  In this paper I describe a simple numerical procedure to compute synthetic
horizon altitude profiles for any given site. The method makes use of a
simplified model of local Earth's curvature, and it is based on the
availability of digital elevation models describing the topography of the area
surrounding the site under study. Examples constructed using the Shuttle Radar
Topographic Mission (SRTM) data (with 90m horizontal resolution) are
illustrated, and compared to direct theodolite measurements. The proposed
method appears to be reliable and applicable in all cases when the distance to
the local horizon is larger than ~10 km, yielding a rms accuracy of ~0.1
degrees (both in azimuth and elevation). Higher accuracies can be achieved with
higher resolution digital elevation models, like those produced by many modern
national geodetic surveys.
