The Nature of Geographic Information

8. Passive Sensing at Visible and Infrared Wavelengths

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Over the next four pages we'll survey some of the sensing systems used to capture Earth imagery in the visible, near-infrared, and thermal infrared bands. A common characteristic of these systems is the passive way in which they measure electromagnetic energy reflected or emitted from Earth's surface. One weakness of the desktop scanner analogy is that the sensors discussed here don't illuminate the objects they scan. We begin by considering aircraft and other platforms used for high resolution sensing of relatively small areas from relatively low altitudes. Then we consider the origins, current status, and outlook for remote sensing from space. The section concludes with a site visit to a leading commercial imagery provider.