2001 Vectorized Shoreline for Breton Island, Louisiana (Geographic, NAD83)

The data were collected using a Twin Otter aircraft. Attached to the aircraft was the NASA Airborne Topographic Mapper (ATM) laser scanner, which collected the data using a green raster scanning laser. The raw and processed data are stored on hard drives and archived at the U.S. Geological Survey's office in St. Petersburg, FL, and the NASA office at Wallops Flight Facility in Virginia. The navigational data were processed at Wallops Flight Facility. The navigational and raw data were downloaded into the Advanced Lidar Processing System (ALPS), where it was converted from units of time to x,y,z points for elevation. The derived surface data can then be converted into raster data in the form of a digital elevation model (GeoTIFFs), which consists of cells containing elevation data. The input parameters for the random consensus filter (RCF) were as follows: grid cell size (buffer) = 8 meters by 8 meters; vertical tolerance (vertical width) = 20 centimeters. The variables measured by ATM are distance between aircraft and GPS satellites (meters), attitude information (roll, pitch, heading in degrees), scan angle (degrees), second of the epoch (seconds), and 1-nanosecond time-resolved return intensity waveform (digital counts). Z value is referenced to orthometric elevations derived from National Geodetic Survey Geoid Model, GEOID03. Raster data are projected to Universal Transverse Mercator (UTM), Zone 16, North American Datum (NAD) 1983, meters (m) coordinates. To vectorize the shorelines, the lidar digital elevation model (DEM) data 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 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 the 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. 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, error markers were added to the shoreline shapefile to show if there were any shorelines that needed to be fixed. These errors were 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 create a foreshore and backshore shoreline. In addition, the following fields were added to the shoreline’s attribute table and calculated as necessary: "UNCERTAINT" (double), "DATE_" (Text/10), "Shoreline_" (Text/20), and "Year" (Text/10).

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.