Papers by Julio Navarrete
Monthly Notices of the Royal Astronomical Society, 2012
Nowadays, the real-time seeing estimation at the focus of a telescope is strongly emphasized beca... more Nowadays, the real-time seeing estimation at the focus of a telescope is strongly emphasized because this knowledge virtually drives the dimensioning of adaptive optics systems and the operational aspects of instruments. In this context, we study the importance of using images from an active optics Shack-Hartmann (AOSH) sensor to provide accurate estimates of the seeing. At the critical location of the focus of the telescope, the AOSH sensor delivers longexposure spot point spread functions, which are directly related to the atmospheric seeing in the line of sight. Although AOSH sensors are specified to measure not spot sizes but slopes, we show that an accurate estimation of the seeing can be obtained from AOSH images using a dedicated algorithm. We analyse the sensitivity of two algorithms and compare them to various parameters in a systematic way, demonstrating that an efficient estimation of the seeing can be obtained by adequate means.
A water vapour radiometer has been permanently deployed on Paranal as a new tool for supporting s... more A water vapour radiometer has been permanently deployed on Paranal as a new tool for supporting science operations at the Very Large Telescope. The instrument allows the water vapour content of the atmosphere above the observatory to be monitored in real time with high precision and time resolution and periods of low precipitable water vapour (PWV) to be selected, providing better atmospheric transmission for observations in the infrared. The PWV measurements will be made available to VISIR users in the form of FITS header keywords. In addition, we expect that over time these data will allow a deeper insight into the atmospheric conditions on Paranal, with implications also for the operation of the European Extremely Large Telescope (E-ELT) on nearby Cerro Armazones.
A water vapour radiometer has been permanently deployed on Paranal as a new tool for supporting s... more A water vapour radiometer has been permanently deployed on Paranal as a new tool for supporting science operations at the Very Large Telescope. The instrument allows the water vapour content of the atmosphere above the observatory to be monitored in real time with high precision and time resolution and periods of low precipitable water vapour (PWV) to be selected, providing better atmospheric transmission for observations in the infrared. The PWV measurements will be made available to VISIR users in the form of FITS header keywords. In addition, we expect that over time these data will allow a deeper insight into the atmospheric conditions on Paranal, with implications also for the operation of the European Extremely Large Telescope (E-ELT) on nearby Cerro Armazones.
Monthly Notices of the Royal Astronomical Society, 2018
Knowledge of the Earth's atmospheric optical turbulence is critical for astronomical instrumentat... more Knowledge of the Earth's atmospheric optical turbulence is critical for astronomical instrumentation. Not only does it enable performance verification and optimization of the existing systems, but it is required for the design of future instruments. As a minimum this includes integrated astro-atmospheric parameters such as seeing, coherence time, and isoplanatic angle, but for more sophisticated systems such as wide-field adaptive optics enabled instrumentation the vertical structure of the turbulence is also required. Stereo-SCIDAR (Scintillation Detection and Ranging) is a technique specifically designed to characterize the Earth's atmospheric turbulence with high-altitude resolution and high sensitivity. Together with ESO (European Southern Observatory), Durham University has commissioned a Stereo-SCIDAR instrument at Cerro Paranal, Chile, the site of the Very Large Telescope (VLT), and only 20 km from the site of the future Extremely Large Telescope (ELT). Here we provide results from the first 18 months of operation at ESO Paranal including instrument comparisons and atmospheric statistics. Based on a sample of 83 nights spread over 22 months covering all seasons, we find the median seeing to be 0.64 with 50 per cent of the turbulence confined to an altitude below 2 km and 40 per cent below 600 m. The median coherence time and isoplanatic angle are found as 4.18 ms and 1.75 , respectively. A substantial campaign of inter-instrument comparison was also undertaken to assure the validity of the data. The Stereo-SCIDAR profiles (optical turbulence strength and velocity as a function of altitude) have been compared with the Surface-Layer Slope Detection And Ranging, Multi-Aperture Scintillation Sensor-Differential Image Motion Monitor, and the European Centre for Medium Range Weather Forecasts model. The correlation coefficients are between 0.61 (isoplanatic angle) and 0.84 (seeing).
