Using Stereophotoclinometry to Map the Solar System
The New York Times profiles Dr. Robert W. Gaskell, who is working on producing topographic maps of various planets and moons of the solar system.
Just now Dr. Gaskell is mapping all of Mercury and eight moons of Saturn. He also has a NASA contract to do part of a topographical map of Earth’s Moon, and he is working on a project to refine his model of the near-Earth asteroid Eros. He has made 12,000 overlay “maplets” of Eros from images produced by the NEAR spacecraft at the turn of the century. In all, NEAR made 160,000 digital images, and “I’m doing 1,000 at a time,” Dr. Gaskell said.
Dr. Gaskell calls what he does “stereophotoclinometry.” Ideally he needs at least three images of the target landscape, usually taken by an orbiting spacecraft or a probe on a flyby to another destination. Only in rare cases can telescope images provide enough detail.
The sun angle must be different for each exposure so each image shows different shadows. By comparing the shadows, the software calculates slopes, which yield the altitudes of target features. The computer solves the equation in three dimensions, producing a patchlike topographical maplet.