Calibration
Process of comparing an instrument's measurements with a standard.

Calorie
Amount of heat required to raise the temperature of 1g of water by 1 °C.

Camouflage detection photographs
Another term for IR color photograph.

Cardinal point effect
In radar, very bright signatures caused by optimally oriented corner reflectors, such as buildings.

Cathode ray tube (CRT)
A vacuum tube with a phosphorescent screen on which images are displayed by an electron beam.

CCD
Charge-coupled detector.

Cell assemblies
The linked receptors, retinal neurons, and neural cells in the visual cortex of the brain which enable interaction between perception and past experience.

Centerpoint
The optical center of a photograph.

Change-Detection Images
A difference image prepared by digitally comparing images acquired at different times. The gray tones or colors of each pixel record the amount of difference between the corresponding pixels of the original images.

Charge-coupled detector (CCD)
A device in which elect surface of a semiconductor.

Chlorosis
Yellowing of plant leaves resulting from an imbalance in the iron metabolism caused by excess concentrations of copper, zinc, manganese, or other elements in the plant.

Chromatic vision
The perception by the human eye of changes in hue.

Circular scanner
Scanner in which a faceted mirror rotates about a vertical axis to sweep the detector IFOV in a series of circular scan lines on the terrain.

Classification
Process of assigning individual pixels of an image to categories, generally on the basis of spectral reflectance characteristics.

Coastal zone color scanner (CZCS)
A satellite-carried multi-spectral scanner designed to measure chlorophyll concentrations in the oceans.

Coherent radiation
Electromagnetic radiation whose waves are equal in length and are in phase, so that waves at different points in space act in unison, as in laser and synthetic aperture radar.

Color composite image
Color image prepared by projecting individual black-and-white multispectral images, each through a different color filter. When the projected images are superposed, a color composite image results.

Color ratio composite image
Color composite image prepared by combining individual ratio images for a scene using a different color for each ratio image.

Complementary colors
Two primary colors of light (one additive and the other subtractive) that produce white light when added together. Red and cyan are complimentary colors.

Conduction
Transfer of electromagnetic energy through a solid material by molecular interaction.

Cones
Receptors in the retina which are sensitive to colour. There are cones sensitive to the red, green, and blue components of light.

Contact print
A reproduction from a photographic negative in direct contact with photosensitive paper.

Context
The known environment of a particular feature on an image.

Contrast
The ratio between the energy emitted or reflected by an object and its immediate surroundings.

Contrast enhancement
Image-processing procedure that improves the contrast ratio of images. The original narrow range of digital values is expanded to utilize the full range of available digital values.

Contrast ratio
On an image, the ratio of reflectances between the brightest and darkest parts of an image.

Contrast stretching
Expanding a measured range of digital numbers in an image to a larger range, to improve the
contrast of the image and its component parts.

Convection
Transfer of heat through the physical movement of heated matter.

Corner reflector
Cavity formed by two or three smooth planar surfaces intersecting at right angles. Electromagnetic waves entering a corner reflector are reflected directly back toward the source.

Cross
polarized-Describes a radar pulse in which the polarization direction of the return is normal to the polarization direction of the transmission. Cross-polarized images may be HV (horizontal transmit, vertical return) or VH (vertical transmit, horizontal return).

Cross
track scanner-Scanner in which a faceted mirror rotates about a horizontal axis to sweep the detector IFOV in a series of parallel scan lines oriented normal to the flight direction.

CRT
Cathode ray tube.

Cut off
The digital number in the histogram of a digital image which is set to zero during contrast stretching. Usually this is a value below which atmospheric scattering makes a major contribution.

Cycle
One complete oscillation of a wave.