Modeling of the Martian Ionosphere Using the Total Electron Content Measurement by the NEIGE/NETLANDER Experiment

The measurement of Doppler shifts by the NEtlander Ionosphere and Geodesy Experiment (NEIGE) of the Netlander mission to Mars fulfills two scientific objectives : the monitoring of the structure and dynamics of the ionosphere of Mars and the precise determination of Mars orientation parameters in order to obtain information on the internal structure of Mars and on the seasonal mass exchange between the atmosphere and the ice caps. The total electron content (TEC) of the Martian ionosphere will be derived from the so-called geometric-free combination of the Doppler shifts which affect radio links in the UHF and S (or X) bands between the Netlander micro-stations on the Mars surface and the relay orbiter. The ionospheric plasma introduces a frequency-dependent phase delay which is a disturbance to be removed for geodesy purposes, but which contains useful information on the TEC and its variation. The Doppler shift in both frequency bands is expected to be measured with an accuracy of 0.1 mm/s. Simulations have been performed to evaluate the resulting precision in the determination of the TEC. In order to simulate different horizontal TEC profiles under different conditions, a coupled kinetic fluid model is used. This model solves a stationnary Boltzmann kinetic equation, the fluid equation (continuity, momentum, energy and heat flow) and also the convection diffusion equation for the induced and horizontal magnetic field. The electron density is typically provided between 100 and 500 km height. The paper shows that the TEC measurements made by NEIGE will have the capability to improve our knowledge of the Martian ionosphere by giving constraints to existing ionospheric models.