Estimation of Doppler Curve for LEO Satellites

Doppler frequency shift which is defined as “the observed changes in frequency of transmitted waves when relative motion exists between the source of waves and an observer”, has wide applications in science, technology and different industries including communications, medicine, aerospace, electronics and etc. One of its common applications in aerospace is its use in tracking satellites and orbit determination. In low earth orbiting satellites, because of their low altitude to earth and their high rotation period around it, Doppler shift is appropriate to be used for tracking. In this paper, satellite distance and its derivative in time which is parameter in obtaining Doppler shift is derived. Position of the satellite is firstly derived using equations governing on them and TLE which contains orbital elements and essential information in different coordinate systems such as ECI, ECEF and topocentric. Then satellite distance to ground station and its changes in time is calculated via transformations of coordinate systems to each other. Having the distance, its derivative and beacon signal frequency, Doppler curve can be estimated in each pass of the satellite. Doppler shift can be used in an appropriate and precise satellite tracking technique.