Data Set and Methods
Determining Operational MHW Elevations to Define Lidar Shorelines
In order to process the large amount of lidar data collected with the ATM, the U.S. coastline is broken up into small areas, or "tiles". Nearly all tiles are the same size (0.25 degrees latitude/longitude on a side), and each state has its own set of tiles (Appendices IV and V). The lidar data are processed state-by-state and tile-by-tile, first to extract profiles and then to derive the shorelines.
"MHW Zones", sections of coast to which one operational MHW elevation is assigned, were created for the East, Gulf, and West Coasts. Zone boundaries were placed at natural geographic breaks to avoid MHW changes along continuous sections of coast. When possible, the variation in MHW elevations from tide stations within a zone did not exceed 20 cm. Also, where possible, lidar tiles were not split between zones. The average MHW elevation from all tide stations within each zone was the operational MHW elevation assigned to that zone. This operational MHW elevation defines the elevation of all lidar shorelines within that zone.
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