HARMONI is the first light visible and near-IR integral field spectrograph for the Extremely Large Telescope. It covers a large spectral range from 470nm to 2450nm with resolving powers from 3300 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes (including a High Contrast capability) - or with Non Adaptive Optics. The project is preparing for Final Design Reviews. In this paper, we present the optical design of the Pre-Optics for Final Design Reviews, the pre-optics take light entering the science cryostat (from the telescope or calibration system), reformatting and conditioning to be suitable for input for the rest of the instrument. This involves many functions, mainly relaying the light from the telescope focal plane to the integral field unit focal plane via a set of interchangeable scale changing optics. The pre-optics also provides components including a focal plane mask wheel, cold pupil masks, spectral order sorting filters, a fast shutter, and a pupil imaging capability to check telescope/instrument pupil alignment.
HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It will use an image slicer to provide spectra over a single contiguous area, providing fields of view on the sky of 9.3x6.3”, 4.2x3.1”, 2.1x1.5” and 0.84x0.62” with increasing spatial resolution (i.e.- 60x30, 20x20, 10x10 and 4x4 mas2) and magnification 2, 3/6, 6/12 and 15/30 respectively. The anamorphic magnifications in 20x20, 10x10 and 4x4 scales are implemented using two toroidal mirrors in each optical path. In this paper, we present a complete tolerance analysis for the anamorphic stages and a compensation procedure to ensure the requirements of the system.
HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. The pre-optics take light entering the science cryostat (from the telescope or calibration system), reformatting and conditioning to be suitable for input for the rest of the instrument. In this paper, we present a complete stray light analysis of the HARMONI pre-optics including scattering from optical surface roughness and coatings, unwanted light from mechanical mounts and mechanisms, ghost reflections and scattering from particulate contaminants. Several solutions to reduce this unwanted light are proposed.
HARMONI is the first light, adaptive optics assisted, integral field spectrograph for the European Southern Observatory’s Extremely Large Telescope (ELT). A work-horse instrument, it provides the ELT’s diffraction limited spectroscopic capability across the near-infrared wavelength range. HARMONI will exploit the ELT’s unique combination of exquisite spatial resolution and enormous collecting area, enabling transformational science. The design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, and provide a summary of the instrument’s design. We also include recent changes to the project, both technical and programmatic, that have resulted from red-flag actions. Finally, we outline some of the simulated HARMONI observations currently being analyzed.
HARMONI is the first light visible and near-IR integral field spectrograph for the Extremely Large Telescope (ELT). It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. The IFS Pre-Optics (IPO), sub-system under the responsibility of the Institute of Astrophysics of the Canary Islands (IAC), contains 30 opto-mechanical mounts working at cryogenic temperatures and are classified into three types depending on the mirror shape: [1] - Sprung kinematic mount for flat mirrors: By spring loading, the mirror is constrained radially against a Vee-groove. - Thermally compensated kinematic sprung mount for power mirrors: It is similar to the previous mount but the radial pads compensate mirror radial movement. - Bonded mount for toroidal mirrors: The mirror is bonded to a rear invar pad, which serves as an interface to the support. This work describes the designs developed for the opto-mechanical modules of the Instrument IPO in order to comply with the sub-system requirements. We also present the prototypes developed to prove some of the adopted concepts in the design.
HARMONI is the first light visible and near-IR integral field spectrograph for the Extremely Large Telescope (ELT). This instrument covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. The Pre-Optics (sub-system under the responsibility of the IAC) contains five mechanisms working at cryogenic temperatures. Three types of mechanisms are needed to provide full functionality: wheels (2), turrets (2) and shutter (1). The wheels and turrets, supported by a series of radial and axial bearings, are driven by stepper motors through a system of gears that provide mechanical reduction. In addition, the focal plane mask wheel has a detent system to improve repeatability to within +/- 2.5 microns. Finally, the shutter consists in two masks with three clover shape blades mounted on a stepper motors. The work describes the main IPO mechanisms requirements and the design developed for every module. We also present some of the prototypes developed to proof the concepts adopted in the design..
HARMONI is the adaptive optics assisted, near-infrared and visible light integral field spectrograph for the Extremely Large Telescope (ELT). A first light instrument, it provides the work-horse spectroscopic capability for the ELT. As the project approaches its Final Design Review milestone, the design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, provide a summary of the instrument’s design, including plans for operations and calibrations, and provide a brief glimpse of the predicted performance for a specific observing scenario. The paper also provides some details of the consortium composition and its evolution since the project commenced in 2015.
