EM 1110-2-1100 (Change 1)
31 Jul 03
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RADAR
An instrument for determining the distance and direction to an object by measuring the time needed for radio
signals to travel from the instrument to the object and back, and by measuring the angle through which the instrument's
antenna has traveled.
RADIOACTIVE DATING (RADIOMETRIC DATING)
Calculating an age in years for geologic materials by measuring the presence of a short-life radioactive element
(e.g., carbon-14) or a long-life element (e.g., potassium-40/argon-40). The term applies to all methods of age determination
based on nuclear decay of naturally-occurring radioactive isotopes. Carbon-14 methods are often used to determine the age of
peat or wood found in BARRIER ISLANDS.
RADIUS OF MAXIMUM WINDS
Distance from the eye of a hurricane, where surface and wind velocities are zero, to the place where surface
windspeeds are maximum.
RAISED BEACH
A wave-cut platform, with or without a covering of beach materials, which is now raised above the present sea-
level.
RANDOM WAVES
The laboratory simulation of irregular sea states that occur in nature.
RANGE OF TIDE
The difference in height between consecutive high and low waters. The MEAN RANGE is the difference between
MEAN HIGH WATER and MEAN LOW WATER. The GREAT DIURNAL RANGE or DIURNAL RANGE is the
difference in height between MEAN HIGHER HIGH WATER (MHHW) and MEAN LOWER LOW WATER (MLLW).
Where the type of tide is diurnal, the mean range is the same as the diurnal range.
RAY, WAVE
See ORTHOGONAL.
RAYLEIGH DISTRIBUTION
A model probability distribution, commonly used in analysis of waves.
REACH
(1) An arm of the ocean extending into the land, e.g., an ESTUARY. (2) A straight section of restricted waterway
that is uniform with respect to discharge, slope, and cross-section.
RECENT
(Geological) A synonym of HOLOCENE. See also QUATERNARY.
RECESSION
(1) A continuing landward movement of the shoreline. (2) A net landward movement of the shoreline over a
specified time.
RECHARGE
The addition of new water to an AQUIFER or to the zone of saturation.
The process of producing, from a tilted or oblique photograph, a photograph from which displacement caused by tilt
has been removed.
A-62
Appendix A Glossary of Coastal Terminology
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