Are you prepared for the national datum changes planned for 2022?  Can you answer these six questions?
by Dave Doyle
NGS Chief Geodetic Surveyor (retired)
Owner, Base 9 Geodetic Consulting Services

1. What is the biggest problem with the North American Datum of 1983 (NAD 83)?
2.  What organization is responsible for the development of the International Terrestrial Reference Frame (ITRF)?
3. Which geodetic measurement systems are used to compute ITRF solutions?
4. What is the approximate percentage of currently published 1^st and 2^nd - Order North American Vertical Datum of 1988 (NAVD 88) bench marks will NGS likely use in the definition of the new vertical reference frame?
5. What are the names of the new reference systems that NGS has adopted?
6. How large are the expected horizontal position and orthometric height changes expected to be across the state of Texas?

Every surveyor in who relies on the use of Global Navigation Satellite System (GNSS) data in the course of their work should be able to answer these questions right off the top of their head. If you can’t, you better start getting up to speed. If everything goes as planned you only have about 3 years before NGS will pull the lever and replace both NAD 83 and NAVD 88.

The transitions from the North American Datum of 1927 (NAD 27) to NAD 83 in 1986 and the National Geodetic Vertical Datum of 1929 (NGVD 29) to NAVD 88 in 1991 had, in general a significant impact on only a modest number of federal, state, county/municipal and private surveying, mapping and charting agencies and companies.  It will be radically different this time. Owing to the widespread use of GNSS and Geographic Information System (GIS) technologies, communities across the country and large numbers of other disciplines will be significantly impacted by these positional changes. They will be depending on professional surveyors to guide them in the adoption of these new datums and management of their legacy data.

So can you answer the posed questions? If you can, then you are likely well prepared to meet the challenges that are coming. If not, then you should take all the classes you can to be informed on the subject.  Start off by getting acquainted with NGSs’ New Datums web site - https://www.ngs.noaa.gov/datums/newdatums/index.shtml - and sign up for their e-mail notification service. Make sure that TSPS conferences feature speakers explaining the rational for these changes, how you can predict the changes coming to your community, and strategies for implementation of those changes. 

It needs to be noted that NGS will also be changing the design of all of the State Plane Coordinate zones and has posted zone design maps to their web site - https://www.ngs.noaa.gov/SPCS/download.shtml. In addition the agency has made a decision that all future SPC coordinates will be defined in meters and what has commonly been referred to as International Feet. Values in U.S. Survey Feet will no longer be published. The agency will also likely publish new false northing and/or easting values so NATRF SPCs will not be confused with NAD 83 values.

Now as for the answers to the six questions – take some time to see what you can find online.

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Briefly stated the answers are:

ANSWERS

1. The major issue with NAD 83 is that the origin of coordinates defined as earth-mass center in 1986 is biased to the best contemporary knowledge of earth geocenter by approximately 1.5 m (5 ft) for the conterminous United States. This can be seen by comparing the X,Y,Z Earth-Centered Earth-Fixed NAD 83 vs. ITRF coordinates for any Continuously Operating Reference Station (CORS) – for example Austin RRP2 (TXDoT) equals 1.634 m (5.36 ft)
2.  The International Earth Rotation and Reference System Service (IERS) headquartered in Paris, France is responsible for the computation of the ITRF, the most current being ITRF14 which NGS has already adopted for all CORS – https/www.iers.org
3. The IERS uses data from four different geodetic measurement services to compute the ITRF – GNSS, Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR) and Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS):

• GNSS – www.igs.org
•  VLBI – https://ivscc.gsfc.nasa.gov
• SLR – https://ilrs.cddis.eosdis.nasa.gov
• DORIS – https://ids-doris.org

4. Sort of a trick question – no bench marks will be used in the defining the new vertical datum, it will based exclusively on a combination of space-based, aircraft

    and terrestrial high accuracy gravity observations.

5. The North American Terrestrial Reference Frame of 2022 (NATRF2022) will replace NAD 83 for the conterminous U.S. and Alaska, and the North American-

    Pacific Geopotential Datum of 2022 (NAPGD2022) will replace NAVD 88 and all of the various state and territory island vertical datums. There will also be

    separate horizontal/geometric systems for the Caribbean, Pacific and Marianas areas to replace NAD 83.

6. While the horizontal and vertical differences will vary across the state of Texas, in general the differences in horizontal position, and orthometric heights will be in

    the range of 1.12 m (3.7 ft) to 1.32 m (4.3 ft) and - 0.02  m (0.1 ft) to -.37 m (-1.2) respectively.  Computing the approximate 3-d positional changes for anywhere

    in the country can be performed using the annual NGS xGEOID beta models – currently xGEOID18 -- https://beta.ngs.noaa.gov/GEOID/xGEOID18/