A test target is a common feature on interplanetary landing craft such as the Viking Lander and Mars Exploration Rovers.
The target is usually a visible marker or plate on the exterior of the vehicle within sight of the lander's imaging system (usually a CCD camera). The target possesses samples of primary colors and a grey scale. The camera uses this much like a photographer would use a chip chart on Earth; the color samples allow the camera to compensate for white balance and contrast. The target provides a visual reference as well, so that the initial orientation of the camera can be fixed.
On the Mars Exploration Rover, the target was designed with a pillar elevated above the main surface, so that it could be used as a sundial.
Famous quotes containing the words test and/or target:
“Whenever a true theory appears, it will be its own evidence. Its test is, that it will explain all phenomena.”
—Ralph Waldo Emerson (1803–1882)
“Well gentlemen, this is it. This is what we’ve been waiting for. Tonight your target is Tokyo. And you’re gonna play ‘em the Star Spangled Banner with two-ton bombs. All you’ve got to do is to remember what you’ve learned and follow your squadron leaders. They’ll get you in, and they’ll get you out. Any questions? All right that’s all. Good luck to you. Give ‘em hell.”
—Dudley Nichols (1895–1960)