1 - NGA

MIL-HDBK-850
observation, condition, or correlate
equations, and expressing a condilion [or a
feast squares adjustment. In a least
squares adjuslmem, values oblained Irom
the solufion of normal equations [either
directly or through the correlale equations)
are applied to the observation or condition
aqualions to obtain the desired corrections.
normal gravity !leld-A mathematically
derived gravity Iiald used in geodesy 10
closely appros.imale the Earth’s actual
gravily field.
normel gravity—A reference gravity field
that k malhemaiicalfy defined tora
normalized earlh which has gravitational
symmetry. It is commonly taken as the field
01 a rotating level ellipsoid bul may be
arbNrarily defined.
normal orbll—The orbit 01 a saletli!e
considered with nodislurbing effects
presemdue loother celestial bodies, or to
some physical phenomena. Also called
unperturbed orbit.
normal section szlmuIh—Tne angle
between lhe geodetic meridian 01 [he
observer and the plsne comaining Ihe
ellipsoidal, normal of the observer. and
measured clockwise from the north in a
plane parpendicularlolhe elfipsoidaf
normal of the observer.
nOMSal section llne—A line on the surface
01 lhe ellipsoid connecting two points on
that surface, and traced by ap!ane
containing the normal al one point and
passing through the other poim.
normal tension—(tapin@ The tension to be
aPPfied 10 a law 10 compensate for the
shortenlngeftecl of sag in order to bring
the tape to standard Ieng!h. Thai pull at
wh!ch the tension correction and sag
exaClly balance each olher,
normal waler level—The mosl prevalenl
water level in a watercourse, reservoir, lake,
or pond. generally defined by a shoreline of
permanent land-type vegetation. Along
Iarge bodies of water, wave aclion may
relard vegetation beyond the normal
shoreline.
normal-angle lens—A fens having an
angle of coverage from 60°to 75”. A lens
172
whose local length is equal approximately
10 Ihe diagonal 01 the formal,
normal—1, Aslraighl line perpendicular to a
surtace or to another line. 2. A condition of
being perpendicular to asurtacaorline.3.
In geodesy, Ihe straight Iina parPandicUlar
Io the surface of the reference ellipsoid.4.
The average, regular, or expected vafue of
a quanlity.
North American datum of 1927 (NAD
27)—The datum which defined the
geodetic positions in the United States and
adjoining countries was derived lrom a
readjustment of the geodetic data as
available up lo 1927. II is based onlhe
Clarke 1866 ellipsoid. See also horizontal
datum.
North American datum of 1983 (NAD
S3)—The newdalum, which replaces NAD
27, is geocentric and based on GRS 80
parameters. llscoverage includes Alaska,
Canada, CONUS, and CentralAmerican
countries Irom Mexico to Panama. Total
number 01 redefined horizontal stations
exceeds 250K. . . . ..
North Slar— See Polaris.
north declination—See decllnatlon,
definition 3.
north geographical pole—The
geographical pole in the Northern
Ilemisphere, at latitude 90” N.
north geomagnetic pole—The
geomagnetic pole in the Northern
Hemisphere.
north magnetic poLs-Tne magnetic pole
in the Northern Hemisphere.
norlh poinl—See celestlal merldlan.
norlh polar circle—See Arctic Clrcla.
northbound node—See ascending
node.
norlhlng—1. (JCS) Northward increasing grid
values on a map. See also talae
northing. 2. (plane surveying) See
Ialilude difference.