Galveston Bay, TX (G260) Bathymetric Digital Elevation Model(30 meter resolution) Derived From Source Hydrographic SurveySoundings
Collected by NOAA
Dataset Identification:
Resource Abstract:
Bathymetry for Galveston Bay was derived from thirty-three surveyscontaining 209,359 soundings. Twelve overlapping, older,
lessaccurate surveys were omitted, and overlap from eight older, lessaccurate surveys was omitted. The average separation
between soundingswas 84 meters. The thirty-three surveys used dated from 1931 to 1983with the oldest surveys in the northern
and southernmost portionsof the bay. The majority of the surveys were from the early 1960 s. Thesoundings ranged from 1.2
meters to -16.5 meters at mean low water. Meanhigh water values of 0.3 or 0.4 meters were assigned to the shoreline.Twelve
points were found that were not consistent with the surrounding points.These were removed prior to tinning. DEM grid values
outside theshoreline (on land) were assigned null values (-32676).Galveston Bay has twenty-nine 7.5 minute DEMs and two one
degreeDEMs. The 1 degree DEMs were generated from the higher resolution 7.5minute DEMs which covered the estuary. A Digital
Elevation Model(DEM) contains a series of elevations ordered from south to northwith the order of the columns from west to
east. The DEM isformatted as one ASCII header record (A- record), followed by aseries of profile records (B- records) each
of which include a shortB-record header followed by a series of ASCII integer elevations(typically in units of 1 centimeter)
per each profile. The lastphysical 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.
Citation
Title Galveston Bay, TX (G260) Bathymetric Digital Elevation Model(30 meter resolution) Derived From Source Hydrographic SurveySoundings
Collected by NOAA
publication Date
1998-06-06
presentationForm
mapDigital
cited responsible party
-
publisher
organisation Name
NOAA's Ocean Service, Special Projects (SP)
Contact information
Address
, Silver Spring, MD
cited responsible party
-
originator
organisation Name
Department of Commerce (DOC), National Oceanic andAtmospheric Administration (NOAA), National Ocean Service (NOS),Special
Projects (SP)
other Citation Details
Cinergi keyword enhanced at Sun Nov 13 17:50:57 UTC 2016
purpose:
Bathymetric DEM's can be used as layers in GeographicInformation Systems (GIS) for earth science analysis. DEM's can alsoserve
as tools for volumetric analysis, for site location ofstructures, or for drainage basin delineation. The source soundingsare
collected by the NOS Office of Coast Survey (OCS).
Resource language:
eng; USA
Resource progress code:
completed
Resource Maintenance Information
maintenance or update frequency:
irregular
Constraints on resource usage:
Constraints
Use limitation statement:
These data were prepared by an agency of theUnited States Government. Neither the United States Government norany agency thereof,
nor any of their employees, make any warranty,expressed or implied, or assumes any legal liability orresponsibility for the
accuracy, completeness, or usefulness of anyinformation, apparatus, product, or process disclosed in this report,or represents
that its use would not infringe privately owned rights.Reference therein to any specific commercial product, process, orservice
by trade name, trademark, manufacturer, or otherwise does notnecessarily constitute or imply its endorsement, recommendation,
orfavoring by the United States Government or any agency thereof. Anyviews and opinions of authors expressed herein do not
necessarilystate or reflect those of the United States Government or any agencythereof. Although all data have been used by
NOAA, no warranty,expressed or implied, is made by NOAA as to the accuracy of the dataand/or related materials. The act of
distribution shall notconstitute any such warranty, and no responsibility is assumed byNOAA in the use of these data or related
materials.
Constraints on resource usage:
Legal Constraints
use constraint:
otherRestrictions
Other constraints
Use Constraints: Not to be used for Navigation.Acknowledgment of the National Oceanic and AtmosphericAdministration- Nation
Ocean Service would be appreciated in productsderived from these data.The datum for these bathymetric DEMs is not the same
as that used bythe US Geological survey (USGS) for land based DEMs which results ina discontinuity if the two datasets are
merged together. Moreover,the shoreline for the USGS DEMs is indeterminate and not the same asthat used for the Bathymetric
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.
