| Section A | A index | 101-109 of 917 terms |
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acidity of water—The quantitative capacity of aqueous media to neutralize strong bases. The acidity of a water sample is determined by titrating it with a strong base (e.g., NaOH) to a defined pH.
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acidity profile—A record of the H+ concentration in an ice core. Unless otherwise stated, the H+ concentration is indirectly determined by the measuring the electrical conductivity. Annual layering, volcanic activity, periods with abundant alkaline dust, and biomass burning can sometimes be detected.
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aclinic line—(Or dip equator, magnetic equator.) The line through those points on the earth's surface at which the magnetic inclination is zero. The aclinic line is a particular case of an isoclinic line. In South America the aclinic line lies at about 15°S latitude, while from central Africa to about Indochina it coincides approximately with the parallel of 10°N latitude. Compare agonic line, geomagnetic equator.
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acoustic array—A sound-transmitting or receiving system with elements arranged to give desired directional characteristics.
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acoustic backscattering—Scattering of sound or ultrasound in the direction of the source.
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acoustic dispersion—The separation of a sound wave into its frequency components as it passes through a given medium. The velocities of the wave components change as they pass through the medium.
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acoustic Doppler current profiler—(Abbreviated ADCP.) A current-measuring instrument employing the transmission of high-frequency acoustic signals in water. The current is determined by a Doppler shift in the backscatter echo from plankton, suspended sediment, and bubbles, all assumed to be moving with the mean speed of the water. Time gating circuitry is employed, which uses differences in travel time to divide the water column into range intervals called bins. The bin determinations allow development of a profile of current speed and direction over the entire water column. The ADCP can be deployed from a moving vessel, towing platform, buoy, or bottom-mounted platform. In the latter configuration, it is nonobtrusive in the water column and thus can be deployed in shipping channels.
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acoustic echo sounding—Measuring the depth of the ocean by determining the time required for the echo of a sound impulse to return to a point near the surface (i.e., the transmitting ship).
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acoustic imaging—The use of acoustic energy to form a representation of a physical object, such as side-scanning sonar imaging of objects on the ocean bottom.
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