S

Salinometer- Any device or instrument for determining salinity, especially one based on electrical conductivity methods.

San marco satellite- A series of satellites from the 1960s developed jointly by the United States and Italy.

Satellite infrared spectrometer- (Abbreviated SIRS.) The first space-based, grating spectrometer used for vertical temperature soundings of the atmosphere. SIRS was flown on Nimbus-3 and -4 launched in April 1969 and April 1970, and was a forerunner of the HIRS-2 operational instrument on the TIROS-N satellites since 1978.

Satellite sounding- Measurements of various atmospheric parameters (such as temperature or water vapor) at various heights or pressure levels, as derived from satellite-based sensors.

Satellite - 1. An artificial platform placed into orbit around the earth, often carrying instruments to gather environmental data. 2. Any natural or man-made object that orbits about an astronomical body.

Savart polariscope - A polariscope consisting of a specially constructed double plate polarizer and a tourmaline plate analyzer. Polarized light passing through the instrument is indicated by the presence of parallel colored fringes, while unpolarized light results in a uniform field. See Voss polariscope.

Scanning microwave spectrometer - (Abbreviated SCAMS) A five channel scanning radiometer on Nimbus-6 (launched June 1975) used to measure temperatures over ocean surfaces, water vapor, and liquid water. SCAMS was a precursor to the MSU used operationally on the TIROS-N (NOAA series) satellites since 1978.

Scanning multifrequency microwave radiometer- (Abbreviated SMMR) An instrument designed to measure precipitation rate, column-integrated liquid water and water vapor, sea surface temperature and wind speed, soil moisture, and sea ice concentration. This radiometer flew on Seasat (launched in June 1978) and Nimbus-7 (launched in October 1978).

Scanning radiometer- A radiometer that used a rotating or an oscillating plane mirror to scan a path normal to the movement of the instrument.

Scatterometer - A radar system that infers wind speed by measuring the backscattering cross section (or normalized radar cross section).

Scintillometer - (Also called scintillation meter.) A type of photoelectric photometer used in a method of determining high-altitude winds on the assumption that stellar scintillation is caused by atmospheric inhomogeneities (schlieren) being carried along by the wind near tropopause level.In one design a star is observed with a single telescope that looks through a four-inch long rotatable slit. Two scintillation frequencies are monitored, one high and one low. The slit is rotated until the ratio of high-frequency to low-frequency scintillation is a minimum. At this point, the slit is oriented parallel to the wind.The magnitude of the frequency ratio is a function of the wind speed. In another design,two telescopes mounted four inches apart are focused on a star.Only one frequency need be monitored. By direct observation of phase relationships as the telescopes are rotated about a mutual axis, both direction and speed can be determined with less ambiguity and uncertainty than with the single telescope type.

Scrubber - A flue gas system that removes most of the sulfur dioxide, SO2, from exhaust gases; generally used for large coal-fired boilers.

Sea-viewing wide field of view sensor- (Acronym SeaWiFS.) A multispectral ocean color sensor developed by NASA and carried on the SeaStar satellite. The scanner produces imagery from six visible and two near-infrared spectral bands optimized for the study of ocean color.

Search radar- A radar designed to determine the approximate location of objects, usually aircraft or ships. The beams of such radars, called fan beams, are usually wider in the vertical than in the horizontal, making it possible to scan large volumes of space quickly. Compare tracking radar.

Seasat- A satellite designed to demonstrate the feasibility of global ocean monitoring from space. After a successful launch on 28 June 1978, Seasat produced promising results, but the mission was terminated after only three months following a failure in the satellite's electrical system.Instrumentation flown on Seasat included a radar altimeter, a microwave scatterometer for measuring surface wind speed and direction, a scanning multichannel microwave radiometer for sea surface temperature, a visible and infrared radiometer, and the first spaceborne synthetic aperture radar.

Seastar- A satellite system jointly developed by NASA and private industry to measure ocean color for research and operations. Ocean color reveals the presence and concentration of phytoplankton, sediments, and dissolved organic chemicals in the uppermost layers of the ocean. Measurements are made with SeaWiFS, a multispectral imaging spectrometer. SeaStar was successfully launched on 1 August 1997.

