Determinación de parámetros atmosféricos procedentes de medidas de irradiancia espectral para su aplicación en modelos de calidad del aire

Con el objetivo de investigar los procesos de la radiaciónultravioleta (UV) en la atmósfera y su impacto en la calidad del aire se ha dotado a la Estación de Observación de la Atmósfera de Santiago de Compostela (EOAS) de un radiómetro multifiltro, que proporciona medidas espectrales de irradiancia en seis longitudes de onda dentro del espectro UV.Basándose en los trabajos de Stamnes et al. (1991) yDahlback (1996) y mediante la aplicación de un modelode transferencia radiativa, se ha desarrollado un procedimientopara la determinación de los valores de columna total de ozono y de columna de agua líquida, de interés como parámetros de entrada en modelos de calidad del aire.Los resultados obtenidos han sido validados utilizando distintas metodologías, dependiendo del parámetro derivado. En todos los casos, las tendencias de los valores estimados mediante la metodología descrita concuerdan con las obtenidas a partir de los parámetros de contraste empleados

Medidas operativas derivadas de un radiómetro GUV2511 multirango

Ponencia presentada en: XXIX Jornadas Científicas de la AME y el VII Encuentro Hispano Luso de Meteorología celebrado en Pamplona, del 24 al 26 de abril de 2006

Inhibition of Linear Absorption in Opaque Materials Using Phase-Locked Harmonic Generation

We theoretically predict and experimentally demonstrate inhibition of linear absorption for phase and group velocity mismatched second- and third-harmonic generation in strongly absorbing materials, GaAs, in particular, at frequencies above the absorption edge. A 100-fs pump pulse tuned to 1300 nm generates 650 and 435 nm second- and third-harmonic pulses that propagate across a 450−μm-thick GaAs substrate without being absorbed. We attribute this to a phase-locking mechanism that causes the pump to trap the harmonics and to impress on them its dispersive properties

Inhibition of Linear Absorption in Opaque Materials Using Phase-Locked Harmonic Generation

We theoretically predict and experimentally demonstrate inhibition of linear absorption for phase and group velocity mismatched second- and third-harmonic generation in strongly absorbing materials, GaAs, in particular, at frequencies above the absorption edge. A 100-fs pump pulse tuned to 1300 nm generates 650 and 435 nm second- and third-harmonic pulses that propagate across a 450−μm-thick GaAs substrate without being absorbed. We attribute this to a phase-locking mechanism that causes the pump to trap the harmonics and to impress on them its dispersive properties

Refractivity and refractivity gradient estimation from radar phase data: a least squares based approach

Tropospheric refractivity, related to temperature, pressure, and humidity, is an interesting parameter for weather analysis, prediction, and study of climate trends. It has been shown to be useful for the detection and forecast of convective events. It has already been demonstrated that tropospheric refractivity can be estimated from radar phase measurements. In this article, a nonlinear least squares based approach for the estimation of the tropospheric refractivity that simultaneously provides the estimates of the refractivity vertical gradient is presented. A significant improvement of the presented technique is that it allows estimation of the refractivity over any terrain orography, flat, or hilly. Furthermore, the method developed can be implemented on klystron as well as on magnetron-based radars. Results for both radar types, at S- and C-bands, located over flat and hilly terrain show the potential of the method.European Climate, Infrastructure and Environment Executive Agency | Ref. Life16 Env/ES/000559Xunta de Galicia | Ref. GRC2019/02

Pre-correction Adaptive Optics performance of a 10 km Laser Link

For the next generation of very high throughput communication satellites, free-space optical (FSO) communication between ground stations and geostationary telecommunication satellites is likely to replace conventional RF links. To mitigate atmospheric turbulence, TNO and DLR propose Adaptive Optics (AO) to apply uplink pre-correction. In order to demonstrate the feasibility of AO pre-correction an FSO link has been tested over a 10 km range. This paper shows that AO pre-correction is most advantageous for low point ahead angles (PAAs), as expected. In addition, an optimum AO precorrection performance is found at 16 AO modes for the experimental conditions. For the specific test site, tip-tilt precorrection accounted for 4.5 dB improvement in the link budget. Higher order AO modes accounted for another 1.5 dB improvement in the link budget. From these results it is concluded that AO pre-correction can effectively improve highthroughput optical feeder links

Design, pointing control, and on-sky performance of the mid-infrared vortex coronagraph for the VLT/NEAR experiment

Vortex coronagraphs have been shown to be a promising avenue for high- contrast imaging in the close-in environment of stars at thermal infrared (IR) wavelengths. They are included in the baseline design of the mid-infrared extremely large telescope imager and spectrograph. To ensure good performance of these coronagraphs, a precise control of the centering of the star image in real time is needed. We previously developed and validated the quadrant analysis of coronagraphic images for tip-tilt sensing estimator (QACITS) pointing estimator to address this issue. While this approach is not wavelength-dependent in theory, it was never implemented for mid-IR observations, which leads to specific challenges and limitations. Here, we present the design of the mid-IR vortex coronagraph for the "new Earths in the α Cen Region (NEAR) experiment with the Very Large Telescope (VLT)/Very Large Telescope imager and spectrometer for the mid-infrared (VISIR) instrument and assess the performance of the QACITS estimator for the centering control of the star image onto the vortex coronagraph. We use simulated data and on-sky data obtained with VLT/VISIR, which was recently upgraded for observations assisted by adaptive optics in the context of the NEAR experiment. We demonstrate that the QACITS-based correction loop is able to control the centering of the star image onto the NEAR vortex coronagraph with a stability down to 0.015 λ / D rms over 4 h in good conditions. These results show that QACITS is a robust approach for precisely controlling in real time the centering of vortex coronagraphs for mid-IR observations.Peer reviewe

E-ELT M4 adaptive unit final design and construction: a progress report

The E-ELT M4 adaptive unit is a fundamental part of the E-ELT: it provides the facility level adaptive optics correction that compensates the wavefront distortion induced by atmospheric turbulence and partially corrects the structural deformations caused by wind. The unit is based on the contactless, voice-coil technology already successfully deployed on several large adaptive mirrors, like the LBT, Magellan and VLT adaptive secondary mirrors. It features a 2.4m diameter flat mirror, controlled by 5316 actuators and divided in six segments. The reference structure is monolithic and the cophasing between the segments is guaranteed by the contactless embedded metrology. The mirror correction commands are usually transferred as modal amplitudes, that are checked by the M4 controller through a smart real-time algorithm that is capable to handle saturation effects. A large hexapod provides the fine positioning of the unit, while a rotational mechanism allows switching between the two Nasmyth foci. The unit has entered the final design and construction phase in July 2015, after an advanced preliminary design. The final design review is planned for fall 2017; thereafter, the unit will enter the construction and test phase. Acceptance in Europe after full optical calibration is planned for 2022, while the delivery to Cerro Armazones will occur in 2023. Even if the fundamental concept has remained unchanged with respect to the other contactless large deformable mirrors, the specific requirements of the E-ELT unit posed new design challenges that required very peculiar solutions. Therefore, a significant part of the design phase has been focused on the validation of the new aspects, based on analysis, numerical simulations and experimental tests. Several experimental tests have been executed on the Demonstration Prototype, which is the 222 actuators prototype developed in the frame of the advanced preliminary design. We present the main project phases, the current design status and the most relevant results achieved by the validation tests