RATIO OP RANGES 



is the decibel per second. (3) See decay, 

 radioactive decay. 



ratio of ranges — (or height ratio ) . The ratio of 

 the height of the tide at the secondary station 

 to the height of the tide at the reference station. 



ray — Any of a large number of elasmobranchi of 

 the order Batoidei, in which the body generally 

 is compressed dorso-ventrally, the eyes are on the 

 upper surface, the gill clefts on the lower surface, 

 and the tail often is reduced to a whiplike 

 appendage. The order includes the electric 

 rays, stingrays, and manta rays. 



rayl — See specific acoustic impedance. 



ray path — The energy associated with a point on a 

 wave front that moves along an imaginary line 

 known as a ray path. The ray paths encoun- 

 tered in acoustics, which are commonly called 

 sound rays, are analogous to the light rays of 

 optics. Ray paths and wave fronts are mutually 

 perpendicular. 



ray pattern — A graphic presentation of the paths 

 of sound rays in relation to depth and range. 



ray theory — A method for determining the path 

 of transmitted underwater sound based on 

 Snell's law. This law describes the change in 

 the sound ray path as it passes through different 

 density (sound velocity) layers. 



reach — 1. An arm of the sea extending into the 

 land. 



2. A straight section of restricted waterway 

 of considerable extent ; may be similar to a nar- 

 rows, except much longer in extent. 

 (T3). 



recession — (also called rei^ro^?'essiow). 1. A con- 

 tinuing landward movement of the shoreline. 



2. A net landward movement of the shoreline 

 over a specified time. 

 (61) 



recognition differential — The recognition differ- 

 ential for a specified listening system is that 

 amount by which the signal level exceeds the 

 noise level jiresented to the ear when there is a 

 50 percent probability of detection of the signal. 

 (3) 



recrystallization — ^The formation of new mineral 

 grains in a rock while in the solid state. 



rectilinear current — See reversing current. 



recurring polynya — See polynya. 



recurved spit — (or hooh, hooked spit). A hook 

 developed when the end of a spit is turned 

 toward the shore by current deflection or by the 

 opposing action of two or more currents. 



RECURVED SPIT 



red alga — One of a division or phylum (Rhodo- 

 phyta) (the Rhodophyceae of another scheme) 

 of reddish, filamentous, membranous, encrusting, 

 or complexly branched plants in which the color 

 is imparted by the predominance of r-phycoery- 

 thrin over the chlorophylls and other pigments. 

 Some notable members of the group are the 

 sources of agar-agar, such as Gelidium., Graci- 

 laria, and Eitcheitma, Irish moss, Ghondrus, and 

 the encrusting calcareous Lithothanvnioti of 

 coral reefs. Red algae are worldwide in their 

 distribution, being more abundant in temperate 

 waters and ranging to greater depths than other 

 algae. 



red mud — A reddish-brown terrigeiious deep sea 

 mud containing up to 25 percent calcium car- 

 bonate which accumulates on the sea floor near 

 deserts and off the mouths of large rivers. (48) 



red tide — A red or reddish-brown discoloration of 

 surface waters, most frequently in coastal 

 regions, caused by concentrations of certain 

 microscopic organisms, particularly dinoflagel- 

 lates. Toxins produced by the dinoflagellates 

 can cause mass kills of fishes and other marine 

 animals. Airborne particles which are optic and 

 respiratory irritants to humans and animals, 

 may be carried from red tide areas overland. 

 Red tides may develop rapidly, apparently as 

 a result of an abrupt change in one or more 

 environmental factors. In some regions at least, 

 notably off the west coast of Florida, the onset 

 of red tide appears to follow increased rainwater 

 runoff from the land; the introduction by this 

 means of one or more scarce nutrient elements 

 into the sea is believed to permit the dinoflagel- 

 lates to multiply rapidly. See discolored 

 water. 



red water — See red tide, discolored water. 



reef — An offshore consolidated rock hazard to 

 navigation with a least depth of 10 fathoms 

 (20 meters) or less. (62) See shoal. {See 

 figure for atoll and coral reef.) 



Note: For many years, a depth of 6 fathoms 

 has been considered critical for navigational 

 safety. Because of the increased drafts of mod- 

 ern ships, a depth of 10 fathoms is now consid- 

 ered critical. 



reef complex — The solid reef core and all con- 

 tinguous detrital limestone and coral and 

 genetically related sediments or rocks. (2) 



reef conglomerate — See reef talus. 



reef flank deposit — See reef talus. 



reef flat — A flat expanse of dead reef rock which 

 is partly or entirely dry at low tide. Shallow 

 pools, potholes, gullies, and patches of coral 

 debris and sand are features of the reef flat. It 

 is divisible into outer and inner sections. (2) 

 {See figure for atoll.) 



reef front — The upper seaward face of the reef, 

 extending above the dwindle point of abundant 

 living coral and coralline algae to the reef 

 edge. This zone commonly includes a shelf. 



132 



