Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Terrain profiles for: (a) Line-of-Sight path over sea. (b) Obstructed path over sea. Brown area indicates the curvature of the earth, modified by the refraction index; Green area is the terrain profile as seen by the radio wave and magenta line corresponds to 60% of the first Fresnel zone at MHz; and blue line is the optical line of sight.