Seawater thermometer - A thermometer designed for use in measuring the temperature of seawater. One form of this instrument consists of a mercury-in-glass thermometer protected by a perforated metal case. This is used to measure the temperature of a sample of seawater. Another form consists of a mercury-in-glass thermometer surrounded by a metal case that forms a well around the bulb of the thermometer. When the thermometer is raised from the water, a sample is retained in the well for temperature measurement. See reversing thermometer, bucket thermometer.

Sectorized image - Satellite imagery that is reformatted into subsections covering specified geographic areas.

Sediment sampler- The apparatus or equipment used to take samples of the mixture of fluid and sediment.

Seeder feeder - Orographic precipitation-enhancement mechanism, in which precipitation from an upper-level precipitating cloud (seeder) falls through a lower-level orographic stratus cloud (feeder) capping a hill or small mountain. Precipitation droplets or ice particles fall from the higher seeder cloud and collect cloud water as they pass through the lower feeder cloud by collision and coalescence or accretion, thus producing greater precipitation on the hill under the cap cloud than on the nearby flat land. The effectiveness of the process depends on sufficiently strong low-level moist flow to maintain the cloud water content in the orographic feeder cloud and the continuing availability of precipitation particles from the seeder cloud.

Seeding devices- A generator used for producing cloud seeding particles and injecting them into clouds. The type is selected for the particular seeding material, application, and delivery system. Different types of seeding devices have been used, including combustion burners, pyrotechnic flares, atomizers, dry powder dispersal systems, dry-ice crushers, and dispensers of liquids that cool substantially on evaporation (such as propane or liquid CO2).

Seismograph- An instrument used to measure and record earthquake vibrations and other earth tremors. It consists essentially of a heavy pendulum hung so that it can swing freely in one direction. A pen is attached to the end of the pendulum so that the pendulum's motion, relative to a recorder fixed solidly to the earth, may be determined. A seismological observatory requires three seismographs in order to measure the three component directions of the tremors and to fix approximately their origin. A study of the records of sensitive seismographs has shown that some of the tremors may be attributed to oceanographic and atmospheric phenomena. See microseism.

Selective chopper radiometer- (Abbreviated SCR.) A 16-channel nonscanning radiometer flown on Nimbus-5 (launched December 1972) for sounding the atmosphere in the infrared spectrum.

Sferics receiver - (Also called lightning direction finder.) An instrument that measures, electronically, the direction of arrival, intensity, and rate of occurrence of atmospherics; a type of radio direction finder, it is most commonly used to detect and locate cloud-to-ground lightning discharges from distant thunderstorms. In its simplest form the instrument consists of two orthogonally crossed antennas that measure the electromagnetic field changes produced by a lightning discharge and determine the direction from which the changes arrived. Negative and positive polarity cloud-to-ground discharges can be distinguished. Cloud-to-cloud discharges can be distinguished based on characteristics of the received signal, and the geometry of nearby discharge channels may be determined. See also narrow- sector recorder, lightning detection network.

Shadow band pyranometer - An instrument for measuring the diffuse sky radiation. A shadow band is added to a conventional pyranometer at such an angle that it blocks out the direct solar radiation throughout the course of a day.

Side scanning sonar- A method of surveying the bottom of the ocean or other body of water to obtain detailed acoustic images, frequently used to locate debris, such as from aircraft accidents or sunken ships. The acoustic beam is directed perpendicularly to the direction of travel. The ship moves at a constant velocity, and each sonar ping insonifies a slightly different wedge of bottom. The apparent depth is actually the slant range from the ship to the target. The display is a map of slant range and distance along the track.

Sidelooking radar- An airborne radar used for high-resolution ground mapping that employs a fixed antenna beam pointing out of the side of the aircraft. Narrow azimuth resolution is obtained with a long aperture mounted along the side of the aircraft or by use of synthetic aperture radar processing.

