EM 1110-2-2907
1 October 2003
Flight path
Line on the ground directly beneath a remote sensing aircraft or
spacecraft. Also called flight line.
Fluorescence
Emission of light from a substance following exposure to radiation from
an external source.
F-number
Representation of the speed of a lens determined by the focal length
divided by diameter of the lens. Smaller numbers indicate faster lenses.
Focal length
In cameras, the distance from the optical center of the lens to the plane
at which the image of a very distant object is brought into focus.
A distortion in radar images causing the lengths of slopes facing the
antenna to appear shorter on the image than on the ground. It is
produced when radar wave fronts are steeper than the topographic
slope.
Format
Size of an image
Forward overlap
The percent of duplication by successive photographs along a flight
line.
Fovea
The region around that point on the retina intersected by the eye's optic
axis, where receptors are most densely packed. It is the most sensitive
part of the retina.
Frequency (v )
The number of wave oscillations per unit time or the number of
wavelengths that pass a point per unit time.
F-stop
Focal length of a lens divided by the diameter of the lens's adjustable
diaphragm. Smaller numbers indicate larger openings, which admit
more light to the film.
G
GAC--Global Area
GAC data are derived from a sample averaging of the full resolution
Coverage
AVHRR data. Four out of every five samples along the scan line are
used to compute one average value and the data from only every third
scan line are processed, yielding 1.1 km by 4 km resolution at the
subpoint.
Gamma
This is a unit of magnetic intensity.
GCP
Ground-control point. GCPs are physical points on the ground whose
positions are known with respect to some horizontal coordinate system
and/or vertical datum. When mutually identifiable on the ground and on
a map or photographic image, ground control points can be used to
establish the exact spatial position and orientation of the image to the
ground. Ground control points may be horizontal control points, vertical
control points, or both.
Gemini
U.S. program of two-man earth-orbiting spacecraft in 1965 and 1966.
Geodetic
Of or determined by geodesy; that part of applied mathematics which
deals with the determination of the magnitude and figure either of the
whole Earth or of a large portion of its surface. Also refers to the exact
location points on the Earth's surface.
Geodetic accuracy
The accuracy with which geographic position and elevation of features
on the Earth's surface are mapped. This accuracy incorporates
information in which the size and shape of the Earth has been taken
into account.
Geographic information
A data-handling and analysis system based on sets of data distributed
system (GIS)
spatially in two dimensions. The data sets may be map oriented, when
they comprise qualitative attributes of an area recorded as lines, points,
and areas often in vector format, or image oriented, when the data are
quantitative attributes referring to cells in a rectangular grid usually in
raster format. It is also known as a geobased or geocoded information
system.
Geometric correction
Image-processing procedure that corrects spatial distortions in an
image.
Glossary-12
Previous Page
