1 - NGA

torrestrld
natlmm.
tmr.strlal
morldlan.
mqfnotimn-Sea gaornag-
morldlan—See ●stronomic
torrostrhl perturbatlorrs-The largest
grsvitsfiorrsl parfurbslions of artifkial eslatliias
which are caused by the fscf fhst the gravily
fiild ef the Earth is nat s#rarically symmetrical.
terrestrial photogrgmmotry— Photogrsmmatry
utiiiiirrg terrestrial phc40grsphs. Also
called ground photogrammotry.
terrostrlal photognrph-A photograph taken
by a csmers Iomtsd on the ground. Also called
ground photograph.
terrestrial planet—A planet that
a~roximstss ihe Earth in size (Mercury, Venus,
Msrs, and Pluto) end phyaicael makeup.
terrestrial pole-See gsiographlml polo.
terrostrlal refraction—The refraction by the
Earth’s atmmphere of light from a terrestrial
source. The path of fight from a terrestrial eeurca
is usually net far from trorizontat ii pssses
through only the lower strata of the atrnnsphere
and suffers refraction thmugheut its entire
length. See also atmosphrdc refraction;
horizontal refraction; lateral refraction.
tarrostrlal ●pher.-The Earth.
terrestrial triangl-A triangle on the swlsce
of the Earth, aspscislly the navigatkmsl triangle.
tesla-(gaomagnetism) The electromagnetic
unit of rnagnet”c inrtucfkm. 1 tesla = 10-9
nanotaskr. See also geuaa.
Tesselatsid $pharold Modal-lV (1$)-A
mordinsta sysrem whiih dwidas the wrld info 5
Iatilude zones to obtain aqusl spscing.
teeaeral harmonics—The sat of all a#herfcal
harrswn”w thsf are functions of bolh Islituda
❑nd brrgiiude. Secforial harmonics ma a special
subsat of tessersl harmonics.
test charf-Saa raeolving powar targat.
teat rsngm suppoti-DfAA provided gaodatic
surveys for the DoD test and trsining rsnges to
MI L-HDBK-B50
256
SwPOrf weapons aysfarns and weapons
eyatems usars raseamh, dsvaloprnmt, lasting
and avalustbn.
taztura-in a photo image, the frequency of
changa ard smangamenf of tone.
thematic mapper (TM)-A severr~hannel,
prademinsntfy 30 meter instantaneous fiefd of
view (IFOV) multiifnd scanner, deei~ad for
rrmnifciing earth resoumsa. TM is uaad on
board LANDSAT =Iellites.
thamatlc map-Sea topical map.
thematically ssparate-The segregation of
a feature w a fimitad nunbw of features within
a data bsse to highlight ths spatial
chsmcfetistics d a aubrsaf er ha snviromnent,
See also layer.
thoodollte magnetometer—An instrument
usad in rnsgnetic suweys consisting of a
Ihaodeliia and a mgnarometor modified to fti
into a oemmen base, wh(ch parmim tha
determination of tha true rnaridisn and the
magnetic meridian in a single observation,
thaodollte-A precision surveying instrument
consisting ef an alidsde with a Ielascopa. It is
mounted on an accumtefy graduated circla and
is equipped wkh nscassary Iavals and rsading
devices. Somelimes! the alidsde carries a
graduatsd vetiical cm4a. See alsa dne
theodolitsi; dlroctlon Instrumwst
theodollte; gyrotheodollta;
phototheodollte; repaatlrrg theodoflte.
theoretical corner-A term adopfad by the
U.S. Gaelegical Survey to designate fhe turners
on the map for which ne msrks era idantifiad on
the ground. The Imstiens ara determined by
adjustment and are indicated on the map only
by the intersection of ths subdiviskm fines.
theoretical ●rror-A systematic error .arfaing
fmm nstural physical candiikms, beyond the
control of the observer. Sss afse external
●rror.
theoroilcal gravity-The value of gravity
dculetsd for a particular tstifuda according to
an accepted formula. See also formula for
theoratlcaf grevlty.
theory of ●nharmonlc ratio-A theory
principally mrrcemsd with the process-es cd
trensfornmtbn and radifiilion wtmrstry
. ... r.