BASIC ELEMENTS OF THE GEODETIC PROBLEM

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP63-00314R000200160043-8
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 4
• Document Creation Date: December 16, 2016
• Document Release Date: March 30, 2005
• Sequence Number: 43
• Content Type: REPORT

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ANNEX
BASIC ELEMENTSOF THE GEODETIC FROBLEIM
A. Origin of the Problem
. Geodetic Syste
End at PO ;it Lines
Ground control points on the Earth's surface conventionally az e
established by measurement from a pre-selected initial point to other
points by means of triangulation (distances between points of triangles
are calculated through the measurement of angles). Since this procedure
is impossible over ocean areas, continental geodetic systems stop at
coast lines. Limited ocean spaces can be covered by direct measuren ertt
of sides a triangles (trilateration) from continent-to islands-to continent,
using electronic techniques. This is called H1RAN. Europe hal, been
tied with North America through Canada with an estimated uncertainty f
plus or minus 240 feet. Such ties were made in the Far East arid are
now being undertaken to interconnect Australia, New Guinea, the Mar-
shall., and other islands farther east. No HIRAN connection between
the Tokyo and North American datums is possible.
B. Sources of Errors
. Sise and Shape of the Earth; Datums
Computing relationships of control points for small areas
(property surveys) is easy because computations are made on a plane
surface. For largo areas where earth curvature is involved, however,
computations are made on a curved surface of a near-sphere with pre.
determined dimensions. Such a figure, the elliksoid of reference, has
definite estimated lengths of the equatorial and polar axes and a ratio
between the two that defines the flattening. Because none of these can
be measured directly, they have throughout the history of geodesy
been differently estimated by geodesists of various countries. The
ellipsoid of reference plus the initial point of a geodetic network
defines a distinctive datum. Any change or difference in any one of
the dimensions of an ellipsoid or in the initial point changes the datum
and the resultant geodetic system. The joining of two or more datums
creates discrepancies at points common to the datums, as at a border
between countries. The US uses the North American Datum, 1927,
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based on the Clarke ellipsoid of 1866. The Soviets use the Ralkovo
Datum, 1942, based on the Krasovskiy ellipsoid of 1940. The joinirg
of the datums of continents is further complicated by the lack of inter
vexing triangulation over bodies of water (now corrected with
HIIKM-
ties by the USAF). thus giving rise to srrors in computing distance'.
and directions between widely separated launch and target points fox
ICBM operations.
Z. Fitting of the Ellips id to the Geoid
Because the earth ie not a true sphere, and hence not a
smoothed surface, xxiathematical difficulties (and discrepancies) ariJe
in fitting the ellipsoid of reference a mathematical approximation t.,
the earth, to the jet.d..4. a generalised, undulating representation of
the sea-level earth surface. The latter cannot be observed directly
but must be deduced from aft:anomie observations or from the mea..,urct
moat of random variations in the force of gravity from point to point on
the earth's surface. Of these, only gravity can be measured on both
land and sea; astronomic determinations at sea cannot be measured
within better than a 1-mile error. The unknown angular separation De -
twee* a geoid and an ellipsoid leads to angular errors -- deflection ? ,f
the vertical -- since the plumb bob of surveying instruments is per-
pendicular to the geoid and not to the ellipsoid on which all ccmputatIcniu
ars mad*. For very srnall countries it has been sufficient to assume
that the geoid and ellipsoid were coincident; for others the errors CcUla
in some cases be corrected by astronomic methods. But, for a count:).
as broad as the USSR, the errors were found to be inadmissible,
tag "to 40-50 times the errors oi field work. In the 1950s the SJI,FieL
learned that the German ellipsoid then in use (Bessel) and the calmer.-
tional western method of computation (development method) gave an error
of some 900 meters (3,000 feet) in the positions of common puints.
a result, a new ellipsoid was computed in 1940, a.nd a new mcthod of
computation was adopted (projection method), in which points are pr,)-
jected perpendicular to the ellipsoid. The Soviets now assert that the
inferiority of the development method will be felt sharply in the futui e
when adjoining nets are connected and that divergencies will laiske carto-
graphic unification impossible. Essential to the projection method are
gravity data, for which the Soviets began systematic surveys to 1932
The technique of this method is similar to that used by the US !J in
positioning Ascension Island to Cape Canaveral, in which an accuracy
of plus or minus 500 feet is claimed. The method is being used by the
Soviets to establish geodetic positions in Antarctica on the Soviet
ellipsoid, a part of the development of a Soviet world geodetic syet
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The USAF has also been engaged in the derivation of a USAF
World Geodetic System based on a gravimetric approach, For this
it has undertaken independent programs for establishing intercontinental
ties (MAN, solar eclipse programs, etc.). Within the past year the
Army and USAF World Geodetic Systems have coordinated their results into
Defense World Geodetic System (DWGS). Major problems still exist,
nevertheless, to make the DWOS fruitful for ICBM system requirements.
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