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.
The main goal of this work is the analysis of new approaches in order to study the properties of astronomical sites. The
objective is to calibrate the atmospheric extinction provided by in situ techniques through remote sensing data retrieved
from satellite-platforms. We have explored the usefulness of data provided by different spectrographs onboard NASA
and ESA satellites with better spatial and temporal resolutions than TOMS and centered on channels of astronomical
interest as a possible tool for site characterization. In addition, from these satellite data is possible to go back at the
cloud coverage, the climatic trend or the atmospheric turbulence from troposphere winds. The main problem to use these
values is their interpretation and their quantitative calibration. Data analysis need to be complemented with those
provided by in situ instruments (telescopes, airborne particles counters, ground meteorological stations, etc.).
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.
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).
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.
The DIMM is a widely accepted and often used instrument for seeing measurements. Nevertheless, its incorrect use may give rise to errors in seeing values. A detailed analysis of the parameters involved in the seeing calculation is being undertaken and the effect of saturation of the spots in particular is analyzed in this contribution. Our results reveal that the saturation increases not only the photon noise but also the speckles, which will acquire a greater relative weight with respect to the stellar spot. The result is an increase in the variance of the centroids, which results in artifically higher seeing values.
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