First Results on Differential Phase Altimetry with CYGNSS

Phase altimetry has been recently introduced for high precision surface height measurements in satellite global navigation satellite system reflectometry. In the presence of coherent scattering the effectiveness of the technique has been demonstrated for sea surface at low grazing angle as well as for rivers and lakes. This study develops the concept of differential phase altimetry for land surfaces, provided that the surface roughness is small and the surface undulations are gentle. Differential phase altimetry is more tolerant with respect to atmospheric and systematic errors but its applicability is difficult in the presence of surface slope variations that may generate phase cycle slips that require complex post processing to unwrap the retrieved phase. To mitigate cycle slips an overlapping correlation process is introduced to generate phase values with high spatial resolution. A first evaluation of performance is presented using the CYclone Global Navigation Satellite System raw intermediate frequency acquisitions over land surface with gentle undulations.