Nonvisible satellite estimation algorithm for improved uav navigation in mountainous regions

Global Navigation Satellite System (GNSS) is one of the most used technologies around the world for navigation. This technology is integrated in aircraft, ship, and submarine guidance systems; it is available in cell phones and cars, and also used to monitor Earth surface movements. The system accuracy spans from a range of a few centimeters up to meters. This variation is related to different sources of error such as the receiver clock error, Earth's ionospheric and tropospheric signal delay, or multipath effect in semiobstructed areas. If the surrounding objects have highly reflective surfaces, the error magnitude might surge to several hundred meters due to multiple reflections that the signal experiences before reaching the receiving antenna. A further source of error is present when the same signal is received more than once. As the present work is focused only on the effect of nonvisible satellites, multipath effect is not further investigated.