Constraints on resource usage:
Legal Constraints
Access Constraints
otherRestrictions
Other constraints
Access Constraints: none
Spatial representation type code:
grid
Resource extent
Geographic Extent
Geographic Bounding Box
westBoundLongitude
-95.294595
eastBoundLongitude
-94.464283
northBoundLatitude
29.825739
southBoundLatitude
29.000501
Temporal Extent
1931-01-01
1983-01-01
Additional information on resource:
The datum for these bathymetric DEMs is not the same as that used bythe United States Geological Survey (USGS) for land based
DEMs whichresults in a discontinuity if the two datasets are merged together.Moreover, the shoreline for the USGS DEMs is
indeterminate and notthe same as that used for the Bathymetric DEMs. Because of these differences, extreme careshould be used
in merging NOAA and USGS DEM data.7.5-minute DEMs have rows and columns which vary in length and arestaggered. The UTM bounding
coordinates form a quadrilateral (no twosides are parallel to each other), rather than a rectangle. The userwill need to pad
out the uneven rows and columns with blanks orflagged data values, if a rectangle is required for the user'sapplication. Some
software vendors have incorporated this functioninto 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.
point of contact
-
pointOfContact
organisation Name
National Oceanic and Atmospheric Administration(NOAA), National Ocean Service (NOS), Special Projects (SP)
position Name Chief, Integrated Planning and Technical Services
Contact information
Telephone
Voice 301-713-3000
Fax 301-713-4384
Address
1305 East West Highway N/MB7, Silver Spring, MD, 20910
source description
Source Contribution: Shoreline position Source Type CD-ROM
representative resolution scale:
Scale denominator: Unknown
source citation
Title Medium Resolution Vector Shoreline
publication Date
1994-01-01
presentationForm
mapDigital
cited responsible party
-
publisher
organisation Name
NOAA's Ocean Service
Contact information
Address
, Boulder, CO
cited responsible party
-
originator
organisation Name
National Oceanic and Atmospheric Administration (NOAA),National Ocean Service (NOS)
Resource extent
Temporal Extent
1970-01-01
1990-01-01
source
source description
Source Contribution: Ground control points Source Type magnetic tape
representative resolution scale:
Scale denominator: Unknown
source citation
Title Project control
publication Date
1992-05-03
cited responsible party
-
publisher
organisation Name
U.S. Geological Survey
Contact information
Address
, Reston, VA
cited responsible party
-
originator
organisation Name
United States Geologic Survey (USGS) or NOAA's NationalGeodetic Survey (NGS)
Resource extent
Temporal Extent
AbsoluteExternalPositionalAccuracy
name Of Measure Horizontal Positional Accuracy Report
evaluation Method Description
The horizontal accuracy of theDEM is expressed as an estimated root mean square error (RMSE). Theestimate of the RMSE is based
upon horizontal accuracy tests of thesource soundings used to generate the DEM. As a first approximationthe locational accuracy
of the source soundings are 0.0015 m atsource "Smooth Sheet" scale (120 m @ 1:80,000 to 15 m @ 1:10,000).Smooth Sheets are
maps generated as a principle product of each(historic) hydrographic survey with fully corrected soundings plottedon them.
AbsoluteExternalPositionalAccuracy
name Of Measure Horizontal Positional Accuracy
measure Description
Digital elevation modelscomply with the National Map Accuracy Standards (NMAS) accuracyrequirements.
