Answer to Last Month's, "Are you Prepared for the National Datum Changes Planned for 2022?"
Friday, December 14, 2018
Posted by: Khea Adams
1. What is the biggest problem with the North American Datum of 1983 (NAD 83)?
The major issue with NAD 83 is that the origin of coordinates defined as earth-mass center in 1986 is biased to our 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 Richmond (VDOT) equals 1.626 m (5.34 ft)
2. What organization is responsible for the development of the International Terrestrial Reference Frame (ITRF)?
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 will adopt for all CORS in the coming months. – https/www.iers.org
3. Which geodetic measurement systems are used to compute ITRF solutions?
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):
4.What is the approximate percentage of currently published 1st and 2nd- Order North American Vertical Datum of 1988 (NAVD 88) bench marks will NGS likely use in the definition of the new vertical reference frame?
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. What are the names of the new reference systems that NGS has adopted?
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. How large are the expected horizontal position and orthometric height changes expected to be across the state of Virginia?
While the horizontal and vertical differences will vary slightly across the state of Virginia, in general the differences in horizontal position, ellipsoid and orthometric heights will be 1.11 m (3.6 ft), 1.32 m (4.3 ft) and 0.33 m (1.1 ft) 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/