Effect of Earth curvature

In GILDAS, the effect of the Earth curvature is approximated by a correction to the usual airmass definition (See Eq. ). Fig.  displays the airmass as a function of the elevation for 3 different atmosphere models: 1) a plane parallel atmosphere, 2) a curved atmosphere with a scale height of 2.7 km, and 3) a curved atmosphere with a scale height of 5.5 km. It is clear that as long as the elevation is larger than 20 deg, the difference in airmass between these different atmosphere models is negligeable.

Figure: Top: Effect of the Earth curvature on the airmass as a function of the elevation. Bottom: Relative difference as a function of the elevation.