HARMONI is a visible and near-infrared (0.5 to 2.45 μm) integral field spectrograph, providing the E-ELT's core spectroscopic capability, over a range of resolving powers from R (λ/Δλ) ~ 3500 to ~18000. The instrument provides simultaneous spectra of ∼32000 spaxels arranged in a sqrt(2):1 aspect ratio contiguous field. The pre-optics take light entering the science cryostat (from the telescope or calibration system), reformatting and conditioning to be suitable for input for the rest of the instrument. This involves many functions, mainly relaying the light from the telescope focal plane to the integral field unit (IFU) focal plane via a set of interchangeable scale changing optics. The pre-optics also provides components including a focal plane mask wheel, cold pupil masks, spectral order sorting filters, a fast shutter, and a pupil imaging capability to check telescope/instrument pupil alignment. In this paper, we present the optical design of the HARMONI pre-optics at Preliminary Design Review and, in particular, we detail the differences with the previous design and the difficulties salved to the Preliminary Design Review.
HARMONI is a visible and near-infrared (0.47 to 2.45 μm) integral field spectrograph, providing the ELT's core spectroscopic capability at first light. A pre-optics subsystem provides four selectable spatial pixel scales, in addition to other beam conditioning functions such as shutter and pupil masks. For the validation of the mechanisms in charge of these functions (fast shutter and the plane mask wheel) we have planned some prototypes to test the design solutions.
The focal plane mask wheel sits in the input focus of the cryostat. It provides 16 user-selectable positions for masks (28x40 mm) used in observation. The key driver for this mechanism is the high repeatability (±2.5 μm) required, equivalent to ~1mas in the input focal plane. The IAC has previously designed, manufactured, tested and put in operation cryogenic wheels with high repeatability; however, the challenge of obtaining a wheel with such repeatability requires testing new concepts of detent positioning systems.
The shutter allows for exposures shorter than the minimum read time of the near-IR detectors and is needed for any CCD observations with the visible cameras. A dual shutter design is needed to achieve the necessary open/close times (<20 ms), but this also provides some redundancy and a graceful failure mode for this critical device. To mitigate risks on the proper behaviour of a fast cryogenics shutter a prototype based on a simple concept has been manufactured. We present the design and results for the performed cryogenic tests of a mask wheel and a shutter prototypes that we have developed.
KEYWORDS: Cryogenics, Prototyping, Camera shutters, Computer programming, Sensors, Commercial off the shelf technology, Temperature metrology, Computer aided design, Control systems, Photonic integrated circuits
HARMONI is an integral field spectrograph working at visible and near-infrared wavelengths. The instrument will be part of the first-light complement at the E-ELT. The IAC is in charge of several work packages and the design of two important components is ongoing: A 'Cryogenic Pupil Mask Rotator' based on a direct drive brushless motor, and a 'Cryogenic Fast Shutter' based on voice coil. One of the main goals of these developments is the use of COTS (Commercial-Off-The-Shelf) parts since their use will reduce costs and short the schedule. Nevertheless, the application of COTS parts in cryo-vacuum is often very difficult and represents a technological challenge.
We are presenting two years (2012 and 2013) of preliminary statistical results of calibrated PWV values from the GPS geodesic antennas (LPAL and IZAN) at Teide and Roque de los Muchachos Observatories (OT and ORM), Canary Islands. To calibrate the PWV from both GPS antennas we have selected a set of simultaneous high vertical resolution radio-sounding profiles from the closest operational balloon station, Güímar (GUI-WMO 60018; ≈15 km distant from OT and ≈150 km from ORM). The calibrations showed a correlation of 0.994 and 0.970 for OT and ORM, respectively, with rmse of 0.44 and 0.70 mm. The calibrated PWV series brought median values of 3.5 mm at OT and 4.0 mm at ORM. The difference is explained by the ~200 m of difference in height of the antennas (LPAL antenna is below the telescopes altitude). Twenty five percent of the time, PWV is less than 1.7 mm.
HARMONI is a visible and near-infrared (0.47 to 2.45 μm) integral field spectrometer, providing the E-ELT's core
spectroscopic capability, over a range of resolving powers from R (≡λ/Δλ)~500 to R~20000. The instrument provides simultaneous spectra of ~32000 spaxels at visible and near-IR wavelengths, arranged in a √2:1 aspect ratio contiguous field. HARMONI is conceived as a workhorse instrument, addressing many of the E-ELT’s key science cases, and will
exploit the E-ELT's scientific potential in its early years, starting at first light. HARMONI provides a range of spatial
pixel (spaxel) scales and spectral resolving powers, which permit the user to optimally configure the instrument for a
wide range of science programs; from ultra-sensitive to diffraction limited, spatially resolved, physical (via morphology),
chemical (via abundances and line ratios) and kinematic (via line-of-sight velocities) studies of astrophysical sources.
