This glossary is designed to help students and educational professionals with their growing understanding of the concepts and terms associated with remote sensing. The glossary was modified from the Virtual Nebraska web pages detailed glossary http://www.casde.unl.edu/vn/glossary/introfr.htm. All the selected terms are not used in this unit, but all the terms are related to the science of remote sensing.

Absorption: The process in which radiant energy is retained by a substance. A further process always results from absorption, that is, the irreversible conversion of the absorbed radiation into some other form of energy within and according to the nature of the absorbing medium. The absorbing medium itself may emit radiation, but only after an energy conversion has occurred.

Bandwidth: The total range of frequency required to pass a specific modulated signal without distortion or loss of data. The ideal bandwidth allows the signal to pass under conditions of maximum AM or FM adjustment. (Too narrow a bandwidth will result in loss of data during modulation peaks. Too wide a bandwidth will pass excessive noise along with the signal.) In FM, radio frequency signal bandwidth is determined by the frequency deviation of the signal.

Canopy: The top layer of a forest formed naturally by the leaves and branches of trees and plants.

Color Composites Images: The human eye is not sensitive to ultra-violet or infrared light. To build a composite image from remote sensing data that makes sense to our eyes, we must use colors from the visible portion of the EM spectrum–red, green, and blue. Three-band composites are created by using the measured reflected energy in each of three Landsat Thematic Mapper (TM) spectral bands to control the amount of blue, green, and red in a color output image. The way in which the seven TM bands are mapped to the three colors in the output image depends on what information is desired to be highlighted in the image. For some applications, it may be desirable that land cover classes be associated with familiar colors, e.g., grass is green. In other cases, contrasting colors are preferred to highlight objects of interest from the background. We give three examples of commonly used band combinations and describe how different features appear in each.

Note: The specific bands used in three-band composites are often identified by giving the band numbers used for red, green, and blue, respectively. Thus, an image using band seven for red, band four for green, and band two for blue would be designated (7,4,2). This unit uses the same convention.

Digital image: An analog image converted to numerical form so that it can be stored and used in a computer. The image is divided into a matrix of small regions called picture elements or pixels. At sub-satellite point each pixel represents a specific amount of area. For example, in Landsat each pixel represents 30 meters. Each pixel has a numerical value or data number value, quantifying the radiance of the image at that spot. The data number value of each pixel usually represents a value between black and white, i.e., shades of gray.