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University of Nebraska–Lincoln

Remote Sensing Glossary

Reference Information for Virtual Nebraska

Terms, Definitions and Concepts



Federal Aviation Administration.


A process by which graphic or photographic information is transmitted or recorded by electronic means.

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See digital image.


Temperature scale designed by the German scientist Gabriel Fahrenheit in 1709, based upon water freezing at 32 degrees Fahrenheit and water boiling at 212 degrees Fahrenheit under standard atmospheric pressure. Compare with centigrade.

far infrared

Electromagnetic radiation, longer than the thermal infrared, with wavelengths between about 25 and 1000 micrometers. See electromagnetic spectrum.


U.S. Federal Emergency Management Agency.


The set of influences (electricity, magnetism, gravity) that extend throughout space.

field of view

The range of angles that are scanned or sensed by a system or instrument, measured in degrees of arc.


Device that while selectively passing desired frequencies removes undesired ones.


See frequency modulation


A cloud on the ground.


Hardened remains or traces of plant or animal life from a previous geological period preserved in the Earth's crust.

fossil fuel

Any hydrocarbon deposit that can be burned for heat or power, such as petroleum, coal, and natural gas.


A single image or picture. A single complete vertical scan of the cathode ray tube (CRT).

free radicals

Atomic or molecular species with unpaired electrons or an otherwise open shell configuration, usually very reactive. Specific to atmospheric chemistry, free radicals are: short-lived, highly reactive, intermediate species produced by dissociation of the source molecules by solar ultraviolet radiation or by reactions with other stratospheric constituents. Free radicals are the key to intermediate species in many important stratospheric chain reactions in which an ozone molecule is destroyed and the radical is regenerated. See ozone.


A boundary between two different air masses. The difference between two air masses sometimes is unnoticeable. But when the colliding air masses have very different temperatures and amounts of water in them, turbulent weather can erupt.

A cold front occurs when a cold air mass moves into an area occupied by a warmer air mass. Moving at an average speed of about 20 mph, the heavier cold air moves in a wedge shape along the ground. Cold fronts bring lower temperatures and can create narrow bands of violent thunderstorms. In North America, cold fronts form on the eastern edges of high pressure systems.


A warm front occurs when a warm air mass moves into an area occupied by a colder air mass. The warm air is lighter, so it flows up the slope of the cold air below it. Warm fronts usually form on the eastern sides of low pressure systems, create wide areas of clouds and rain, and move at an average speed of 15 mph.


When a cold front follows and then overtakes a warm front (warm fronts move more slowly than cold fronts) lifting the warm air off the ground, an occluded front forms.


Water condensation occurring on surfaces below freezing. Condensing water turns to ice.