Recently, the HARMONI design has undergone substantial changes due to significant modifications to the interface with
the telescope and the architecture of the E-ELT Nasmyth platform. We present an overview of the capabilities of
HARMONI, and of its design from a functional and performance viewpoint.
In order to improve the signal-to-noise ratio of HARMONI (E-ELT first light visible and near-infrared integral field VIR
spectrometer), a pupil mask has been identified to be included at the fore-optics to limit the background radiation coming
into the spectrographs. This mask should rotate synchronously with the telescope pupil during observations, taking into
account the combined effects of the telescope tracking and the de-rotation of the FOV. The implementation of the pupil
mask functionality will require complex movements with high precision at cryogenic temperatures which implies an
important technological challenge.
This paper details a set of experiments completed to gain knowledge and experience in order to accomplish the design
and control of cryogenic mechanisms reaching this type of pupil motion. The conceptual design of the whole mechanism
started from the feedback acquired from those experiments is also described in the following sections.
Modern optical and infrared astronomical sites are getting used to a flexible way of operation, namely queue
modes, allowing astronomical observations in the most appropriate weather conditions for each specific observing
scientific program. The forecast of weather conditions is then a mandatory issue to plan in advance the
observations queue for each night in order to exploit efficiently the astronomical facilities with the largest high
quality data output for scientific exploitation. The precipitable water vapour is the parameter accounting for
the infrared (IR) quality of an astronomical site. The temporal fluctuation of this parameter drastically affects
the quality of the IR data recorded at ground telescopes. An optical/IR telescope needs the forecasting of the
precipitable water vapour for a proper queue scheduling of IR observations. The Roque de los Muchachos Observatory
(ORM) on the island of La Palma (Spain) presents an abrupt topography which difficult the forecasting
at this astronomical site. We discuss the performance of a mesoscale numerical weather model (WRF, Weather
Research and Forecasting) applied to ORM region including the comparison with local precipitable water vapour
estimations from GPS (Global Positioning System).
Measurements of ground displacement have been carried out on the entire active volcanic island of Tenerife, Canary
Islands, by means of classical and advanced DInSAR techniques. The main limiting factor on the accuracy of DInSAR
measurements is the distribution of the water vapour in the lower troposphere. Hence, it is yet necessary to perform a
detailed spatial and temporal characterization of water vapour to understand, and to be able to carry out a direct
computation of, the effect of the tropospheric delay on DInSAR results. In this sense, satellite and balloon data have
been analysed to infer the variability in the distribution of water vapour and hence, the robustness of DInSAR results on
the island of Tenerife.
Future large and extremely large ground-based telescopes will demand stable geological settings.Remote sensing could
be an unvaluable tool to analyse the impact of geological activity at selected astronomical sites, namely the observatories
of El Teide (Tenerife, Canary Islands), Roque de los Muchachos (La Palma, Canary Islands), Mauna Kea (Hawaii) and
Paranal (Chile) and the candidate site of Cerro Ventarrones (Chile). In this sense, the extent of lava flows, eruptive
clouds or ground deformation associated to seismic and/or volcanic activity could be analysed and characterised through
remote sensing.
The development of adaptive optics systems for projects related to large telescopes demands a proper knowledge of the
atmospheric turbulence. Due to the lack of long-term information on optical turbulence, high-altitude winds (in particular
winds at the 200-mbar pressure level) were adopted as a parameter for estimating the total turbulence at a particular site,
since there are large wind databases spanning for several decades. On-site measurements of CN2(h) profiles (more than 20200 turbulence profiles) from G-SCIDAR observations and wind vertical profiles from balloons have been used tocalculate the seeing, the isoplanatic angle and the coherence time for the Teide Observatory (Canary Islands, Spain). The connection of these parameters to wind speeds at ground and 200-mbar pressure level have been studied and discussed.
