Dutton e-Education Institute Ryan Baxter, Senior Research Assistant, John A. Instructors and contributors: Jim Sloan, Senior Lecturer, John A. Dutton e-Education Institute, and Director of Education, Industry Solutions, Esri. Later in this chapter, we'll discuss some of the image processing techniques that are used to correct remotely sensed image data.Īuthor: David DiBiase, Senior Lecturer, John A. All of these complexities combine to yield data with geometric and radiometric distortions that must be corrected before the data are used for analysis. And while a document in a desktop scanner is illuminated uniformly and consistently, the amount of solar energy reflected or emitted from the Earth's surface varies with latitude, the time of year, and even the time of day.
In the desktop scanner, the scan head and the document are separated only by a plate of glass satellite-based sensing systems may be hundreds or thousands of kilometers distant from their targets, separated by an atmosphere that is nowhere near as transparent as glass. Documents lie still while they are being scanned, but the Earth rotates continuously around its axis at a rate of over 1,600 kilometers per hour. Documents are flat, but the Earth's shape is curved and complex. Unlike the document, the Earth's surface is too large to be scanned all at once, and so must be scanned piece by piece, and mosaicked together later. As you might imagine, scanning the surface of the Earth is considerably more complicated than scanning a paper document with a desktop scanner.
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