Study of Delay Drift in GNSS-R Altimetry

Differently to the case of a conventional spaceborne nadir-looking mono-static radar altimeter, where the fly-around time of the pulses remains basically constant (assuming an almost circular orbit around an almost spherical Earth), the bistatic geometry of GNSS-R with the transmitter and the receiver embarked on different satellites imprints a significant temporal variation to the delays of the direct and reflected signals. Within a GNSS-R-based spaceborne ocean altimeter using the PARIS concept, such temporal variation in the delay has to be compensated for with the objective to finely adjust the delay of the direct signal to permanently match with that of the reflected signal according to some a priori model of the geometry. The impact of the residual delay drift on the accuracy and the precision of the range observations is assessed here.