Abstract: A radio occultation instrumentation system includes a first satellite arranged with a transmitter for transmitting a signal with a carrier frequency and a second satellite arranged with a receiver for receiving the signal. The receiver receives information I(x,v) regarding the position and velocity of the first and second satellite and provides a prediction of the Doppler shift displacement of the carrier frequency of the signal for use in tracking the signal. The predicted Doppler shift displacement is also used to determine atmospheric conditions.

Abstract: Apparatus for performing open loop tracking of a signal in a radio occultation instrumentation system including a first satellite arranged with a transmitting means arranged for transmitting a signal with well defined carrier frequency and a second satellite arranged with signal receiving means receiving said signal, wherein said transmitted signal has a ray path from said first satellite to said second satellite which descends into and ascends from the atmosphere, said apparatus including means for providing a control signal to a frequency control unit for signal acquisition included in said receiving means, means for receiving information I(x,v) regarding the position and velocity of the first and second satellite; arrangement for providing a prediction of Doppler shift displacement of a transmitted signal in such a radio occultation system; and method for determining atmospheric conditions from information of Doppler shift displacement in a radio occultation instrumentation system.