ICESat and Envisat are both altimeters that surveyed ice sheets at the same time from 2003 to 2009. Envisat is a radar altimeter using the Ku-band whereas ICESat is a laser altimeter. This difference is of great importance : in radar altimetry over ice sheets, there are major errors that bias the retrieved elevation height, thus biasing the volume balance estimation. The slope effect can be corrected but there is a physical effect still hardly understandable : the penetration of the radar wave into the snowpack. In this article, we show empirical observations that help us to constrain the penetration effect over land ice. The laser altimetry is free from the slope or the penetration effects due to a narrower footprint and the laser. Consequently, by comparing both measurements from both altimeters at crossover points, we study the penetration bias as long as we focus on the flat surfaces. We show here that the mean penetration depth is between -0.5 and 1 meter and especially affects the leading edge width. By fitting a linear model between the leading edge width and the we show that the predominant effect over flat surfaces is the penetration one. We then show that an empirical correction can be applied and the rms of the corrected retrieved elevation height is lower than for the uncorrected elevation. In conclusion, we can compare the results between ICESat and Envisat with other missions in order to pursue this analysis. This poster aims to show all the analysis done for Ku-band, and the benefits of concordant missions for ice sheets survey.

Figure legend : mean elevation difference in meters between Envisat and ICESat over Antarctica for the 2003-2009 period.