A measure of the relative power, or of the relative values of two flux densities, especially of sound intensities and radar power densities. The decibel is derived from the less frequently used unit, the bel, named in honor of Alexander Graham Bell.

An instrument used to indicate wind direction.

A method of streamflow routing which assumes that storage is a linear function of the weighted flow in the reach and is adaptable to a simple mathematical solution.

A basic equation in night visual range theory, relating the illuminance of a point source of light to distance and the transmissivity of the atmosphere.

The condition of the atmosphere when the amount of water vapor present is the maximum possible at the existing temperature.

meter-An instrument for measuring the transmissivity of the atmosphere; a type of transmissometer. It consists of a constant- intensity collimated light source located at a suitable distance from a photoelectric cell. Variation in the turbidity of the atm ...

A general term for instruments designed to measure the speed or force of the wind.

A measure, proposed by Angstrom, of the precipitation effectiveness of a region.

A unit of distance equal to 5280 feet. It is sometimes referred to as a land mile.

A rainbow seen in the spray of the ocean. It is optically the same phenomenon as the ordinary rainbow.

See calorie.

A technique for making winds aloft observations in which two theodolites located at either end of a baseline follow the ascent of a pilot balloon. Synchronous measurements of the elevation and azimuth angles of the balloon. taken at periodic intervals, pe ...

A transducer which converts electromagnetic radiation in the infrared, visible, and ultraviolet regions into electrical quantities such as voltage, current, or resistance. Also called photo cell.

A defective maximum thermometer of the liquid-inglass type in which the mercury flows too freely through the constriction. Such a thermometer will indicate a maximum temperature that is too low.

An instrument designed to measure the effect of sunlight on evaporation from plant foliage. It consists of a porous clay atmometer whose surface has been blackened so that it absorbs radiant energy.

A generic term for any machine that enables a human being to communicate with a computer.

A hydrostatic principle that pressure supplied to an enclosed fluid is transmitted undiminished to every portion of the fluid and to the walls of the containing vessel.

That temperature at which, in a specified latitude, the reading of a particular barometer requires no temperature or latitude correction.

Abbreviation for precipitation-evaporation quotient.

The difference between the true value of some quantity and its observed value. Every observation is subject to certain errors. Systematic errors affect the whole of a series of observations in nearly the same way. For example, the scale of an instrument m ...