Mapping submarine glacial landforms using acoustic methods

The mapping of submarine glacial landforms is largely dependent on marine geophysical survey methods capable of imaging the seafloor and sub-bottom through the water column. Full global coverage of seafloor mapping, equivalent to that which exists for the Earth's land surface, has, to date, only been achieved by deriving bathymetry from radar altimeters on satellites such as GeoSat and ERS-1 (Smith & Sandwell 1997). The horizontal resolution is limited by the footprint of the satellite sensors and the need to average out local wave and wind effects, resulting in a cell size of about 15 km (Sandwell et al. 2001). A further problem in high latitudes is that the altimeter data are extensively contaminated by the presence of sea ice, which degrades the derived bathymetry (McAdoo & Laxon 1997). Consequently, the satellite altimeter method alone is not suitable for mapping submarine glacial landforms, given that their morphological characterization usually requires a much finer level of detail. Acoustic mapping methods based on marine echo-sounding principles are currently the most widely used techniques for mapping submarine glacial landforms because they are capable of mapping at a much higher resolution

Tracking and control in multi-function radar

The phased array multi-function radar is an effective solution to the requirement for simultaneous surveillance and multiple target tracking. However, since it is performing the jobs usually undertaken by several dedicated radars its radar time and energy resources are limited. For this reason, and also due to the large cost of active phased array antennas, it is important for the strategies adopted in the control of the radar to be efficient. This thesis investigates and develops efficient strategies for multi-function radar control and tracking. Particularly the research has focused on the use of rotating array antennas and simultaneous multiple receive beam processing. The findings of the research challenge the traditional view that three or four fixed (static) array faces is the best antenna configuration for a multi-function radar system. By developing novel methods for the comparison of systems utilising different antenna configurations it is shown that a rotating array multi-function radar performs the surveillance function with a greater efficiency in its use of radar time than a static array system. Also, a rotating array system benefits from the ability to distribute the radar resources over the angular coverage in a way that is impossible with a static array system. A novel strategy is presented to achieve this, which allows the rotating array system to better support the realistic situation of a high concentration of radar tasks in a narrow angular sector. It is shown that the use of broadened transmit beams coupled with simultaneous multiple narrow receive beams can eliminate the compromise on radar beamwidth between the surveillance and tracking functions that is associated with multi-function radars. This technique would allow construction of multi-function radar systems with narrow beamwidths, giving improved tracking performance, without extending search frame times excessively. Efficient tracking strategies for both static array and rotating array multi-function radars are developed. They are applied through computer simulation to demonstrate tracking of highly manoeuvrable targets with a narrow beam multi-function radar. Track robustness is attained through the use of multiple beam track updating strategies at little cost in terms of radar time

Airframe assembly, systems integration and flight testing of a long endurance electric UAV

The need to adopt new techniques and practices in the Aerospace Industry branch is a consequence of technological development. The present work aims to study the use of solar power as a main energy source in the aviation, in this case for a flight of long endurance of an unmanned air vehicle. This master thesis follows on previous works of the LEEUAV, where it was done the design and construction of a long endurance unmanned aerial system. Thus, the main objective of this work is the systems integration, flight testing and concepts validation. LEEUAV, a prototype of 4.5 meters’ wingspan and ultralight structure partially covered by solar cells was designed to fulfil a continuous flight mission of at least 8 hours on the equinox. The 5.42Kg remotely piloted aircraft was successfully tested showing the agreement with theoretical calculations already made. The longest flight achieved lasted more than 8.5 hours’ resulting in a total distance travelled of more than 75 km. In order to validate the airworthiness concept of the LEEUAV several flight tests were performed and their respective data (static and total pressure, air temperature, ground speed and pitch angle) was collected for further analysis, using a flight controller with multiple sensors on board. The results obtained allowed to study the general performance of the aircraft, the main defects, agreement with the theoretical results as well as determine the real values of aerodynamic coefficients (????, ????), through a reading and processing flight data algorithm in Software MATLAB. Finally, some future expectations for upcoming work are suggested in order to make the LEEUAV an Unmanned Aerial Vehicle of reference.A necessidade de adoção de novas técnicas e práticas no ramo da Indústria Aeronáutica é uma consequência do desenvolvimento tecnológico. O presente trabalho aborda o uso de energia solar como principal fonte de energia na aviação, com enfoque num voo de grande autonomia de uma aeronave não tripulada. Esta tese de mestrado surge na sequência de trabalhos anteriores relativos ao LEEUAV, nos quais se efetuou o projeto e construção de uma aeronave não tripulada de grande autonomia. Assim, o principal objetivo deste trabalho é a integração de sistemas, testes de voo e validação de conceitos. O UAV Solar LEEUAV é um protótipo de 4.5 metros de envergadura e de estrutura ultraleve parcialmente coberto de células fotovoltaicas sendo projetado para cumprir uma missão de voo contínuo de pelo menos 8h no equinócio. O avião de 5.42kg foi testado com sucesso mostrando a concordância com os cálculos teóricos já elaborados. O voo mais longo conseguido foi de 3.13 horas correspondendo a uma distância total percorrida de 96.265 km. De modo a validar o conceito de aeronavegabilidade do LEEUAV foram efetuados vários voos de teste e recolhidos dados de voo (pressão estática e dinâmica, temperatura do ar, velocidade no solo e ângulo de arfagem) para posterior análise, utilizando um controlador de voo com múltiplos sensores a bordo. A análise dos resultados obtidos permitiu precisar o desempenho geral da aeronave, os principais defeitos, concordância com os resultados teóricos assim como determinar os valores reais dos coeficientes aerodinâmicos (???? , ????) através de um algoritmo de leitura e processamento de dados de voo, em Software MATLAB. Por fim, são referidas algumas sugestões para o desenvolvimento de novos trabalhos com o objetivo de tornar O LEEUAV num veículo aéreo não tripulado de referência

