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The American Association for Geodetic Surveying (AAGS) would like to make you aware of potential future problems with the release of the new geopotential vertical datum in 2022. As you may already know, the National Geodetic Survey (NGS) is no longer supporting passive control such as bench marks unless it has been occupied by a GPS/GNSS receiver for 4 or more hours and submitted to OPUS-Shared Solutions at OPUS-Shared Solutions. By August 2018, NGS would like to have data from all states to complete the GPS on bench marks campaigns. Most states have several areas that have a weak Geoid model with uncertainties in the 0.2 ft or more range, and thus need GPS on bench marks to strengthen the geoid model. Surveys starting in 2022 involving flood plain maps and so forth will require bringing orthometric heights (elevations) to the job site using GNSS, which in turn requires a better geoid model. The NGS has created listings of bench marks by state that the NGS would like to see occupied before August, 2018. This is an opportunity for surveyors to help all improve the geoid models. The provided list contains all the bench marks that NGS would like to have occupied with GPS and then shared with them. The NGS no longer has field crews so they are relying on private surveyors to help them. Time is running short to ensure that future surveys that require heights tied to the national datum have an accurate geoid model to assist in this endeavor. It is in your best interest to assist the NGS in performing this important task to help strengthen the geoid model. Dave Zilkoski recently published an article on this for GPS World, which can be viewed at GPS World . The NGS is also having a special webinar on this subject on Thursday, February 15, at 2 PM.

Plots of Changes from GEOID12B to GEOID18v2.2