The proper characterization of the turbulence structure in an astronomical site requires a statistical analysis of the
refractive index structure constant, CN2(h). Our team has been monitoring this variable since November 2002 at the Teide Observatory (Tenerife, Canary Islands, Spain). We have derived the seasonal evolution of turbulence structure at this site
using data from more than 150 nights of useful G-SCIDAR measurements. The monthly statistical profiles for different
years present a similar structure for different years, suggesting a stable seasonal evolution of the turbulence at the Canary
Islands sites. From this statistical analysis, we have derived the seasonal evolution of the Fried's parameter, the
isoplanatic angle and the coherence time. The average values for these parameters are < r0 >=15.1±4.6 cm, <θ0 >= 2.7±1.3 arcsec and <τ0 >= 5.8 ± 3.1 ms. Uncertainties indicate the standard deviation of the averaged measurements. These statistical values for atmospheric adaptive optics parameters and their smooth seasonal behavior bring up the sky quality of the Canary Islands astronomical sites for the implementation of adaptive optics systems.
The requirements for current large and future extremely large telescopes as well as the quick development of IR
instrumentation demand a proper characterization of precipitable water vapour (PWV) above astronomical sites. A
comparison of PWV estimations from a photometer and a GPS (Global Positioning System) above the Observatorio del
Roque de los Muchachos (ORM, La Palma, Canary Islands, Spain) was carried out and it was found a linear relation
between both measurements. Such relationship will allow the calibration of the GPS measurements recorded at ORM for
the period June 2001- December 2008. These large time series of PWV estimations from GPS were used to perform a
statistical analysis of water vapour content above this astronomical site. Average annual value of night-time PWV of
4.86 mm was found. It was also found a clear seasonal behavior of the PWV above ORM, with smaller water-vapour
columns during winter nights (average 3.36 mm). The largest values of PWV are reached in the summer nights (average
6.75 mm). The data indicate that a significant percentage of nights (~38%) are well suited for thermal infrared
observations (with PWV < 3 mm), and 71% of nights present a "fair" or better IR observation opportunity at ORM.
We have been testing at laboratory commercial variable attenuators commonly used in telecommunication applications
for their used in astronomy. Such variable attenuators are going to be included in the central fibers
of the integral field unit (IFU) of the prototype instrument EDiFiSE (Equalized and Diffraction-limited Field
Spectrograph Experiment). The EDiFiSE IFU is conformed by a lenslet array of 331 lenses, 331 fibers and seven
variable attenuators (inserted in the seven central fibers of the bundle). We present here the characterization of
the attenuator devices tested for their use in astronomy and, in particular, to their application in the observation
of object of large dynamic range using equalized integral field spectroscopy. We also present the optical tests we
have carried out to characterize the performances of two lenslet arrays acquired in the framework of the EDiFiSE
project.
We present EDiFiSE, a prototype instrument for the observation of high-contrast systems, combining an adaptive
optics (AO) system and an equalized integral field unit (EIFU). The design of the AO system takes into account
the statistical behaviour of the atmospheric turbulence structure at the Canary Islands (Spain) astronomical
observatories: Roque de los Muchachos (ORM) on the island of La Palma and Teide observatory (OT) in
Tenerife. The AO will have the capability of adapting to the prevailing turbulence conditions; in this sense,
the EDiFiSE AO unit will be an 'adaptable' adaptive optics system. The corrected beam feeds an hexagonal
integral field unit formed by 331 micro-lenslets, which focus the intensity distribution at the focal plane into 331
optical fibers. The central seven fibers of the bundle include variable attenuators for the equalization of these
fibers output intensities, matching them to the dynamical range of the detector and reducing the optical cross
talk inside the spectrograph. This technique, called equalized integral field spectroscopy (Arribas, Mediavilla &
Fuensalida 19981), permits to obtain spectral and spatial information of the equalized object and its surroundings
as well as accurate relative photometry and astrometry.
Seismicity induces ground vertical and horizontal displacements that could affect the image quality obtained by
telescopes in a similar fashion than atmospheric turbulence. In this work, we study the effect of local seismicity relative
to atmospheric turbulence upon the image quality of astronomical observations at El Teide observatory, Canary Islands.
Three different aspects of seismicity are studied, namely regional seismicity (that is compared with other astronomical
sites), seismic noise and possible resonances between seismic noise and the structure of telescopes.
We present in this paper the new cute-SCIDAR instrument, entirely developed by the Instituto de Astrofísica de Canarias
(IAC), delivered recently at the European Southern Observatory (ESO) Paranal Observatory (Chile). This instrument,
supported by the European Community (Framework Programme 6, Extremely Large Telescope Design Study), carries
out the generalized SCIntillation Detection And Ranging (g-SCIDAR) technique to obtain the temporal evolution of
turbulence profiles CN
2 with height. A new design was made in order to fit the VLT Auxiliary Telescopes (ATs)
interfaces and control requirements. Also, a new software architecture allows a full remote control, and a data analysis
pipeline provides turbulence profiles in real-time, which is the main achievement of this new cute-SCIDAR. Details of
its design and results of its excellent performance are included.