Distributed Communication in Swarms of Autonomous Underwater Vehicles

Effective communication mechanisms are a key requirement for schools of submersible robots and their meaningful deployment. Large schools of identical submersibles require a fully distributed communication system which scales well and optimises for ”many-to-many” communication (omnicast, also known as gossiping). As an additional constraint, communication channels under water are typically very low bandwidth and short range. This thesis discusses possible electric and electro-magnetic wireless communication channels suitable for underwater environments. Theoretical findings on the omnicast communication problem are presented, as well as the implementation of a distributed time division multiple access (TDMA) scheduling algorithm in simulation and in hardware. It is shown theoretically and in simulation that short range links in a robotic swarm are actually an advantage, compared to links that cover large parts of the network. Experiments were carried out on custom-developed digital long-wave radio and optical link modules. The results of the experiments are used to revisit the initial assumptions on communication in multi-hop wireless networks

Architectures and Algorithms for the Signal Processing of Advanced MIMO Radar Systems

This thesis focuses on the research, development and implementation of novel concepts, architectures, demonstrator systems and algorithms for the signal processing of advanced Multiple Input Multiple Output (MIMO) radar systems. The key concept is to address compact system, which have high resolutions and are able to perform a fast radar signal processing, three-dimensional (3D), and four-dimensional (4D) beamforming for radar image generation and target estimation. The idea is to obtain a complete sensing of range, Azimuth and elevation (additionally Doppler as the fourth dimension) from the targets in the radar captures. The radar technology investigated, aims at addressing sev- eral civil and military applications, such as surveillance and detection of targets, both air and ground based, and situational awareness, both in cars and in flying platforms, from helicopters, to Unmanned Aerial Vehicles (UAV) and air-taxis. Several major topics have been targeted. The development of complete systems and innovative FPGA, ARM and software based digital architectures for 3D imaging MIMO radars, which operate in both Time Division Multiplexing (TDM) and Frequency Divi- sion Multiplexing (FDM) modes, with Frequency Modulated Continuous Wave (FMCW) and Orthogonal Frequency Division Multiplexing (OFDM) signals, respectively. The de- velopment of real-time radar signal processing, beamforming and Direction-Of-Arrival (DOA) algorithms for target detection, with particular focus on FFT based, hardware implementable techniques. The study and implementation of advanced system concepts, parametrisation and simulation of next generation real-time digital radars (e.g. OFDM based). The design and development of novel constant envelope orthogonal waveforms for real-time 3D OFDM MIMO radar systems. The MIMO architectures presented in this thesis are a collection of system concepts, de- sign and simulations, as well as complete radar demonstrators systems, with indoor and outdoor measurements. Several of the results shown, come in the form of radar images which have been captured in field-test, in different scenarios, which aid in showing the proper functionality of the systems. The research activities for this thesis, have been carried out on the premises of Air- bus, based in Munich (Germany), as part of a Ph.D. candidate joint program between Airbus and the Polytechnic Department of Engineering and Architecture (Dipartimento Politecnico di Ingegneria e Architettura), of the University of Udine, based in Udine (Italy).Questa tesi si concentra sulla ricerca, lo sviluppo e l\u2019implementazione di nuovi concetti, architetture, sistemi dimostrativi e algoritmi per l\u2019elaborazione dei segnali in sistemi radar avanzati, basati su tecnologia Multiple Input Multiple Output (MIMO). Il con- cetto chiave `e quello di ottenere sistemi compatti, dalle elevate risoluzioni e in grado di eseguire un\u2019elaborazione del segnale radar veloce, un beam-forming tri-dimensionale (3D) e quadri-dimensionale (4D) per la generazione di immagini radar e la stima delle informazioni dei bersagli, detti target. L\u2019idea `e di ottenere una stima completa, che includa la distanza, l\u2019Azimuth e l\u2019elevazione (addizionalmente Doppler come quarta di- mensione) dai target nelle acquisizioni radar. La tecnologia radar indagata ha lo scopo di affrontare diverse applicazioni civili e militari, come la sorveglianza e la rilevazione di targets, sia a livello aereo che a terra, e la consapevolezza situazionale, sia nelle auto che nelle piattaforme di volo, dagli elicotteri, ai Unmanned Aerial Vehicels (UAV) e taxi volanti (air-taxis). Le tematiche affrontante sono molte. Lo sviluppo di sistemi completi e di architetture digitali innovative, basate su tecnologia FPGA, ARM e software, per radar 3D MIMO, che operano in modalit`a Multiplexing Time Division Multiplexing (TDM) e Multiplexing Frequency Diversion (FDM), con segnali di tipo FMCW (Frequency Modulated Contin- uous Wave) e Orthogonal Frequency Division Multiplexing (OFDM), rispettivamente. Lo sviluppo di tecniche di elaborazione del segnale radar in tempo reale, algoritmi di beam-forming e di stima della direzione di arrivo, Direction-Of-Arrival (DOA), dei seg- nali radar, per il rilevamento dei target, con particolare attenzione a processi basati su trasformate di Fourier (FFT). Lo studio e l\u2019implementazione di concetti di sistema avan- zati, parametrizzazione e simulazione di radar digitali di prossima generazione, capaci di operare in tempo reale (ad esempio basati su architetture OFDM). Progettazione e sviluppo di nuove forme d\u2019onda ortogonali ad inviluppo costante per sistemi radar 3D di tipo OFDM MIMO, operanti in tempo reale. Le attivit`a di ricerca di questa tesi sono state svolte presso la compagnia Airbus, con sede a Monaco di Baviera (Germania), nell\u2019ambito di un programma di dottorato, svoltosi in maniera congiunta tra Airbus ed il Dipartimento Politecnico di Ingegneria e Architettura dell\u2019Universit`a di Udine, con sede a Udine

