Altimetry Waveform Inversion over Antarctica

Abstract:

Measurement provided by radar altimeters is much richer than the few
parameters traditionnally used in the applications (mainly ground altitude
and backscatter). Indeed, the whole history of the radar return is available,
this is called radar waveforms.

By a careful analysis of sequences of consecutive waveforms, it is possible to
retrieve crucial information about the nature of the soil backscatter as well
as details about the topography at a resolution much better than the footprint
of the altimeter. In particular the shape of the waveforms allows us to
discriminate the power return by the surface from the return by the subsurface.
These parameters can then be used to provide information about geophysical
characteristics of the terrain (snow grain size, etc) and its temporal
evolution through the analysis of the penetration of the radar wave in the
snow.

This presentation will describe the technics we have developped to perform
waveforms inversions through the use of an accurate waveform simulation model
that is able to handle the Envisat mission (Ku band, 13.6 GHz) as well as the
new AltiKa mission from CNES/ISRO that provides measurements in Ka band
(35.75 GHz) on the same orbit.

We will also show how we can use good high resolution DEM, e.g. from
the Spirit projet (CNES/SPOT IMAGE), in order to improve the retrievals
in regions which are notoriously difficult for radar altimetry
(near the coast).
Finally we will show results obtained on a few places of the
Antarctica icesheet.