Atmospheric extinction evaluates the sky transparency. Besides the natural extinction due to the molecules of the atmosphere, other sources of sky transparency degradation are clouds and aerosols.
Sky quality parameters
CN2 turbulent vertical distribution
The parameters relevant for Adaptive Optics can be obtained from the optical turbulence profile, given by the refractive-index structure constant of the turbulence, CN2 (h), where h is the altitude
Meteorology and climate
Wind speed and direction, wind gust, relative humidity, air temperature, rainfall, insolation, etc.
Night Sky Background
The sky brightness (SB) is the routine measurement of the night sky brightness in units of magnitudes per arcsecond2 in a moonless night. This allows for identifying possible contaminating sources
Precipitable Water Vapour
The principal molecule responsible for the absorption in IR is water vapour (WV). The total amount of WV above a particular location is highly variable and commonly expressed as the Precipitable Water
Seeing and coherence time
Astronomical seeing (units arcesec) refers to the blurring or instantaneous image broadening of astronomical objects caused by turbulent mixing in the Earth's atmosphere due to the variations of the