San Antonio Bay, TX (G290) Bathymetric Digital Elevation Model (30 meter resolution)
Derived From Source Hydrographic Survey Soundings Collected by NOAA
Bathymetry for San Antonio Bay was derived from five surveys containing 32,829 soundings.
Two older, overlapping, less accurate surveys were deleted before tinning. The average
separation between soundings was 134 meters. The five surveys used dated from 1934
and 1935. The range of soundings was 0.2 meters to -12.2 meters at mean low water.
Mean high water values between 0.2 and 0.4 meters were assigned to the shoreline.
No points were edited out of the data set. DEM grid values outside the shoreline (on
land) were assigned null values (-32676). San Antonio Bay has twelve 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.
||1934-01-01 to 1935-01-01
|Spatial Reference System
|Spatial Bounding Box Coordinates
|Spatial Coverage Map
|Data Presentation Form
|Dataset Progress Status
||Complete - production of the data has been completed
|Data Update Frequency
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.
||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).
- Not to be used for navigation. Although these data are of high quality and useful
for planning and modeling purposes, they are not suitable for navigation. For navigation,
please refer to the NOS nautical chart series.
- Produced by the NOAA National Geophysical Data Center. Not subject to copyright protection
within the United States.
- Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA),
National Ocean Service (NOS), Special Projects (SP)
- NOAA's National Ocean Service, Special Projects (SP)
||Global Change Master Directory (GCMD) Science Keywords
- Earth Science > Oceans > Bathymetry/Seafloor Topography > Seafloor Topography
- Earth Science > Oceans > Bathymetry/Seafloor Topography > Bathymetry
- Earth Science > Oceans > Bathymetry/Seafloor Topography > Water Depth
- Earth Science > Oceans > Coastal Processes > Coastal Elevation
- Coastal Relief
- Gridded elevations
- San Antonio Bay, TX
- United States
|Data Resolution keywords
||Global Change Master Directory (GCMD) Horizontal Data Resolution KeywordsGlobal Change Master Directory (GCMD) Vertical Data Resolution Keywords
||No constraint information available
- Distribution liability: NOAA and NCEI make no warranty, expressed or implied, regarding
these data, nor does the fact of distribution constitute such a warranty. NOAA and
NCEI cannot assume liability for any damages caused by any errors or omissions in
these data. If appropriate, NCEI can only certify that the data it distributes are
an authentic copy of the records that were accepted for inclusion in the NCEI archives.
|| Fee information not available.
Lineage information for: dataset
- DOC/NOAA/NESDIS/NCEI > National Centers for Environmental Information, NESDIS, NOAA,
U.S. Department of Commerce
- The production procedures, instrumentation, hardware, and software used in the collection
of standard National Oceanic and Atmospheric Administration (NOAA) Bathymetric Digital
Elevation Models (DEMs) vary depending on systems used at the time of the survey.
Log sheets were kept at all stages of processing to track file names,dates, hydrographic
survey coverage, and soundings or hydrographic surveys that were deleted as part of
the quality control process. A short summary of the processing steps for each estuary
is available on the individual data pages. In addition, a list of each of the surveys
which were included is accessible through the individual data pages. Original hydrographic
data from the National Ocean Service and it predecessors was used exclusively as source
data. Processing was performed on desktop computers using a variety of commercial
and custom software systems. The two main software systems used were Digital Optimization
of Grid Systems (DOGS) version 1.5x software developed by NOAA and MapInfo Professional
version 4.5 published by MapInfo augmented by a MapInfo add-on named Vertical Mapper
published by Northwood Geosciences. The processing sequence for each estuary started
with the generation of a comprehensive source data set from the NOS archives, These
source sounding were quality controlled to eliminate outliers and superseded surveys,
optimized to reduce the number of data values, augmented with points representing
the Mean High Water shoreline, and then gridded. The gridded data sets were converted
from the internal proprietary grid format to Digital Elevation Model (DEM) format
for public distribution. Creating Point Sets of Hydrographic Survey Data: Sounding
data obtained from Hydrographic Surveys were extracted using DOGS from the GEODAS
CD distributed by the National Geophysical Data Center using each estuary's shoreline
as a clipping boundary. Large estuaries were broken into several overlapping regions
and subsets of points were extracted and processed. Most historic hydrographic surveys
are included on the GEODAS CD. For those regions which were missing data (parts of
southern Florida and Chesapeake Bays only), soundings were digitized from a hard copy
smooth sheets generated by the Hydrographic Surveys. Editing and Quality Control of
Bathymetry Point Data: The first step of the quality control was to review the data
using the DOGS software. The data were first examined for surveys or parts of surveys
that are redundant. For many areas there are more surveys than are actually useful.
