For determining elevation, how many satellites are necessary?

To accurately determine elevation using satellite technology, a minimum of four satellites is required. This is because the position of an object in three-dimensional space needs to be calculated using a method known as trilateration.

When only three satellites are used, the system can ascertain a two-dimensional position (latitude and longitude) on the Earth's surface but will not provide accurate elevation (altitude). The fourth satellite enables the calculation of a third dimension, allowing for precise elevation readings by accounting for the variations in the satellite signals and the satellite geometry to effectively resolve the position in 3D space.

This requirement also accounts for the inherent error in GPS measurements and the need for redundancy to ensure a reliable fix. Without the data from the fourth satellite, the calculation cannot overcome the ambiguity that arises in determining altitude, making four satellites essential for accurate elevation determination.