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.
We combined aerosol index measurements of TOMS/Nimbus-7 and Earth Probe observations with CAMC visual extinction over La Palma from 1984 to 1997, to investigate the possibility to calibrate TOMS data in terms of astronomical extinction.
The results show that the correlation of the two sets of data is quite good for extinction values greater than about Av = 0.2 mag./airmass. A detailed analysis reveals that the satellite aerosol index is indeed sensitive to the desert dust, but does not show evidence of the extinction contribution of the volcanic smoke due to the Mt. Pinatubo eruption which affected astronomical observations in 1992-1993.
This calibrated aerosol index is then used to investigate the number and distribution of dusty events over the astronomical site of Oukaimeden, Morocco. We find a remarkable correlation of the extinction over the two sites.
Finally we study the long term variability of the extinction over the region including Oukaimeden and La Palma, and we conclude that there is some correlation with the Northern Atlantic Oscillation.
The ESO OWL site survey plan includes the analysis of the astronomical
quality of the Atlas mountains in Morocco. In this paper we are presenting the first long time measurement of optical turbulence at Oukaimeden site. For this work we built an instrument called ADIMM for an Automated Differencial Image Motion Monitor, and we use it to the measure the optical turbulence at the Oukaimeden Site. We are describing the instrument and reporting the first results obtained after six month of working on this project. The results of night-time seeing measurements carried out during the period from Jun 14 up to October 01 2003 are presented. The median and mean values of the seeing for the entire period of observations are respectively 0.75" and 0.84".
This work was organized in the framework of contract Num.69651/ODG/02/9005/GWI between the European Southern Observatory (ESO) and Astrophysics and Physics of High Energy Laboratory of the Faculty of Sciences, Cadi Ayyad University (LPHEA).