NFIRAOS First Facility AO System for the Thirty Meter Telescope

NFIRAOS, the Thirty Meter Telescope's first adaptive optics system is an order 60x60 Multi-Conjugate AO system with two deformable mirrors. Although most observing will use 6 laser guide stars, it also has an NGS-only mode. Uniquely, NFIRAOS is cooled to -30 C to reduce thermal background. NFIRAOS delivers a 2-arcminute beam to three client instruments, and relies on up to three IR WFSs in each instrument. We present recent work including: robust automated acquisition on these IR WFSs; trade-off studies for a common-size of deformable mirror; real-time computing architectures; simplified designs for high-order NGS-mode wavefront sensing; modest upgrade concepts for high-contrast imaging.Comment: ..submitted to SPIE 9148 Astronomical Telescopes and Instrumentation - Adaptive Optics Systems IV (2014

Results of the NFIRAOS RTC trade study

With two large deformable mirrors with a total of more than 7000 actuators that need to be driven from the measurements of six 60x60 LGS WFSs (total 1.23Mpixels) at 800Hz with a latency of less than one frame, NFIRAOS presents an interesting real-time computing challenge. This paper reports on a recent trade study to evaluate which current technology could meet this challenge, with the plan to select a baseline architecture by the beginning of NFIRAOS construction in 2014. We have evaluated a number of architectures, ranging from very specialized layouts with custom boards to more generic architectures made from commercial off-the-shelf units (CPUs with or without accelerator boards). For each architecture, we have found the most suitable algorithm, mapped it onto the hardware and evaluated the performance through benchmarking whenever possible. We have evaluated a large number of criteria, including cost, power consumption, reliability and flexibility, and proceeded with scoring each architecture based on these criteria. We have found that, with today’s technology, the NFIRAOS requirements are well within reach of off-the-shelf commercial hardware running a parallel implementation of the straightforward matrix-vector multiply (MVM) algorithm for wave-front reconstruction. Even accelerators such as GPUs and Xeon Phis are no longer necessary. Indeed, we have found that the entire NFIRAOS RTC can be handled by seven 2U high-end PC-servers using 10GbE connectivity. Accelerators are only required for the off-line process of updating the matrix control matrix every ~10s, as observing conditions change

An innovative, highly sensitive receiver system for the Square Kilometre Array Mid Radio Telescope

International audienceThe Square Kilometre Array (SKA) Project is a global science and engineering project realizing the next-generation radio telescopes operating in the metre and centimetre wavelengths regions. This paper addresses design concepts of the broadband, exceptionally sensitive receivers and reflector antennas deployed in the SKA1-Mid radio telescope to be located in South Africa. SKA1-Mid (350 MHz - 13.8 GHz with an option for an upper limit of 24 GHz) will consist of 133 reflector antennas using an unblocked aperture, offset Gregorian configuration with an effective diameter of 15 m. Details on the unblocked aperture Gregorian antennas, low noise front ends and advanced direct digitization receivers, are provided from a system design perspective. The unblocked aperture results in increased aperture efficiency and lower side-lobe levels compared to a traditional on-axis configuration. The low side-lobe level reduces the noise contribution due to ground pick-up but also makes the antenna less susceptible to ground-based RFI sources. The addition of extra shielding on the sub-reflector provides a further reduction of ground pick-up. The optical design of the SKA1-Mid reflector antenna has been tweaked using advanced EM simulation tools in combination with sophisticated models for sky, atmospheric and ground noise contributions. This optimal antenna design in combination with very low noise, partially cryogenic, receivers and wide instantaneous bandwidth provide excellent receiving sensitivity in combination with instrumental flexibility to accommodate a wide range of astronomical observation modes

Fontes e sumidouros de vapor d'água e calor sensivel sobre o pantanal

O objetivo deste trabalho é avaliar as fontes e sumidouros de vapor dágua e calor sensível sobre a região do Pantanal, através da análise dos fluxos de superfície. Para isto, foram usados os dados coletados durante o experimento IPE (Experimento Interdisciplinar do Pantanal) da época mais seca (IPE 2) e da época de solo inundado (IPE 3). Na estimativa dos fluxos de calor latente e sensível foi aplicado o método de Penman-Monteith, o que mostrou que durante a época inundada o fluxo de calor latente foi cerca de 5% maior do que na fase seca; já os fluxos de calor sensível foram praticamente iguais. Outra característica apresentada é que os picos dos fluxos observados na fase inundada apresentaram valores de 590 Wm-2 de calor latente e 25 Wm-2 de calor sensível, além de um atraso de aproximadamente 4 horas comparados com os picos dos fluxos observados na fase seca, que tiveram valores de quase 500 Wm-2 de fluxo de calor latente e 24 Wm-2 de fluxo de calor sensível. Considerando o sítio experimental representativo de toda a área do Pantanal, fez-se o confronto dos resultados de fluxo de calor latente com os dados de precipitação, cuja média diária foi de 0.7 mm no IPE 2 e 2.2 mm no IPE 3. Este confronto mostrou quando a região do Pantanal atua como fonte ou sumidouro de calor latente e sensível. Uma explicação para a diferença entre a precipitação e os fluxos de calor latente é a atuação de fontes externas de umidade, principalmente a Amazônia. Desta forma também foi analisada heuristicamente a influência do Jato de Baixos Níveis na convergência de umidade no Pantanal