This is a portion of a Cassini radar mapper image obtained by the Cassini spacecraft on its December 21, 2008, flyby of Saturn's moon Titan.
The area shown covers the southern boundary of an equatorial band where longitudinal dunes (dunes that form along the wind direction) are pervasive. Here the dunes are apparently created by winds locally coming from the west and north-west, and generally blowing toward the east. The dunes are interspersed with radar-bright features that are inferred to rise above the surrounding terrain.
In the lower part of the image there are no dunes at all, and the texture is more typical of featureless plains observed in many other areas of Titan that lack dunes. In this transition zone, the sand-sized particles that make up the dunes might not be so plentiful. In this case, insufficient sand to replenish the dunes makes them gradually disappear.