spase://CNES/NumericalData/CDPP-AMDA/MEX/MARSIS/mex-marsis-ele

The level 5 TEC data are derived following a method described in details by Mouginot et al. Planetary Space Science, V56, 2008. The correction method consists in finding the three parameters [ a1 ; a2 ; a3 ] defining the signal distortion phase Δφ induced by the ionosphere. In the time domain, the ionosphere distortion generates a delay and a spreading of the radar pulse. It is clearly visible on MARSIS radargram without correction. A by-product of the ionospheric correction is the TEC, that can be easily obtained from the [ a1 ; a2 ; a3 ] parameters. [ a1 ; a2 ; a3 ] are investigated in ordrer to get Δφ with the best SNR As initial conditions for this optimization, we use the parameters fitting with a simplified Gaussian density-profile of the ionosphere. Then the optimization is done by using the following constraints: * A constraint on the vertical position of the surface echo estimated with the digital elevation model MOLA. * A constraint on the SNR. The signal amplitude must be maximal after correction.