EMPIRICAL MICROWAVE BACKSCATTERING OVER ANTARCTICA - APPLICATION TO RADAR ALTIMETRY

In order to validate the satellite altimeter measurements over Antarct ica, we analyze the Seasat scatterometer backscatter coefficient which has been measured at different incidence and azimuth angles and for t he two polarizations. We show that the signal at large incidence angle s is a mixed signal of volume, backscattered by subsurface layering an d surface scattering whose proportions depend on physical characterist ics of the snow. Only the effect of the volume scattering by spherical grains on the altimetric signal can be estimated: It is of the order of a few percents of the total altimetric signal and the induced heigh t error is lower than 25 +/- 20 cm, if the echo is properly retracked. Other effects, such as internal density boundary are not estimated bu t a mean to detect the areas of great effect is given.