EM 1110-2-2907
1 October 2003
Areal
Relating to or involving an area.
Artifact
A feature on an image, which is produced by the optics of the system or
by digital image processing, and sometimes masquerades as a real
feature.
ASA index
Index of the American Standards Association designating film speed, or
sensitivity to light. Higher values indicate higher sensitivity. The ASA
index has been replaced by the ISO index.
Ascending node
Direction satellite is traveling relative to the Equator. An ascending
node would imply a northbound Equatorial crossing.
ATI
Apparent Thermal Inertia.
Atmosphere
Layer of gases that surrounds some planets.
Atmospheric correction
Image-processing procedure that compensates for effects of selectivity
scattered light in multispectral images.
Atmospheric shimmer
An effect produced by the movement of masses of air with different
refractive indices, which is most easily seen in the twinkling of stars.
Atmospheric window
Wavelength interval within which the atmosphere readily transmits
electromagnetic radiation.
Attributes
Attributes, also called feature codes or classification attributes, are
used to describe map information represented by a node, line, or area.
For example, an attribute code for an area might identify it to be a lake
or swamp; an attribute code for a line might identify a road, railroad,
stream, or shoreline.
Attitude
Angular orientation of remote sensing system with respect to a
geographic reference system.
AVHRR
Advanced Very High Resolution Radiometer, a multispectral imaging
system carried by the TIROS-NOAA series of meteorological satellites.
AVIRIS
Airborne visible and infrared imaging spectrometer.
Azimuth
Geographic orientation of a line given as an angle measured in degrees
clockwise from north.
Azimuth direction
In radar images, the direction in which the aircraft is heading. Also
called flight direction.
Azimuth resolution
In radar images, the spatial resolution in the azimuth direction.
B
Background
Area on an image or the terrain that surrounds an area of interest, or
target.
Backscatter
In radar, the portion of the microwave energy scattered by the terrain
surface directly back toward the antenna.
Backscatter coefficient
A quantitative measure of the intensity of energy returned to a radar
antenna from the terrain.
Band
A wavelength interval in the electromagnetic spectrum. For example, in
Landsat images the bands designate specific wavelength intervals at
which images are acquired.
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.
Base height ratio
Air base divided by aircraft height. This ratio determines vertical
exaggeration on stereo models.
Glossary-3
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