The German Aerospace Center (DLR) and the European Southern Observatory (ESO) performed a measurement campaign together in April and July 2016 at Teide-Observatory (Tenerife), with the support of the European Space Agency (ESA), to investigate the use of laser guide stars (LGS) in ground to space optical communications. Atmospheric turbulence causes strong signal fluctuations in the uplink, due to scintillation and beam wander. In space communications, the use of the downlink channel as reference for pointing and for pre-distortion adaptive optics is limited by the size of the isokinetic and isoplanatic angle in relation to the required point-ahead angle. Pointing and phase errors due to the decorrelation between downward and upward beam due to the point-ahead angle may have a severe impact on the required transmit power and the stability of the communications link. LGSs provide a self-tailored reference to any optical ground-to-space link, independently of turbulence conditions and required point-ahead angle. In photon-starved links, typically in deep-space scenarios, LGSs allow dedicating all downlink received signal to communications purposes, increasing the available link margin. The scope of the joint DLR-ESO measurement campaign was, first, to measure the absolute value of the beam wander (uplink-tilt) using a LGS, taking a natural star as a reference, and, second, to characterize the decrease of correlation between uplink-tilt and downlink-tilt with respect to the angular separation between both sources. This paper describes the experiments performed during the measurement campaigns, providing an overview of the measured data and the first outcomes of the data post-processing.
We report on the comparison between observations and simulations of a completed 12-month field observation campaign at Observatorio del Teide, Tenerife, using ESO's transportable 20 watt CW Wendelstein laser guide star system. This mission has provided sodium photon return flux measurements of unprecedented detail regarding variation of laser power, polarization and sodium D2b repumping. The Raman fiber laser and projector technology are very similar to that employed in the 4LGSF/AOF laser facility, recently installed and commissioned at the VLT in Paranal. The simulations are based on the open source LGSBloch density matrix simulation package and we find good overall agreement with experimental data.
The atmospheric extinction is an important parameter for an astronomical site. The extinction directly affects
the observations reducing the available radiation, but the most relevant effect on the quality of the astronomical
data is the variation of the extinction across the sky and in the course of the observation at night. The aim is
to trace the atmospheric transparency at any astronomical site using MASS data.
The main goal of the present work is estimating the atmospheric extinction coefficient (mag/airmass) from
MASS database. Multi Aperture Scintillation Sensor called MASS is an instrument to measure the vertical
distribution of turbulence in terrestrial atmosphere by analyzing the scintillation of bright stars. Here we are
briefly reminding you of the principles of a MASS instrument and presenting also the detailed description of the
output data. In order to gain better understanding of the atmospheric photometry, we compute the atmospheric
extinction coefficient, its rms, and the associated information from MASS database using the evolution of flux
values of a star measured at ground level versus air mass which accounts for the flux loss. The technique used is
based on the Bouguer low. To treat the statistics data correctly and compute the correct extinction, one has
to know the filter. Correct value of the extinction is critical at most. For this reason, the atmospheric extinction
must be extracted only by good measurements. We then used the quality control of MASS data.
Also, in the current paper, we focus on the evaluation of nocturnal atmospheric extinction coefficient
(mag/airmass) and others statistics (time of acquisition, accumulation time, air mass, and HR number is used as
a star name only for information . . .) at Paranal observatory (70°24’05” W, 24°37’24” S, altitude 2635 m a.s.l,
in Chile.). In addition, the rms error of the coefficient has been calculated. It is absolutely needed to evaluate
the accuracy of each extinction measurement. For the first time, they were obtained from MASS database photo metric processing during 885 nights in the years 2004, 2005, 2006 and 2007. These results will almost lead to
complete its characterization. The project is implemented in the frame of the European Southern Observatory
contract No. PO 014190/HNEU.
A one year database has been gathered from the VLT active optics Shack-Hartmann (S-H) wavefront sensor images taken at each operating focus about every 30 seconds. The VLT telescope control software includes a dedicated code to extract the median full width at half maximum of the unvignetted S-H spots which is used for this study. This code applies a 1-D fit, assuming circular Hartmann spots, which allows to work only on foci equipped with atmospheric dispersion correction, or when the telescopes are observing close to zenith. The S-H image size measured inside the 30m enclosures is compared the outside seeing measured at 6m above ground by the VLT Astronomical Site Monitor (DIMM). A method for correcting DIMM measurements from surface layer turbulence contamination is proposed.
In the past years, intensive Site Characterization campaigns have been performed to chose the sites for the future giant ELTs. Various atmospheric turbulence profilers with different resolution and sensed altitude ranges have been used, as well as climatological tools and satellite data analysis. Mixing long term statistics at low altitude resolution with high resolution data collected during short term campaigns allows to produce the reference profiles as input to the Adaptive Optics instrument performance estimators. In this paper I will perform a brief review of the principal and most used instruments and tools in order to give to the reader a panorama of the work and the efforts to monitor the atmospheric turbulence for astronomical purposes.
Sodium laser guide stars (LGS) are used, or planned to be used, as single or multiple artificial beacons for Adaptive
Optics in many present or future large and extremely large telescopes projects.
In our opinion, several aspects of the LGS have not been studied systematically and thoroughly enough in the past to
ensure optimal system designs.
