Because hills and valleys under the aircraft make the magnetic readings rise and fall, a radar altimeter keeps track of the transducer's deviation from the nominal altitude above ground. There may also be a camera that takes photos of the ground. The location of the measurement is determined by also recording a GPS.
because hills and valleys under the aircraft make the magnetic readings rise and fall a radar altimeter keeps track of the transducer's deviation from the nominal altitude above ground there may also be a camera that takes photos of the ground the location of the measurement is determined by also recording a gps