MULTISPECTRAL IMAGERY (MSI)
Definition: Images obtained simultaneously in a number of discrete bands (specific sections) of the electromagnetic spectrum.
All material reflects or emits electromagnetic radiation in different ways (just as grass appears green and asphalt black). By specifically imaging the earth in discrete bands, i.e. only green, only visible red, only near infrared, etc., features of the earth can be identified, classified, and displayed with greater accuracy. The multispectral nature of the imagery is important to distinguish between features that otherwise appear the same. For instance, a green painted parking lot would appear the same as a green grass field in a standard aerial photograph. When combined with a near infrared image of the same parking lot and field, the grass would appear much brighter than the parking lot due to the higher reflectance of near infrared radiation by the grass. Extending this example one step further, the parking lot may emit more thermal infrared radiation (be hotter) than the grass. By looking at the thermal image the difference between the grass and parking lot would be obvious.
By using a computer to compare, combine, and analyze these images, the differences among ground surface cover types can be rapidly determined and displayed. Since a Landsat image is approximately 185 km wide and 170 km (116 miles by 106 miles) long this multispectral procedure can be used to depict a fairly large area.
Multispectral imagery used by Army topographers during DESERT SHIELD and DESERT STORM came primarily from the Landsat satellite. The Landsat satellite images the earth in seven different bands (spectra), producing seven different pictures of the earth.
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