July 12, 2014

Slightly Inconstant Gray Card

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image by NASA/Goddard Space Flight Center

The video above and this article explain how the Moon is used to calibrate the sensors of the Landsat 8 satellite that images Earth. It is interesting that they say the Moon is a constant, because we know it isn't. Their calibration images are taken over two Landsat orbits at full Moon, so the terminator moves only very slightly so that shadows near the poles change only slightly too. But of course, depending on where you look, even the full Moon lunar surface is brighter and darker than the global average. Although none of this is specifically mentioned I can't imagine that NASA isn't fully aware of this and compensates in the calibration.

Chuck Wood

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