Kurt W. Hess

VDatum and Strategies for National Coverage

VDatum is a software tool being developed by the National Ocean Service that allows users to vertically transform geospatial data among a variety of ellipsoidal, orthometric and tidal datums. This is important to coastal applications that rely on vertical accuracy in bathymetric, topographic, and coastline data sets. The VDatum software can be applied to a single point location or to a batch data file. Applying VDatum to an entire data set can be particularly useful when merging multiple data sources together, where they must first all be referenced to a common vertical datum. Contemporary technologies, such as lidar and kinematic GPS data collection, can also benefit from VDatum in providing new approaches for efficiently processing shoreline and bathymetric data with accurate vertical referencing. VDatum is currently available for Tampa Bay, New York Bight, Delaware Bay, Louisianas Calcasieu River and Lake Charles, central California, Puget Sound, Strait of Juan de Fuca, and north/central North Carolina. In addition, VDatum development is near completion for Chesapeake Bay, Mobile Bay to Cape San Bias, Southern California, Long Island Sound and New York Harbor, and projects are also commencing for an area from New Orleans to Mobile Bay, the Gulf of Maine and the Pacific Northwest. Given the numerous applications that can benefit from having a vertical datum transformation tool, the goal is to develop a seamless nationwide VDatum utility that would facilitate more effective sharing of vertical data and also complement a vision of linking such data through national elevation and shoreline databases.

Development of a Continuous Bathymetric/Topographic Unstructured Coastal Flooding Model to Study Sea Level Rise in North Carolina

A model to examine the impacts of long term sea level rise (SLR) is being implemented in the coastal North Carolina ecosystem. This area is particularly vulnerable to SLR, as a fragile system of barrier islands protects an extensive but sensitive estuarine system. The primary impact of SLR is to the hydrodynamic response of the system: circulation, tidal amplitude, and inundation patterns due to tides, winds, and storms can all change in response to rising sea level. Rates of SLR in the region are just under 3 mm/year and are increasing, and inundation is tied to inlet conveyance which can be modified by SLR. A Coastal Flooding Model (CFM) has been developed for the region by combining a finite element hydrodynamic model with a continuous bathymetric and topographic elevation dataset. The CFM domain extends from 90 km offshore of the Outer Banks to the 15 m topographic contour and from northern Currituck Sound south to the New River. The CFM provides high resolution of coastal features down to 20 m. High resolution topographic elevation data relative to the North American Vertical Datum of 1988 (NAVD 88) was combined with bathymetric sounding data relative to local tidal datums by transforming the tidal datums to NAVD 88 with the VDatum vertical transformation tool developed by the National Oceanic and Atmospheric Administration’s (NOAA) National Ocean Service (NOS). The VDatum tool allows for transformation among nearly 30 different tidal, orthometric, and ellipsoidal vertical datums. A 6 m horizontal resolution continuous bathymetric/topographic (bathy/topo) Digital Elevation Model (DEM) was constructed for accurate modeling of inundation. The CFM is relative to the NAVD 88 vertical datum and was populated with DEM elevations where available and other topographic and bathymetric data relative to NAVD 88 elsewhere to create a continuous bathy/topo elevation field. A two-dimensional barotropic model is used to simulate the tidal response in the CFM to study changes due to SLR and will also be used to model regional synoptic wind events and hurricane storm surge propagation with SLR. Accurate National Oceanic and Atmospheric Administration, National Ocean Service, Coast Survey Development Laboratory, Marine Modeling and Analysis Programs, N/CS13, 1315 EastWest Highway, Silver Spring, Maryland 20910; phone (301)-713-2809 2 NOAA/NOS/Coast Survey Development Laboratory 3 NOAA/NOS/National Geodetic Survey, Remote Sensing Division 4 NOAA/NOS/Center for Operational Oceanographic Products and Services

Tidal Datum Modeling in Support of NOAA's Vertical Datum Transformation Tool

Many coastal modeling applications rely on accurate bathymetry and/or topography data. The best data sets are often synthesized products with data collected from several sources which may be referenced to different vertical datums including Mean Low Water (MLW), Mean Lower Low Water (MLLW), North American Verical Datum of 1988 (NAVD 88), and others, depending on the age and source of the data. Transforming all of the data to a common vertical datum is a non-trivial problem, and so the National Ocean Service (NOS) of the National Oceanic and Atmospheric Administration (NOAA) has created a software tool called VDatum, which is designed to transform among approximately 30 vertical reference datums (including ellipsoidal, orthometric, and tidal datums). This program transforms among ellipsoidal datums using Helmert transformations, between the North American Datum of 1983 (NAD 83) (an ellipsoidal datum) and NAVD 88 (an orthometric datum) using a geoid model; between NAVD 88 and Mean Sea Level (MSL) using a topography of the sea surface model; and among tidal datums using tidal datum models. Regions where tidal datum models have been implemented include: Puget Sound and the Strait of Juan de Fuca, central California, southern coastal Louisiana, Lake Charles, Louisiana, Tampa Bay, the Outer Banks area in North Carolina, Delaware Bay, the New York Bight and Long Island Sound. A large collaboration of partners within NOS has participated to create this tool. The focus of this paper is on the work done in the Coast Survey Development Laboratory (CSDL) on the tidal datum modeling. Three types of models that have been employed to determine the tidal datum fields for the regional scale models are discussed: spatial interpolation of the datums, computation of the datums from a harmonic constant database, and computation of the datums from a regional hydrodynamic model. The results from these models are then interpolated onto the structured grid used with the VDatum software.

Tide Modeling in Support of NOAA's National VDatum Program

NOAAs National Ocean Service (NOS) has developed the VDatum software to allow users the ability to easily transform vertical elevation data among tidal, orthometric, and ellipsoid-based 3D reference systems, VDatum applications are developed on a regional basis with the goal of attaining seamless coverage for all U.S. near-coastal waters. Development of VDatum is coordinated among three NOS offices: the Coast Survey Development Laboratory (CSDL), the National Geodetic Survey (NOS), and the Center for Operational Oceanographic Products and Services (CO-OPS). As part of this collaborai ion, CSDL develops the tidal datum fields used as input to the VDatum software. This paper describes the standard modeling procedures CSDL uses to develop the tidal datum fields, how these are built into the VDatum framework of vertical datum transformations, and the community modeling framework that is envisioned for VDatum-derived models and products.