Ocean Remote Sensing Using GNSS-R - GNSS Remote Sensing: Theory, Methods and Applications - page 222

Fig. 9.6 Sketch of the re-tracking concept, to align the individual waveforms before integration,
and thus avoid the defocusing introduced by coarse time-batched a-priori delay model used by the
receiver
dynamic scenarios (space- and air-based receivers), and whenever the a-priori
estimation of the nominal delay by the receiver, or some of its parameters, are not
updated as fast as the dynamic changes of the geometric conditions, a re-alignment
of the waveforms must be conducted before its integration. This re-alignment uses
refined a-posteriori estimates of the involved parameters. This process is called re-
tracking, and consists in delay-shifts of each individual waveform with respect to the
rest, using the a-posteriori interpolated geometric information (receiver trajectory
and attitude, transmitter precise orbits, clock errors information). The concept is
illustrated in Fig. 9.6 .