Signal generator - An electronic instrument used for the production of electromagnetic or acoustic signals with certain desired characteristics. It is useful in testing and calibration.

Significant weather chart- Chart displaying the observed or forecast significant weather phenomena at different flight levels that may affect the operation of the aircraft.

Silver disk pyrheliometer- An instrument used for the measurement of direct solar radiation. It consists of a silver disk located at the lower end of a tube containing a diaphragm that serves as the radiation receiver for a calorimeter. Radiation falling on the silver disk is periodically intercepted by means of a shutter located in the tube, causing temperature fluctuations of the calorimeter that are proportional to the intensity of the radiation. The instrument is normally used as a secondary instrument and is calibrated against the water-flow pyrheliometer. It was used by the U.S. Weather Bureau as a standard instrument. Currently, this instrument's function has been replaced by an absolute cavity radiometer. See pyrheliometer, cavity radiometer.

Sine galvanometer- A magnetometer of the electromagnetic type that is used to measure the horizontal intensity of the earth's magnetic field. The instrument serves as a national standard for measurement of this quantity.

Siphon barometer- A mercury barometer so constructed that the upper and lower mercury surfaces have the same diameter. It is not a standard meteorological instrument, but is sometimes utilized for special purposes. See float barograph.

Six's thermometer - A combination of maximum thermometer and minimum thermometer. The tube is shaped in the form of a “U” having a bulb at either end. One bulb is filled with a clear liquid that expands or contracts with temperature variation, forcing before it a short column of mercury having iron indices at either end. The indices remain at the extreme positions reached by the mercury column, thus indicating the maximum and minimum temperatures. The indices can be reset with the aid of a magnet.

Skew T–logp diagram - An emagram (temperature and logarithm of pressure as coordinates) with the isotherms rotated 45° clockwise to produce greater separation of isotherms and dry adiabats.

Skyhook balloon- A large plastic constant-level balloon for duration flying at very high altitudes, used for determining wind fields and measuring upper-atmospheric parameters.

Sling psychrometer- A psychrometer in which the wet- and dry-bulb thermometers are mounted upon a frame connected to a handle at one end by means of a bearing or length of chain. Thus, the psychrometer may be whirled by hand in order to provide the necessary ventilation.

Snow gauge- An instrument for measuring the vertical depth of snow. The eight-inch rain gauge is adapted for snow measurement by removing the funnel and measuring tube so that snow is collected in the overflow can. The weighing rain gauge is also used for measuring snowfall by removing the funnel portion of the collector. Other instruments used for measuring snow depth include the snow sampler and snow stake.

Snow mat- A special device used to mark the surface between old and new snow. It consists of a piece of white duck 28 inches square, having in each corner triangular pockets in which are inserted slats placed diagonally to keep the mat taut and flat. See snow board, snow gauge.

Snow pillow - An instrument designed to provide a direct estimate of water equivalence of a snowpack by measuring the pressure due to the mass of overlying snow.

Snow roller- A rolled-up, cylindrical mass of snow, rather common in mountainous or hilly regions. It occurs when snow, moist enough to be cohesive, is picked up by wind blowing down a slope and rolled onward and downward until it either becomes too large or the ground levels off too much for the wind to propel it farther. Snow rollers vary in size from very small cylinders to some as large as 1.5 m long and more than 2 m in circumference.

Snow stake - (Also called snow scale.) A wooden scale, calibrated in inches or centimeters, used in regions of deep snow to measure its depth. The scale is bolted to a wood post or angle iron set in the ground.

Sodar- (Coined word from sound detection and ranging.) Sound-wave transmitting and receiving equipment operated on principles analogous to those of radar. Irregularities in atmospheric temperature and wind velocity constitute sources of scattering for acoustic waves.Sodars measure vertical profiles of the mean and turbulent properties of the sound to heights of several hundred meters by transmitting acoustic waves upward and measuring the Doppler shift in the backscattered acoustic signals. Sodar is sometimes inappropriately called acoustic radar.

