High accuracy synthetic aperture radar (SAR) processor for UAV platforms

The usual SAR processing algorithms used in LEO satellites or Ground Based SAR systems are not optimal for UAV based SAR formation (UPC Arbres system). The large dynamics and unstability characteristics of Multicopter UAV produce large defocusing and loss of detail in the SAR images. To prevent these problems the present operating parameters of Arbres must be optimized and a new algorithm able to operate with low Sweep Repetition Frequency (SRF) must be designed and evaluated based on simulated and/or experimental data.The combination of frequency-modulated continuous-wave (FMCW) technology and synthetic aperture radar (SAR) techniques leads to lightweight cost-effective imagining sensor of high resolution. One limiting factor to use of FMCW sensors is the well-known presence of nonlinearities in the transmitted signal. This results in contrast when the system is intended for high-resolution long-range applications, as it is the case for SAR. There are many algorithms to implement SAR formation but in this case the system it is placed in a UAV (UPC ARBRES system). The large dynamics and instability characteristics of drone UAV produce large defocusing and loss of detail in the SAR images. In this project is presented an algorithm to form synthetic apertures and compensate the defocusing and other aspects that are produced by the motion of the system. Firstly, the system it is assuming the Stop and Go assumption. Finally, the algorithm generates the raw data and the SAR image without assuming Stop and Go.La combinación de la tecnología de onda continúa modulada en frecuencia (FMCW, por sus siglas en inglés) y la tecnología de radar de apertura sintética (SAR, por sus siglas en inglés) conduce a un sensor de alta resolución, liviano y económico. Una limitación para el uso de sensores FMCW es la presencia conocida de no linealidades en la señal transmitida. Por otro lado, contrasta cuando el sistema está diseñado para aplicaciones de largo alcance de alta resolución, como es el caso de SAR. Hay muchos algoritmos para implementar la formación de imágenes SAR, pero en este caso el sistema se coloca en un UAV (sistema UPC ARBRES). La gran dinámica y las características de inestabilidad de los aviones no tripulados UAV producen gran desenfoque y pérdida de detalle en las imágenes de SAR. En este proyecto se presenta un algoritmo para formar aberturas sintéticas y compensar el desenfoque y otros aspectos que son producidos por el movimiento del sistema. En primer lugar, el sistema está asumiendo el supuesto de Stop and Go. Finalmente, el algoritmo genera los datos y la imagen SAR sin asumir Stop and Go.La combinació de la tecnologia d'ona continua modulada en freqüència (FMCW, per les seves sigles en anglès) i la tecnologia de radar d'obertura sintètica (SAR, per les seves sigles en anglès) condueix a un sensor d'alta resolució, lleuger i econòmic. Una limitació per a l'ús de sensors FMCW és la presència coneguda de no-liníalitats en el senyal transmès. D'altra banda, contrasta quan el sistema està dissenyat per a aplicacions de llarg abast d'alta resolució, com és el cas de SAR. Hi ha molts algorismes per implementar la formació d'imatges SAR, però en aquest cas el sistema es col·loca en un UAV (sistema UPC *ARBRES). La gran dinàmica i les característiques d'inestabilitat dels avions no tripulats UAV produeixen gran desenfoqui i pèrdua de detall en les imatges SAR. En aquest projecte es presenta un algorisme per formar obertures sintètiques i compensar el desenfoqui i altres aspectes que són produïts pel moviment del sistema. En primer lloc, el sistema està assumint el supòsit de Stop and Go. Finalment, l'algorisme genera les dades i la imatge *SAR sense assumir Stop and Go

Highly Integrated Low-Profile Multilayer Dual-Polarized Phased Array Antenna with Truncated Cavities for First Pulsed Bistatic L-band Airborne SAR Sensor