Entire surveys or large portions of surveys were deleted for the following reasons:
Another more recent survey fully covers the same area. The survey has questionable
values which can not be fixed by way of figuring out a mathematical update value for
the entire survey, and there are too many bad points to pick out probable "good" values.
Sections of surveys were omitted if they were overlapped by more accurate surveys
or by similar yet denser coverage. The second step was to display the data by depth
values and to remove stray points that were obvious outliers from the surrounding
data values. Optimizing the Bathymetry Point Data using DOGS: The data was first triangulated
in DOGS in order to optimize the set of points. The computer program DOGS can analyze
a large set of bathymetric data and create from it a smaller set of optimized points
which describes the bathymetry of a geographic region to within a user defined error.
This smaller data set then can be used on its own as a representation of the area's
bathymetry, or as input in to other computer programs or Geographical Information
Systems. There are two calculation options for triangulation in DOGS: relative and
absolute. Bathymetry point files were cut into sections for separate processing based
on mean depth of 10 meters. A relative height error criteria of 0.01 was used for
the triangulation of regions whose depths averaged above 10 meters. An absolute height
error criteria of 0.1 meters was used for areas with average depths less than 10 meters.
The two resultant files were saved as text files. After combining these files, the
vertical error associated with the optimized data set was 1 percent of depth or 0.1
meters, whichever was greater. The optimized DOG file was imported into MapInfo's
MapInfo Professional desktop mapping software. Augmenting the data set with Shoreline
Points: The final bathymetry was clipped to NOAA's 1:250,000 Coastal Assessment Framework
(CAF) shoreline. A copy of the shoreline file was edited to create a point file from
the vector vertices and optimized using DOGS to produce a more workable, smaller file,
with little compromise to the shape of the shoreline. Mean High Water tide level was
assigned to the shoreline points to give them a height. These Shoreline data points
were added to the set of bathymetry points before doing the final triangulation in
MapInfo. Generation of a Gridded Bathymetry Dataset: Linear triangulation of the combined
point files were done in MapInfo using the Vertical Mapper 2.0 partner product software.
The resultant TIN file was then used to create a continuous grid file with 30 meter
resolution on a UTM projection using a NAD27 horizontal datum. A second grid was created
from the first by aggregating the 30 meter grid values to 90 meter resolution and
exporting the 90m center points. A new TIN was created after reattaching the shoreline
pts. The triangle side lengths and coincident point distances were small enough to
disallow interpolation outside the 90m distance, so as to emulate a rectangular interpolation
and still allow the shoreline to be represented without averaging out the values.
The result of the new file is a geographic 3 arc second resolution grid. Both grids
were cut to the estuary boundary shoreline. 7.5 minute and 1 degree sections were
then created from these grids. The 7.5 minute grids have 30 meter resolution in a
UTM projection using the NAD27 datum. The 1 degree grids have a 3 arc second resolution
in a geographic projection (Latitude/Longitude) using the NAD27 datum. In their native
form, both of these grids are in proprietary formats. Creating DEM files: The MapInfo
grid files were converted to a public domain USGS format DEM files using the NOAA
DEM maker software. The formats available for downloading are 30 meter and 3 arc second
DEMs in USGS DEM format. DEMs are viewed on interactive editing systems to identify
and correct blunder and systematic errors. DEMs are verified for physical format and
- 2017-04-14T00:00:00 - Original data files were converted to netCDF with GDAL transform utility.
- National Ocean Service- Hydrographic Survey Data
- Description of Source: Source Contribution: Hydrographic Soundings; Source Type: CD-ROM
- Temporal extent used:
1934-01-01 to 1935-01-01
- Medium Resolution Vector Shoreline
- Description of Source: Source Contribution: Shoreline position; Source Type: CD-ROM
- Temporal extent used:
1970-01-01 to 1990-01-01
- Project control
- Description of Source: Source Contribution: Ground control points; Source Type: magnetic tape
Last Modified: 2018-06-11
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