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Section S S index 781-789 of 1376 terms
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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. See pyrheliometer, spectrophotometer.
spectroscope—An apparatus to effect dispersion of radiation and visual display of the spectrum obtained.
spectroscopy—The study of the interaction between matter and radiation. Since the energy levels in all atoms and molecules are discrete (quantized), the absorption or emission of radiation occurs at distinct energies (frequencies) characteristic of a given chemical. The energy levels probed may be rotational (microwave region), vibrational (infrared region), or electronic (visible or ultraviolet). In mass spectroscopy, molecules are ionized and the different masses selected by use of an electric or magnetic field. Many spectroscopic techniques have been used to identify molecules or atoms in the atmosphere.
spectrum—1. Radiant energy (e.g., electromagnetic, acoustic) per unit frequency (or wavelength) interval over some range of frequencies; may also be applied to any distribution function. For example, the distribution of droplet sizes in clouds is sometimes called a size spectrum. 2. Mathematically, same as spectral function.
specular reflection—Reflection as from a mirror.
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.
speed of light—Without qualification usually means the speed of propagation of electromagnetic radiation of any frequency in free space, a universal constant with the value 2.99792 × 108 m s−1. Could also mean the phase velocity or group velocity of an electromagnetic wave in a material medium.
speed of sound—1. (Also velocity of sound.) Usually taken to mean the phase speed of an acoustic (or sound) wave. In an ideal, stationary gas the speed of sound c is a thermodynamic property depending only on the equilibrium state of the gas and is given by where γ is the ratio of specific heat capacities, at constant pressure and volume, respectively; R is the gas constant; and T is absolute temperature. 2. In seawater, a function of temperature, salinity, and pressure.
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