Its main objective is the detection and mapping of water, both liquid and solid, in the subsurface of Mars, revealing much about the composition of the top 5 km of crust in general.
It features ground-penetrating radar capabilities, which uses synthetic aperture techniques and a secondary receiving antenna to isolate subsurface reflections. This technique has been used before on Earth. Similar instruments have been flown on low-flying aircraft to probe deep into the ice sheets of Antarctica and Greenland. At Mars, the instrument with its long antenna flies over the planet, bouncing radio waves over a selected area and then receiving and analyzing the “echoes.” Any near-surface liquid water should send a strong signal, while ice would be more difficult to detect since its electrical radar signal would be about the same as rock. The echoes will also help characterize the materials and roughness of the surface.
(click on the image for the legend)