AP7 – 96 – Additional constraints may be included in the determination of the maximum and minimum values of horizon antenna gain where an earth station operates with a constellation of non-geostationary satellites that are not in near-polar orbit. In this case, depending on the latitude of the earth station, there may be portions of the hemisphere above the horizontal plane at the earth station in which no satellite will appear. To include these visibility limitations within this method, it is first necessary to determine, for a closely spaced set of azimuth angles around the earth station, the minimum elevation angle at which a satellite may be visible. This minimum satellite visibility elevation angle () may be determined from consideration of the visibility of the edge of the shell formed by all possible orbits having the orbital inclination and altitude of the satellites in the constellation. The lowest elevation angle towards which the main-beam axis of the earth station antenna will point on any azimuth is the minimum composite elevation angle (c), which is equal to the greater of the minimum satellite visibility elevation angle () and the minimum elevation angle of the earth station (sys). After the minimum composite elevation angle has been determined for all azimuths by the procedure of § 1.1 of this Annex, the resulting profile of the minimum composite elevation angles can be used, in the procedure of § 1.2 of this Annex, to determine the maximum and minimum values of horizon gain at any azimuth. Further information and an example of this method may be found in the most recent version of Recommendation ITU-R SM.1448. ANNEX 5 Determination of the coordination area for a transmitting earth station with respect to receiving earth stations operating with geostationary space stations in bidirectionally allocated frequency bands 2 Determination of the bidirectional coordination contour for propagation mode (1) MOD 2.1 Calculation of horizon gain for unknown receiving earth stations operating with geostationary space stations The value of Gr, the horizon gain of the receiving earth station, for each azimuth, α, at the transmitting earth station is found by the following steps: