Looking for the Satellite

As seen from a specific Observer, the satellite has 3 coordinates in a spherical coordinate system: Azimuth - the (true) compass direction to the satellite; Elevation - the angle above the horizon; and Slant Range - the distance to the satellite. In addition to the changing azimuth and elevation (az/el - sometimes referred to as look angle), the changing range causes a Doppler shift of the radio signals between the observer and the satellite.