Table of Contents
Understanding Hyperspectral Imagery
The Invisible World
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©Rob Whittington CMST 386 Section 6380 Spring Semester 2002 University of Maryland University College 10 July 2002
As you may already know, the infrared region transitions into visible light at the red end of the electromagnetic spectrum's visible range (hence its name) and the ultraviolet region lies on the other side of the visible range just beyond the blue (violet) band. Infrared light ranges greatly in wavelength-from the longer, far infrared wavelengths that are about the size of a pinhead and the shorter, near infrared ones that are the size of microscopic human cells. Near infrared is closest in wavelength to visible light and far infrared is closer to the microwave region of the electromagnetic spectrum. Far infrared waves are thermal-we experience this type of infrared radiation every day in the form of heat, while the shorter, near infrared waves are not hot at all-in fact you cannot even feel them.
Likewise, the ultraviolet part of the electromagnetic spectrum is characterized by how far it ranges from the visible part of the spectrum and has been divided into three regions: near ultraviolet, far ultraviolet, and extreme ultraviolet. Near ultraviolet is the light closest to visible light, extreme ultraviolet is the ultraviolet light closest to X-rays, and far ultraviolet lies between the near and extreme ultraviolet regions.
The ability to detect energy within the infrared and ultraviolet regions, in addition to the traditional visible bands, allows hyperspectral sensors to create a three dimensional image in which two of the dimensions provide spatial information and the third provides spectral information.
As you can imagine, analyzing this third dimension's spectral bands that can number up to 400 and range in such a wide area of the electromagnetic spectrum produces many military and civilian applications. First let's take a look at some military applications.