EM 1110-2-2907
1 October 2003
UTM--Universal
UTM is a widely used map projection that employs a series of identical
Transverse Mercator
projections around the world in the mid-latitude areas, each spanning
Projection
six degrees of longitude and oriented to a meridian. This projection is
characterized by its conformality; that is, it preserves angular
relationships and scale plus it easily allows a rectangular grid to be
superimposed on it. Many worldwide topographic and planimetric maps
at scales ranging between 1:24,000 and 1:250,000 use this projection.
UV
Ultraviolet region of the electromagnetic spectrum ranging in
wavelengths from 0.01 to 0.4m.
V
Variance
A measure of the dispersion of the actual values of a variable about its
mean. It is the mean of the squares of all the deviations from the mean
value of a range of data.
VAS
Atmospheric Sounder, carried by GEOS satellites
Vector
Any quantity, which has both magnitude and direction, as opposed to
scalar that has only magnitude.
Vector Data
Vector data, when used in the context of spatial or map information,
refers to a format where all map data is stored as points, lines, and
areas rather than as an image or continuous tone picture. These vector
data have location and attribute information associated with them.
Vector format
The expression of points, lines, and areas on a map by digitized
Cartesian coordinates, directions, and values.
Vegetation anomaly
Deviation from the normal distribution or properties of vegetation.
Vegetation anomalies may be caused by faults, trace elements in soil,
or other factors.
Vertical exaggeration
In a stereo model, the extent to which the vertical scale appears larger
than the horizontal scale.
Vertical Positional
Vertical positional accuracy is based upon the use of USGS source
Accuracy
quadrangles, which are compiled to meet National Map Accuracy
Standards (NMAS). NMAS vertical accuracy requires that at least 90
percent of well defined points tested be within one half contour interval
of the correct value. Comparison to the graphic source is used as
control to assess digital positional accuracy.
Vidicon
An imaging device based on a sheet of transparent material whose
electrical conductivity increases with the intensity of EM radiation falling
on it. The variation in conductivity across the plate is measured by a
sweeping electron beam and converted into a video signal. Now largely
replaced by cameras employing arrays of charge-coupled devices
(ccds).
Vignetting
A gradual change in overall tone of an image from the center outwards,
caused by the imaging device gathering less radiation from the
periphery of its field of view than from the center. Most usually
associated with the radially increasing angel between a lens and the
Earth's surface, and the corresponding decrease in the light-gathering
capacity of the lens.
Visible radiation
Energy at wavelengths from 0.4 to 0.7mm that is detectable by the
human eye.
Visual dissonance
The disturbing effect of seeing a familiar object in an unfamiliar setting
or in an unexpected color.
VISSR
Visible Infrared Spin-Scan Radiometer carried by the GOES satellites.
Volume scattering
In radar, interaction between electromagnetic radiation and the interior
of a material.
Glossary-30
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