gravel which is coarser than ordinary gravel, es- 

 pecially if consisting of flat or flattish pebbles. 

 (27) 



SHIP-BORNE WAVE RECORDER . An Instrvunent which 

 measures waves directly aboard ship. It combines 

 the sea pressure at a point on the hull of the 

 ship with the vertical displacement of this point 

 which is obtained by double integration of the out- 

 put of a vertical accelerometer . (35) 



SHIP MOTION . The complex motion imparted to a 

 ship upon encountering waves . All the motions 

 can be regarded as combinations of three oscil- 

 lations about horizontal or vertical axes (ROLL, 

 PITCH, and YAW), and three linear displacements 

 of the center of gravity (HEAVE, SURGE, and SWAY). 

 (12) 



SHIPS INTERNAL NAVIGATION SYSTEM . See SINS. 



SHIPS OF OPPORTUNITY . These include, but are not 

 restricted to: (1) certain U. S. Navy combatant 

 Fleet units such as aircraft carriers, cruisers, 

 destroyers, amphibious ships, mine sweepers, and 

 submarines, (2) U. S. Navy Radar Picket Ships 

 (YAGR's and DER's), (3) certain U. S. Navy auxi- 

 liary units (oilers, refrigerator ships, cargo 

 ships, ice breakers), (4) units of Military Sea 

 Transportation Service, (5) units of U. S. Mer- 

 chant Marine, (6) U. S. Air Force Ocean Range 

 Vessels, (7) larger units of U. S. Fishing Fleet. 

 The installation and operation of instrument 

 packages on these ships and vessels is predicated 

 on a not-to-interfere basis with the ships 's pri- 

 mary mission. 



SHOAL . 1. A detached elevation of the bottom 

 comprised of any material except rock or coral, 

 and which may endanger surface navigation. 



2. To become shallow gradually. 



3. To cause to become shallow. 



4. To proceed from a greater to a lesser 

 depth of water. (11) 



SHOALING COEFFICIENT . The ratio of the height of 

 a wave in water of any depth to its height in deep 

 water with the effect of refraction eliminated. 

 Sometimes called shoaling factor or depth factor. 

 (11) 



SHOALING FACTOR . See SHOALING COEFFICIENT. 



SHORAN (SHORT RANGE NAVIGATION) . A precision elec- 

 tronic position fixing system which uses the UHF 

 band (200-300 megacycles) with ranges restricted 

 to approximate line of sight distances. 



Position is determined by measuring the time 

 required for the high frequency signal to travel 

 from the mobile station to the transponder beacons 

 and return. Two fixed shore stations are required 

 and several mobile stations can use the same two 

 fixed stations. Lines of position are concentric 

 circles. High accuracies with ranges as much as 

 about 40 nautical miles can be obtained depending 

 upon the elevations available for the shore sta- 

 tions. The system is quite suitable for launch 

 hydrography. High precision SHORAN is called 

 HIRAN. (29) 



SHORE . That strip of ground bordering any body of 

 water which is alternately exposed, or covered by 

 tides and waves. A shore of unconsolidated materi- 

 al is usually called a BEACH. (27) 



SHOREBASED RECORDER OF LOW-FREQUENCY OCEAN WAVES . 

 This instrument has a pressure head on the sea bot- 

 tom that contains a hydraulic filter. The filter 

 attenuates high-frequency signals caused by ordi- 

 nary gravity waves and very low frequency signals 

 caused by tides. The maximum response is for fre- 

 quencies of about one cycle per 1,000 seconds. A 

 , strain-gauge transducer converts the filtered pres- 

 sure fluctations into electrical signals, which are 



transmitted to shore through a cable. Two identi- 

 cal bellows are used in the compliant chambers, but 

 the capillary tubes are adjusted so that their re- 

 sistances to the flow of hydraulic fluid have a 

 ratio of about four to one. (35) 



SHOREFACE . The narrow zone seaward from the low 

 tide SHORELINE permanently covered by water, over 

 which the beach sands and gravels actively oscillate 

 with changing wave conditions. Also called inshore. 

 (27) 



SHORE ICE . See FAST ICE. 



SHORELINE . The intersection of a specified plane 

 of water with the SHORE. The line delineating 

 the shoreline on U. S. Coast and Geodetic Survey 

 nautical charts and surveys approximates the mean 

 highwater line. (27) 



SHORE TERRACE . A terrace made along a coast by 

 the action of waves and shore currents; it may 

 become land by the uplifting of the shore or the 

 lowering of the water. (27) 



SHORT-CRESTED WAVE . An ocean wave whose crest is 

 of finite length, i.e., the type actually found 

 in nature. (12) 



SHORT SEA . A sea in which the waves are short, 

 irregular, and broken. (17) 



SHORT WAVE . See DEEP-WATER WAVE. 



SI (Smithsonian Institution) . Within the National 

 Oceanographic Program, the main responsibility of 

 the Smithsonian Institution is the collection, 

 preservation, and study of marine materials made 

 by the Smithsonian Institution itself, by other 

 Federal agencies, and by private organizations 

 referring collections to the Institution. The 

 Smithsonian Oceanographic Sorting Center will 

 process specimens collected for the National Pro- 

 gram as a service to the scientific community. 



SIAM . Society of Industrial and Applied Mathe- 

 matics . 



SIGMA-T (SYMBOL CTt ) • A conveniently abbreviated 

 value of the density of a sea water sample of tem- 

 perature t and salinity S: ^^ ^ rp(S,t)- fix 10^ 



where p(S,t) is the value of the sea-water density 

 in c.g.s. units at standard atmospheric pressure. 

 If, for example, P(S,t) = 1.02648, then tr^ =26.48. 

 (24) 



SIGMA-T. P . (Symbol CTf, p .) SIGMA-T, corrected to 

 the hydrostatic pressure in situ. (24) 



SIGMA-ZERO (SYMBOL '^0 ) . SIGMA-T at ff°C. Knud- 

 sen's tables give values of sigma-zero as a func- 

 tion of salinity or chlorinity, as well as correc- 

 tions to be applied to obtain sigma-t. (24) 



SIGNAL. See SIGNAL WAVE. 



SIGNAL-TO-INTERFERENCE RATIO . The magnitude of a 

 signal wave relative to the magnitude of a wave 

 which interferes with its reception may properly 

 be described as the signal-to-interference ratio. 

 (4) 



SIGNAL-TO-NOISE RATIO . See SIGNAL-TO-INTERFERENCE 

 RATIO. 



SIGNAL TRANSMISSION LEVEL . The signal transmission 

 level in a transmission system is the signal level 

 (of a kind to be specified) at a designated position 

 in the system. (2) 



SIGNAL WAVE . Any sound wave upon which it is 



107 



