English

(U.S. disk). Rotating storage medium composed of one or two usable surfaces or a vertical assembly of such discs with a common axis. Typically discs combine high storage volumes and short access time allowing fast access to data which is distributed randomly over the medium.

Unnatural coloured areas in the SEA due to the existence of SHOALS. SEA WATER having a colour other than the blues and greens normally seen. Variations of the colours red, yellow, green and brown, as well as black and white, have been reported. Dis­colorations may appear in patches, streaks, or large areas and may be caused by concentrations of inorganic or organic particles or PLANKTON. See RED TIDE.

A difference between results of duplicate or comparable measures of a quantity. The difference in computed values of a quantity obtained by different processes using DATA from the same SURVEY.

A radar circuit that produces a RESPONSE which depends upon the FREQUENCY of the input signal. A transponder beacon circuit which accepts PULSES of proper duration and rejects others. That part of a frequency modulation receiver which converts the modulated SIGNALS directly into audiofrequency signals.

The separation of RADIANT ENERGY into its various components. In optics, the separation of light into its component colours by its passage through a diffraction grating or by REFRACTION such as that provided by a prism. In OCEANOGRAPHY, the separation of a complex surface gravity wave disturbance into its component parts.

In RADIOLOCA­TION, the half of the band of uncertainty having as its centre line an ELECTRONIC LINE OF POSITION. In PHOTOGRAMMETRY, any shift in the position of an IMAGE on a PHOTOGRAPH which does not alter the perspective characteristics of the PHOTOGRAPH (i.e. shift due to TILT of the PHOTOGRAPH, scale change in the PHOTOGRAPH, and RELIEF of the objects photographed).

A RADIOBEACON equipped with a synchronized SOUND SIGNAL to provide a means of determining distances from the source of the SOUND, by measuring the difference in the time of reception of the SIGNALS.

An undesired change in WAVEFORM. In optics, an aberration affecting the position of the IMAGES off the AXIS, in which objects at different ANGULAR DISTANCES from the AXIS undergo different MAGNIFICATIONS. Also called lens distortion. In PHOTOGRAPHY, any shift in the position of an IMAGE on a PHOTOGRAPH which alters the perspective characteristics of the PHOTOGRAPH. Causes of image distortion include lens aberration, DIFFERENTIAL SHRINKAGE of film or paper, and motion of the film or CAMERA.