Ocean Remote Sensing Using GNSS-R - GNSS Remote Sensing: Theory, Methods and Applications - page 219

Fig. 9.3 Sketch of the low
receiver altitude altimetric
model, assuming parallel
incidence, and planar
horizontal reflecting surface
correlation function), called group-delay or pseudo-range. When the carrier phase
can be tracked, variations in the range can be monitored with much better precision,
since an entire cycle corresponds to 20 cm change ( 0.5 mm/carrier phase
degree). This latter approach is called carrier phase altimetry, but it is usually not
applicable to Oceanic observations. The reason is the roughness, which introduces
random phase behavior and thus impedes long coherence times of the reflected
signals. A recent method has been presented to perform carrier-based altimetry
over rough Ocean conditions from low altitude receivers. Under such conditions, the
spectral analysis of the Doppler residual still carries altimetric information content,
despite roughness conditions. The method is explained in Semmling et al. ( 2012 ),
where a precision of the order of 10 cm in 20 min arch is reported from a coastal
experiment on top of a 700 m high cliff. The phase-delay altimetry will not be
detailed in this Chapter, but it has also been successfully applied over continental-
ice ( Cardellach et al. 2004 , spaceborne) and sea-ice ( Semmling et al. 2011 ; Fabra
et al. 2011 ).