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The effect of the atmospheric surface layer (the first 30 
50 m)
on the local seeing has been for
a long time a main preoccupation of astronomers.
Therefore the preferred sites
for astronomical observatories are mountain summits which
rise steeply in the free atmosphere and where
the prevailing winds hardly flow up the mountain slope.
In fact many infrastructural, operational and logistics requirements conflict often with this ideal. An observatory site must be on a reasonably accessible location. Often, for reasons of scale economy, several telescopes share the best astronomical sites and not all can be located on the highest and best exposed locations. Also, once the facility is completed with roads, buildings, parking lots, etc., the site itself has only a vague resemblance to its virgin appearance. As a consequence a telescope seldom stands in an atmospheric environment which is not affected by the proximity of the ground and other artificial structures.
The general issue of seeing in the atmospheric surface and boundary layers has been treated in [Sarazin 92], a PhD dissertation which also includes several papers published on the subject. Therefore we will limit the scope of this work to two aspects which are particularly relevant to the civil engineering design of an astronomical observatory: