R

R-meter- Analog radar device used in the 1950s to measure the fluctuation rate of the detected target signal from which may be estimated the root-mean-square relative velocity among the scatterers in the pulse volume.

R-scope- A radar display with coordinates of received signal amplitude versus range but differing from the A-display by starting from a range offset from zero.

Radiation Controlled Ballon- RACOON - A zero-pressure balloon flying high above a very cold tropopause in tropical or summer midlatitudes. When the balloon cools and descends at night, its radiation temperature does not change, but its lift increases as it descends to the colder levels. The lost lift is overcome and the balloon floats at a lower altitude without the need for ballast. The flight altitude of the balloon is radiation- controlled.

Radar- (Coined word for radio detection and ranging.) An electronic instrument used for the detection and ranging of distant objects of such composition that they scatter or reflect radio energy.

Radar altimeter- (Also called radio altimeter.) An onboard radar for determining the altitude of an aircraft above an underlying surface. Pulse-radar techniques measure altitude in terms of the transit time of the radar pulse; continuous-wave radar measures altitude in terms of the phase difference between the transmitted and received signals.

Radar hygrometer - An instrument that measures the refractive index of air by determining changes in humidity.

Radar scatterometer- An active microwave instrument designed to infer wind speed and direction by precisely measuring the backscattering cross section (or normalized radar cross section).

Radar signal spectrograph- Analog radar device used in the 1950s to provide the power spectrum of the fluctuations in the received signal intensity, which may be interpreted in terms of the relative velocities among the scatterers in the pulse volume.

Radarscope - A cathode-ray oscilloscope on which radar echoes are displayed.

Radarsonde- (Same as radar wind system.) Use of radar for determining the azimuth, elevation, and range of a balloon- borne target and, from this position information as a function of time, the wind speed and direction.

Radar theodolite- (Also called radio direction finder or radio goniometer or radio theolite.) A radar that is used to obtain the azimuth, elevation, and slant range of an airborne target.

Radar wind system- Use of radar for determining the azimuth, elevation, and range of a balloon- borne target and, from this position information as a function of time, the wind speed and direction.

Radiant energy thermometer - (Same as radiation thermometer.) An instrument that determines the blackbody temperature of a substance by measuring its thermal radiation. The substance need not be thermally black over the whole spectrum, since it is possible to limit the measurement to those frequencies where it is black.

Radiation shield- A device used on certain types of instruments to prevent unwanted radiation from biasing the measurement of a quantity.

Radio acoustic sounding system - A ground-based remote sensing method that combines radar and acoustic techniques to determine the vertical profile of virtual temperature, often used in conjunction with wind profilers.

Radio atmometer - An instrument designed to measure the effect of sunlight upon evaporation from plant foliage.

Radio beacon- A type of radio transmitter system having wide-angle coverage. It may emit signals continuously or, like the transponder, may respond to a received signal before operating.

Radioactive snow gauge- A device that automatically and continuously records the water equivalent of snow on a given surface as a function of time. A small sample of a radioactive salt is placed in the ground in a lead-shielded collimator that directs a beam of radioactive particles vertically upward. A Geiger–Müller counting system (located above the snow level) measures the amount of depletion of radiation caused by the presence of the snow.

Radiomaximograph- A device for measuring the field strength of spherics.

Radiometer- An instrument that measures radiated electromagnetic power. Radiometers operating at infrared and microwave frequencies are used in passive atmospheric remote sensing.

Radiosonde - An expendable meteorological instrument package, often borne aloft by a free-flight balloon, that measures, from the surface to the stratosphere, the vertical profiles of atmospheric variables and transmits the data via radio to a ground receiving system.

Radiosonde balloon - A balloon used to carry a radiosonde aloft. Radiosonde balloons are larger than pilot balloons and ceiling balloons, are generally filled with hydrogen or helium to achieve lift, and burst at altitudes of about 30 km in daytime and 25 km at night.

Radome- A dome used to cover the antenna assembly of a radar to protect it from the effects of weather.

Raindrop spectrograph- An instrument that automatically determines the raindrop size distribution.

Rain gauge - Any instrument designed to measure rain amount; includes recording, nonrecording, and rain-intensity gauges.

Rain gauge shield- (Also called rain-gauge wind shield or wind shield.) A device that surrounds a rain gauge and acts to maintain horizontal flow in the vicinity of the funnel so that the catch will not be influenced by eddies generated near the gauge.

Rain intensity gauge- (Also called rain-rate gauge, rate-of-rainfall gauge.) An instrument that measures the rate at which rain is falling.

Rain simulator- (Also called sprinkler infiltrometer.) A device used for rainfall-runoff studies, erosion plot studies, and infiltration that applies water in the form and at a rate comparable with natural rainfall.

