signal introduced into the first detector circuit 

 for heterodyning with the incoming echo signal. (5) 



INLET . Short narrow waterway connecting a bay, 

 lagoon, or similar body of water with a large 

 parent body of water. An arm of the sea (or other 

 body of water), that is long compared to its width, 

 and that may extend a considerable distance inland. 

 (11) 



INPFC. International North Pacific Fisheries 

 Commission. 



INPUT CURRENT . The input current of a transducer 

 connecting a given source and given load is the rms 

 current through the terminals connecting that trans- 

 ducer and that source. (4) 



INPUT IMPEDAMCE . The input impedance of a trans- 

 ducer connected to a given load is the impedance 

 which would be measured at its source terminals if 

 they were not connected to a source. (4) 



INPUT POWER . The input power of a transducer con- 

 necting a given source and a given load is the 

 average rate of flow of energy through the ter- 

 minals connecting that transducer and that source. 

 (4) 



INPUT VOLTAGE . The input voltage of a transducer 

 connecting a given source and a given load is the 

 rms voltage between the terminals connecting that 

 transducer and that source. (4) 



INSERTION LOSS . The insertion loss in DECIBELS 

 resulting from the insertion of a transducer into 

 a transmission system is ten times the logarithm 

 to the base ten of the ratio of the power delivered 

 to that part of the system that follows the trans- 

 ducer, before the insertion of the transducer, to 

 the power delivered to that same part of the system 

 after insertion of the transducer. In short, this 

 term is intended to give an idea of how much the 

 output of a system is changed by the insertion of 

 a transducer. (9) 



INSHORE . See SHOREFACE. 



INSHORE (Zone) . In beach teirminology, the zone of 

 variable width extending from the shore face through 

 the breaker zone. (11) 



IN SITU . In the natural or original position. 

 INSOLATION . The absorption of solar energy by the 



INTEGRATING WATER SAMPLER. This device consists of 



(15) 



INSPIRATORY RESERVE VOLUME . The amount of air 

 that can be brought in by forcible inspiration 

 after completion of a normal inspiration. It 

 averages about 2 1/2 liters at rest and becomes 

 smaller as the tidal volume increases. (37) 



INSULAR . (1) Of or pertaining to an island or 

 islands. (2) Detached; standing alone. (27) 



INSULAR SHELF . The zone surrounding an island 

 extending from the line of permanent immersion to 

 the depth (usually about 100 fathoms) where there 

 is a marked or rather steep descent toward the 

 great depths. (11) 



INSULAR SHOULDER . See INSULAR TALUS. 



INSULAR SLOPE . A declivity from the outer edge of 

 an INSULAR SHELF into greater depths. See also 

 INSULAR TALUS, 



INSULAR TALUS (INSULAR SHOULDER, INSULAR SLOPE) . 

 The slope from the lower edge of an insular shelf 

 into deeper water. A similar slope from the lower 

 edge of a continental shelf is called CONTINENTAL 

 TALUS. (17) 



a plastic cylinder containing a free piston whose 

 movement is controlled by the evacuation of a 

 charge of fresh water. Sea water enters the samp- 

 ler following the piston. As the device moves 

 through the sea a rotor-driven pump evacuates the 

 fresh water, thereby moving the piston at a rate 

 directly determined by the sampler's travel through 

 the water. Sea water enters the projecting mouth 

 of the sampler. Thus, a sample representative of 

 a horizontal column of water several miles long 

 can be collected in a short time. Several samplers 

 can be attached to a hydrographic cable to sample 

 at different depths at one time. (30) 



INTENSITY LEVEL (SOUND ENERGY FLUX DENSITY LEVEL) . 

 The intensity level, in decibels, of a sound is 

 10 times the logarithm to the base 10 of the 

 ratio of the intensity of this sound to the refer- 

 ence intensity. The reference intensity shall be 

 stated explicitly. (2) 



INTERFERENCE . Any wave which would interfere with 

 an attempted observation of a signal is known as 

 interference. (4) 



INTERMEDIATE WAVES . Waves under conditions 



where the relative depth (water depth/wave length) 



lies between 0.5 and 0.05. 



INTERNAL WAVES (BOUNDARY WAVES) . Internal waves 

 or boundary waves are created below the surface, 

 at the boundaries between water strata of different 

 densities. Since the density differences between 

 adjacent water strata in the sea are considerably 

 less than that between sea and air, internal waves 

 are much more easily formed than surface waves, and 

 they are often much larger. The maximum height of 

 wind waves on the surface is about 60 feet, but 

 internal wave heights as great as 300 feet have 

 been encountered. 



Internal waves are detected by a number of 

 observations of the vertical temperature distribu- 

 tion, using recording devices such as the BATHY- 

 THERMOGRAPH. They have periods as short as a few 

 minutes, and as long as 12 or 24 hours, these 

 greater periods being associated with the tides. 



The full significance of internal waves has 

 not been determined , but it is known that they 

 may cause submarines to rise and fall like a ship 

 at the surface, and they may also affect sound 

 transmission in the sea. (12) 



INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA) . Head- 

 quarters in Vienna. Established October, 1955 in 

 New York. An autonomous International organization 

 under the aegis of the United Nations. 



Activities: Sponsors symposia and provides a 

 mechanism for international discussion and agree- 

 ment on many topics including safe procedures for 

 handling and disposal of radioactive wastes. 



INTERNATIONAL LOW WAT ER. A hydrographic datum 

 originally suggested for international use at the 

 International Hydrographic Conference in London in 

 1919 and later discussed at the Monaco Conference 

 in 1926. The proposed datum, which has not yet 

 been generally adopted, was to be "a plane so low 

 that the tide will but seldom fall below it." This 

 datura was the subject of International Hydrographic 

 Bureau's Special Publication No. 5 (March 1925) 

 and No. 10 (January 1926), these publications were 

 afterwards reproduced in the Hydrographic Reviews 

 for May 1925 and July 1926. (14) 



INTERTIDAL ZONE . Generally considered to be the 

 zone between mean high water and mean low water 

 levels. (27) 



INTERTROPICAL CONVERGENCE ZONE (EQUATORIAL 

 CONVERGENCE ZONE) . 1. The axis, or a portion 

 thereof, of the broad TRADE-WIND current of the 

 tropics. This axis is the dividing line between 

 the southeast trades and the northeast trades (of 



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