ENVISAT and AltiKa/SARAL observations of the Antarctic ice sheet: a comparison between Ku- and Ka-band.
Event: 2014 SARAL/AltiKa workshop
Session: Land ice and Sea ice
Presentation type: Type Poster
Contribution: PDF file
The AltiKa altimeter on-board SARAL, a joint CNES/ISRO mission, was launched in February 2013 on the same 35-day orbit than previous European altimeters, Envisat and ERS1-2. SARAL/AltiKa is thus a unique opportunity to extend the repeat observations of this orbit, surveyed since 1991. However, the altimeter operates in Ka-band, a higher frequency than previous ones and thus offers new fields of investigation. First, one of the major limitations for ice sheet survey with altimetry is the penetration of the radar wave within the snowpack because variations in the snowpack properties lead to an artificial change in height. Theory suggests that the penetration depth ranges between 5 m and 12 m in Ku-band and decreases to around 1 m in Ka-band. Indeed, the space and time observations of AltiKa at cross-over points and along-track indicate that the impact of backscatter changes on height decreases from 0.3 m/dB for Ku-band to only 0.05 m/dB for Ka-band. So, the AltiKa height measurement is much more stable in time for Ka-band. Secondly, we show that the volume echo in Ka-band results from the near subsurface layer and is mostly controlled by ice grain size, whereas in Ku-band, internal stratifications also play a role. AltiKa thus offers an opportunity to estimate the snow densification, by providing a direct relation between backscatter and grain size.