GEODETIC SURVEY TOWERS IN NORTH VIETNAM

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04560A006400010035-0
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 9
• Document Creation Date: December 28, 2016
• Document Release Date: April 11, 2000
• Sequence Number: 35
• Publication Date: September 1, 1968
• Content Type: MEMO

App( (jUDNWtase 2000/06/30 CIA-RDP78BO456OA00640001003.5-0
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PHOTOGRAPHIC INTERPRETATION MEMORANDUM
GEODETIC SURVEY TOWERS
IN NORTH VIETNAM
N P I C/ R-107/68
SEPTEMBER 1968
Declass Review, NIMA/DoD
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 Approved For Release 2000/06/30 : CIA-RDP78BO456OA006400010035-0
This document contains information affecting
the national defense of the United States,
within the meaning of Title 18, sections
793 and 794, of the U.S. Code, as amended.
Its transmission or revelation of its contents
to or receipt by an unauthorized person is
prohibited by law.
Approved For Release 2000/06/30 : CIA-RDP78BO456OA006400010035-0
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TITLE Approved or a ease
NPIC/R,_107/68 SEPTEMBER 1968 c/NOFORN
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 Approved For Release29d&06/30 :(iU1 MQ456OA006400010 3 _107/68
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GEODETIC SURVEY TOWERS IN
NORTH VIETNAM
Analysis of recent low level photography of North Vietnam reveals
that 30 large towers previously believed to be associated with microwave
communication are geodetic survey towers and are used for triangulation
(Figure 1).
The towers are 85- to 110-feet high and consist of an instrument
(inner) tower for the survey instrument and an observer (outer) tower
which has a signal source triangle head, lightkeeper platform, and an
observer platform (Figure 2).
When conducting a geodetic survey, horizontal control is achieved by
means of triangulation and it is necessary that, stations be intervisible
over long distances; therefore, towers are required in flat and timbered
regions. The United States Coast and Geodetic Survey uses the Bilby
steel tower (Figure 3) which is similar to those in North Vietnam and
consists of one tripod support for the instrument within another support
for the observer platform. This double tower combination enables the
instrument to be completely stable and free from disturbance by the
observer's weight and movement.
The Bilby towers used in the United States are designed so that they
can be dismantled after use and rebuilt at another station. The Vietnamese
towers have been in place for several years, so it is possible that the
war interrupted a survey project that has not been completed.
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FIGURE 2. NORTH VIETNAMESE TOWER.
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Approved For Release 2000/06/30 : CIA-RDP78BO456OA006400010035-0
Approved For Release 2000/06/30 : CIA-RDP78BO456OA006400010035-0