Great Bay, NH (N130) Bathymetric Digital Elevation Model (30 meter resolution) Derived From Source Hydrographic Survey Soundings Collected by NOAA
Bathymetry for Great Bay was derived from six surveys containing 30,640 soundings.
One older, less accurate, overlapping survey was omitted before tinning the data.
The average separation between soundings was 39 meters. There was a survey in the
southeast that dated from 1950. The other five surveys dated from 1953 or 1954. The
total range of soundings was 3.4 meters to -24.7 meters at mean low water. Mean high
water values between 2.1 and 2.7 meters were assigned to the shoreline. Ten 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). Great Bay has five 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:great_bay_n130_30m
Search Data |
|
Download Data |
|
Distribution Formats |
|
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 | 1950-01-01 to 1954-01-01 |
Spatial Reference System | urn:ogc:def:crs:EPSG::586626919 |
Spatial Bounding Box Coordinates |
West:-70.932275
East:-70.687632
South:43.039643
North:43.190601
|
Spatial Coverage Map |
General Documentation |
|
Associated Resources |
|
Publication Dates |
|
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.
|
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). |
Use Limitations |
|
Originators |
|
Publishers |
|
Theme keywords | Global Change Master Directory (GCMD) Science Keywords
|
Place keywords | None
|
Data Resolution keywords | Global Change Master Directory (GCMD) Horizontal Data Resolution Keywords
|
Use Constraints | No constraint information available |
Access Constraints |
|
Fees | Fee information not available. |
Processor |
|
Processing Steps |
|
Source Datasets |
|
Last Modified: 2018-06-12
For questions about the information on this page, please email:dem.info@noaa.gov