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Words begining with "F"
Federal Aviation Administration.
A process by which graphic or photographic information is
transmitted or recorded by electronic means.
See digital image.
Temperature scale designed by the German scientist Gabriel
Fahrenheit in 1709, based upon water freezing at 32 degrees and water
boiling at 212 degress under standard atmospheric pressure. Compare
Electromagnetic radiation, longer than the thermal infrared, with
wavelengths between about 25 and 1000 micrometers. See elctromagnetic
A metallic cylinder closed at one end, used to obtain and direct
radio frequency (RF) energy reflected
from a satellite dish. It acts as a wave guide at microwave
frequencies. RF energy inside the horn is picked up by a small probe;
once inside the horn, the wavelength (energy) of the microwave
radiation changes to a guided
U.S. Federal Emergency Management Agency.
Chinese geostationary environmental satellite that was destroyed
by an explosion before launch in April 1994. The name Feng Yun,
meaning Wind and Cloud, was originally applied to the Chinese
polar-orbiting environmental satellite launched in September 1991
(Feng Yun 1-2), which offered direct
readout services. The Chinese polar-orbiter program has since
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
See frequency modulation.
- In optics, the distance usually expressed in millimeters -
from the principal point of a lens or concave mirror to its
- The distance, measured from the center of the surface of a
parabolic or spherical reflector (e.g., satellite dish) where RF
energy is brought to essential point focus.
The area where weak signals collected by a satellite dish,
concentrated into a smaller receiving area, converge.
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.
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).
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
Number of cycles and parts of cycles completed per second. F =
1/T, where T is the length of one cycle in seconds.
Frequency Division Multiplexing
The combining of a number of signals to share a medium by dividing
it into different frequency bands for each signal. See signal.
Frequency Modulation (FM)
The instantaneous variation of the frequency of a carrier wave in
response to changes in the amplitude of a modulating signal. As
applied to APT, the radio signal from
the satellite is broadcast on an FM transmitter and received on the
ground on an FM radio receiver. See frequency
division multiplexing, signal.
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.
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