| Summary: | A unique advantage of the ENVISAT altimeter system is the acquisition in S band as well as the classical Ku band. This S band frequency is designed to measure the ionospheric delay over the ocean surfaces. Over land and ice, however, the returned radar echo differences between the two frequencies are also function of the properties of the sensed medium. This is particularly the case over the Antarctic snow. The 2 waves get a different interaction with the snow surface roughness, density, stratifications, snow grains. Here, we study the 4 years time-series of the RA-2 EN-VISAT waveform parameters over the whole ice-sheet. The time series present both a stationnar and a seasonal signature. The analysis of the stationar signature show the importance of the surface roughness at a cm-scale in the altimetric waveform. In particular, we show that the snow surfaces must sometimes be considered smooth, with an important coherent scattering component at the vertical. This observation is integrated in a altimetric echo model. We then simulate the seasonal densification of the snowpack and show that it reproduces simultaneously the observations in the two radar bands. From this modelling, we conclude that the seasonal densification of the snowpack creates artificial bias in the altitude series retracked from the altimetric data. Key words: Altimetry; dual-frequency; Antarctic; snow properties. The RA-2 altimeter onboard the ENVISAT satellite launched in 2002, provides a S band dataset at 3.2 GHz, in addition to the classical Ku band data at 13.6 GHz. On the Antarctic ice-sheet, this dual-frequency signal is highly sensitive to the different snowpack properties (Legresy et al., 2005, Lacroix et al., 2007). The radar signals are impacted by the snow surface roughness at different scales (Legresy and Remy, 1997), as well as the subsurface
|
|---|