The type of terrain that surrounds an observing site may cause movements of air that degrade the quality of seeing. If there are uneven ground features nearby (such as the steep slopes of a mountain or hill, gorges or gullies), then nocturnal drainage may generate moving currents of relatively dense air that can adversely impact image quality. 

The type of ground cover immediately surrounding an observing site will often impact the quality of seeing. If the ground is allowed to heat up during the daylight hours by absorbing the sun’s shortwave radiation, that stored heat will be reradiated back into space during the night, causing micro-scale turbulence in the process. Surfaces that either dissipate or reflect the sun’s energy are preferred.

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