3,851 research outputs found
Advanced Synthetic Aperture Radar Based on Digital Beamforming and Waveform Diversity
This paper introduces innovative SAR system
concepts for the acquisition of high resolution radar images with
wide swath coverage from spaceborne platforms. The new concepts
rely on the combination of advanced multi-channel SAR front-end
architectures with novel operational modes. The architectures
differ regarding their implementation complexity and it is shown
that even a low number of channels is already well suited to
significantly improve the imaging performance and to overcome
fundamental limitations inherent to classical SAR systems. The
more advanced concepts employ a multidimensional encoding of
the transmitted waveforms to further improve the performance
and to enable a new class of hybrid SAR imaging modes that are
well suited to satisfy hitherto incompatible user requirements for
frequent monitoring and detailed mapping. Implementation
specific issues will be discussed and examples demonstrate the
potential of the new techniques for different remote sensing
applications
Ultra Wide Swath Imaging With Multi-Channel SAR Systems
Multi-channel radar systems allow for overcoming the inherent limitation of conventional synthetic aperture radar (SAR). An example is the combination of digital beamforming on receive in elevation with multi-aperture SAR signal reconstruction in azimuth which enables high-resolution wide-swath. As a next step, focus is turned to advanced concepts for the imaging of even wider swaths with high azimuth resolution. In this regard, the paper investigates the operation of multi-channel SAR systems in burst modes like ScanSAR or TOPS-SAR and analyses aspects of applying the multi-aperture reconstruction algorithm in combination with burst mode operation. The impact of the digital processing network on the SNR and the azimuth ambiguity-to-signal-ratio in multi-channel burst mode systems are considered and embedded in the design example of a ScanSAR system that enables the imaging of a 400 km wide swath with a geometric resolution of 5
PotĂŞncia aerĂłbica máxima, frequĂŞncia cardĂaca e capacidade vital em ambientes normo e hiperbárico
Desde a antiguidade, o homem se deslumbra com o mundo submarino. AtravĂ©s da histĂłria, tanto a humanidade em geral como alguns homens de espĂrito aventureiro, buscavam descobrir nas profundezas dos oceanos o sentimento que o mar exerce sobre cada um e sobre a espĂ©cie em geral. Partindo desta constatação, propõe-se nesta dissertação verificar variáveis fisiolĂłgicas. Revisando a literatura sobre o presente estudo, levantaram-se vários tratados, especificando as reações e adaptações tanto fisiolĂłgicas quanto comportamentais ocorridas no organismo durante a imersĂŁo. Seguiu-se o modelo da pesquisa descritiva do tipo Survey, onde participam mergulhadores da Marinha do Brasil, do sexo masculino, participantes de atividades fĂsicas, num total de 9, com mĂ©dia da idade de x= 28 ± 4,3 anos, peso 76,7 ± 8,32 Kg e estatura 173,8 ± 6,33 cm. Todos foram submetidos Ă avaliação de vários parâmetros fisiolĂłgicos determinados para o estudo ao nĂvel do mar (ambiente normobárico) e aos 18 metros de profundidade (ambiente hiperbárico), pressurizados em câmara hiperbárica, sendo verificadas as variáveis propostas em exercĂcio. A amostra foi homogeneizada atravĂ©s do cálculo de percentual de gordura, da perimetria e testes neuromotores de performance. Os resultados sĂŁo analisados no nĂvel de significância p 0,05, denota nĂŁo existir diferença significativa entre os ambientes verificados. O consumo máximo de oxigĂŞnio p=0,00013 < 0,05, e a capacidade vital p=0,00126 < 0,05, denotam existir diferenças significativas entre os ambientes. Finalmente, atravĂ©s dos dados obtidos, concluiu-se que o ambiente influĂŞncia diretamente o consumo de oxigĂŞnio e a capacidade vital. Quanto a frequĂŞncia cardĂaca, contatou-se influencia direta provocada pela intensidade e duração do protocolo de exercĂcio aplicado independente do ambiente. Isso comprova a importância de conhecer as reações fisiolĂłgicas avaliadas e revisadas na literatura como componentes essĂŞncias da performance, confirmando a necessidade de criar programas de treinamento fĂsico adequados aos mergulhadores
System Concepts for Bi- and Multi-Static SAR Missions
The performance and capabilities of bi- and multistatic spaceborne synthetic aperture radar (SAR) are analyzed. Such systems can be optimized for a broad range of applications like frequent monitoring, wide swath imaging, single-pass cross-track interferometry, along-track interferometry, resolution enhancement or radar tomography. Further potentials arises from digital beamforming on receive, which allows to gather additional information about the direction of the scattered radar echoes. This directional information can be used to suppress interferences, to improve geometric and radiometric resolution, or to increase the unambiguous swath width. Furthermore, a coherent combination of multiple receiver signals will allow for a suppression of azimuth ambiguities. For this, a reconstruction algorithm is derived, which enables a recovery of the unambiguous Doppler spectrum also in case of non-optimum receiver aperture displacements leading to a non-uniform sampling of the SAR signal. This algorithm has also a great potential for systems relying on the displaced phase center (DPC) technique, like the high resolution wide swath (HRWS) SAR or the split antenna approach in the TerraSAR-X and Radarsat II satellites
Advanced Concepts for Ultra-Wide-Swath SAR Imaging
This paper reviews advanced multi-channel SAR system
concepts for the imaging of ultra-wide swaths with high azimuth
resolution. Novel system architectures and operational
modes are introduced and compared to each other with regard
to their performance
Como integrar as TIC em contexto didático das Artes explorando a distribuição EVTux na área do cinema de animação
Com a implementação do Plano Tecnológico da Educação e consequente apetrechamento das Escolas com recursos tecnológicos avançados, surge agora a necessidade de criar condições favoráveis para a efetiva integração das TIC
no currĂculo, nomeadamente na área das Artes. Decorrente das caracterĂsticas
singulares desta área curricular, são muitas as ferramentas digitais que podemos
utilizar em contexto educativo mobilizando-as para experiências de aprendizagem baseadas em projetos que integrem as tecnologias. Este é o caso do EVTux, uma distribuição livre de Linux que permite a criação efetiva de projetos de
cinema de animação em contexto educativo com recurso às tecnologias, caso
que agora se apresenta como exemplo neste artigo e que atualmente faz parte de uma sĂntese do trabalho que se integra no projeto europeu TACCLE2 no qual participamos.With the introduction of the Technological Program for Education,
schools were equipped with the right conditions to really implement and use
technological resources. It is now the time to create favorable conditions to an
effective integration of Information and Communication Technologies in the
curricula, namely in the Arts field. Because this is a very specific field of studies,
there are many digital tools that may be used in an educational context and then
transferred into learning experiences based on projects using technologies. This is what EVTux is all about – a free Linux distribution that allows the creation of
animated film projects in educational contexts using technologies. This case is
presented as an example in this article and is, at the moment, part of a work
integrated in the European project TACCLE2 in which we participate
Nzinga Mbandi: from story to myth
The figure of Queen Nzinga Mbandi continues to be appreciated in fictional and/or historical narratives as a myth of postcolonial Angolan identity, allowing a continuous approach as to what concerns the modes of cultural representation. In this article, the works of Manuel Pedro Pacavira, Nzinga Mbandi (1975), Pepetela, A gloriosa famĂlia: o tempo dos flamengos (1997) and JosĂ© Eduardo Agualusa, A Rainha Ginga e de como os africanos inventaram o mundo (2014) will be analyzed, as these authors, in different moments of the recent Angolan history, look at this emblematic figure, drawing on historical information produced by Cavazzi, Cadornega or Jean Louis Castilhon, among others. The works now in analysis reiterate the mythical figure of resistance to the European invaders, which was Nzinga Mbandi, or a strong orientation towards the nationalist exaltation supported by it, an evident strategy which, by the rescue of figures and cultural practices, is defined as a means to affirm negritude
Arm TrustZone: evaluating the diversity of the memory subsystem
Dissertação de mestrado em Engenharia Eletrónica Industrial e ComputadoresThe diversification of the embedded market has led the once single-purpose built embedded
device to become a broader concept that can accommodate more general-purpose solutions,
by widening its hardware and software resources. A huge diversity in system resources and
requirements has boosted the investigation around virtualization technology, which is becoming
prevalent in the embedded systems domain, allowing timing and spatial sharing of hardware and
software resources between specialized subsystems. As strict timing demands imposed in realtime
virtualized systems must be met, coupled with a small margin for the penalties incurred
by conventional software-based virtualization, resort to hardware-assisted solutions has become
indispensable.