We have built a hybrid turbulence profiler measuring simultaneously the atmospheric turbulence structure with a Shack-
Hartmann wave front sensor and a G-SCIDAR (scintillation sensor). This is the first instrument combining two different
techniques to measure simultaneously the turbulence structure. The hybrid profiler has been installed at the Carlos
Sánchez Telescope (TCS) at the Teide Observatory (OT), in Tenerife Spain. The G-SCIDAR arm is already working
properly and we are still testing the Shack-Hartmann arm.
The determination of turbulent-layers wind speed observed through Generalized SCIDAR technique (G-SCIDAR)
requires an efficient and contrasted code. We have developed a fully automated algorithm based on wavelet
transforms to derive the velocity magnitude and direction of atmospheric turbulent layers from G-SCIDAR
measurements. The algorithm makes use of five cross-correlations of a series of scintillation patterns separated by
lapses of Δt, 2Δt, 3Δt, 4Δt and 5Δt. The wavelet analysis of such cross-correlation images provides the position,
direction and altitude of the different turbulent layers detected in each image. The comparison and consistency
of results in consecutive cross-correlations allows the determination of the turbulence layers velocities and avoids
misidentifications associated with noise and/or overlapping layers. The software includes the correction due to
the projection effects on the observing direction of the actual velocity vector of turbulence layers. The algorithm
has been applied to simulated data with excellent results, as well as to actual G-SCIDAR observations. For the
validation of velocities derived for real G-SCIDAR data we have compared them to the velocities provided by
balloon measurements. The software has been designed to analyze huge amounts of G-SCIDAR measurements.
The characterization of the vertical turbulence distribution on an astronomical site should be based on statistical
behaviour, as it is required for other parameters in site testing. We present the statistical results of the optical-turbulence
profiles at the Roque de los Muchachos and Teide observatories at the Canary Islands (Spain). The
data were obtained using the generalized scintillation detection and ranging technique at the 1m Jacobus Kapteyn
Telescope and 1.5m Carlos Sánchez Telescope. Statistical results are based on 68 nights in 2004 and 38 nights
in 2005 of measurements at the Roque de los Muchachos observatory (La Palma) and 27 nights of observations
at Teide Observatory (23 in 2004 and 4 in 2005). Statistically, most of the turbulence is concentrated close
the ground level (2400 m above sea level) with no more than two relative intense turbulent layers at higher
altitudes. The temporal evolution of the monthly statistical turbulence profiles indicates that the turbulence is
concentrated at low altitude layers in winter.
We have developed an algorithm to eliminate the dome seeing contribution to turbulence profiles derived from G-SCIDAR
data. The algorithm, based on the parity of functions, is completely automated and it takes only a few
seconds to process a full night of G-SCIDAR data. Seeing measurements obtained from turbulence profiles derived
from G-SCIDAR observations and removing the dome contribution with our algorithm are in good agreement
with seeing data obtained using Differential Image Motion Monitors (DIMMs). An important advantage of the
proposed procedure is that it permits an automated reduction during the calculation process and it could be
implemented to work in real time. The formulation to identify the shape of the dome seeing could be extended
to other problems of shape recognition whenever it is even.
In order to characterized the vertical atmospheric structure at the Teide Observatory (Tenerife, Spain), we are
using two different remote sensing technics: SODAR (SOund Detection And Ranging) and SCIDAR (SCIncitillation
Detection And Ranging) at this astronomical site. We present in this work the preliminar results on the
comparison of the simultaneous data from four consecutive nights in March 2007 using both technics. We have
analized the SCIDAR C2N
profiles as well as an estimation of the structure constante of temperature function,C2T,
provided by SODAR. Such C2T
were compared to the simultaneous C2N
profiles from SCIDAR, determining
a calibration factor between the measurements provided by SCIDAR and SODAR. As it was expected, our
preliminary results indicate that this calibration factor is very sensitive to the variations of weather conditions.
