Shapefile of Historical Bathymetric Soundings for Mississippi and Alabama Derived from National Ocean Service (NOS) Hydrographic Sheets

Hydrographic sheets (H-sheets) and nautical charts produced by the National Ocean Service (NOS) during the 1800s provide historic sounding (water depth) measurements of coastal areas. The data can be vectorized into a geographic information system (GIS), adjusted to a modern vertical datum, and converted into a digital elevation model to provide an interpretation of the historic seafloor elevation. These data were produced to provide an estimate of historical bathymetry for the Mississippi-Alabama coastal region to aid geologic and coastal hazards studies. This data release includes georeferenced H-sheets, depth soundings, and a bathymetric grid derived from the 1847 and 1895 soundings. The original NOS H-sheets and nautical charts were scanned by the National Oceanic and Atmospheric Administration (NOAA) and are available through the National Geophysical Data Center (NGDC) website (NOAA, 2021) as non-georeferenced digital raster files. U.S. Geological Survey St. Petersburg Coastal and Marine Science Center (USGS SPCMSC) staff performed the following procedures: H-sheets were georeferenced, georeferenced raster images were projected to a modern datum, and historical bathymetric sounding measurements were digitized to create a vector point shapefile. Sounding data were converted from feet (ft) and fathoms (fm) to meters (m), projected to modern mean low water (MLW), and converted to the North American Vertical Datum of 1988 (NAVD88) GEOID12A using NOAA's datum transformation software, VDatum. Please read the full metadata for details on data collection, digitized data, dataset variables, and data quality.