SONIC MARINE MAMMALS 



snow sludge — A soft elastic cnist formed on 

 fallen snow on a water surface. (59) 



snow slush — A viscous mass formed as a result of 

 a thick snowfall into cooled water. (74) 



snow water on the ice — (or puddle). Ice whose 

 surface is covered with snow water (that is, an 

 accumulation on the ice of melt water mainly 

 due to snow melting). 



sofar — 1. An acronym derived from the expres- 

 sion ".sound /ixing and ranging." 



2. A position-fixing system by which hyper- 

 bolic lines of position are determined by measur- 

 ing, at shore listening stations, the difference in 

 the time of reception of sound signals produced 

 in a sound channel in the sea. (66) 



sofar channel — See sound channel. 



solar constant — The rate at which solar radiation 

 is received outside the earth's atmosphere on a 

 surface normal to the incident radiation, and at 

 the earth's mean distance from the sun. For 

 decades the tentative result was 1.94 or 1.95 

 gram-calories per square centimeter per minute, 

 however recent studies of the infrared and ultra- 

 violet portions of the solar spectrum suggest a 

 value of about 2.00 gram-calories per square 

 centimeter per minute. (5) 



solar declination — The angular distance of the 

 sun expressed north or south of the celestial 

 equator; it is indicated 'as { + ) when north and 

 ( — ) when south of the equator. Maximum 

 declination is about 231/2 degrees north and south 

 of the Equator ; maximum north declination oc- 

 curs about June 21 and maximum south declina- 

 tion about December 21. (50) 



solar tide — The tide caused solely % the tide- 

 producing forces of the sun. (50) 



solid — A state of matter in which the relative 

 motion of the molecules is restricted and they 

 tend to retain a definite fixed position relative 

 to each other, giving rise to crystal structure. 

 A solid may be said to have a definite shape and 

 volume. (27) 



solitary wave — A wave consisting of a single ele- 

 vation (above the water surface), its height 

 not necessarily small compared to the depth, 

 and neither followed nor j^receded by another 

 elevation or depression of the water surface. 

 (61) 



solstice — One of the two points in the sun's orbit 

 (the ecliptic) farthest from the celestial equa- 

 tor; the instant when tlie sun's declination is 

 maximum. See summer solstice, winter sol- 

 stice. 



solstitial tide — The tide occurring near the times 

 of the solstices when the sun reaches maximum 

 north and south declinations ; the tropic range 

 at these times is greatest. 



solubility — The extent to which a substance 

 (solute) mixes with a liquid (solvent) to pro- 

 duce a homogeneous system (solution). 



solution — The state in which a substance, or 

 solute, is homogeneously mixed with a liquid 



called the solvent. Thus, pure water is a sol- 

 vent and sea water is a solution of many 

 substances. 



solution basin — A shallow depression on a reef or 

 beach rock surface produced by solution of the 

 surface. (2) 



Somali Current— /S'ee East Africa Coast Cur- 

 rent. 



sonar — 1. An acronym derived from the expres- 

 sion "sound navigation and ranging." The 

 method or the equipment for determining by 

 underwater sound techniques the presence, lo- 

 cation, or nature of objects in the sea. (3) 



2. A system for determining distance of an 

 underwater object by measuring the interval of 

 time between transmission of an underwater 

 sonic or ultrasonic signal and return of its echo. 

 (66) See active sonar, passive sonar. 



sonar background noise — See background noise. 



sonar projector — See transducer. 



sonar performance figure — The source level of 

 a surface ship active sonar minus the equivalent 

 plane wave noise in the receiving band. 



sonic bearing — (or acoustic bearing) . A bearing 

 detei'mined by measuring the direction from 

 which a sound wave is coming. 



sonic fishes — ( or soniferous fishes ) . Those fishes 

 which are capable of producing sounds, usually 

 by means of specialized organs such as the air 

 bladder or pharyngeal teeth. The spectra of 

 fish sounds generally have their limits betM'een 

 50 and 5,000 cps, with most of the sound energy 

 concentrated betw-een 100 and 800 cps. Air 

 bladder sounds range from about 50 to 1,500 

 cps, with principal frequencies in the region of 

 100 to 300 cps ; sounds produced by stridulation 

 of hard parts, such as teeth or spines, may have 

 components from 50 to 800 cps or more, but 

 typically show the greatest energy from about 

 500 to 3,000 cps. 



sonic frequency — See audio frequency. 



sonic layer depth — The depth of the surface layer 

 into which sound rays are trapped by upward 

 refraction effects. The sonic layer depth is in- 

 dicated on a sound velocity versus depth trace 

 by the point of near surface maximum sound 

 velocity. 



sonic marine animals — (or so>ii ferrous marine 

 animals). Organisms living in the sea which 

 are capable of producing sounds, either purpose- 

 ful by means of specialized organs, or incidental 

 to the course of normal activity such as 

 feeding or swimming. These animals include 

 certain invertebrates (principally crusta- 

 ceans), several groujjs of fishes, and most 

 marine mammals. See snapping shrimp, sonic 

 fishes, sonic marine mammals. 



sonic marine mammals — (or soniferous marine 

 mammah) . Those mammals which are capable 

 of producing somids, includuag most, perhaps 

 all, of the whales, poi-poises, and seals. A great 

 variety of sound lias been recorded from ceta- 



151 