Adaptive optics devices in astronomy compensate the distortions introduced by the atmosphere in the quality and resolution of images taken by ground-based telescopes. The proper knowledge of the spatial and temporal behaviour of the atmospheric turbulence is crutial for optimizing the design of multiconjugate adaptive optics systems to satisfy the excellent image quality requirements of the new generation of large and extremelly large telescopes. Atmospheric turbulence monitoring is being carried out at astronomical sites using different techniques, being generalized SCIDAR one of the most popular. Generalized SCIDAR technique provides enough information to derive the vertical structure of the atmospheric turbulence (C2N(h)) as well as the velocity of the turbulent layers (Vtur(h)). In this work, we present a new and automatic method to derive Vtur(h) from generalized SCIDAR data based on wavelet analysis.
Roque de los Muchachos Observatory (ORM) at La Palma (Canary Islands) is one of the two top sites selected for hosting the future European Large Telescope (ELT) (http://www.eso.org/projects/e-elt/), the other being Paranal (in Chile). Meteorological and seeing conditions are crucial for the site selection. New concepts related to geophysical properties (seismicity and microsismicity), local climate variability, the presence of aerosols, atmospheric conditions related to the optical turbulence (tropospheric and ground wind regimes) have recently been introduced for selecting sites for a new generation of Extremely Large Telescopes (Munoz-Tunon 2002, Munoz-Tunon et al. 2003 a, 2003 b; Varela et al., 2002; Varela & Munoz-Tunon, 2004; Varela et al., 2004 a, 2004 b) and also for telescope design and feasibility studies for adaptive optics. Wind speed at 200 mbar is one of the key parameters proposed for characterizing atmospheric turbulence above the Observatory (Sarazin & Tokovinin, 2002, Garcia-Lorenzo et al., 2005). A lower average 200 mbar wind speed is obtained at the ORM in comparison with other astronomical sites; furthermore, the ORM ranks first in in suitability for adaptive optics suitability (Garcia-Lorenzo et al., 2005). The usefulness of this value might be conditional on the continuity of the wind value and wind direction from the upper troposphere to the ground level. With this motivation we are undertaking a study of tropospheric and ground winds at several observing sites.
Satellite data measuring aerosols over the Canary Islands need to be correctly interpreted in accordance with the spatial resolution and spectroscopic channels used. In situ data are still a necessary reference for calibrating and interpreting the aerosol index provided by different spectrometers onboard satellites.
A comparison of both techniques (in situ and remote) is discussed in this paper, showing there is no linear correlation between the aerosol index and the extinction coefficient. Here, we present an interpretation of different situations arising and discuss critically the correct interpretation of the aerosol index and images provided by the TOMS in accordance with the dust presence over the Observatories. The aerosol index measured at sectors centered at both Observatories (Observatorio del Roque de los Muchachos -ORM-, on La Palma and Observatorio del Teide -OT-, on Tenerife) is also compared.
The infrared sky quality is an important parameter to take into account for the evaluation of astronomical sites. The traditional idea of considering higher altitude sites as better for infrared astronomical observations than sites at lower altitudes is not in agreement with observational data. It has been shown that the observational infrared spectrum at the Observatorio del Teide (OT) at an altitude of 2400m on the island of Tenerife (Spain) is similar to that expected for a site at the altitude of Mauna Kea (4100m) in Hawaii (USA). This result suggests that other parameters besides site altitude is playing an important role in determining the quality of a particular location for infrared astronomical observations. In this paper, we propose the troposphere thickness as one of the parameters that determine the suitability and quality of an astronomical site for infrared observations. The tropopause altitude defines the tropospheric thickness and hence, we present in this paper a statistical study of the tropopause layer altitude for four different astronomical sites. The results presented in this work suggest that the infrared quality at La Palma, La Silla and Mauna Kea could be similar in some epochs of the year, although they are located at different altitudes above the sea level. Mauna Kea presents the
thinnest troposphere during Summer and Autumn among the four studied sites, whereas La Palma exhibits the lowest altitude of the tropopause in Winter and Spring. Paranal presents most of the
time the thickest troposphere, suggesting worse infrared conditions for astronomical observations (based only in the thickness parameter) at this site, when compared to the other three in study.
We present the statistical results of the optical-turbulence profiles at the Observatorio del Roque de los Muchachos over a period of six consecutive months. The data were obtained using the generalized SCIDAR technique at the 1m Jacobous Kaptein Telescope. In general, most of the turbulence is concentrated close to the observatory level (2400 m above sea level) with no more than two turbulent layers at higher altitudes. The temporal evolution along six consecutive months indicates that the turbulence is concentrated at lower altitude layers during winter. Large isoplanatic angles are also reached in winter compared to the values in spring. For the turbulence profiles measured in February, March and April we have analized the statistical position of demorfable mirrors in an ideal Multi-Conjugate Adaptive Optics system (with two or three deformable mirrors) and the improvements in the isoplanatic angles.
