EM 1110-2-2907
1 October 2003
Radiance
Measure of the energy radiated by an object. In general, radiance is a
function of viewing angle and spectral wavelength and is expressed as
energy per solid angle.
Radiant energy peak
Wavelength at which the maximum electromagnetic energy is radiated
at a particular temperature.
Radiant flux
Rate of flow of electromagnetic radiation measured in watts per square
centimeter.
Radiant temperature
Concentration of the radiant flux from a material. Radiant temperature
is the kinetic temperature multiplied by the emissivity to the one-fourth
power.
Radiation
Propagation of energy in the form of electromagnetic waves.
Radiometer
Device for quantitatively measuring radiant energy, especially thermal
Random line dropout
In scanner images, the loss of data from individual scan lines in a
nonsystematic fashion.
Range
In radar usage this is the distance in the direction of radar propagation,
usually to the side of the platform in an imaging radar system. The slant
range is the direct distance from the antenna to the object, whereas the
distance from the ground track of the platform to the object is termed
the ground range.
Range direction
See look direction.
Range resolution
In radar images, the spatial resolution in the range direction, which is
determined by the pulse length of the transmitted microwave energy.
Raster
The scanned and illuminated area of a video display, produced by a
modulated beam of electrons sweeping the phosphorescent screen line
by line from to bottom at a regular rate of repetition.
Raster format
A means of representing spatial data in the from of a grid of DN, each
line of which can be used to modulate the lines of a video raster.
Raster pattern
Pattern of horizontal lines swept by an electron beam across the face of
a CRT that constitute the image display.
Ratio image
An image prepared by processing digital multi-spectral data as follows:
for each pixel, the value for one band that is divided the value of
another. The resulting digital values are displayed as an image.
Rayleigh criterion
In radar, the relationship between surface roughness, depression
angle, and wavelength that determines whether a surface will respond
in a rough or smooth fashion to the radar pulse.
Rayleigh scattering
Selective scattering of light in the atmosphere by particle that is small
compared with the wavelength of light.
RBV
Return-beam vidicon.
Real-aperture radar
Radar system in which azimuth resolution is determined by the
transmitted beam width, which is in turn determined by the physical
length of the antenna and by the wavelength.
Real time
Refers to images or data made available for inspection simultaneously
with their acquisition.
Recognizability
Ability to identify an object on an image.
Rectilinear
Refers to images with no geometric distortion in which the scales in the
horizontal and vertical directions are identical.
Redundancy
Information on an image, which is either not, required for interpretation
or cannot be seen. Redundancy may be spatial or spectral. The term
also refers to multispectral data where the degree of correlation
between bands is so high that one band contains virtually the same
information as all the bands.
Reflectance
Ratio of the radiant energy reflected by a body to the energy incident on
it. Spectral reflectance is the reflectance measured within a specific
wavelength interval.
Glossary-24
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