Within the framework of the site prospection for the future European Extremely Large Telescope (E-ELT), a wide site characterization was achieved. Aklim site located at an altitude of 2350 m at the geographical coordinates: lat.= 30°07’38” N, long.= 8°18’31” W , in the Moroccan Middle Atlas Mountains, was one of the candidate sites chosen by the Framework Programme VI (FP6) of the European Union. To complete the fulfilled study ([19]; [21]), we have used the ModelOTP (model of optical turbulence profiles) established by [15] and improved by [6]. This model allows getting the built-in profiles of the optical turbulence under various conditions. In this paper, we present an overview of the Aklim database results, in the boundary layers and in the free atmosphere separately and we make a comparison with Cerro Pachon result [15].
In site selection processes, one key parameter is the extinction coefficient. This parameter depends on aerosol load, water
vapor content and atmospheric gazes. Actually a lot of satellite instruments give the aerosol optical thickness over the
earth with good spatial and temporal resolutions.
The determination of the extinction coefficient at elevated altitudes from photometric surface measurements at lower
altitudes is very important in the field of site testing.
In the first part of this paper we make a comparison between the extinction coefficient measured at ground level and the
aerosol optical thickness measured from space at La Palma observatory in order to study the reliability of the aerosol
satellite instruments. We used the most popular ones: MODIS Terra and Aqua, MISR and Envisat Meris.
In the second part of the paper, we use three AERONET (Aerosol Robotic Network) stations close to one another at the
Canary Islands; Izana (longitude=16.5°W, latitude=28.3° N, altitude= 2367m), La laguna (longitude=16.32°W,
latitude=28.50°N, altitude=568 m) and Santa-Cruz Tenerife (longitude=16.25°W, latitude=28.5°N, altitude=52 m). The
aerosol optical thicknesses relative to these stations were studied in order to develop some empirical relationships that
help determine photometric quality of an astronomical observatory from satellite measurements (even with very low
resolution) or from in-situ measurements of very low elevated nearby places. LIDAR (Ligth Detection and Ranging) data
of Santa-Cruz Tenerife provided by the MPLNET (Micro-Pulse Lidar Network) network were also used.
We present a characterization of meteorological parameters: Wind and direction speed, temperature, relative
humidity and pressure. Data set is provided by the system of NCEP/NCAR Re-analysis. The statistical
treatment of data will cover the years between 2003 and 2006 for the Observatory Oukaïmeden. An analysis of
monthly, seasonal, and annual results is presented. We calculated the Richardson number for each month of the
year. In addition, this paper describes a comparison between balloon-sounding made at different stations and
coincident model-based meteorological analysis. The comparison allows the assessment reliability of the analysis
in studied period.
Candidate sites of the future European Extremely Large Telescopes (E-ELT) need to be assessed and analytically
compared in their observing characteristics. In the site selection process, meteorological, photometric and seeing
qualities have to be studied and measured carefully.
Aklim site in Morocco is one among four candidates in the ELT project. In this paper, we present meteorological studies
of the Aklim site over eleven years. The meteorological parameters include wind speed and direction, relative humidity,
air temperature, cloud cover and water vapour content. Most of these data are taken from the National Center for
Environmental Prediction/National Center for Atmospheric Research NCEP/NCAR Reanalysis. The meteorological
analysis covers the vertical profile as well as surface layer meteorology.
Furthermore, in extensive literature, it has been demonstrated that the global circulation of atmospheric wind at 200 mb
can be used as a criterion to establish the suitability for the development of adaptive optics techniques. By using the
NOAA NCEP/NCAR reanalysis database, we analyse the monthly average wind velocity at 200 mb for eleven years
period and compare with famous observatories.
The aim of this paper is to characterize the aerosol loadings, their optical and microphysical properties over Morocco, by
use of the AERONET network and satellite data. Three AERONET stations in Morocco; Saada, Ras_El_Ain and Dakhla
are considered in this work. The aerosol parameters studied are the aerosol optical thickness, the Angstrom parameter,
the size distribution, the single scattering albedo and the refraction index. An inter-comparison with satellite data has
been achieved. The most popular satellite products, TOMS (Earth Probe and OMI), MODIS and MISR have been
considered. It comes out from this study that the mean aerosol optical thickness (550 nm) vary from 0.22 to 0.3, with a
peak in summer time of 0.56 for Dakhla, 0.42 for Ras_El_Ain and 0.35 for Saada. The Angstrom parameter mean is 0.6
for Dakhla and 0.75 for Saada and Ras_El_Ain with a summer minimum of 0.32 for Dakhla and 0.55 for Saada and
Ras_El_Ain. The size distribution is bimodal with a predominance of the coarse mode except for Saada in winter and
autumn. This region depicts desert dust predominant environment with a single scattering albedo varying from 0.72 to
0.96. Saada and Ras_El_Ain being at 52 km apart, their coincident daily AOT correlate with a correlation coefficient;
R=0.93. Concerning the correlation between satellite data and AERONET AOT, TOMS EP has a correlation coefficient
of 0.53 for Saada (all data), 0.68 for Dakhla (all data). TOMS OMI correlation coefficient is 0.68 for Saada (all data) and
0.71 for Ras_El_Ain (year 2006). MISR (level 3 data) correlation coefficient is 0.77 for Saada (all data) and 0.85 for
Dakhla (all data). MODIS (level 3) correlation coefficient is 0.86 for Saada (all data) and 0.92 for Dakhla (all data).
Level 2 MODIS correlation coefficient is 0.69 for Saada (year 2006), 0.86 for Ras_El_Ain (year 2006) and 0.97 for
Dakhla (year 2003).
In order to prospect for good astronomical sites in Morocco, we make a preliminary study in terms of aerosol characterization. For that purpose we use AERONET data and the Aerosol Index provided by Earth Probe platform. After establishing a good correlation between the aerosol optical thickness (AOT) and the aerosol index (AI) in three sites located in the area of interest, we try to extrapolate to areas where AERONET data are not available. The studied areas are: Marrakech, Dakhla located in Morocco, and Izana in the Canary Islands.
These areas exhibit a predominance of desert dust aerosol particles. The altitude seems to be the predominant factor influencing the distribution of the aerosol optical thickness during the year. A full characterization of these sites makes possible a determination of the aerosol optical thickness of neighbouring areas.
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