![]() ![]() North American Vertical Datum of 1988 (NAVD 88) has a bias of 0.5 meters and a tilt of 1 meter coast-to-coast in its zero-elevation definitional surface relative to today’s global mean sea level. The solution lies in the CORS network, which helps define the modernized geometric references frames and facilitates their access. This effort was complicated by the vastly differing nature of these passive and active networks. Caccamise II called “Pathway to 2022: The Ongoing Modernization of the United States National Spatial Reference System,” which was presented at the American Geophysical Union fall 2017meeting, recent realizations in both 20 of NAD 83 attempted to bring the episodically occupied passive geodetic control network of 80,000 stations and the nationwide GNSS CORS network of 2,000 stations into a state of consistency. ![]() That means it is misaligned with the primary global GNSS reference frames and antenna models.Īccording to a poster created by William A. The North American Datum of 1983 (NAD 83) has a known non-geocentricity of 2.2 meters, relative to today’s knowledge of the geocenter. ![]() Because of that, it was determined that they must address the serious issues of inaccuracy in the realizations of both NAD 83 and NAVD 88. ![]() To fulfill its mission of providing the geodetic reference frame for any and all United States geospatial activities, NGS must be as scientifically accurate as possible. The NSRS, though satisfactory to most current geospatial user requirements, has its shortcomings. The decision to modernize the datums has been evolving over time. Objective three of the 10-year NGS plan is to increase the efficiency and accuracy for soliciting, accepting, storing, etc., the results of all survey data, while maintaining the high standard of quality that is expected. One challenge the NGS will attempt to solve during this redevelopment is developing a comprehensive strategy for incorporating past and future leveling data into a GNSS/geoid-based vertical datum, as well as ensuring an actual connection to the NSRS with charting data. The NGS will be combining improvements in all of these areas, to prepare for the replacement of NAVD 88 with a four-dimensional geopotential field capable of describing heights, deflections, and other aspects of the gravity field surrounding Earth’s surface. The program’s effectiveness has improved the hybrid geoid model, as it has also grown to support the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project, which will be instrumental in replacing NAVD 88. This program was used previously to improve access to NAVD 88 by using GNSS to establish orthometric heights. The NGS will be implementing the National Height Modernization Program (Height Mod) in order to help accomplish this objective. As the plan states, vertical motion is not tracked in any sort of systematic way. And to access it appropriately, users must collect hours of GNSS data or rely on decades-old heights. Definition-wise, NAVD 88 has a bias of half-a-meter and a 1 meter tilt. The North American Vertical Datum of 1988 requires improvements in both definition and services provided in order to access it. Similar to objective 1, this is nicknamed, “Replace NAVD 88.” Visit the New Datums website to get more information to help you prepare for the change.Objective two of the second goal states that, by 2022, the National Geodetic Survey aims to reduce all definitional and access-related errors in orthometric heights in the geopotential reference frame to 2 centimeters when using 15 minutes of GNSS data. In SoCal, based on the graphics above (and a good eye), we will probably see an approximate horizontal change of 1.47 meters and an approximate orthometric height change of -0.625 meters. How will these new reference frames affect positions and height? These new reference frames will be easier to access and to maintain than NAD 83 and NAVD 88, which rely on physical survey marks that deteriorate over time. The new reference frames will rely primarily on Global Navigation Satellite Systems (GNSS), such as the Global Positioning System (GPS), as well as on a gravimetric geoid model that is being collected now through the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Project. To improve the National Spatial Reference System (NSRS), NGS will replace the North American Datum of 1983 (NAD 83) and the North American Vertical Datum of 1988 (NAVD 88) with a new geometric reference frame and geopotential datum in 2022. The new replacement datums are coming in 2022. Back in 2015 I wrote about the planned retirement of NAD 83 and NAVD 88. ![]()
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