This manuscript presents a novel highly integrated dual-polarized multilayer phased array antenna of 40 elements with beam steering in elevation for a bistatic L-band airborne SAR system. The proposed work exploits efficiently the restricted antenna aperture size on the aircraft by reducing the array interelement spacing and improves the antenna element isolation by means of truncated cavities, which allows to maximize the density of array elements. To further extend the degree of integration, the antenna along with the feeding network is assembled in a flight-certified housing where the electrical interconnection is performed without cables. In comparison with the L-band antenna of the current operative DLR's airborne SAR sensor, F-SAR, the presented design provides 66% more antenna elements considering the same antenna aperture size. Thus, the high density of array elements of the proposed solution allows to enhance the beamforming capabilities that are required for next-generation SAR sensors. Precisely, the proposed antenna will be installed under two aircrafts for the operational implementation of the first pulsed bistatic L-band airborne SAR system that will support the technological development of future bistatic spaceborne SAR missions

Calibration of airborne L-, X-, and P-band fully polarimetric SAR systems using various corner reflectors

Synthetic aperture radar polarimetry is one of the current developments in the field of remote sensing, due to the ability of delivering more information on the physical properties of the surface. It is known as the science of acquiring, processing and analysing the polarisation state in an electromagnetic field. The increase of information with respect to scalar radar comes at a price, not only for the high cost of building the radar system and processing the data or increasing the complexity of the design, but also for the amount of effort needed to calibrate the data. Synthetic aperture radar polarimetric calibration is an essential pre- processing stage for the correction of distortion interference which is caused by the system inaccuracies as well as atmospheric effects. Our goal, with this thesis, is to use multiple passive point targets to establish the difference between fully, and compact polarimetric synthetic aperture radar systems on both calibration, and the effects of penetration. First, we detail the selection, design, manufacture, and deployment of different passive point targets in the field for acquiring X- and P-band synthetic aperture radar data in the Netherlands. We started by presenting the selection and design of multiple passive point targets. These were a combination of classic trihedral and dihedral corner reflectors, as well as gridded trihedral and dihedral corner reflectors. Additionally, we detailed the construction of these corner reflectors. The number of constructed corner reflector totalled sixteen, where six are for X-band and six for P-band, as well as four gridded corner reflectors for X-band. Finally, we present the deployment of the corner reflectors at three different sites with carefully surveyed and oriented positions. a Then, we present the calibration of three different fully polarimetric synthetic aperture radar sensors. The first sensor is the L-band synthetic aperture radar sensor and we acquired data using two square trihedral corner reflectors. The calibration includes an evaluation of two crosstalk methods, which are the Quegan and the Ainsworth methods. The results showed that the crosstalk parameters for the Quegan method are all between -17 dB to -21 dB before calibration, while there is a small improvement in the range of 3 dB after calibration. While the Ainsworth method shows around -20 dB before calibration, and around -40 dB after calibration. Moreover, the phase, channel imbalance, and radiometric calibration were corrected using the two corner reflectors. Furthermore, the other two synthetic aperture radar sensors are X- and P-band synthetic aperture radar sensors, and we acquired polarimetric data using our sixteen corner reflectors. The calibration includes the crosstalk estimation, and correction using the Ainsworth method and the results showed the crosstalk parameters before calibration for X-band are around -23 dB, and they are around -43 dB after calibration, while crosstalk parameters before calibration for P-band are around -10 dB, and they are around -30 dB after calibration. The calibration also includes the phase, channel imbalance, and radiometric calibration, as well as geometric correction and signal noise ration measurement, for both X- and P-band. Next, we present the performance of gridded trihedral and dihedral corner reflectors using an X-band synthetic aperture radar system. The results showed both gridded trihedral and dihedral reflectors are perfect targets for correcting the amplitude compared to classical corner reflectors; however, it is not possible to use the gridded reflectors to correct the phase as we need a return from two channels to have a zero-phase difference between the polarisation channels H - V. Furthermore, we detail the compact polarimetric calibration over three com- pact polarimetric modes using a square trihedral corner reflector for the X-band dataset. The results showed no change in the π/mode while a 90ᵒ phase bias showed in the CTLR mode. Finally, the DCP mode showed a 64.43° phase difference, and it was corrected to have a zero phase, and the channel imbalance was very high at 45.92, the channels were adjusted to have a channel imbalance of 1. b Finally, an experiment to measure the penetration and reduction of P-band signal from a synthetic aperture radar system was performed using two triangular trihedral corner reflectors. Both of them have 1.5 m inner leg dimensions. The first triangular trihedral corner reflector was deployed in a deciduous grove of trees, while the other one was deployed a 10 m distance away on a grass covered field. After system calibration based on the reflector in the clear, the results showed a reduction of 0.6 dB in the HH channel, with 2.28 dB in the W channel. The larger attenuation at W is attributable to the vertical structure of the trees. Additionally, we measured the polarimetric degradation of the triangular trihedral corner reflector immersed in vegetation (trees). Further, after calibration, the co-polarisation phase difference is zero degrees for the triangular corner reflector which was outside the trees, and 62.85ᵒ for the corner reflector inside the trees. The designed and fabricated X- and P-band SAR can work operationally with the calibration parameters obtained in this thesis. The data generated through the calibration experiments can be exploited for further applications