Soil thermograph - A remote-recording thermograph with a sensing element that may be buried at various depths in the earth.

Soil thermometer- (Also called earth thermometer) A thermometer used to measure the temperature of the soil. Two forms of the mercury-in-glass thermometer are used for this purpose. For measurement at small depths, a thermometer with a right-angle bend in the stem is used. The bulb is inserted into a hole in the ground with the stem lying along the surface. A thermometer that has been fused into an outer protecting glass shield is used for measurement at greater depths. Wax is inserted between the bulb and the shield to increase the time constant. To obtain a measurement, the instrument is lowered into a steel tube that has been driven into the soil to the desired depth.

Solar radiation observation - An evaluation of the radiation from the sun that reaches the observation point. The observing instrument is usually a pyrheliometer or pyranometer. Two types of such observations are taken. The more common consists of measurements of the radiation reaching a horizontal surface, consisting of both radiation from the sun (direct solar radiation) and that reaching the instrument indirectly by scattering in the atmosphere (diffuse sky radiation). The second type of observation involves the use of an equatorial mount that keeps the instrument pointed directly at the sun at all times. The sensitive surface of the instrument is normal to the path of solar radiation and is shielded from indirect radiation from the sky.

Solarimeter- 1. A pyranometer developed by W. Gorczy?ski, consisting of a Moll thermopile shielded from the wind by a bell glass. 2. Name sometimes used as a generic term in place of pyranometer.

Sonic anemometer- An anemometer that measures linear components of the wind vector by determining the effect of the wind on transit times of acoustic pulses transmitted in opposite directions across known paths. It operates on the principle that the propagation velocity of a sound wave in a moving medium is equal to the velocity of sound with respect to the medium plus the velocity of the medium. The wind velocity vector is determined by measuring the wind speed along three independent linear paths, for example, three orthogonal paths. The sonic anemometer is an absolute instrument and has the advantages of a very short time constant and an absence of moving mechanical parts.

Sonic thermometer - A thermometer based on the principle that the velocity of a sound wave is a function of the virtual temperature of the medium through which it passes. By transmitting acoustic pulses in opposite directions between two transducers, the travel time difference can be used to infer the virtual temperature, provided that the wind speed across the acoustic path is known. Three-axis sonic anemometers, in addition to measuring three-dimensional winds, are also used as sonic thermometers. Sonic thermometers possess very short time constants and eliminate radiation error.

Sounder - An instrument that acquires multispectral measurements from which vertical profiles of atmospheric temperature and humidity can be derived.

Sounding balloon- A free, unmanned balloon instrumented and/or observed for the purpose of obtaining a sounding of the atmosphere.

Sounding pole- (Also called sounding rod.) Graduated rigid pole or rod for measuring the depth of water.

Special observation- A category of aviation weather observation taken to report significant changes in one or more of the observed elements since the last record observation. The specific criteria demanding a special observation change from time to time. Basically they cover 1) significant changes in ceiling and visibility, particularly in the low ranges; 2) the appearance of low clouds; 3) the appearance and disappearance of a tornado or thunderstorm; 4) the beginning and ending of frozen or freezing precipitation; 5) pressure jumps; and 6) significant changes in the wind.

Special sensor microwave imager- (Abbreviated SSM/I.) A passive conical-scanning multichannel microwave radiometer on DMSP satellites that is used to derive parameters such as land and sea surface temperature, ocean surface wind speed, precipitable water, rainfall rate, and snow/ ice cover.

Special Sensor Microwave Temperature- (Abbreviated SSM/T.) The microwave temperature and water vapor sounders on the DMSP polar-orbiting satellites. SSM/T is a temperature sounder, while SSM/T2 is a water vapor profiler. Many of the capabilities of the SSM/T and SSM/T2 instruments will be duplicated on the AMSU.

Spectral hygrometer- (Also called optical hygrometer.) A hygrometer that determines the amount of precipitable moisture in a given region of the atmosphere by measuring the attenuation of radiant energy caused by the absorption bands of water vapor. The instrument consists of a collimated energy source, separated by the region under investigation from a detector that is sensitive to those frequencies that correspond to the absorption bands of water vapor. The basis for determining the water vapor concentration is Beer's Law: I/ I0 = exp(?kx), where I is the light intensity after passing through the sample, I0 is the incident intensity, x is the pathlength reduced to some absolute standard like STP, and k is the absorption coefficient. The most useful regions of the electromagnetic spectrum for this purpose lie in the ultraviolet and infrared regions. The most widespread application is the monitoring of very-high- frequency variations in humidity, as the time constant of a spectral hygrometer is typically just a few milliseconds. The use of spectral hygrometers remains mostly restricted to research applications. See Krypton hygrometer, Lyman-alpha hygrometer, differential absorption hygrometer.

Spectrobolometer- A bolometer that has some capability to resolve the electromagnetic spectrum.

Spectroheliograph- An instrument for taking photographs (spectroheliograms) of an image of the sun in monochromatic light.

Spectrometer - A generic term for a device that measures the intensity of radiation as a function of frequency (or wavelength) of the radiation or that breaks down any signal into its frequency components.

Spectrophotometer - A photometer that measures the intensity of radiation as a function of frequency (or wavelength) of the radiation. In one design, radiation enters the spectrophotometer through a slit and is dispersed by means of a prism. A bolometer having a fixed aperture scans the dispersed radiation so that the intensity over a narrow wave band is obtained as a function of frequency. See Dobson spectrophotometer.

Spectropyrheliometer- An instrument that measures the spectral distribution of the intensity of direct solar radiation.

Spectroscope - An apparatus to effect dispersion of radiation and visual display of the spectrum obtained.

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.

Spherical pyranometer- Radiometer designed to measure only solar radiation incident on the surface of an infinitesimally small sphere. Practically, the sphere of the radiometer is at least 2 cm in diameter.

Spherical pyrgeometer- Radiometer designed to measure only thermal infrared radiation incident on the surface of an infinitesimally small sphere.

Spherical pyrradiometer- Radiometer designed to measure both solar and thermal infrared radiation incident on the surface of an infinitesimally small sphere.

Spirit thermometer- A liquid-in-glass thermometer that uses an organic substance such as alcohol as the thermometric liquid. This type of thermometer has a very low freezing point and a high coefficient of expansion. The accuracy of thermometers using an organic liquid, however, is much less than that of thermometers using mercury. Spirit thermometers are used when the low freezing point is important, and in such special application as the minimum thermometer.

Static pressure port- A termination device permitting pressure sensors to measure the true atmospheric pressure in the presence of winds.

Stevenson screen- A type of instrument shelter. The shelter is a wooden box painted white with double louvered sides and mounted on a stand 122 cm (4 ft) above the ground. In addition to the dry- and wet-bulb thermometers, it usually contains maximum and minimum thermometers.

Stilling well gauges - An instrument system for measuring sea levels; tidal changes of levels are detected by the movement of a float in a well, which is connected to the open sea by a restricted hole or narrow pipe.

Stratospheric aerosol measurement - (Abbreviated SAM.) A single channel sun photometer centered at 1 micron used to measure aerosol extinction above the earth tangent point by looking at the sun during spacecraft sunrise and sunset. SAM was initially tested as a hand-held sun photometer on Apollo–Soyuz in 1975. A follow- on SAM-II instrument was carried onboard Nimbus-7 (launched October 1978).

Stratospheric and Mesospheric Sounder- (Abbreviated SAMS.) A multichannel infrared limb sounder on Nimbus-7 (launched October 1978) designed to extract vertical temperature soundings from upper atmospheric emissions.

Stratospheric sounding unit- (Abbreviated SSU.) A three-channel infrared sounder on operational NOAA polar-orbiting satellites. The three channels are used to determine profiles of temperature in the stratosphere.

Stream hydrograph- A plot of stream discharge as a function of time.

Subsurface float- A centrally buoyant device, designed to drift at a specific depth below the water's surface, used to measure water velocity at that depth.

