Theoretical Doppler of satellite (true dop) -The expected Doppler frequency based on satellite's motion relative to the receiver. It is computed using satellite's coordinate and velocity, and receiver's coordinate and velocity. Apparent Doppler for this receiver (app dop) -Same as Theoretical Doppler of satellite, with clock drift correction added. NOTE: The True Doppler and Appaent Doppler values that are available in the SATVIS log of the NovAtel OEM4 GPS receiver are meant to provide a brief overview. The satellite positions and velocities used in the computation of this log are based on Almanac orbital parameters, not the higher precision Ephemeris parameters.