My previous newsletter highlighted the Fall HSRP meeting that discussed how The Ohio State University and Michigan State University have made great progress in developing useful tools for the development and implementation of the new, modernized National Spatial Reference System (NSRS) in 2025. This newsletter will highlight the updates to vertical datums that The National Oceanic and Atmospheric Administration (NOAA) is working on.

My last newsletter described some of the activities of the National Ocean Service (NOS) program offices at the 2024 Hydrographic Survey Review Panel (HSRP) Fall Meeting. As I mentioned in last month’s newsletter, the Hydrographic Survey Review Panel is a federal advisory committee that provides NOAA with advice. The National Ocean Service program offices – National Geodetic Service (NGS), the Center for Operational Oceanographic Products and Services (CO-OPS), the Office of Coast Survey (OCS), as well as the University of New Hampshire’s Joint Hydrographic Center and Center for Coastal and Ocean Mapping, provide updates related to navigation services. 

Below is an excerpt of the agenda for the material that I will highlight in this newsletter. As I mentioned in my last newsletter, the HSRP website provides links to reference documents, presentations and recordings. I would encourage everyone to download the presentations or listen to the recordings to obtain all the details.

This newsletter will highlight the session on the vertical datums, including the International Great Lakes Datum (IGLD).

Excerpt from HSRP Fall Public Meeting

Agenda: https://www.nauticalcharts.noaa.gov/hsrp/meetings/2024/fall-2024.html

Reference materials and links: National Geodetic Survey, A Tale of Three Datums

Presentations: Sept. 25, 2024;

1. Vdatum

2. International Great Lakes Datum (IGLD)

Webinar recordings:

NGS has created a website that provides brief explanations with additional links for detailed information on the National Tidal Datum Epoch (NTDE), International Great Lakes Datum (IGLD) and Gravity for the Redefinition of the Vertical Datum (GRAV-D). The site highlights that NOAA is currently working on three major updates to vertical datums: the 1983-2001 NTDE, the International Great Lakes Datum of 1985 (IGLD 85), and the North American Vertical Datum of 1988 (NAVD 88). The site provides information on why the datums need to be updated.

The box titled “Excerpt from NTDE“ provides information about the NTDE.  It explains what the NTDE is, what NOS is doing, and why the NTDE needs to be updated.  If you click on the link titled “National Tidal Datum Epoch update” on the right side of the webpage, it provides more information and links about the NTDE update, such as how will the NTDE update impact you. 

The following is an exerpt from the National Tidal Datum Epoch update:

National Tidal Datum Epoch

The National Tidal Datum Epoch (NTDE) is a 19-year time period established by the National Ocean Service for collecting observations on water levels and calculating tidal datum values (e.g. mean sea level, mean lower low water). The NTDE needs to be regularly revised to account for long-term effects of land movement, sea level rise, and changes in tidal constituents. Tidal datums and their data are used to generate products and services necessary for safe navigation, coastal hazard mitigation, ecosystem research, coastal engineering and marine boundary demarcations.

The NTDE Update: New Tidal Datums are Coming!

NOAA currently utilizes the 1983-2001 National Tidal Datum Epoch. This epoch is now undergoing revision and will be replaced by the fifth iteration of the NTDE. Measurements for the update will be based on water level data spanning the years 2002-2020. Once all data has been collected, NOAA will review, analyze, and generate revised datums. The current proposed release date for new NTDE products is after 2026.

The website also highlights two other NOS projects – the International Great Lakes Datum and the Gravity for the Redefinition of the Vertical Datum (GRAV-D). Again, if you click the “International Great Lakes Datum update” link on the right side of the webpage, it provides more information and links about the IGLD update such as how will the IGLD update impact you. Clicking the “Gravity for the Redefinition of the Vertical Datum” link on the right side of the webpage provides some more information and links about vertical datums.

On the second day of the meeting, Jacob Heck, NOAA National Geodetic Survey (NGS), and Sierra Davis, NOAA Center for Operational Oceanographic Products & Services (CO-OPS), gave a presentation providing details on the update to the International Great Lakes Datums of 1985 (IGLD 85). The presentation addressed the following topics:

• Define IGLD
• Significance of the Great…