This is the second article of a series devoted to European Extremely Large Telescope (E-ELT) site... more This is the second article of a series devoted to European Extremely Large Telescope (E-ELT) site characterization. In this article we present the main properties of the parameters involved in high angular resolution observations from the data collected in the site testing campaign of the E-ELT during the Design Study (DS) phase. Observations were made in 2008 and 2009, in the four sites selected to shelter the future E-ELT (characterized under the ELT-DS contract): Aklim mountain in Morocco, Observatorio del Roque de los Muchachos (ORM) in Spain, Mac\'on range in Argentina, and Cerro Ventarrones in Chile. The same techniques, instruments and acquisition procedures were taken on each site. A Multiple Aperture Scintillation Sensor (MASS) and a Differential Image Motion Monitor (DIMM) were installed at each site. Global statistics of the integrated seeing, the free atmosphere seeing, the boundary layer seeing and the isoplanatic angle were studied for each site, and the results ar...
The Science Operation Department is composed of Astronomers, Telescope Instruments Operators (TIO... more The Science Operation Department is composed of Astronomers, Telescope Instruments Operators (TIO) and Data Handling Administrators (DHAs). Their main goal is to produce top-quality astronomical data by operating a suite of 9 telescopes, 14 Instruments and related systems, supporting the execution of Visitor Mode Observations or executing Service Mode Observations. Astronomers and TIOs have to deal with atmospheric parameters like seeing, coherence time, isoplanatic angle, precipitable water vapor, etc. in order to take in real time the best decisions on the best program to be executed according to the current conditions. We describe the tools available in the control room, provided by the environmental monitoring and forecast system.
This is an open access article under the terms of the Creat ive Commo ns Attri bution License, wh... more This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Optical turbulence affects significantly the quality of ground-based astronomical observations. A... more Optical turbulence affects significantly the quality of ground-based astronomical observations. An accurate and reliable forecast of optical turbulence can help to optimize the scheduling of the science observations and to improve both the quality of the data and the scientific productivity of the observatory. However, forecasts of the turbulence to a level of accuracy which is useful in the operations of large observatories are notoriously difficult to obtain. Several routes have been investigated, from detailed physical modelling of the atmosphere to empirical data-driven approaches. Here, we present an empirical approach exploiting spatial diversity and based on simultaneous measurements between two nearby sites, Cerro Paranal, host of the Very Large Telescope (VLT), and Cerro Armazones, future host of the Extremely Large Telescope (ELT) in Chile. We study the correlation between the high-altitude turbulence as measured between those two sites. This is part of the on-going effort...
The optical turbulence profile is a key parameter in tomographic reconstruction. With interest in... more The optical turbulence profile is a key parameter in tomographic reconstruction. With interest in tomographic adaptive optics for the next generation of ELTs, turbulence profiling campaigns have produced large quantities of data for observing sites around the world. In order to be useful for Monte Carlo AO simulation, these large datasets must be reduced to a small number of profiles. There is commonly large variation in the structure of the turbulence, therefore statistics such as the median and interquartile range of each altitude bin become less representative as features in the profile are averaged out. Here we present the results of the use of a hierarchical clustering method to reduce the 2018A Stereo-SCIDAR dataset from ESO Paranal, consisting of over 10,000 turbulence profiles measured over 83 nights, to a small set of 18 that represent the most commonly observed profiles.
Several challenges will have to be faced by the staff at Paranal Observatory in order to be well ... more Several challenges will have to be faced by the staff at Paranal Observatory in order to be well prepared for a seamless integration of the ELT in the current VLT operations scheme. The Telescopes and Instruments Operator group (TIO) is already undergoing changes connected with some of the identified technological and operational needs for the ELT. This paper will have detailed information about the current training needs, group structural changes, the current activities using the adopted engineering-TIO [2] (eTIO) scheme and the staffing plan that will have to be applied in order to keep the centralized support of the biggest world infrastructure in astronomy at the time of the ELT, to handle daily science operations for seven different telescopes, the VLT interferometer and twenty-one scientific instruments in parallel.
Revista Mexicana De Astronomia Y Astrofisica, 2011
Resumen en: The MASS-DIMM database at Paranal and Armazones has been reprocessed with the latest ... more Resumen en: The MASS-DIMM database at Paranal and Armazones has been reprocessed with the latest version of the ATMOS reprocessing software. The atmospheric time con...
The vertical distribution of atmospheric optical turbulence has a significant impact on the perfo... more The vertical distribution of atmospheric optical turbulence has a significant impact on the performance of widefield adaptive optics systems. StereoSCIDAR is an instrument capable of measuring the vertical profile of the turbulence strength and velocity with high sensitivity and altitude resolution. Stereo-SCIDAR, developed in close collaboration with Durham University, was successfully tested at the La Silla Paranal Observatory in mid-2016. This visitor instrument is located at the coudé focus of one of the Auxiliary Telescopes and will record atmospheric turbulence profiles above Paranal for one year starting in October 2016. These measurements are required for the specification and implementation of adaptive optics for the European Extremely Large Telescope.
