HOPKINS GLOSSARY OF WEATHER TERMS R

radar (radio detection and ranging)

• An electronic instrument that broadcasts a microwave electromagnetic radiation signal and receives the reflected portion of this signal from a target. In meteorology, the signal from a weather radar unit is reflected and scattered from precipitation particles (rain, hail, snow) to determine the location, height and intensity of precipitation areas; comparison of multiple radar echoes permits determination of changes in intensity and the speed and direction of the areal movement. See also Doppler radar .

radio-direction finder

• An instrument that intercepts and uses electromagnetic radiation in the radio portion of the spectrum to determine the direction of the radio transmitter.

radiometer

• Any instrument or device that senses and measures the radiant energy in electromagnetic radiation.

radiosonde

• A small, expendable, balloon-borne instrument package with a radio transmitter used to measure the air temperature, pressure and humidity of the atmosphere above the earth's surface to approximately 30 km; the wind direction and wind speed aloft are determined from ground based tracking of the radiosonde; see also rawinsonde . The weather data are electronically transmitted to the launch station, where they are decoded and plotted as a sounding.

rain gauge- Any instrument used to measure the total amount of precipitation that falls upon a given unit area during a specified time interval. Gauges can be adapted to collect snow for the determination of liquid water equivalent of snowfall. Recording rain gauges measure precipitation rates over fixed time intervals to provide an indication of rainfall intensity . Essentially all gauges are calibrated in units of depth of accumulation, e.g., millimeters or inches.

range - (1) The distance between two objects, usually an observation point and an object under observation, see also slant range and horizontal range. (2) A maximum distance attributable to some process, as in visual range, radar range or the "range'' of an aircraft.

Range Height Indicator (RHI)

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rawinsonde - An upper-air weather observation system (from the surface to approximately 30 km altitude) made by balloon-borne instrument package (radiosonde) that provides direct measurement of ambient air temperature, pressure, and humidity as well as the evaluation of the wind speed and direction aloft by means of tracking the position change of the radiosonde by directional radio techniques.

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reflectivity

relative humidity

• At a given ambient air temperature, the dimensionless ratio between the actual vapor pressure of air to the saturation vapor pressure. Corresponding ratios of mixing ratio can be substituted. Relative humidity is usually expressed as a percentage.

remote

remote sensing

resistance thermometer

• An electrical-type thermometer that utilzes a thermal element consisting of a material whose electrical resistance varies with temperature. A thermistor is a variety of resistance therometer commonly used onboard radiosondes.

ROBIN

1. Acronym for ROcket Balloon INstrument.

rocketsonde

• An instrument package carried aloft by a meteorological rocket to make a measure one or more weather elements in a sounding of the upper atmosphere, at altitudes usually higher than can be obtained by radiosonde or aircraft.

rocket sounding

• A probe of the upper atmosphere with a meteorological rocket to produce a record of the vertical variation of a weather element such as air temperature, density, composition or winds.