Contribution to ground-based and UAV SAR systems for Earth observation

Mankind's way of life is the main driver of a planetary-scale change that is marked by the growing of human population's demand of energy, food, goods, services and information. As a result, it have emerged new ecological, economical, social and geopolitical concerns. In this scenario, SAR remote sensing is a potential tool that provides unique information about the Earth's properties and processes that can be used to solve societal challenges of local and global dimension. SARs, which are coherent systems that are able to provide high resolution images with weather independence, represent a suitable alternative for EO with diverse applications. Some examples of SAR application areas are topography (DEM generation with interferometry), agriculture (crop classification or soil moisture), or geology (monitoring surface deformation). In this framework, the encompassing objective of the present doctoral work has been part of the implementation and the subsequent evaluation of capabilities of two X-band SAR sensors. On the one hand, the RISKSAR-X radar designed to be operated at ground to monitor small-scale areas of observation and, on the other, the ARBRES-X sensor designed to be integrated into small UAVs. Despite its inherently dissimilar conception, the concurrence of both sensors has been evidenced along this manuscript. By taking advantage of the similarities between them, it has been possible to analogously assess both sensors to obtain conclusions. In this context, the common link has been the development of the polarimetric OtF operation mode of the RISKSAR-X, allowing this sensor to be operated equivalently to the ARBRES-X. Regarding the RISKSAR-X SAR sensor, several hardware contributions have been developed during part of this Ph.D. with the aim of improving the system performance. By endowing the system with the capability to operate in the fully polarimetric OtF acquisition mode, the relative long scanning time has been reduced. It is of great interest since the measured scatterers that present a short term variable reflectivity during the scanning time, such as moving vegetation, may degrade the extracted parameters from the retrieved data and the SAR image reconstruction. During this doctoral activity, it has been studied the image blurring, the decorrelation and the coherence degradation introduced by this effect. Furthermore, a new term in the differential interferometric coherence that takes into account the image blurring has been introduced. Concerning the ARBRES-X SAR system, one of the main objectives pursued during this Ph.D. has been the integration of the sensor into a small UAV MP overcoming restrictions of weight, size and aerodynamics of the platform. The use of this type of platforms is expected to open up new possibilities in airborne SAR remote sensing, since it offers much more versatility than the commonly used fixed wings UAVs. Different innovative flight strategies with this type of platforms have been assessed and some preliminary results have been obtained with the use of the ARBRES-X SAR system. During the course of the present doctoral work, much effort has been devoted to achieve the first experimental repeat-pass interfereometric results obtained with the UAV MP together with the ARBRES-X. Moreover, the sensor has been endowed with fully polarimetric capabilities by applying the improvements developed to the RISKSAR-X radar, which is another example of the duality between both systems. Finally, a vertical and a semicircular aperture have been successfully performed obtaining SLC images of the scenario, which envisages the capability of the UAV MP to perform tomographic images and complete circular apertures in the future. In conclusion, the UAV MP is a promising platform that opens new potentials for several applications, such as repeat-pass interferometry or differential tomography imaging with the realization of almost arbitrary trajectories.El