The ITU Radiocommunication Assembly considering a)that techniques exist for monitoring tropospheric and ionospheric characteristics by means of low orbiting satellites observing GPS satellites near the Earth’s limb;b)that ionospheric effects along these paths may dominate over tropospheric effects in some situations and, for extrapolation to other scenarios, separation of these two components is necessary;c)that intersatellite links and compatibility may be affected by the ionosphere and the troposphere.