2013 Vectorized Shoreline for Breton Island, Louisiana (Geographic, NAD83)

A topographic lidar survey was conducted on July 12-14, 2013 over Dauphin Island, Alabama and Chandeleur, Stake, Grand Gosier and Breton Islands, Louisiana. The data were collected at a nominal pulse space of 1 meter (m) and processed to identify bare earth elevations. Bare earth Digital Elevation Models (DEMs) were generated based on these data. The bare earth DEMs are 32-bit floating point ERDAS Imagine (IMG) files with a horizontal spatial resolution of 1-m by 1-m. They are projected to Universal Transverse Mercator (UTM), Zone 16, North American Datum (NAD) 1983, meters (m) coordinates. To vectorize the shorelines, the DEMs were added to ArcMap 10.2.2. The symbology of the map was changed to classify the image into two elevation classes at 0.23 meters, delineating the location of the average mean high water (MHW) shoreline for the Breton Island area. The MHW elevation was determined by tide gauge measurements and is reported in Morton and others (2004). The two-class raster was then examined against aerial imagery and it was determined that this elevation provided a good approximation of the MHW shoreline via visual inspection of the wet/dry sand line. After the value of 0.23 was chosen, the ArcMap tool "Contour List" was used to create a shoreline. To remove any sharp edges from the shoreline the ArcMap tool "Smooth Line" was used. Using ArcMap’s “Edit” tool, any extra lines, overlapping lines, and remaining sharp angle lines were removed. If needed, some areas were hand digitized to ensure they matched the Lidar data, which was classified to 0.23 m. After the shoreline was edited, it was checked for any remaining errors using ArcMap 10.2.2 "Create Topology" tool. Five rules were added to ensure that the shorelines were matching up correctly. The five rules are that the shorelines must not have dangles, must not intersect (line), must not overlap (line), must not self intersect (line), and must not self-overlap (line). Next, using the “Validate Topology” tool, errors were flagged in the shoreline shapefile and fixed accordingly to ensure that the shoreline was continuous and free of errors. Shorelines were then split at the northern most point and the southern most point to get a foreshore and backshore shoreline. Added "UNCERTAINT" (double), "DATE_" (Text/10), "Shoreline_" (Text/20), and "Year" (Text/10) fields.

Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog.

Added keywords section with USGS persistent identifier as theme keyword.