mode de viure de la humanitat és el principal motor d'un canvi a escala planetària que està marcat per la creixent demanda d'energia, d'aliment, de béns, de serveis i d'informació de les poblacions humanes. Com a resultat, han sorgit noves inquietuds ecològiques, econòmiques, socials i geopolítiques. En aquest escenari, la detecció remota SAR és una eina potencial que proporciona informació única sobre les propietats i processos de la Terra que es pot utilitzar per resoldre reptes socials de dimensió local i global. Els SARs, que són sistemes coherents que poden proporcionar imatges d'alta resolució amb independència del temps, representen una alternativa adequada per a l'observació de la Terra. Alguns exemples d'àrees d'aplicació SAR són la topografia (generació de DEM amb interferometria), l'agricultura (classificació de cultius o humitat del sòl) o la geologia (monitoratge de deformació superficial). En aquest context, l'objectiu general del present doctorat ha estat part de la implementació i posterior avaluació de les capacitats de dos sensors SAR de banda X. D'una banda, el radar RISKSAR-X dissenyat per funcionar a terra i monitoritzar àrees d'observació a petita escala i, d'altra, el sensor ARBRES-X dissenyat per ser integrat en petits UAVs. Malgrat la seva concepció inherentment diferent, la concurrència d'ambdós sensors s'ha evidenciat al llarg d'aquest manuscrit. Aprofitant les similituds entre ells, s'han pogut avaluar de forma anàloga els dos sensors per obtenir conclusions. En aquest sentit, el vincle comú ha estat el desenvolupament del mode de funcionament polimètric OtF del RISKSAR-X, permetent que aquest sensor operi de forma equivalent a l'ARBRES-X. Pel que fa al sensor RISKSAR-X, s'han desenvolupat diverses contribucions hardware durant part d'aquest doctorat amb l'objectiu de millorar el rendiment del sistema. En dotar el sistema de la possibilitat d'operar en el mode d'adquisició totalment polarimètric OtF, s'ha reduït el relatiu llarg temps d'escaneig. Això és de gran interès ja que els blancs mesurats que presenten una reflectivitat variable a curt termini, com ara la vegetació en moviment, poden degradar els paràmetres extrets de les dades recuperades i la reconstrucció d'imatges SAR. Durant aquesta activitat doctoral s'ha estudiat el desenfocat de la imatge, la decorrelació i la degradació de la coherència introduïts per aquest efecte. A més, s'ha introduït un nou terme en la coherència interferomètrica diferencial que té en compte el desenfocat de la imatge. Pel que fa al sistema ARBRES-X, un dels principals objectius perseguits durant aquest doctorat ha estat la integració del sensor en un petit UAV MP superant les restriccions de pes, grandària i aerodinàmica de la plataforma. S'espera que l'ús d'aquest tipus de plataformes obri noves possibilitats en la detecció remota SAR aerotransportada, ja que ofereix molta més versatilitat que els UAV d'ales fixes habituals. S'han avaluat diferents estratègies de vol innovadores amb aquest tipus de plataformes i s'han obtingut resultats preliminars amb l'ús del sistema ARBRES-X. Durant el transcurs del present treball, s'ha dedicat molt esforç a assolir els primers resultats experimentals d'interferometria de múltiple passada obtinguts amb l'UAV MP conjuntament amb l'ARBRES-X. A més, el sensor ha estat dotat de capacitats totalment polarimètriques aplicant les millores desenvolupades al radar RISKSAR-X, el qual constitueix un altre exemple de la dualitat entre ambdós sistemes. Finalment, s'han realitzat amb èxit una apertura vertical i semicircular obtenint imatges SLC de l'escenari, el qual permet preveure la capacitat de l'UAV MP per a realitzar imatges tomogràfiques i apertures circulars completes en el futur. En conclusió, l'UAV MP és una plataforma prometedora que obre nous potencials per a diverses aplicacions, com ara la interferometria de múltiple passada o la tomografia diferencial amb la realització de trajectòries gairebé arbitràries.Postprint (published version