Quantitative Result
result value 3
value Units
AbsoluteExternalPositionalAccuracy
name Of Measure Vertical Positional Accuracy Report
evaluation Method Description
The vertical RMSE statistic is used to describe the vertical accuracyof a DEM. It encompasses both random and systematic errors
introducedduring production of the data. The RMSE is encoded in element number5 of record C of the DEM. This accuracy estimate
includes componentsrelated to quantization of the source soundings (1.3 to 0.15 m), thesystematic editing of the source data
(1percentor 0.10m), un-sampledbathymetric features (estimated at less than 5percentof depth), timerelated changes (erosion,
deposition, and seismic shifts), anddredging operations (cut and fill).It is estimated that the accuracy of the Bathymetric
DEMs is2percentof depth or 1 meter for depths grater than 20 meters and 2percentof depth or 0.20 meters for depths shallower
than 20 meters.THESE DEMs SHOULD NOT BE USED FOR NAVIGATION.There are three types of DEM vertical errors: blunder, systematic,and
random. These errors are reduced in magnitude by editing butcannot be completely eliminated. Blunders are errors of majorproportions
and are easily identified and removed during interactiveediting. Systematic errors follow some fixed pattern and areintroduced
by data collection procedures and systems. Systematicerror artifacts include vertical unsampled elevation shifts, relativespacing
of the source soundings, misinterpretation of terrain surfacecaused by softness or poor reflectivity and by the resolution
of thecollected soundings (feet, feet and fractions, fathoms, fathoms andfractions, meters, tenths of meters etc.). Random
errors result fromunknown or accidental causes. The 1 degree (DSQ) DEMs are generatedfrom 30 m grids on UTM projection. The
RMSE difference between thesesurfaces is an estimate of the vertical accuracy of the DSQ DEMs.
Completeness Commission
evaluation Method Description
The DEM is visually inspected for completeness on a DEM view and editsystem for the purpose of performing a final quality
control and ifnecessary, edit of the DEM. The physical format of each DEM isvalidated for content completeness and logical
consistency duringproduction quality control.Due to the variable orientation of the 7 1/2 minute quadrilateral inrelation
to the Universal Transverse Mercator (UTM) projection grid,profiles that pass within the bounds of the DEM quadrilateral may
bevoid of elevation grid points and are not represented in the DEM.This condition occurs infrequently and is always the first
or lastprofile of the dataset.DEM's may contain void areas caused by elevations being above MeanHigh Water or on non-tidal
land. Void elevations are assigned thevalue of -32,767. In addition, suspect elevation areas may exist inthe DEM but are not
specifically identified.Only available data digitized before 1997 were used in this project.Additional sounding information
may exist for areas which have holesin the bathymetric data set, but was not available at the time thisproject was completed.
No additional updates or error corrections areplanned for this data set.
Completeness Omission
evaluation Method Description
The DEM is visually inspected for completeness on a DEM view and editsystem for the purpose of performing a final quality
control and ifnecessary, edit of the DEM. The physical format of each DEM isvalidated for content completeness and logical
consistency duringproduction quality control.Due to the variable orientation of the 7 1/2 minute quadrilateral inrelation
to the Universal Transverse Mercator (UTM) projection grid,profiles that pass within the bounds of the DEM quadrilateral may
bevoid of elevation grid points and are not represented in the DEM.This condition occurs infrequently and is always the first
or lastprofile of the dataset.DEM's may contain void areas caused by elevations being above MeanHigh Water or on non-tidal
land. Void elevations are assigned thevalue of -32,767. In addition, suspect elevation areas may exist inthe DEM but are not
specifically identified.Only available data digitized before 1997 were used in this project.Additional sounding information
may exist for areas which have holesin the bathymetric data set, but was not available at the time thisproject was completed.
No additional updates or error corrections areplanned for this data set.
ConceptualConsistency
measure Description
The fidelity of the relationships encodedin the data structure of the DEM are automatically verified using aNOAA-NOS software
program upon completion of the data productioncycle. The test verifies full compliance to the DEM specification.
Description USGS standard DEM: The standard USGS DEM can be described as an ASCIIformatted elevation file preceded by a metadata header
file of one1024 byte ASCII record
notes: This metadata was automatically generated from the FGDC Content Standards for Digital GeospatialMetadata standard (version
FGDC-STD-001-1998) using the 2012-06-20T17:21:00 version of the FGDC RSE to ISO 19115-2 transform.
Metadata contact
-
pointOfContact
organisation Name
National Oceanic and Atmospheric Administration(NOAA), National Ocean Service (NOS), Special Projects (SP)
position Name Chief, Integrated Planning and Technical Services
Contact information
Telephone
Voice 301-713-3000
Fax 301-713-4384
Address
1305 East West Highway N/MB7, Silver Spring, Maryland, 20910