Shorelines Extracted from 1984-2015 Landsat Imagery: Dauphin Island, Alabama (Polygon: Individual Dates)

Landsat 5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), and Landsat 8 Operational Land Imager (OLI) satellite imagery were acquired in digital format from the U.S. Geological Survey Global Visualization Viewer (http://glovis.usgs.gov/). Images were selected based on cloud-free areas of interest. Landsat 7 ETM+ images after May 2003 were not used due to striping caused by the failure of the instrument's scan-line corrector. The Landsat images were processed using ArcGIS. Images were subset (trimmed) to the area of interest and isolines were generated based on the numerical values of band 7. Band 7, an infrared band (2.08-2.35 µm for TM, 2.09-2.35 µm for ETM+, 2.11-2.29 µm for OLI), clearly distinguishes land from water due to the absorption of these wavelengths by water (Lillesand and Kiefer, 1987) resulting in a low reflectance in contrast to the higher reflectance of land areas, particularly sand. Each isoline was visually compared with its corresponding image and the isoline that best represented the land/water line was selected to represent the shoreline and saved to a shapefile. When necessary, small hand edits were made to the selected isolines. The line features were then converted to polygons. Wet, marshy shorelines were less reliably delineated using this method and varied more with tide level than the sandy shorelines. Predicted tide levels relative to Mean Lower Low Water (MLLW) from the Dauphin Island tide station were obtained from a tide and current prediction program, WXTide32, (www.wxtide32.com) and added as an attribute to dauphin_po_19840325_20150421.shp. No adjustments were made to the shorelines for varying tide levels.

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.