Aeronautical Engineering, A Continuing Bibliography With Indexes

This bibliography lists 693 reports, articles and other documents introduced into the NASA scientific and technical information system in September 1984

The measurement of underwater acoustic noise radiated by a vessel using the vessel's own towed array

The work described in this thesis tested the feasibility of using a towed array of hydrophones to: 1. localise sources of underwater acoustic noise radiated by the towvessel, 2. determine the absolute amplitudes of these sources, and 3. determine the resulting far-field acoustic signature of the tow-vessel. The concept was for the towvessel to carry out a U-turn manoeuvre so as to bring the acoustic section of the array into a location suitable for beamforming along the length of the tow-vessel. All three of the above were shown to be feasible using both simulated and field data, although no independent field measurements were available to fully evaluate the accuracy of the far-field acoustic signature determinations. A computer program was written to simulate the acoustic signals received by moving hydrophones. This program had the ability to model a variety of acoustic sources and to deal with realistic acoustic propagation conditions, including shallow water propagation with significant bottom interactions. The latter was accomplished using both ray and wave methods and it was found that, for simple fluid half-space seabeds, a modified ray method gave results that were virtually identical to those obtained with a full wave method, even at very low frequencies, and with a substantial saving in execution time. A field experiment was carried out during which a tug towing a 60-hydrophone array carried out a series of U-turn manoeuvres. The signals received by the array included noise radiated by the tow-vessel, signals from acoustic tracking beacons mounted on the tow-vessel, and transient signals generated by imploding sources deployed from a second vessel.Algorithms were developed to obtain snapshots of the vertical plane and horizontal plane shapes of the array from the transient data and to use range data derived from the tracking beacon signals to track the hydrophones in the horizontal plane. The latter was complicated by a high proportion of dropouts and outliers in the range data caused by the directionality of the hydrophones at the high frequencies emitted by the beacons. Despite this, excellent tracking performance was obtained. Matched field inversion was used to determine the vertical plane array shapes at times when no transient signals were available, and to provide information about the geoacoustic properties of the seabed. There was very good agreement between the inversion results and array shapes determined using transient signals. During trial manoeuvres the array was moving rapidly relative to the vessel and changing shape. A number of different array-processing algorithms were developed to provide source localisation and amplitude estimates in this situation: a timedomain beamformer; two frequency-domain, data independent beamformers; an adaptive frequency-domain beamformer; and an array processor based on a regularised least-squares inversion. The relative performance of each of these algorithms was assessed using simulated and field data. Data from three different manoeuvres were processed and in each case a calibrated source was localised to within 1 m of its known position at the source's fundamental frequency of 112 Hz.Localisation was also successful in most instances at 336 Hz, 560 Hz and 784 Hz, although with somewhat reduced accuracy due to lower signal to noise ratios. Localisation results for vessel noise sources were also consistent with the positions of the corresponding items of machinery. The estimated levels of the calibrated source obtained during the three manoeuvres were all within 4.1 dB of the calibrated value, and varied by only 1.3 dB between manoeuvres. Results at the higher frequencies had larger errors, with a maximum variation of 3.8 dB between serials, and a maximum deviation from the calibrated value of 6.8 dB. An algorithm was also developed to predict the far-field signature of the tow-vessel from the measured data and results were produced. This algorithm performed well with simulated data but no independent measurements were available to compare with the field results