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Matagorda Bay, TX (G280) Bathymetric Digital Elevation Model (30 meter resolution) Derived From Source Hydrographic Survey Soundings Collected by NOAA
Bathymetry for Matagorda Bay was derived from twenty-three surveys containing 250,396 soundings. Six overlapping, older, less accurate surveys were omitted, and the overlap from six older surveys was also omitted. The average distance between surveys was 67 meters. The twenty-three surveys used dated from 1934 to 1992. Seven surveys from 1934 and 1935 cover the northeast, northwest, and southern extremes of Matagorda Bay. Sixteen surveys from 1991 and 1992 cover the central and eastern portions of the bay. The range of soundings for the 23 surveys used was 0.2 meters to -26.6 meters at mean low water. Mean high water values between 0.1 and 0.3 meters were assigned to the shoreline. Twenty-nine points were found that were not consistent with the surrounding points; twenty-eight of these were from the same survey. All of these were removed prior to tinning. DEM grid values outside the shoreline (on land) were assigned null values (-32676). Matagorda Bay has twenty-one 7.5 minute DEMs and two one degree DEMs. The 1 degree DEMs were generated from the higher resolution 7.5 minute DEMs which covered the estuary. A Digital Elevation Model (DEM) contains a series of elevations ordered from south to north with the order of the columns from west to east. The DEM is formatted as one ASCII header record (A- record), followed by a series of profile records (B- records) each of which include a short B-record header followed by a series of ASCII integer elevations (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 the Universal Transverse Mercator (UTM) projection. It provides coverage in 7.5- by 7.5-minute blocks. Each product provides the same coverage as a standard USGS 7.5-minute quadrangle but the DEM contains over edge data. Coverage is available for many estuaries of the contiguous United States but is not complete.