EM 1110-2-2907
1 October 2003
Principal-component (PC)
Digitally processed image produced by a transformation that recognizes
image
maximum variance in multispectral images.
Principal point
Optical center of an aerial photograph.
Printout
Display of computer data in alphanumeric format.
Probability density
A function indicating the relative frequency with which any
function (PDF)
measurement may be expected to occur. In remote sensing it is
represented by the histogram of DN in one band for a scene.
Projection
Orderly system of lines on a plane representing a corresponding
system of imaginary lines on an adopted terrestrial or celestial datum
surface. Also, the mathematical concept of such a system. For maps of
the Earth, a projection consists of (1) a graticule of lines representing
parallels of latitude and meridians of longitude or (2) a grid.
Pulse
Pulse length
Duration of a burst of energy transmitted by a radar antenna, measured
in microseconds.
Pushbroom scanner
An alternate term for an along-track scanner
Pushbroom system
An imaging device consisting of a fixed linear array of many sensors,
which is swept across an area by the motion of the platform, thereby
building up an image. It relies on sensors whose response and reading
is nearly instantaneous, so that the image swathe can be segmented
into pixels representing small dimensions on the ground.
Q
Quantum
The elementary quantity of EM energy that is transmitted by a particular
wavelength. According to the quantum theory, EM radiation is emitted,
transmitted, and absorbed as numbers of quanta, the energy of each
R
Radar
Acronym for radio detection and ranging. Radar is an active form of
remote sensing that operates in the microwave and radio wavelength
regions.
Radar altimeter
A non-imaging device that records the time of radar returns from
vertically beneath a platform to estimate the distance to and hence the
elevation of the surface; carried by Seasat and the EAS-ERS-1
platforms.
Radar cross section
A measure of the intensity of backscattered radar energy from a point
target. Expressed as the area of a hypothetica surface, which scatters
radar equally in all directions and which would return the same energy
to the antenna.
Radar scattering
A measure of the back-scattered energy from a target with a large area.
coefficient
Expressed as the average radar cross section per unit area in decibels
(db). It is the fundamental measure of the radar properties of a surface.
Radar scatterometer
A non-imaging device that records radar energy backscattered from
terrain as a function of depression angle.
Radar shadow
Dark signature on a radar image representing no signal return. A
shadow extends in the far-range direction form an object that intercepts
the radar beam.
Radial relief displacement
The tendency of vertical objects to appear to learn radially away from
the center of a vertical aerial photograph. Caused by the conical field of
view of the camera lens.
Radian
Angle subtended by an arc of a circle equal in length to the radius of
the circle 1 rad = 57.3.
Glossary-23
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