San Francisco Bay, CA (P090) Bathymetric Digital ElevationModel (30 meter resolution) Derived From Source Hydrographic SurveySoundings Collected by NOAA

Bathymetry for San Francisco Bay was derived from thirty surveys containing417,452 soundings. Older, less accurate, overlapping surveys wereeither partially or entirely omitted. The average separation between soundingswas 53 meters. Four surveys in the southern part of the bay dated from1956. The remaining surveys dated from 1971 to 1993. The total range ofsounding data was 12.1 meters to -12.7 meters at mean low water. Mean highwater values between 1.2 and 2.3 meters were assigned to the shoreline.Twenty-five points were found that were not consistent with the surroundingdata. These were removed prior to tinning. DEM grid values outside the shoreline (on land) wereassigned null values (-32676).San Francisco Bay has twenty-four 7.5 minute DEMs and three onedegree DEMs. The 1 degree DEMs were generated from the higherresolution 7.5 minute DEMs which covered the estuary. A DigitalElevation Model (DEM) contains a series of elevations ordered fromsouth to north with the order of the columns from west to east. TheDEM is formatted as one ASCII header record (A- record), followed bya series of profile records (B- records) each of which include ashort B-record header followed by a series of ASCII integerelevations (typically in units of 1 centimeter) per each profile.The last physical record of the DEM is an accuracy record(C-record).The 7.5-minute DEM (30- by 30-m data spacing) is cast on theUniversal Transverse Mercator (UTM) projection. It provides coveragein 7.5- by 7.5-minute blocks. Each product provides the samecoverage as a standard USGS 7.5-minute quadrangle but the DEMcontains over edge data. Coverage is available for many estuaries ofthe contiguous United States but is not complete.