AEOLIAN SANDS 



acoustic scattering — The irregular reflection, 

 refraction, or diffraction of a sound in many 



directions. (3) 



acoustic screen — A blanket of air bubbles that 

 eri'ectively entraps backscattered sound energy. 



acoustic signature — The graphic noise output 

 characteristic of and identified with a specific 

 noise source, for example, the noise output of a 

 particular class of submarine. 



acoustic sounding — tSee echo sounding. 



acoustic wave — See sound wave. 



acre-foot — The volume of \Yater required to cover 

 one acre to a depth of one foot, hence 43,560 cubic 

 feet ; a convenient unit for measuring irrigation 

 water, runoff volume, and reservoir capacity. 



actinometry — The science of measurement of 

 radiant energy, particularly that of the sun, 

 in its thennal, chemical (actinic), and luminous 

 aspects. (5) 



actinotrocha — The planktonic larva of the bottom 

 dwelling worm Phoroms. 



activated water — A transient chemically reactive 

 state created in water by absorbed ionizing radia- 

 tions. The passage of ionizing radiation 

 through water produces, temporarily, ions, 

 atoms, radicals, or molecules in a chemically 

 reactive state. The combined effect of all such 

 entities is said to be due to activated water. 

 Their identity has not been established with cer- 

 tainty, although evidence exists of the presence 

 of free hydroxyl radicals and hydrogen atoms. 

 (41,70) 



activation — The process of inducing radioactiv- 

 ity through neutron bombardment or by other 

 types of irradiation. (41 ) 



activation analysis — A method of elemental 

 analysis, especially for small traces of material, 

 based on the detection of characteristic radio- 

 nuclides following a nuclear bombardment. 

 (41) 



active glacier — A glacier which has an accumu- 

 lation area, in contrast to a stagnant glacier. 

 An acti^'e glacier need not have an advancing 

 front. (59) 



active material — Fissionable material, such as 

 plutonium, uranium enriched in the isotope 233 

 or 235, and any other material capable of releas- 

 ing substantial quantities of atomic energy. In 

 the military field of atomic energy, the term 

 refers to the nuclear components of nuclear 

 weapons exclusive of the natural uranium parts; 

 or, in the field of nuclear power, it refers to the 

 nuclear fuel in atomic reactors. (63) 



active sonar — The method or equipment by which 

 information concerning a distant object is ob- 

 tained through evaluation of the sound signal 

 reflected from the object to the generatmg 

 equipment. <S'ee passive sonar. 



activity — 1. The number of atoms decaying per 

 unit of time. The unit of activity is the curie, 

 3.7 X 10" disintegrations per second. (41) 



2. A measure of the intensity of emission 

 from a radioactive substance in terms of ob- 

 servable efl'ects, often expressed in counts per 

 unit of time. (41) 



3. A term frequently used to designate a par- 

 ticular radioactive nuclide. (41) 



4. A term frequently used to designate a par- 

 ticular radiation component, for example, the 

 gamma activity of a source. ( 41 ) 



5. A term commonly used for radioactivity. 



(41) 



6. In practice, activity is often expressed in 

 terms of observable effects, such as counts per 

 minute or roentgens per hour at one meter. 

 (41) 



7. Chemical activity of dissolution of salts. 

 adfreezing — The process by which one object be- 

 comes adhered to another by the binding action 

 of ice. ( 5 ) 



adiabatic phenomena — Those phenomena which 

 occur without a gain or loss of heat. 



adiabatic process — A thermodynamic change of 

 state of a system in which there is no transfer of 

 heat or mass across the boundaries of the system. 

 In an adiabatic process, compression always 

 results in warming, expansion in cooling. (5) 



adiabatic temperature changes^ — ^The compres- 

 sion of a fluid without gain or loss of heat to the 

 surroundings is work performed on the system 

 and produces a rise or fall of temperature. Such 

 a rise or fall of temperature occurs with chang- 

 ing depth. 



adjacent seas — See marginal seas. 



adrift — Floating without moorings or anchor: 

 drifting at the mercy of the sea and weather. 

 See stopped. 



adsorption — The adhesion of a thin film of liquid 

 or gas to a solid substance. The solid does not 

 chemically combine with the adsorbed sub- 

 stance. (5) 



advance (of a shoreline) — 1. A continuing sea- 

 ward movement of the shoreline. 



2. A net seaward movement of the shoreline 

 over a specified time. (61) 



advection — 1. In oceanography, advection refers 

 to the horizontal or vertical flow of sea water as 

 a current. 



2. The process of ti'ansport of an atmospheric 

 property solely by the mass motion (velocity 

 field) of the atmosphere. In meteorology, ad- 

 vection describes the predominantly hori- 

 zontal, large-scale motions of the atmosphere. 



advection fog— 1. A type of fog caused by the 

 advection of moist air over a cold surface, and 

 the consequent cooling of that air to below its 

 dew point. 



A very common advection fog is that caused 

 by moist air in transport over a cold body of 

 water (sea fog). 

 2. Sometimes applied to steam fog. 



(5) 

 aeolian sands — See eolian sands. 



