This three-frequency space radar image of west central Egypt shows detailed patterns of eroded sedimentary rock formations emerging through a vast sea of sand dunes. The broad black bands that dominate the image are thick ridges of sand known as longitudinal dunes. In this region of the Sahara, a single ridge may be as long as several hundred kilometers. Thin red lines within the black bands are bright reflections from the steep crests of the sand ridges. Between the dunes are colorful patterns of rock outcrops that are either exposed at the surface or covered with very thin layers of sand that the radar "sees