SOmro RAY. See RAY PATH. 



SPC. South Pacific Commission. 



SOURCE ADMITTANCE . The source admittance of a 

 transducer may be defined as the quotient obtained 

 by dividing the phasor representing the short- 

 circuited source current by the phasor representing 

 the open-circuited source voltage. (4) 



SOnRCE CURRENT . The source current of an energy 

 source is the rms current which would be measured 

 at the terminals of that source if they were short- 

 circuited. (4) 



SOURCE POWER . The source power of an energy source 

 is the available power o£ that source. (4) 



SOURCE TRANSITION LOSS . The source transition loss 

 at the junction between an energy source and a 

 transducer connecting that source to an energy load 

 is the transmission loss measured by the ratio of 

 the source power of the source to the input power 

 of the transducer. (4) 



SOURCE VOLTAGE . The source voltage of an energy 

 source is the rms voltage which would be measured 

 at the terminals of that source if they were open- 

 circuited. (4) 



SOUTH ATLANTIC CURRENT . An Atlantic Ocean current 

 flowing eastward from south of Rio de Janeiro to 

 west of the Cape of Good Hope, and then curving 

 northward along the west coast of South Africa and 

 continuing as the BENGUELA CURRENT. The South 

 Atlantic current is formed by the merging of the 

 BRAZIL CURRENT and the FALKLAND CURRENT and forms 

 the southern part of the general counterclockwise 

 oceanic circulation of the South Atlantic Ocean. 

 (17) 



SOUTHEAST DRIFT CURRENT . A North Atlantic Ocean 

 current flowing southeastward and southward from a 

 point west of the Bay of Biscay toward southwestern 

 Europe and the Canary Islands, where it continues 

 as the CANARY CURRENT. The Southeast Drift Current 

 is the continuation of the southern branch of the 

 NORTH ATLANTIC CURRENT, and forms the northeastern 

 and eastern parts of the general clockwise oceanic 

 circulation of the North Atlantic Ocean. (17) 



SOUTH EQUATORIAL CURRENT . In the Atlantic the 

 south equatorial current starts off the west coast 

 of Africa, south of the Gulf of Guinea, and flows 

 in a generally westerly direction at an average 

 speed of about 0.6 knots. However, the speed 

 gradually increased until it may reach a value of 

 2:5 knots or more off the east coast of South 

 America. As the current approaches Cabo de Sao 

 Roque, the eastern extremity of South America, it 

 divides, the southern part curving toward the south 

 along the coast of Brazil, and the northern part 

 being deflected by the continent of South America 

 toward the north. In the Pacific the south equa- 

 torial current flows westward in the region of 

 the southeast trades and is present on both sides 

 of the Equator. Off South America the flow is 

 directed more or less parallel to the coast line, 

 turning gradually west when approaching the 

 Equator. (12,13) 



SPAR (SEAGOING PLATFORM FOR ACOUSTIC RESEARCH) . 

 SPAR is a 354 foot cylindrical vessel which is 16 

 feet in diameter and has a uniform circular cross 

 section throughout its length (with the exception 

 of the ends which are modified cones) with the bow 

 shaped to minimize resistance when under tow in the 

 horizontal attitude and the stem shaped to conform 

 to good vessel design. The weight of the structure 

 with zero liquid load is 587 tons. In the horizon- 

 tal attitude with this liquid loading the vessel 

 has a mean draft of 11 feet, being trimmed 4 feet 

 by the stem. When in the vertical attitude the 

 displacement of the SPAR, including the free flood- 

 ing water, is 1720 tons with a draft of 300 feet. (35) 



SOUTH PACIFIC CURRENT . An eastward flowing current 

 of the South Pacific Ocean that is continuous with 

 the northern edge of the ANTARCTIC CIRCUMPOLAR 

 CURRENT. (24) 



SPAR . Any log or built-up section of wood or 

 metal shaped to serve as a mast, yard, boom, 

 SPAR BUOY, etc. (17) 



SPAR BUOY . A buoy made of a tapered log or of 

 metal shaped like a tapered log, and secured so 

 as to float in an approximately vertical position. 

 (17) 



SPECIFIC ACOUSTIC IMPEDANCE . The quotient obtained 

 by dividing (1) the maximum value of the sinusoldal- 

 ly varying acoustic pressure at a point on a plane 

 surface in a fluid medium due to plane waves of 

 acoustic energy propagated in a direction perpen- 

 dicular to that surface, by (2) the maximum value 

 of the accompanying sinusoldally varying volume 

 velocity per unit area through the surface at that 

 point. (4) 



SPECIFIC GRAVITY . The ratio of the density of a 

 given substance to that of distilled water at 4°C 

 and at a pressure of 1 atmosphere. 



SPECIFIC HEAT . The number of calories required to 

 raise the temperature of 1 g. of a substance 1°C. 

 Specific heat decreases with increasing salinity. 

 Temperature and pressure effects are the same as 

 those for pure water. 



SPECTRUM . (1) The spectrum of a function of time 

 is a description of its resolution into components, 

 each of different frequency and (usually) different 

 amplitude and phase. (2) "Spectrum" is also used 

 to signify a continuous range of components, usual- 

 ly wide in extent, within which waves have some 

 specified common characteristics; e.g., "Audio- 

 Frequency Spectrum." (2) 



SPECTRUM CHARACTERISTIC . When the power per unit 

 band of a wave having a continuous spectrum is 

 plotted as a function of frequency, a curve is ob- 

 tained which represents the manner in which the 

 energy of that wave is distributed in frequency. 

 Such a curve may be called a spectrum characteris- 

 tic . (4) 



SPECTRUM DENSITY . The spectrum density of an os- 

 cillation is the mean-square amplitude of the out- 

 put of an ideal filter with unity gain responding 

 to the oscillation, per unit bandwidth; i. e., the 

 limit for vanlshingly small bandwidth of the quo- 

 tient of the mean-square amplitude divided by the 

 bandwidth. (2) 



SPECTRUM INTERVALS . Frequency bands represented by 

 intervals on either a linear or a logarithmic fre- 

 quency scale are sometimes spoken of as spectrum 

 intervals. (4) 



SPECTRUM LEVEL . The spectrum level of a specified 

 signal at a particular frequency is the level of 

 that part of the signal contained within a band one 

 cycle per second wide, centered at the particular 

 frequency. Ordinarily this has significance only 

 for a signal having a continuous distribution of 

 components within the frequency range under con-i 

 sideratioh. The phrase "spectrum level" cannot be 

 used, but must appear in combination with a modi- 

 fier, as, for example, pressure, velocity, voltage, 

 etc. (9) 



SPECTRUM LEVEL CHARACTERISTIC . The graph obtained 

 by plotting spectrum level as a function of frequen- 

 cy is known as a spectrum level characteristic. (4) 



SPECTRUM PATTERN . A graph showing the relative 



in 