Climate diagnostic studies combine data from different sources (radiosoundes, satellites, meteorological masts, etc) and meteorological models to predict the climate conditions and evolution at a particular site or globally. Products from climate diagnosis are archived in long-term databases that may constitute a useful tool for site characterization. However, a rigorous control of data quality, analysis and cross-comparison to in-situ meteorological measurements need to be performed before the method becomes extensively used for site characterization. We present a statistical analysis for wind vertical profiles, an important parameter for site characterization, using data from a climate diagnostic archive and in-situ measurements (ground-level and balloon data).
We present a new generation SCIDAR instrument that is a fully automatically controlled device with a user-friendly interface. Alignment and observation are reduced to easy and rapid handling without the effort operating in the dome. This instrument is installed in the Jacobus Kapteyn Telescope on La Palma. We describe our progress from prototype to second generation instrument, emphasizing the design and the software for Cute SCIDAR, and show profiles from systematic monitoring using the prototype instrument on Tenerife and Cute SCIDAR on La Palma.
The statistics of vertical structure of the turbulence affect the complexity of the design and implementation of Multi-Conjugate Adaptive Optics (MCAO) systems. The operation of these systems could be optimized if the stability of the layers were such as to permit to fix the deformable mirrors (DMs) at specific heights. Moreover, it is desirable to know the effects on the placement of the DMs and the gain of the isoplanatic angle in terms of site characterization.
From the turbulence profiles measured with the G-SCIDAR technique we have analyzed the statistics of the heights of the DMs and the resulting isoplanatic angles. These results are based on the data from a long ongoing campaign at Roque de los Muchachos Observatory (La Palma) and Teide Observatory (Tenerife) with the highest statistical coverage to date. We have used two ideal MCAO systems, consisting of two and three DMs, and, from a specific comparison in simultaneous measurements over two nights, we show the evolution of the position of DMs and isoplanatic angles in both sites, which can sporadically reach values greater than 60" in 500 nm. We also study the effects of the stability of the conjugate planes on the improvements in the isoplanatic angles.
Climate diagnostic archives appears to be a very useful tool for astronomical site assessment. These climatological databases combine data from meteorological archives for different data sources (radiosoundings, satellites, etc) and meteorological models to derived any parameter at a particular selected location. Although the products from climate diagnostic archives are heavily constrained by observational data, a rigorous control of data quality, analysis and cross comparison needs to be performed before the method becomes extensively used for site characterisation. In this talk we present an statistical analysis of winds, an important parameter for site characterisation, using in-situ measurements (ground level and balloon data) and data derive from climate diagnostic archives. The cross-comparison of results obtained from the two set of data allow us to propose some restrictions in the use of climate diagnostic products for site characterisation.
Satellite data measuring aerosols over the Canary Islands need to be correctly interpreted in accordance with the spatial resolution and spectroscopic channels used. In situ data are still a necessary reference for calibrating and interpreting the aerosol index provided by different spectrometers onboard satellites.
Most of the airmass flux component arriving at the Canarian Archipelago comes from the North Atlantic Ocean and consists of sea aerosols, i.e. absorbent chloride in the UV which does not affect the extinction in the visible range.
African dust intrusions affect the western and eastern Canary Islands differently. Moreover, the presence of a stable inversion layer and the sharp orography of the western islands (La Palma at Tenerife) produce different mass flux patterns in the low (mixing) layers closer to the sea and in the median-upper (or free) troposphere layer. The aerosol index provided by the TOMS (Total Ozone Mapping Spectrometer) is one of the most widely accepted products to detect the daily aerosol content. On the other hand, several techniques have been developed in situ to characterize the presence of dust locally at the Canarian Observatories. In particular, a parameter related to sky transparency, the atmospheric extinction coefficient, has been measured at the Roque de los Muchachos Observatory (ORM) on La Palma since 1984 by the Carslberg Automatic Meridian Circle Telescope (CAMC). In situ aerosols are also available for the Teide Observatory (OT) on Tenerife, from 1986 onwards. In this work we compare aerosol index data of TOMS/Earth Probe observations and atmospheric optical extinction coefficient from CAMC in the period 1996-2004.
