PROTON 



pressure level — The sound intensity, as measured 

 in decibels relative to units of dynes per square 

 centimenter, such as 0.0002 dyne per square 

 centimeter, 20 times the common logaritlun of 

 tlie acoustic pressure. 



pressure ridge — A ridge or wall of hummocks 

 where one ice floe has been pi-essed against an- 

 other. (74) 



Ridges may be several miles long and up to 100 

 feet high. A corresponding ridge may also oc- 

 cur on the underside of the ice canopy and is 

 called an ice keel. (7) 



pressure wave — A short -j^eriod oscillation of 

 pressure such as that associated witli the propa- 

 gation of sound througli the atmosphere ; a type 

 of longitudinal wave. (5) 



prevailing current — The flow most frequently 

 observed during a given period, usually a month, 

 season, or year. 



Price-Gurley current meter — A battery powered 

 electromechanical current meter which measures 

 current speed only. 



primary bench mark — See bench mark. 



primary film — (or diiiie flm^ diatom flm., bac- 

 terial fllni) . The thin slimy layer that usually 

 forms initially on a surface placed in sea water; 

 it is composecl of bacteria, diatoms, or both, and 

 is believed by some to be a necessary precursor 

 to attachment of larger fouling organisms. 



primary production — (or g7'oss primary jn-oduc- 

 tion^ primary productivity) . The amount of or- 

 ganic matter synthesized by organisms from in- 

 organic substances in unit time in a unit volume 

 of water or in a column of water of unit area 

 cross section and extending from the surface to 

 the bottom. (40) 



primary productivity — See primary production. 



primary tide station — A place at which contin- 

 uous tide observations are made over a number 

 of years. (68) See reference station. 



prime meridian — The meridian of longitude 

 degrees, used as the origin for measurements of 

 longitude. The meridian of Greenwich, Eng- 

 land is the internationally accepted prime merid- 

 ian on most charts. However, local or national 

 prime meridians are occasionally used. 



priming of the tides — ^The periodic acceleration 

 in the time of occurrence of high and low wa- 

 ter because of changes in the relative positions 

 of the moon and the. sun. The opposite effect 

 is called lagging of the tides. 



primitive period — The primitive period of a peri- 

 odic quantity is the smallest increment of the 

 independent variable for which the function re- 

 peats itself . (6) 



principal axis — In a transducer used for sound 

 emission or reception, a reference direction for 

 angular coordinates used in describing the di- 

 rectional characteristics of the transducer. It 

 is usually an axis of structural symmetry or the 

 direction of maximum response, but if these do 



not coincidej the reference direction must be de- 

 scribed explicitly. (69) 



probability — The chances that a prescribed event 

 will occur, represented as a pure number p in tlie 

 range O^p^l. The probability of an impossi- 

 ble event is zero and that of an inevitable event 

 is unity. 



Probability is estimated empirically by rela- 

 tive frequency, that is, the number of times the 

 particular event occurs divided by the total 

 count of all events in the class considei'ed. (5) 



probability theory — See probability. 



probe — A measuring device or sensor inserted into 

 the environment to be measured. As applied to 

 oceanography the term is used for devices which 

 are lowered into the sea for in situ measure- 

 ments. 



production — The sum of the organic matter pro- 

 cluced by living org-anisms in a given area or 

 volume in a given time, inclusive of such orga- 

 nisms which might have developed and disap- 

 peared in the given time. 



productivity — An inexact term, indicating the 

 fertility of an ocean area. Most authorities have 

 albandoned the term and use primary produc- 

 tion or production instead to which specific 

 definitions have been assigned. 



profile — 1. A drawing showing a vertical section 

 along a surveyed line. 



2. A graph showing as ordinate the A'^ariation 

 of some oceanographic quantity along a straight 

 line against horizontal distance on this line as 

 abscissa. 



3. See trace. 



progressive wave — A wave which is manifested 

 by the progressive movement of the wave form. 

 (61) {See figure for standing wave.) 



prohibited anchorage — See anchorage. 



promontory — A high point of land extending into 

 a body of water. (30) See cape, headland, 

 bluff. 



propagation — The transmission of energy 

 through a medium. 



propagation anomaly — In underwater acoustics 

 the difference between the actual propagation 

 loss for a given length of water path and the 

 nominal value of propagation loss identified 

 witli the distance covered by that path. (28) 



propagation loss — The transmission loss asso- 

 ciated with -Aiw given length of ray path in the 

 water. (28) " 



propeller noise — Noise produced by cavitation at 

 the propellers. 



protected thermometer — A reversing thermom- 

 eter which is encased in a strong glass outer shell 

 that protects it against hydrostatic pressure. 



(5) 

 proton — An elementary nuclear particle witli a 

 positive electric charge equal numerically to the 

 charge of the electron and a mass of 1.007594 

 mass units. It is one of the constituents of every 

 nucleus. (70) 



127 



