Transcontinental Traverse
File:Transcontinental Traverse map from Geodesy for the Layman.png
The Transcontinental Traverse (TCT) was a geodetic survey traverse conducted in the continental United States by the United States Coast and Geodetic Survey between 1961 and 1970 and the U.S. National Geodetic Survey between 1970 and 1976. It was the most accurate large-area survey ever done prior to Global Positioning System surveys. TCT included over 2,700 survey stations, covered over {{convert|13,600|mi|sigfig=3}}, and passed through 44 U.S. states.[https://celebrating200years.noaa.gov/magazine/tct/welcome.html#trans The High-precision Transcontinental Traverse: Improving the Scale of the U.S. Survey Network], NOAA (page "the traverse")
This nationwide survey increased the accuracy of the existing U.S. survey network. It was also fundamental to the sophisticated mathematical readjustment of the nation's survey network known as the North American Datum of 1983.{{citation|title=The High-precision Transcontinental Traverse: Improving the Scale of the U.S. Survey Network|work=NOAA Celebrates 200 years|type=website|publisher=U.S. National Oceanographic and Atmospheric Administration|url=https://celebrating200years.noaa.gov/magazine/tct/welcome.html}} It was the "end of an era" as the last conventional, purely terrestrial large scale survey.{{sfn|Wilford2001|p=366}}
Forerunner surveys
The first major transcontinental survey was the Transcontinental Arc of Triangulation, completed in 1896 along the 39th parallel north with coastal endpoints at Cape May Lighthouse at Cape May, New Jersey, and Point Arena Light near Point Arena, California. It established the Meades Ranch survey marker, also called the Geodetic Center of the United States.{{citation|title=Meades Ranch|author=Jerry Penry|date=June 4, 2015|work=The American Surveyor|publisher=Cheves Media|url=http://www.amerisurv.com/content/view/13900/}}[https://www.ngs.noaa.gov/web/about_ngs/history/milestones.shtml Milestones of the Survey], National Geodetic Survey, June 5, 2017
The Transcontinental Traverse, commonly known as the "TCT", grew out of smaller surveying projects that the U.S. Coast and Geodetic Survey (USC&GS) conducted for the United States Air Force missile-tracking program in an area near Cape Canaveral, Florida, during the 1960s. The USC&GS developed unique specifications for this work that resulted in one part in 1,000,000, exceeding Air Force requirements.[https://celebrating200years.noaa.gov/magazine/tct/welcome.html#capec Cape Canaveral Triangulation Survey Yields High-Precision Results], NOAA This led USC&GS officials to conclude that applying the same specifications to a nationwide traverse, a surveying method, would dramatically improve the scale of the entire U.S. survey network. Soon after completing its work for the Air Force in Florida in 1961, the USC&GS embarked on the TCT.
Route and history
The Geodimeter electronic distance measurement device was rapidly tested and adopted by U.S. national agencies for long-distance mapping. The last base line to be measured with tape happened near Salmon, Idaho, in 1958.