ESO has designed and built, with support from industry, an experimental transportable laser guide star unit, composed of
a compact laser based on the ESO narrow-band Raman Fiber Amplifier patented technology, attached to a 30cm launch
Besides field tests of the new laser technology, the purpose of the transportable unit is to conduct field experiments
related to LGS and LGS-AO, useful for the optimization of future LGS-AO systems. Among the proposed ones are the
validation of ESO LGS return flux simulations as a function of CW and pulsed laser properties, the feasibility of line-of-sight
sodium profile measurements via partial CW laser modulation and tests of AO operation with elongated LGS in the
EELT geometry configuration.
After a description of the WLGSU and its main capabilities, results on the WLGSU commissioning and LGS return flux
measurements are presented.
The asteroid 2005 YU55 swept past the Earth on November 8, 2011 at 23:28 UTC at 0.85 lunar distance. Such
events provide an excellent opportunity to study the physical and chemical properties and the surface details
of the asteroids through spectroscopic and imaging observations. 2005 YU55 was observed by several ground
and space based observatories during its closest approach. Here, we report the details of the speckle imaging
observations of 2005 YU55 carried out the La-Silla Paranal Observatory with the NACO-VLT (no-AO mode)
in the Ks band. The angular speed of the asteroid decreased from 8.5 arcsec/sec to 7.6 arcsec/sec during our
observations and the tangential speed decreased from 13.5 km/s to 12.7 km/s. We reconstructed the images
of 2005 YU55 with our speckle masking code. The average reconstructed images show spheroidal shape with
diameter of 270 m. These observations demonstrate the potential of speckle technique in imaging low contrast,
near-earth objects and deducing their overall sizes and shapes even under moderate observing conditions.
The performances of a modern telescope and its safety are dependent on the presence of atmospheric dust. The TNG
telescope at ORM (Canary Islands) was one of the first sites monitored on a continuous basis by an automatic dust
monitor. This paper presents the analysis of about 10 years of atmospheric dust content collected at the ORM using the
TNG facilities. We have detected particles of 0.3, 0.5, 1.0, 3.0, 5.0 and 10.0 μm size. In this study particles of 0.5 and 5.0
μm measured at Paranal Observatory (Chile) are also compared to those similar at TNG. The seasonal behavior of the
particles content in the atmosphere is compared between the two sites. The contribution of the dust emissivity to the sky
brightness in the NIR is computed for the first time. To complete this study we defined the aerosol mass critical limit to
be used as a safety limit for the observations. We found a limit of 12 μg m-3 as total mass of (0.5 + 5.0) μm particles.
In this paper the Paranal Surface Layer characterization is presented. Causes, physics and behavior of the SL above
Paranal surface are discussed. The analysis is developed using data from different turbulence profilers operated during
several campaigns between 2007 and 2009. Instruments used are SL-SLODAR, DIMM, Elevated DIMM, MASS, Lunar
Scintillometer and Ultrasonic Anemometers with temperature sensors positioned at different strategic heights.
We describe the current status of the SLODAR optical turbulence monitors, developed at Durham University, for support
of adaptive optics for astronomy. SLODAR systems have been installed and operated at the Cerro Paranal and Mauna
Kea observatories, and a third will be deployed at the South African Astronomical Observatory in 2008. The instruments
provide real-time measurements of the atmospheric turbulence strength, altitude and velocity. We summarize the
capabilities of the systems and describe recent enhancements. Comparisons of contemporaneous data obtained with
SLODAR, MASS and DIMM monitors at the ESO Paranal site are presented.
We present an analysis of the atmospheric dust content and its effects on astronomical observations at Observatorio del Roque de Los Muchachos (ORM), in La Palma Island (Canaries). We have detected atmospheric particles having size 0.3, 0.5, 1.0 and 5.0 μm, closer to Telescopio Nazionale Galileo (TNG) dome and using a power law we have derived the content of 10.0 µm particles. Using a model we have calculated the contribute of aerosols to astronomical extinction in B, V and I from a 5 years series database in two typical conditions: clear and dusty days. A correlation is also analysed comparing the aerosol extinction and total astronomical extinction using the Carlsberg Automatic Meridian Circle (CAMC) extinction database in V. We have estimated that the dust reach an altitude of about 5 km above the sea level during the sand storms. Finally we have concluded that in the visible band extension is dominated by particles at 1.0, 5.0, and 10.0 μm.
We have recombined turbulence profiles from MASS and SLODAR at Paranal Observatory using a new grid of atmospheric layers defined on the basis of the comparison between the MASS and SLODAR weighting functions. A statistical analysis of the relation between the total Paranal DIMM Cn2, the ground layer Cn2 and the free atmosphere Cn2 is presented. Taking into account the height of the VLT Unit Telescopes we have recalculated the seeing skipping the atmosphere below that height, obtaining an estimation of the real turbulence affecting science at the Very Large Telescope and its evolution from January 2005 to June 2007.
MAD5 is a Multi-Conjugate Adaptive Optics (MCAO) system conceived to demonstrate the feasibility of MCAO on the sky. The wave front sensor part is divided in two channels: a Shack-Hartmann sensor and a Layer Oriented sensor. We will describe the construction of the latter one. Assembly, integration and test of the instrument are the first steps for ESO acceptance, before integrating the Layer Oriented sensor with the other components of MAD. We will show qualitative and quantitative results of optical and mechanical tests: in particular we will describe the alignment of the references selection unit, constituted by sixteen motorized linear positioners and eight star enlargers, of the beam compressor and of the two re-imaging objectives, each one conjugated to a different altitude. Being the pyramid the core of this kind of wave front sensor, we will focus our attention on its construction difficulties and we will discuss all the optical tests made to choose the best ones to be installed on the wave front sensor. Finally we will present the sensor performance showing the first open loop results.