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Validation of altimeter measurements over ice.

Benoit Legr├ęsy(1)

(1) CNRS, Legos, 31041 Toulouse CEDEX 09, France


We've been investigating the altimeter measurements from ENVISAT satellite over ice sheets of greenland and antarctica. The measurements are mapped on the ice sheet scale on both Antarctica and Greenland for every cycle. The result shows an overall good behaviour of the radar altimeter with most of the time high resolution measurements over ice appart from strong transitions. The crossover difference of the height, backscatter, leading edge width and trailing edge slope show caracteristic behaviour. This behaviour stays stable from cycle to cycle and compare well ith ERS1 and ERS2 series. We investigated the difference between ERS2 and ENVISAT along track. Although few measurements are available on common cycles and many of the tracks show large across track distance after ERS2 attitude difficulties, the results on the small safe dataset will be shown. In addition to these glabal analysis, we made survey on smaller identified targets. One target is the lake vostok area where the time variations of the signal are supposed to be small, the surface is very flat and shows little undulations, the accumulation is very small as well as the wind, the atmosphere stays clear most of the time and we have extremely fine topography issued from revised ERS1 geodetic data and controlled with icesat data. The other target of interest is on the Amery where we designed a spiderweb around an ENVISAT crossover point. The web has been surveyed in 2003-2004 by roving GPS and the tides have been investigated to validate an adapted ocean tide model. The GPS roving has been processed to produce a local very high resolution topography and statistics of the surface roughnesss. This crossover point will be again surveyed in 2005-2006. We will show results on the data analysis for those targets and on altimeter echo modelling to improve the analysis of the altimeter data. Emphasis will be done, based on these analysis, on the quality of the data, on the best operational modes of the altimeter and on the routine survey of altimeter data over ice.



                 Last modified: 07.10.03