ENVISAT radar altimeter as a sounding radar on the Amery Ice shelf
Pascal Lacroix(1) , Benoit Legresy(1) , Richard Coleman(2) , and Frederique Remy(1)
18, av Edouard Belin,
(2) University of Tasmania, Private Bag 78, TAS 7001 Hobart, Australia
An unique advantage of the ENVISAT altimeter system is the acquisition in S band as well as the classical Ku band. This double frequency approach is designed to measure the ionospheric delay to correct altimetric measurements. In contrast to ocean surfaces, over land and ice, the difference in frequency measurement is also influenced by surface properties such as ground slope and penetration into the surface medium. This is particularly the case for the Antarctic snow.
Here, we present an original application of the use of these dual frequencies to sound the Amery Ice Shelf snow pack. We used along-track GDR data processed with the Ice2 algorithm to profile various parameters of waveforms for both frequencies and to map the points of interest, where measures in Ku and S differ. Comparison of altimetry data with MODIS image and simultaneous observations from helicopter and airplane, clearly shows that the anomalies between the 2 frequencies correspond to the crevasses identified on satellite image, as S band penetrates much deeper in the firn.
The radar waveforms are analysed over space and time to strengthen the detection and better explain the radar behaviour over the crevassed area. Conclusions are drawn on algorithms to be designed to characterise the crevassing.