Please Participate in the National Geodetic Survey’s GNSS Data Collection Project

The National Geodetic Survey (NGS) is actively improving the accuracy of its hybrid geoid model and will replace GEOID12B with GEOID18 in early 2019.  This new hybrid geoid model will improve the derivation of orthometric heights (elevations) referenced to the North American Vertical Datum of 1988 (NAVD 88) using Global Navigation Satellite System (GNSS) technology. The new model will also thereafter serve as the official means for obtaining NAVD 88 heights via GNSS.

NGS will use GNSS data collected on bench marks to create the new hybrid geoid model.  Recent analyses have revealed 25 areas in Massachusetts where the collection and submission of additional GNSS data will improve the geoid model by either confirming or updating the relationships between ellipsoid, orthometric, and geoid heights. This updated GNSS data on bench marks will also enable NGS to develop more accurate models for transforming survey data referenced to NAVD 88 to data referenced to the future North American-Pacific Geopotential Datum of 2022 (NAPGD2022). Starting in 2022, surveys involving flood plain maps and so forth will require establishment of vertical control using GNSS, which makes improving the accuracy of the geoid model an important endeavor.

Interested MALSCE members are asked to participate in this project by occupying with GNSS one or more of the 25 identified bench marks and sharing the collected GNSS data with NGS. Submitted data received prior to August 31, 2018 will be used in the development of GEOID18. NGS will continue to accept data on marks through 2020 for the development of the transformation models for 2022.

Click here to view a list of the 25 bench marks that NGS has identified. As of September 2018, data for 20 of these bench marks has successfully been collected, five bench marks still need attention. This list is also shown in a useful, online tracking map.  For each identified bench mark, NGS is asking occupying project participants to:

1. Attempt to locate the marks on the list and submit a mark recovery through DS World. Check this NGS page for more information on mark recovery.
2. Collect four or more hours (more is better) of GNSS data on the mark following NGS guidelines, submit the data to OPUS and select the option to Share.  When sharing an OPUS solution, NGS will also request a brief description and photos of the mark for quality control.  Two independent OPUS solutions for each mark are highly desirable for confirming results.

To avoid duplication of effort, MALSCE members who participate in this initiative are asked to keep MALSCE informed of their efforts by  sending an email to malsce@engineers.org identifying the bench mark(s) they have chosen to occupy and after they shared their data with NGS. The spreadsheet will be updated to reflect the selection of bench marks by participating members.

Please contact MALSCE President Paul R. Foley with more questions.