Contribution to ground-based and UAV SAR systems for Earth observation

Mankind's way of life is the main driver of a planetary-scale change that is marked by the growing of human population's demand of energy, food, goods, services and information. As a result, it have emerged new ecological, economical, social and geopolitical concerns. In this scenario, SAR remote sensing is a potential tool that provides unique information about the Earth's properties and processes that can be used to solve societal challenges of local and global dimension. SARs, which are coherent systems that are able to provide high resolution images with weather independence, represent a suitable alternative for EO with diverse applications. Some examples of SAR application areas are topography (DEM generation with interferometry), agriculture (crop classification or soil moisture), or geology (monitoring surface deformation). In this framework, the encompassing objective of the present doctoral work has been part of the implementation and the subsequent evaluation of capabilities of two X-band SAR sensors. On the one hand, the RISKSAR-X radar designed to be operated at ground to monitor small-scale areas of observation and, on the other, the ARBRES-X sensor designed to be integrated into small UAVs. Despite its inherently dissimilar conception, the concurrence of both sensors has been evidenced along this manuscript. By taking advantage of the similarities between them, it has been possible to analogously assess both sensors to obtain conclusions. In this context, the common link has been the development of the polarimetric OtF operation mode of the RISKSAR-X, allowing this sensor to be operated equivalently to the ARBRES-X. Regarding the RISKSAR-X SAR sensor, several hardware contributions have been developed during part of this Ph.D. with the aim of improving the system performance. By endowing the system with the capability to operate in the fully polarimetric OtF acquisition mode, the relative long scanning time has been reduced. It is of great interest since the measured scatterers that present a short term variable reflectivity during the scanning time, such as moving vegetation, may degrade the extracted parameters from the retrieved data and the SAR image reconstruction. During this doctoral activity, it has been studied the image blurring, the decorrelation and the coherence degradation introduced by this effect. Furthermore, a new term in the differential interferometric coherence that takes into account the image blurring has been introduced. Concerning the ARBRES-X SAR system, one of the main objectives pursued during this Ph.D. has been the integration of the sensor into a small UAV MP overcoming restrictions of weight, size and aerodynamics of the platform. The use of this type of platforms is expected to open up new possibilities in airborne SAR remote sensing, since it offers much more versatility than the commonly used fixed wings UAVs. Different innovative flight strategies with this type of platforms have been assessed and some preliminary results have been obtained with the use of the ARBRES-X SAR system. During the course of the present doctoral work, much effort has been devoted to achieve the first experimental repeat-pass interfereometric results obtained with the UAV MP together with the ARBRES-X. Moreover, the sensor has been endowed with fully polarimetric capabilities by applying the improvements developed to the RISKSAR-X radar, which is another example of the duality between both systems. Finally, a vertical and a semicircular aperture have been successfully performed obtaining SLC images of the scenario, which envisages the capability of the UAV MP to perform tomographic images and complete circular apertures in the future. In conclusion, the UAV MP is a promising platform that opens new potentials for several applications, such as repeat-pass interferometry or differential tomography imaging with the realization of almost