LYRA is a solar EUV/VUV radiometer that will embark in early 2009 on-board the PROBA2 mission. Its heliosynchronous orbit generates brief eclipses, during which we intend to study the vertical distribution of the global extinction coefficient, using the solar occultation method. We also consider the potential of our approach in retrieving the thermospheric N2, O, O2 and mesospheric O2 and O3 densities from the extinction coefficient. A forward model of the atmosphere transmittance is presented. This model includes the ability to incorporate the inhomogeneities of solar emission over the Sun's surface to enhance the vertical resolution in the results. The chosen inversion method is provided as well, and tested with simulated data. © 2009 Springer-Verlag Berlin Heidelberg.