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.