Narragansett Bay, RI (M020) Bathymetric Digital Elevation Model (30 meter resolution) Derived From Source Hydrographic Survey Soundings Collected by NOAA
Bathymetry for Narragansett Bay was derived from fifteen surveys containing 165,184
soundings. Three older, less accurate, overlapping surveys were entirely omitted,
and the overlap from six older, less accurate surveys was omitted before tinning the
data. The average separation between soundings was 50 meters. The fifteen surveys
used dated from 1943 to 1957. The total range of sounding data was 1.2 meters to -
58.8 meters at mean low water. Mean high water values between 0.9 and 1.4 meters were
assigned to the shoreline. Four points were found that were not consistent with the
surrounding data. These were removed prior to tinning. DEM grid values outside the
shoreline (on land) were assigned null values (-32676). Narragansett Bay has thirteen
7.5 minute DEMs and a single one degree DEM. 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.
Cite this dataset when used as a source.
- ID not available.
gov.noaa.ngdc.mgg.dem:narragansett_bay_m020_30m
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Download Data |
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Distribution Formats |
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Distributor | DEM Information NOAA National Centers for Environmental Information dem.info@noaa.gov |
Dataset Point of Contact | DEM Information NOAA National Centers for Environmental Information dem.info@noaa.gov |
Time Period | 1943-01-01 to 1958-01-01 |
Spatial Reference System | urn:ogc:def:crs:EPSG::586626919 |
Spatial Bounding Box Coordinates |
West:-71.473528
East:-71.101234
South:41.426327
North:41.872718
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Spatial Coverage Map |
General Documentation |
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Associated Resources |
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Publication Dates |
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Edition | First |
Data Presentation Form | mapDigital |
Dataset Progress Status | Complete - production of the data has been completed |
Data Update Frequency | Irregular |
Supplemental Information |
The datum for these bathymetric DEMs is not the same as that used by the United States
Geological Survey (USGS) for land based DEMs which results in a discontinuity if the
two datasets are merged together. Moreover, the shoreline for the USGS DEMs is indeterminate
and not the same as that used for the Bathymetric DEMs. Because of these differences,
extreme care should be used in merging NOAA and USGS DEM data. 7.5-minute DEMs have
rows and columns which vary in length and are staggered. The UTM bounding coordinates
form a quadrilateral (no two sides are parallel to each other), rather than a rectangle.
The user will need to pad out the uneven rows and columns with blanks or flagged data
values, if a rectangle is required for the user's application. Some software vendors
have incorporated this function into their software for input of standard formatted
USGS DEMs. The data within the bathymetry file is floating point. When using the data
within a GIS care must be taken to ensure that the data are being read as floating
point and not integer data.
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Purpose | Bathymetric DEM's can be used as layers in Geographic Information Systems (GIS) for earth science analysis. DEM's can also serve as tools for volumetric analysis, for site location of structures, or for drainage basin delineation. The source soundings are collected by the NOS Office of Coast Survey (OCS). |
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Originators |
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Publishers |
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Theme keywords | Global Change Master Directory (GCMD) Science Keywords
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Place keywords | None
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Data Resolution keywords | Global Change Master Directory (GCMD) Horizontal Data Resolution Keywords
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Use Constraints | No constraint information available |
Access Constraints |
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Fees | Fee information not available. |
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Last Modified: 2018-07-16
For questions about the information on this page, please email:dem.info@noaa.gov