Although not a virtualization but security-oriented technology, Arm TrustZone is seen by many
as a reliable hardware-based virtualization alternative, with the low cost and high spread of
TrustZone-enabled processors standing as strong arguments for its acceptance. But, since Trust-
Zone only dictates the hardware infrastructure foundations, providing SoC designers with a range
of components that can fulfil specific functions, several key-components and subsystems of this
technology are implementation defined. This approach may hinder a system designer’s work, as
it may impair and make the portability of system software a lot more complicated.
As such, this thesis proposes to examine how different manufacturers choose to work with
the TrustZone architecture, and how the changes introduced by this technology may affect the
security and performance of TrustZone-assisted virtualization solutions, in order to scale back
those major constraints. It identifies the main properties that impact the creation and execution
of system software and points into what may be the most beneficial approaches for developing
and using TrustZone-assisted hardware and software.A recente metamorfose na área dos sistemas embebidos transformou estes dispositivos,
outrora concebidos com um Ăşnico e simples propĂłsito, num aglomerado de subsistemas prontos
para integrar soluções mais flexĂveis. Este aumento de recursos e de requisitos dos sistemas
potenciou a investigação em soluções de virtualização dos mesmos, permitindo uma partilha
simultânea de recursos de hardware e software entre os vários subsistemas. A proliferação destas
soluções neste domĂnio, onde os tempos de execução tĂŞm de ser respeitados e a segurança Ă©
um ponto-chave, tem levado à adoção de técnicas de virtualização assistidas por hardware.
Uma tecnologia que tem vindo a ser utilizada para este fim Ă© a Arm TrustZone, apesar de
inicialmente ter sido desenvolvida como uma tecnologia de proteção, dado a sua maior presença
em placas de médio e baixo custo quando comparada a outras tecnologias. Infelizmente, dado
que a TrustZone apenas fornece diretrizes base sobre as quais os fabricantes podem contruir
os seus sistemas, as especificações da tecnologia divergem de fabricante para fabricante, ou
até entre produtos com a mesma origem. Aliada à geral escassez de informação sobre esta
tecnologia, esta caracterĂstica pode trazer problemas para a criação e portabilidade de software
de sistema dependente desta tecnologia.
Como tal, a presente tese propõe examinar, de uma forma sistematizada, de que forma diferentes
fabricantes escolhem implementar sistemas baseados na arquitetura TrustZone e em que
medida as mudanças introduzidas por esta tecnologia podem afetar a segurança e desempenho
de soluções de virtualização baseadas na mesma. SĂŁo identificadas as principais caracterĂsticas
que podem influenciar a criação e execução de software de sistema e potenciais medidas para
diminuir o seu impacto, assim como boas práticas a seguir no desenvolvimento na utilização de
software e hardware baseados na TrustZone
SAR Signal Reconstruction from Non-Uniform Displaced Phase Centre Sampling
The displaced phase centre (DPC) technique will enable a wide swath SAR with high azimuth resolution. In a classic DPC system, the PRF has to be chosen such that the SAR carrier moves just one half of its antenna length between subsequent radar pulses. Any deviation from this PRF will result in a nonuniform sampling of the synthetic aperture. This paper shows that an unambiguous reconstruction of the SAR signal is also possible in case of such a non-optimum PRF. For this, an innovative reconstruction algorithm is derived, which enables a recovery of the unambiguous Doppler spectrum also in case of a non-uniform sampling of the synthetic aperture. This algorithm will also have a great potential for multistatic satellite constellations as well as the dual receive antennas in Radarsat II and TerraSAR-X
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