Descent imaging provides pictures during entry, descent, and landing. It is one of the advanced terrain-sensing techniques for the detection and avoidance of surface hazards during descent through the martian atmosphere. Onboard computer software analyzes this data to help determine horizontal velocity at which the lander is moving relative to the surface. This measurement also helps determine what rockets should be fired to correct the spacecraft's path. Descent imaging also allow mission teams to make early determinations about the precise place the rover has landed based on images of the martian surface collected on the way down.

This image simulates how the descent imager for the Mars Exploration Rovers took three pictures of the surface and compared high-contrast features (e.g., craters) to determine the spacecraft's horizontal velocity during entry, descent, and landing. This measurement helped determine which transverse rockets should be fired to keep the spacecraft within its planned landing area.

In addition to stunning video, the data the camera collects will allow scientists and engineers to: observe geological processes at a variety of scales, sample the horizontal wind profile, create detailed geologic, geomorphic and traverse planning and relief maps of the landing site.