An aneroid barograph designed to record atmospheric pressure variations of very small magnitude.

An instrument which measures the rate of evapotranspiration. It consists of a vegetation soil tank so designed that all water added to the tank and all water left after evapotranspiration can be measured.

Frequency Shift Keying. A form of frequency modulation of a data signal performed by a modem for transmission over dedicated wire or phone lines.

Pertaining to measurements or devices in which the output vanes in discrete steps, i.e. on-off or pulse signals. Compare to analog.

The size of the area comprising a watershed or river basin. Also called catchment area.

The succession of stages through which water passes on the ground and in the atmosphere: evaporation from land or bodies of water, condensation to form clouds, precipitation, accumulation in the soil or in bodies of water, and re-evaporation.

Movernent of water through the soil surface into the soil, or the quantity of water entering the soil. Infiltration is equal to the total precipitation less the losses due to interception by vegetation. retention in depressions on the land surface, evapor ...

General term for any device that measures precipitation: principally a rain gauge or snow gauge.

An instrument used to measure the amount of dew formed on a given surface.

Anemometer which measures wind speed by measuring the degree of cooling of a metal film heated by an electric current. A type of cooling-power anemometer.

See calorie.

The elevation of the water surface in a stream as measured by a river gauge with reference to some arbitrarily selected zero datum.

A momentary decrease in the speed of the wind.

The combined processes by which water is transferred from the earth's surface to the atmosphere: evaporation of liquid or solid water plus transpiration from plants.

An instrument consisting of a series of graduated cylinders possessing selective collection efficiencies. It is used for the measurement of quantities relating to the size distribution of cloud droplets.

A hydrometeor consisting of a visible aggregate of minute water droplets suspended in the atmosphere near the earth's surface. Fog differs from cloud only in that the base of fog is at the earth's surface while clouds are above the surface.

Any emission of light at temperatures below that required for incandescence.

Rate of flow of water past a point in a stream, expressed as volume per unit time, i.e. cubic feet per second.

The sum of solar and terrestrial radiation.

Liquid water at temperatures colder than freezing.