A preliminary comparison of both techniques (in situ and remote) is discussed in this paper, showing there is no linear correlation between the aerosol index and the extinction coefficient. Here, we present an interpretation of different situations arising and discuss critically the correct interpretation of the aerosol index and images provided by the TOMS in accordance with the dust presence over the Observatories.
SCIDAR has proved to be the most efficient technique to obtain the optical vertical structure of the atmospheric turbulence measured from ground level. However, the common procedure of obtaining the data, as well as its 'a posteriori' treatment, requires a huge number of highly qualified human resources. A systematic monitoring program becomes really onerous. Consequently, the development of a full automatically controlled SCIDAR device seems to be evidently justified. We have recently developed a SCIDAR instrument providing high performances in automatic control and data reduction, presently in test pahse. It has been designed for the Jacobus Kapstein Telescope at the Roque de los Muchachos Observatory, with the goal of monitoring the vertical turbulence with a high temporal coverage. This device is not only restricted to the JKT but can also be used for other telescopes.
We present a comprehensive and reliable statistics of 200 mbar wind speeds at the Canary Islands based on long term climate diagnostics archive data and balloon measurements. The results demonstrate the remarkable stability of the Canarian sky, with low mean values of V200 = 22.12 ms-1 at the Roque de los Muchachos Observatory (ORM, La Palma, Spain) and provide independent confirmation of the potential of Canary Islands for adaptive optics. A comparison of V200 values from a climatological database and in situ measurements with radiosondes launched from Santa Cruz de Tenerife (Tenerife Island, Spain) reveals an excellent level of agreement, which lends confidence to the claim that climate diagnostics measurements provide a useful tool for astronomical site assessment, although a rigorous control of data quality, analysis and cross comparison needs to be performed before the method becomes extensively used. Moreover, the correlation of results for La Palma and Tenerife confirms the homogeneity of the Canarian sky at the tropopause level. The analysis of frequencies and variability of V200 led us to propose a seasonal perodicity of V200. We also compare the results obtained at La Palma with those from Mauna Kea, Paranal, and La Silla.
Knowledge of vertical structure of the turbulence in a site is an essential input for the requirements, performances and operation of Adaptive Optics systems. The statistics of the turbulence intensity and the coherence time of the layers affect the complexity of the design and implementation of a particular MCAO system. On the other hand, the operation of such systems could be optimized if the height and velocity of the layers were available in real time. We present statistical results of the SCIDAR turbulence profiles obtained at the observatories Canary Islands. Statistics of characteristic parameters, of special interest for MCAO, are presented here, together with their temporal evolution. The results have been checked with simultaneous meteorological measurements. We have used the balloon sounding meteorological database of the Instituto Nacional de Meteorologia of the Santa Cruz station (Tenerife) to evaluate the physical conditions related with the behavior of the optical propagation. We have compared this study with the database of indirect measurements from satellites. The reliability of these data has been proved in relation to the balloon meteorological database for all height levels on Tenerife.
The experimental study of laser beam propagation in turbulence is relevant to fields such as adaptive optics and optical communications. Turbulence sensing for astronomical purposes requires a convergent laser beam adequately focused on the sodium mesospheric layer. Free Optical communications ground-to-satellite usually are based on divergent laser beams travelling partially through the atmosphere. We present several measurements of the gaussian beam radius for divergent and convergent laser beams propagated in vertical paths. The determinations were carried out at the Teide Observatory (Canary Islands) from the analysis of Rayleigh scattering. The turbulence profile was simultaneously measured with a SCIntillation Detection And Ranging (SCIDAR) instrument. This way, we analyse the influence of the different turbulence layers in the focusing problem through the empirical relation between the beam waist radius and the intensity of the turbulence. We present the experimental set-up, the first results of the experiment and the plans to conduct a statistical study in the future.
The possibility of using high-data-rate optical transmitters for satellite communication has generated interest in laser communication systems for ground-to-space and space-to-ground data links. Among the parameters useful to model propagation along a vertical path are the refractive index structure constant Cn2 profile and boundary layer turbulent strength. One of the most widely used turbulent models is the Hufnagel-Valley (HV) which depend on vertical wind profile and integrated turbulence along the propagation path. We have developed a statistical studied of the input parameters above Canary Island Observatories using a metereological database to collect the wind profiles and DIMM database to evaluate zero order moment. We are estimated the isoplanatic angle and the down-link scintillation. To check the consistency of the model, we are compared the isoplanatic results with isoplanatic angle measured by SCIDAR campaigns (17 nights along the year). To establish the average turbulence wind speed, we are used an observational correlation finds by Sarazin at other high mountain observatories.
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