An optical instrument which consists of a sighting telescope mounted so that it is free to rotate around horizontal and vertical axes, with graduated scales so that the angles of rotation may be measured. Used to observe the motion of a pilot balloon.

To free something from the binding action of ice by warming it to a temperature above the melting point of ice. Also, a warm spell when ice and snow melt.

Rate of wind movement in distance per unit time.

See calorie.

A unit of pressure which directly expresses the force exerted by the atmosphere. Equal to 1000 dynes/cm2 or 100 pascals.

The amount of precipitation captured by a rain gauge.

The temperature registered by a thermometer with its bulb at the level of the tops of the grass blades in short turf.

The temperature to which a sample of air must be cooled, while the mixing ratio and barometric pressure remain constant, in order to attain saturation by water vapor. When this temperature is below O

A river gauge in which a weight suspended on a wire is lowered to the water surface from a bridge or other overhead structure to measure the distance from a point of known elevation to the water surface.

The smallest change in the environment that causes detectable change in the indication of an instrument. Compare to sensitivity.

The source of illumination for an antenna reflector. Also called antenna feed.

A special form of the aspiration psychrometer. developed by Assmann, in which the thermometric elements are well shielded from radiation. Psychrometric measurements may be taken with the instrument in the presence of direct solar radiation.

Electromagnetic radiation lying within the wavelength interval to which the human eye is sensitive, the spectral interval from approximately 0.4 to 0.7 microns (4000 to 7000 angstroms). Bounded on the short-wavelength end by ultraviolet radiation and on t ...

The range of operating conditions of a device within which operating influences are negligible. The range is usually narrow. Reference operating conditions are the conditions under which reference performance is stated and the base from which the values o ...

The standard deviation of a sufficiently large number of measurements of the same quantity by the same instrument or method. The non-correctable part of the inaccuracy of an instrument, it represents the limit of measurement precision. The uncertainty of ...

The process in which incident radiation is retained by a substance. A further process always results from absorption.

Radiation with wavelengths greater than 4 microns. (In meteorology, same as infrared radiation.)

A device for measuring the frequency of occurrence of atmospherics whose intensity is greater than a predetermined level.

Instrument used to measure the amount of water evaporated from the soil surface during a given time interval.

The actual time during which physical events take place.