APPENDIX A 



GLOSSARY OF SELECTED TECHNICAL TERMS 



This Appendix defines the technical terms used in this report; a few related terms are 

 also included. The definitions generally agree with those given by Schureman (1975) or 

 Mitchell (1969). Some new definitions have been added. 



anomalistic— Pertaining to the periodic return of the Moon to its perigee, or of the Earth to 

 its periheUon. The anomalistic month is the average period of the revolution of the Moon 

 around the Earth in respect to the lunar perigee, and is approximately 27.554550 days in 

 length. The anomahstic year is the average period of the revolution of the Eartli around 

 the Sun in respect to its perihelion, and is approximately 365.2596 days in length. 



aphelion— The point in the Earth's orbit fartliest from the Sun. 



apogean tides or tidal currents— Tides of decreased range or currents of decreased speed 

 occurring monthly as the result of the Moon in apogee (farthest from the Earth). The 

 apogean range (An) of the tide is the average semidiurnal range occurring at the time of 

 apogean tides and is most conveniently computed from the harmonic constants. It is 

 smaller than the mean range, where the type of tide is either semidiurnal or mixed, and is 

 of no practical significance where the type of tide is diurnal. 



apogee— The point in the Moon's orbit farthest from the Earth. 



bench mark (BM)— A fixed physical object used as reference for a vertical datum. A tidal 

 bench mark is one near a tide station to which the tide staff and tidal datums are 

 referred. A primary tidal bench mark is the principal (or only) mark of a group of tidal 

 bench marks to which the tide staff and tidal datums are referred. The NOS standard 

 tidal bench mark is a copper or aluminum alloy disk 3.5 inches in diameter, containing 

 the inscription "NATIONAL OCEAN SURVEY," together with other individual 

 identifying information. A geodetic bench mark identifies a surveyed point in the 

 National Geodetic Vertical Network. Geodetic bench-mark disks contain the inscription 

 "VERTICAL CONTROL MARK NATIONAL GEODETIC SURVEY" with other 

 individual identifying information. Bench-mark disks of either type may, on occasion, 

 serve simultaneously to reference both tidal and geodetic datums. Numerous bench 

 marks, both tidal and geodetic, still bear the inscription "U.S. COAST AND GEODETIC 

 SURVEY." 



chart datum— The tidal datum to which soundings on a chart are referred. It is usually taken 

 to correspond to a low water stage of the tide, and its depression below mean sea level is 

 represented by the symbol Zo. See also datum. 



coastal boundary— A general term for a boundary defined as the line (or measured from the 

 line or points thereon) used to depict the intersection of the ocean surface and the land 

 at an elevation of a particular datum. 



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