Validation of VDatum in Southeastern Louisiana and Western Coastal Mississippi

Abstract

We present a novel study to utilize US Geological Survey water level gauges that were not meant for tidal studies to diagnose errors in the National Oceanic and Atmospheric Administration (NOAA) Vdatum tool in southeastern Louisiana and western coastal Mississippi. The US NOAA developed a Vertical Datum Transformation tool (VDatum) that allows for conversions between geodetic, orthometric, and tidal vertical datums. However, in southeastern Louisiana and western Mississippi, VDatum uncertainties have been reported by NOAA to be perhaps as high as 0.20–0.50 m (https://vdatum.noaa.gov/). These uncertainties exceed IHO S44 special order and order 1. We performed validation measurements for VDatum in the region of concern at three USGS water level gages (CSX Railroad, Delacroix, and Rigolets) and one offshore location (Chandeleur East) utilizing a HydroLevel buoy. Tidal datums estimated using Modified Range Ratio method at these stations were compared with the corresponding tidal datums determined using VDatum. We hypothesize that the errors in VDatum are due to errors in: the tuning of the model or in the model bathymetry and coastline resulting in an incorrect tidal range, and in the topography of the sea surface in that region.

Keywords:

• Datum
• ellipsoid
• gages
• MLLW
• NOAA
• USGS
• VDatum

Acknowledgments

We greatly thank the services of Mike Runner and Scott Perrin of USGS for providing the various information about the coastal USGS gauges and allowing us to perform GPS surveys at the gauges of our choice. We cherish the invaluable contributions of the reviewers of the article. We also appreciate the contributions of Marvin Story, Kevin Martin, and Brian Parker of the University of Southern Mississippi, Venice Tang of Waypoint Support, NovAtel Inc. and Michael Michalski of NOAA/NOS/CO-OPS. A special acknowledgment is due to the former Director of the USM Hydrographic Science Research Center, the late RDML (ret.) Ken Barbor whose leadership made this work possible.

Additional information

Funding

The funds for this project were provided by NOAA through a grant to the USM Mapping Center of the USM Hydrographic Science Research Center. This work was also supported by NOAA's Office of Ocean and Atmospheric Research and U.S. Department of Commerce.