Reconstructions obtained by backpropagation in the frequency domain using the calculated fields with a single transmitter and a single receiver and the frequency band between 2 and 10 GHz. The direction of wave propagation is plotted with a dashed line. The coloured areas corresponding to the different parts of the analogue, taking into account the Born compensation and their boundaries, are summarised in Table 3: the green one refers to the boundaries air/mantle and mantle/air, the blue one refers to the reflections mantle/interior and interior/mantle, and the yellow one refers to the reflections interior/void and void/interior.