, which models these forces in more detail than in previous, similar mission concept studies. This interaction model is then used in the mission simulation to statistically determine the impact of the mission over a 10-year operation period. The concept is then adapted for the application of collision avoidance using photon pressure, investigating the achievable deflection of a debris fragment given some notice period, and the time until a threatening fragment passes close enough to a satellite in the constellation to be affected.This thesis presents instrumentation models and mission simulations for three novel use cases of lasers in space. Firstly, the use of laser ranging in a gravimetry experiment to estimate the masses of near-Earth asteroids and other small solar system objects is presented in the context of a dual-flyby CubeSat mission. The technique is shown to be capable of estimating the mass of small bodies to better accuracy and lower mass than has previously been demonstrated using traditional radioscience. Secondly, a new method of laser ranging relevant to the above mission scenario is proposed and simulated, which utilises a CCD array as its primary sensor, along with a long-pulse or modulated CW laser. Despite the simple hardware, the new technique is shown to have great potential for precise range measurement which is sufficient for the application of asteroid mass estimation. Finally, a mission concept for the removal of space debris using a small constellation of satellites carrying high-power lasers is proposed and simulated in detail to determine its impact on a debris population designed to represent a post-collision debris shell. A high-fidelity model of the reaction forces due to photon pressure and laser ablation is developed, which models these forces in more detail than in previous, similar mission concept studies. This interaction model is then used in the mission simulation to statistically determine the impact of the mission over a 10-year operation period. The concept is then adapted for the application of collision avoidance using photon pressure, investigating the achievable deflection of a debris fragment given some notice period, and the time until a threatening fragment passes close enough to a satellite in the constellation to be affected

Technology for large space systems: A bibliography with indexes (supplement 22)

This bibliography lists 1077 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System between July 1, 1989 and December 31, 1989. Its purpose is to provide helpful information to the researcher or manager engaged in the development of technologies related to large space systems. Subject areas include mission and program definition, design techniques, structural and thermal analysis, structural dynamics and control systems, electronics, advanced materials, assembly concepts, and propulsion

Knowledge-Driven Semantic Segmentation for Waterway Scene Perception

Semantic segmentation as one of the most popular scene perception techniques has been studied for autonomous vehicles. However, deep learning-based solutions rely on the volume and quality of data and knowledge from specific scene might not be incorporated. A novel knowledge-driven semantic segmentation method is proposed for waterway scene perception. Based on the knowledge that water is irregular and dynamically changing, a Life Time of Feature (LToF) detector is designed to distinguish water region from surrounding scene. Using a Bayesian framework, the detector as the likelihood function is combined with U-Net based semantic segmentation to achieve an optimized solution. Finally, two public datasets and typical semantic segmentation networks, FlowNet, DeepLab and DVSNet are selected to evaluate the proposed method. Also, the sensitivity of these methods and ours to dataset is discussed