The survey began in 1961 in Florida and ended in 1976 in Michigan. It crisscrossed North America along three east-west and five north-south corridors. A portion that had been planned to traverse the U.S.-Canada border to Maine was canceled due to advances in satellite geodesy.{{citation|title=GEODETIC SURVEYING 1940 - 1990|author=Joseph F. Dracup|via=NOAA|url=https://www.ngs.noaa.gov/PUBS_LIB/geodetic_surveying_1940.html}}
Equipment and methods
File:Bilby towers on Transcontinental Traverse.png
The traverse made use of the Geodimeter, a lightwave phase electronic distance measurement instrument that had just been invented when the traverse began.{{citation|publisher=Smithsonian Institution|title=EDM (Geodimeter Model 2A)|work=Database: Physical Sciences Collection - Surveying and Geodesy|id=catalog number 1998.3094.01|url=https://amhistory.si.edu/surveying/object.cfm?recordnumber=748815|access-date=2018-05-02}}[https://celebrating200years.noaa.gov/magazine/tct/welcome.html#improv The High-precision Transcontinental Traverse: Improving the Scale of the U.S. Survey Network], NOAA (page "improving distance measurement") The instruments were located atop Bilby towers many meters above ground level to avoid obscuring objects and to get a smoother air temperature profile for accuracy. Due to the light source then in use, the Geodimeter could only be operated at night.{{citation|publisher=Government of Australia|work=Australian Web Archive|title=NATMAP's INTRODUCTION OF ELECTRONIC DISTANCE MEASURING TO AUSTRALIA - SIXTY YEARS ON|author=Paul Wise|year=2014|url=http://www.xnatmap.org/adnm/docs/2013/aganasm/nasm.html|url-status=bot: unknown|archive-url=https://webarchive.nla.gov.au/awa/20180226150600/http://pandora.nla.gov.au/pan/166632/20180227-0206/www.xnatmap.org/adnm/docs/2013/aganasm/nasm.html|archive-date=2018-02-26}}{{cbignore|bot=medic}}
=Satellite triangulation=
File:BC-4 World Primary Network.jpg stations in Maryland and Washington State]]
{{Further|Satellite geodesy#Optical tracking|Balloon satellite#Pageos and the global network}}
Photographic satellite triangulation stations were tied in to the traverse at Moses Lake, Washington; Chandler, Minnesota; Beltsville, Maryland; and four other locations. The Moses Lake and Beltsville sites became part of a worldwide satellite geodesy network.{{sfn|National Academy of Sciences|1971|p=80}}[http://www.photolib.noaa.gov/htmls/geod0009.htm Worldwide BC-4 Network], NOAA Photo Library
See also
References
{{Reflist}}
=Sources=
- {{Citation|title=The Mapmakers
|chapter=Baselines across a continent
|pages=353–366
|first=John Noble |last=Wilford
|publisher=Vintage Books|year=2001
|isbn=0375708502|chapter-url=https://books.google.com/books?id=OG98OxaehFkC&pg=PA353}}
- {{citation|title=North American Datum: A Report, Issue 81|author=Committee on the North American Datum, National Academy of Sciences / National Research Council / National Academy of Engineering|publisher=U.S. Government Printing Office|lccn=72-608706|year=1971 |chapter-url=https://books.google.com/books?id=upMrAAAAYAAJ&pg=PA73 |chapter=Appendix D: High-precision transcontinental traverse surveys in the United States and Appendix E: Satellite Triangulation for North America|pages=73–80|ref={{harvid|National Academy of Sciences|1971}}}}
{{USGS|title=The High-precision Transcontinental Traverse: Improving the Scale of the U.S. Survey Network|url=https://celebrating200years.noaa.gov/magazine/tct/welcome.html}} in NOAA Celebrates 200 years
Further reading
- [https://www.ngs.noaa.gov/PUBS_LIB/Geodesy4Layman/TR80003A.HTM Geodesy for the Layman], USAF via NOAA, 1959, mentions this traverse planned at the time
- {{citation|title=Surveying and Towers for Triangulation With an Emphasis on the Bilby Steel Tower|author=C. Barton Crattie|url=http://bw-03c6b06952c750899bb03d998e631860-bwcore.s3.amazonaws.com/photos/bilby-the-final-WV-paper-revd-for-TAPS-201732.pdf}}
- {{citation|title=Bilby Steel Tower for Triangulation|author=James K. Richards|id=Publication 62-3|year=1965|publisher=United States Coast and Geodetic Survey |archive-url=https://web.archive.org/web/20190617210255/ftp://ftp.library.noaa.gov/docs.lib/htdocs/rescue/cgs_specpubs/QB275U352no62-3.PDF|archive-date=2019-06-17|url-status=dead|url=ftp://ftp.library.noaa.gov/docs.lib/htdocs/rescue/cgs_specpubs/QB275U352no62-3.PDF}}
External links
- {{Commons category-inline|Transcontinental Traverse}}