Revista Mexicana De Astronomia Y Astrofisica, 2011
Resumen en: Real-time seeing estimation at the focus of a telescope is nowadays strongly emphasiz... more Resumen en: Real-time seeing estimation at the focus of a telescope is nowadays strongly emphasized as this knowledge virtually drives the dimensioning of adaptive o...
A new version of the cute-SCIDAR instrument, which employs the generalised SCIntillation Detectio... more A new version of the cute-SCIDAR instrument, which employs the generalised SCIntillation Detection And Ranging technique to obtain detailed atmospheric turbulence profiles with height, has been designed, developed and tested by the Instituto de Astrofísica de Canarias. The instrument was developed to match the requirements of the ESO VLT Auxiliary Telescopes, within the framework of the European Extremely Large Telescope site characterisation project. Commissioning at Paranal was successfully carried out in November 2007. This upgraded ver sion of the original instrument, presently working at the Roque de los Muchachos Observatory, allows g-SCIDAR turbulence profiles to be obtained in real time, a novel achievement in site testing and also a crucial tool for the optimum design and operation of Adaptative Optics and Multi-Conjugate Adaptive Optics systems.
The multi-aperture scintillation sensor (MASS) is a widely-used robotic turbulence profiling inst... more The multi-aperture scintillation sensor (MASS) is a widely-used robotic turbulence profiling instrument that measures the turbulence strength in 6 altitude resolution elements centered at 0.5, 1, 2, 4, 8 and 16 km. Paranal Observatory has a facility MASS instrument that is used to support adaptive optics operations. The observatory also has a stereo scintillation detection and ranging (S-SCIDAR) instrument that is typically operated for several nights per month, measuring the full turbulence profile with a resolution of several hundred metres. We make a comparison between concurrent S-SCIDAR and MASS measurements by binning the S-SCIDAR profiles according to the MASS response functions and performing a layer-by-layer comparison of the 6 MASS layers. We show that some layers tend to be significantly over- or underestimated by MASS, compared to S-SCIDAR, but the sum of all 6 layers is quite consistent between the two instruments. We present a detailed Monte Carlo simulation of the MAS...
Since the commissioning of the VLT it has been known that the image quality delivered by the tele... more Since the commissioning of the VLT it has been known that the image quality delivered by the telescopes is better, and often much better, than predicted by the seeing monitor. The advent of new sensitive instruments to measure the optical turbulence profile of the atmosphere over Paranal has finally allowed us to understand the origin of this discrepancy: the presence of a highly turbulent layer so close to the ground that it is seen by the seeing monitor, but not by the VLT unit telescopes. In this article we tell the story of this elusive surface layer.
Preliminary results from the Stereo-SCIDAR at the VLT Observatory: extraction of reference atmospheric turbulence profiles for E-ELT adaptive optics instrument performance simulations
The Stereo-SCIDAR (Scintillation Detection and Ranging) atmospheric turbulence profiler, built fo... more The Stereo-SCIDAR (Scintillation Detection and Ranging) atmospheric turbulence profiler, built for ESO by Durham University, observes the scintillation patterns of binary elements with one of the four VLT-Interferometer 1.8m auxiliary telescopes at the ESO Paranal Observatory. The primary products are the vertical profiles of the index of refraction structure coefficient and of the wind velocity which allow to compute the wavefront coherence time and the isoplanatic angle with a vertical resolution of 250m. The several thousands of profiles collected during more than 30 nights of operation are grouped following criteria based on the altitude distribution or on principal component analysis. A set of reference profiles representative of the site is proposed as input for the various simulation models developed by the E-ELT (European Extremely Large Telescope) instruments Consortia.
Comparison between scintillation-based atmospheric turbulence profiling instruments
Imaging and Applied Optics 2019 (COSI, IS, MATH, pcAOP)
The Paranal Surface Layer
Optical Turbulence, 2010
The Science Operation Department is composed of Astronomers, Telescope Instruments Operators (TIO... more The Science Operation Department is composed of Astronomers, Telescope Instruments Operators (TIO) and Data Handling Administrators (DHAs). Their main goal is to produce top-quality astronomical data by operating a suite of 9 telescopes, 14 Instruments and related systems, supporting the execution of Visitor Mode Observations or executing Service Mode Observations. Astronomers and TIOs have to deal with atmospheric parameters like seeing, coherence time, isoplanatic angle, precipitable water vapor, etc. in order to take in real time the best decisions on the best program to be executed according to the current conditions. We describe the tools available in the control room, provided by the environmental monitoring and forecast system.
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Papers by Julio Navarrete