Validation Of Vdatum In Southeastern Louisiana And Western Coastal Mississippi

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 (). 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.