Ram penetrometer- (Also called ramsonde.) A cone-tipped metal rod designed to be driven downward into deposited snow or firn. The measured amount of force required to drive the rod a given distance is an indication of the physical properties of the snow or firn.

Range height indicator- A type of radar display on which the reflectivity or other properties of echoes are displayed as a function of range and elevation angle in polar coordinates.

Rate of climb indicator- An instrument that shows the rate at which an aircraft is gaining or losing altitude. It is in actuality a rate-of-pressure-change indicator, a sensitive aircraft aneroid barometer with a slow leak to the aneroid capsule calibrated in terms of altitude change.

Rating flume- A flume used for the purpose of calibrating flow measuring devices.

Receiver- An instrument used to detect the presence of and to determine the information carried by electromagnetic radiation.

Recording albedometer- An instrument that chronicles the ratio of the radiation reflected by a surface to the radiation incident upon it.

Recording instrument- A device that makes a record (written or by other means) of observations of a meteorological quantity.

Recording potentiometer - An instrument that automatically records as a function of time the voltage applied to it. It is frequently used in meteorology in conjunction with thermocouples to record temperature.

Recording rain gauge- An instrument that automatically records the amount of precipitation collected as a function of time.

Reflection nephoscope- (Also called mirror nephoscope or cloud mirror.) A nephoscope in which the motion of the cloud is observed by its reflection in a mirror.

Reflector - The part of a radio or radar antenna system that focuses and directs the transmitted wave.

Refractometer- An instrument for measuring the index of refraction of a liquid, gas, or solid. Refractometers in general use in meteorology operate in the microwave region and are based on the principle that the resonant frequency of a cavity depends on the dielectric constant of its contents. In the Crain refractometer, a microwave oscillator is stabilized by the cavity at its resonant frequency. Two such stabilized systems are used, one with a sealed cavity and one with a perforated cavity open to the atmosphere. These are spaced in frequency by 30–50 MHz, and the difference frequencies are measured. The change in difference frequency is almost linearly related to the change in refractive index of the perforated cavitys contents. The Birnbaum refractometer is similar in its operating principles.

Regular reflector- (Also called specular reflector.) A mirrorlike surface for which the angle of reflection equals the angle of incidence; to be contrasted with a diffuse reflector. Most natural surfaces are too irregular to act as good specular reflectors of solar radiation, the main exception being calm water surfaces.

Relative ionospheric opacity meter- (Also called riometer.) A device for measuring the electromagnetic capacity of the ionosphere using the strength of a cosmic radio source relative to that during minimums of ionospheric disturbances.

Resistance thermometer- (Also called electrical resistance thermometer) A type of electrical thermometer in which the thermal element is a substance with an electrical resistance that varies with the temperature.

Resonator- In radio and radar applications, a circuit that will resonate at a certain frequency, or over a range of frequencies, when properly excited. An important type of resonator is the cavity resonator, a closed hollow volume having conducting walls. The frequency at which such cavities resonate is a function of their volume and shape. They are used for making accurate frequency comparisons and for generating radio frequencies, usually in the microwave region.

Responder- In general, an instrument that indicates reception of an electric or electromagnetic signal.

Retreater- A defective maximum thermometer of the liquid-in-glass type in which the mercury flows too freely through the constriction.

Retroreflector - Any instrument used to cause reflected radiation to return along paths parallel to those of their corresponding incident rays.

Reversing thermometer- A mercury-in-glass thermometer that records temperature upon being inverted and thereafter retains its reading until returned to the first position.

Rime rod- A simple, cooled cylindrical rod, usually of metal or glass, that is exposed to the airflow in a cloud to collect supercooled cloud droplets for chemical analysis.

River gauge - (Also called stream gauge.) A device for measuring the river stage.

Robitzsch actinograph- A pyranometer developed by M. Robitzsch. Its design utilizes three bimetallic strips that are exposed horizontally at the center of a hemispherical glass bowl. The outer strips are white reflectors, and the center strip is a blackened absorber. The bimetals are joined in such a manner that the pen of the instrument deflects in proportion to the difference in temperature between the black and white strips and is thus proportional to the intensity of the received radiation. This instrument must be calibrated periodically.

Rocketsonde- A meteorological instrument package that measures vertical profiles of atmospheric winds and either temperature or density upon descent after ejection from a rocket at or near apogee.

Rotating-beam ceilometer- An automatic, active, remote-sensing instrument for detecting the presence of clouds overhead and measuring the height of their bases.

Rotating multicylinder- 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.

Rotoscope- A device used in experimental meteorology for viewing the relative motions in a rotating fluid system.