Sun-synchronous satellite- A satellite in an orbit that precesses 360° during the course of the year, permitting the satellite to obtain views of a given geographical area at the same local time each day. A sun-synchronous satellite always crosses the equator on the ascending node at the same local solar time.

Sunshine recorder- An instrument designed to record the duration of sunshine without regard to intensity at a given location. Sunshine recorders may be classified into two groups according to the method by which the recorder timescale is obtained. In one class of instruments the timescale is obtained from the motion of the sun in the manner of a sundial (see Campbell–Stokes recorder, Jordan sunshine recorder, Pers sunshine recorder). In the second class of instruments the timescale is supplied by a chronograph (see Marvin sunshine recorder). Compare actinometer; see also heliograph, twilight correction.

Surface chart- —(Also called surface map, sea level chart, sea level pressure chart.) An analyzed chart of surface weather observations. Essentially, a surface chart shows the distribution of sea level pressure, including the positions of highs, lows, ridges, and troughs and the location and character of fronts and various boundaries such as drylines, outflow boundaries, sea-breeze fronts, and convergence lines. Often added to this are symbols of occurring weather phenomena, analysis of pressure tendency (isallobars), indications of the movement of pressure systems and fronts, and perhaps others, depending upon the intended use of the chart. Although the pressure is referred to mean sea level, all other elements on this chart are presented as they occur at the surface point of observation. A chart in this general form is the one commonly referred to as the weather map. When the surface chart is used in conjunction with constant-pressure charts of the upper atmosphere (e.g., in differential analysis), sea level pressure is usually converted to the height of the 1000-mb surface. The chart is then usually called the 1000-mb chart.

Surface composition mapping radiometer- (Abbreviated SCMR.) A three-channel scanning radiometer on Nimbus-5 (launched December 1972) measuring radiation in the visible and infrared spectrum to determine the composition of the earth's surface.

Surface forecast chart- Prognostic chart for a given time, that is, 24 hours ahead of the surface synoptic situation.

Surface thermometer - In oceanography, a thermometer used in a bucket of seawater to measure sea surface temperature.

Swallow float- In oceanography, a special drifting buoy named after British Oceanographer John Swallow that is neutrally buoyant and can measure subsurface conditions.

Synchronous Meteorological satellites- The first operational geostationary meteorological satellites. SMS-1 was launched in 1974, following the success of the ATS series of experimental geosychronous satellites. The ATS and SMS satellites were operated by NASA. was followed by the GOES series of satellites operated by NOAA.

Synoptic chart- In meteorology, any chart or map on which data and analyses are presented that describe the state of the atmosphere over a large area at a given moment in time. The possible variety of such charts is almost limitless, but in meteorological history there has been a more or less standard set of synoptic charts, including surface charts and the constant- pressure charts of the upper air.other synoptic charts include isentropic charts and constant- height charts, both used for upper-air analysis. There are a number of auxiliary and special- purpose synoptic charts, including thickness charts, tropopause charts, stability charts, change charts, continuity charts, etc., that have useful applications for preparing forecasts of weather events at various locations. See also mean chart, prognostic chart, cross section, profile.

Synoptic wave chart - A chart of an ocean area on which are plotted synoptic wave reports from vessels, along with computer-generated wave heights for areas where reports are lacking. Atmospheric fronts, highs, and lows are also shown. Isolines of wave height and the boundaries of areas having the same dominant wave direction are drawn.

Synthetic aperture radar- (Abbreviated SAR). Radar deployed aboard aircraft and satellites that produces a two-dimensional image of the target surface. The position of an object along the direction parallel to the movement of the observing platform is determined by the Doppler shift of the received signal.Phenomena observed by SAR include swell waves, current patterns imaged because of the varying sea surface roughness due to wave– current interaction, and oil spills and natural films that appear as areas of low image intensity as a result of their damping effect on centimeter-scale surface waves. See also Doppler radar, marine radar, microwave radar, high-frequency radar.

Synthetic hydrograph - An empirical unit hydrograph, developed for ungauged watersheds, that is based upon measurable physical basin characteristics.