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.

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.