arbitrary trajectories.El mode de viure de la humanitat és el principal motor d'un canvi a escala planetària que està marcat per la creixent demanda d'energia, d'aliment, de béns, de serveis i d'informació de les poblacions humanes. Com a resultat, han sorgit noves inquietuds ecològiques, econòmiques, socials i geopolítiques. En aquest escenari, la detecció remota SAR és una eina potencial que proporciona informació única sobre les propietats i processos de la Terra que es pot utilitzar per resoldre reptes socials de dimensió local i global. Els SARs, que són sistemes coherents que poden proporcionar imatges d'alta resolució amb independència del temps, representen una alternativa adequada per a l'observació de la Terra. Alguns exemples d'àrees d'aplicació SAR són la topografia (generació de DEM amb interferometria), l'agricultura (classificació de cultius o humitat del sòl) o la geologia (monitoratge de deformació superficial). En aquest context, l'objectiu general del present doctorat ha estat part de la implementació i posterior avaluació de les capacitats de dos sensors SAR de banda X. D'una banda, el radar RISKSAR-X dissenyat per funcionar a terra i monitoritzar àrees d'observació a petita escala i, d'altra, el sensor ARBRES-X dissenyat per ser integrat en petits UAVs. Malgrat la seva concepció inherentment diferent, la concurrència d'ambdós sensors s'ha evidenciat al llarg d'aquest manuscrit. Aprofitant les similituds entre ells, s'han pogut avaluar de forma anàloga els dos sensors per obtenir conclusions. En aquest sentit, el vincle comú ha estat el desenvolupament del mode de funcionament polimètric OtF del RISKSAR-X, permetent que aquest sensor operi de forma equivalent a l'ARBRES-X. Pel que fa al sensor RISKSAR-X, s'han desenvolupat diverses contribucions hardware durant part d'aquest doctorat amb l'objectiu de millorar el rendiment del sistema. En dotar el sistema de la possibilitat d'operar en el mode d'adquisició totalment polarimètric OtF, s'ha reduït el relatiu llarg temps d'escaneig. Això és de gran interès ja que els blancs mesurats que presenten una reflectivitat variable a curt termini, com ara la vegetació en moviment, poden degradar els paràmetres extrets de les dades recuperades i la reconstrucció d'imatges SAR. Durant aquesta activitat doctoral s'ha estudiat el desenfocat de la imatge, la decorrelació i la degradació de la coherència introduïts per aquest efecte. A més, s'ha introduït un nou terme en la coherència interferomètrica diferencial que té en compte el desenfocat de la imatge. Pel que fa al sistema ARBRES-X, un dels principals objectius perseguits durant aquest doctorat ha estat la integració del sensor en un petit UAV MP superant les restriccions de pes, grandària i aerodinàmica de la plataforma. S'espera que l'ús d'aquest tipus de plataformes obri noves possibilitats en la detecció remota SAR aerotransportada, ja que ofereix molta més versatilitat que els UAV d'ales fixes habituals. S'han avaluat diferents estratègies de vol innovadores amb aquest tipus de plataformes i s'han obtingut resultats preliminars amb l'ús del sistema ARBRES-X. Durant el transcurs del present treball, s'ha dedicat molt esforç a assolir els primers resultats experimentals d'interferometria de múltiple passada obtinguts amb l'UAV MP conjuntament amb l'ARBRES-X. A més, el sensor ha estat dotat de capacitats totalment polarimètriques aplicant les millores desenvolupades al radar RISKSAR-X, el qual constitueix un altre exemple de la dualitat entre ambdós sistemes. Finalment, s'han realitzat amb èxit una apertura vertical i semicircular obtenint imatges SLC de l'escenari, el qual permet preveure la capacitat de l'UAV MP per a realitzar imatges tomogràfiques i apertures circulars completes en el futur. En conclusió, l'UAV MP és una plataforma prometedora que obre nous potencials per a diverses aplicacions, com ara la interferometria de múltiple passada o la tomografia diferencial amb la realització de trajectòries gairebé arbitràries

