The visibility along an identified runway, determined from a specified point on the runway with the observer facing in the same direction as a pilot using the runway. Compare to runway visible range.

The intensity (flux per unit solid angle) of visible radiation weighted to take into account the variable response of the human eye as a function of the wavelength of light. Usually expressed in candles.

In general, solar radiation received at the earth's surface. Contracted from incoming solar radiation.

A systematic observational error due to the characteristics of the observer. The uncertainty in a reading made by an observer may be acertained by a statistical analysis of his or her readings.

The sum of solar and terrestrial radiation.

An instrument for the measurement of the rate of ice accretion on an unheated body.