Generic Radar Processing Methods for Monitoring Tasks on Bridge Infrastructure

Kritische Verkehrsinfrastrukturen, wie z. B. Brücken, können nur dann sicher betrieben werden, wenn ihr Zustand regelmäßig bewertet wird. Neben visuellen Inspektionen umfasst die Bewertung auch Messungen des Brückenverhaltens auf statische oder dynamische Lasten. Diese Messungen werden in der Regel mit einer Vielzahl von Sensoren durchgeführt, die direkt an der Brücke befestigt sind. Zunehmend werden jedoch auch Fernerkundungssensoren eingesetzt, wie z.B. das bodenbasierte interferometrische Radar (engl.: ground-based interferometric radar - GBR). GBR können aus der Ferne Verschiebungen mit einer Genauigkeit im Submillimeterbereich messen, indem sie eine elektromagnetische Welle aussenden, die von Strukturen an der Unterseite der Brücke reflektiert wird. Im Vergleich zu direkt befestigten Sensoren wird die Installationszeit verkürzt und der normale Betrieb der Brücke wird nicht beeinträchtigt. Vergleichbare Messunsicherheiten lassen sich jedoch nur erreichen, wenn bei der Prozessierung der Messungen bestimmte Herausforderungen berücksichtigt werden. Dabei geht es vor allem um die Entfernung externer Einflüsse wie Störungen des Signals oder Veränderungen atmosphärischer Parameter. Die Messungen werden außerdem durch statischen Clutter und Projektionsfehler beeinflusst, die zu systematischen Abweichungen führen. Statischer Clutter wird mit einer angepassten Kreisschätzung bestimmt, während Projektionsfehler durch die Verwendung mehrerer Sensoren zur Schätzung separater Verschiebungskomponenten vermindert werden. Mit diesen zusätzlichen Prozessierungsschritten erreicht GBR eine ähnliche Unsicherheit wie andere Fernerkundungssensoren, was durch Vergleiche mit Referenzsensoren validiert wird. Verbleibende Unterschiede zu diesen Referenzsensoren lassen sich durch Unsicherheiten bei der Schätzung von Clutter und durch die begrenzte Auflösung einzelner Reflexionen erklären. Die resultierenden Verschiebungsmessungen werden dann zur Schätzung schadensempfindlicher Merkmale wie Eigenfrequenzen und Eigenformen verwendet. Eigenfrequenzen werden bestimmt, indem ein Modell einer gedämpften Sinuskurve für die Schwingung nach einer Fahrzeugüberfahrt geschätzt wird. Mit diesem Ansatz wird jede Fahrzeugüberfahrt separat analysiert, was eine Unterscheidung zwischen verschiedenen Fahrzeugmassen ermöglicht. Außerdem erlaubt die große Anzahl von Frequenzschätzungen eine zuverlässigere Bestimmung des Temperatureinflusses auf die Eigenfrequenzen. Für die Bestimmung der Eigenformen wird ein alternativer Messaufbau erarbeitet. Dieser Aufbau nutzt die flache Unterseite einer Brücke, um das ausgesendete Signal auf einen Reflektor auf dem Boden zu spiegeln. Eine permanente Installation von Reflektoren an der Brückenunterseite ist daher nicht erforderlich, wodurch die Anwendung von GBR auf eine große Anzahl von Brücken erweitert wird. Darüber hinaus kann die Messung nicht durch andere Verschiebungskomponenten beeinflusst werden, was das Auftreten von systematischen Abweichungen verringert. Folglich sind die Eigenformen empfindlicher gegenüber Schäden, da die Unsicherheiten reduziert werden. Das zugrunde liegende Prinzip dieses alternativen Messaufbaus wird wiederum durch Vergleiche mit Referenzsensoren validiert

The future of energy transition between critical materials and geopolitics. Lithium and the South American context

L'abstract è presente nell'allegato / the abstract is in the attachmen

Design Optimization of Wind Energy Conversion Systems with Applications

Modern and larger horizontal-axis wind turbines with power capacity reaching 15 MW and rotors of more than 235-meter diameter are under continuous development for the merit of minimizing the unit cost of energy production (total annual cost/annual energy produced). Such valuable advances in this competitive source of clean energy have made numerous research contributions in developing wind industry technologies worldwide. This book provides important information on the optimum design of wind energy conversion systems (WECS) with a comprehensive and self-contained handling of design fundamentals of wind turbines. Section I deals with optimal production of energy, multi-disciplinary optimization of wind turbines, aerodynamic and structural dynamic optimization and aeroelasticity of the rotating blades. Section II considers operational monitoring, reliability and optimal control of wind turbine components

Design Optimization of Wind Energy Conversion Systems with Applications

Modern and larger horizontal-axis wind turbines with power capacity reaching 15 MW and rotors of more than 235-meter diameter are under continuous development for the merit of minimizing the unit cost of energy production (total annual cost/annual energy produced). Such valuable advances in this competitive source of clean energy have made numerous research contributions in developing wind industry technologies worldwide. This book provides important information on the optimum design of wind energy conversion systems (WECS) with a comprehensive and self-contained handling of design fundamentals of wind turbines. Section I deals with optimal production of energy, multi-disciplinary optimization of wind turbines, aerodynamic and structural dynamic optimization and aeroelasticity of the rotating blades. Section II considers operational monitoring, reliability and optimal control of wind turbine components