Estuarine Bathymetric Digital Elevation Models (30 meter and 3 arc second resolution) Derived From Source Hydrographic Survey Soundings Collected by NOAA

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Frequently anticipated questions:


What does this data set describe?

Title:
Estuarine Bathymetric Digital Elevation Models (30 meter and 3 arc second resolution) Derived From Source Hydrographic Survey Soundings Collected by NOAA
Abstract:
These Bathymetric Digital Elevation Models (DEM) were generated from original point soundings collected during hydrographic surveys conducted by the National Ocean Service and its predecessors. Mean High Water shoreline was used as a constraining boundary and assigned its local elevation relative to the local datum (typically Mean Low Water). DEM grid values outside the shoreline (on land) were assigned null values (-32676). In the event of multiple surveys in a region, the most recent survey soundings were retained. Both 7.5 minute and 1 degree DEMs are available. The 1 degree DEMs were generated from the higher resolution 7.5 minute DEMs which covered the estuary. These DEMs are available as either Untiled (large grids) or sets of Tiled DEMs (at 7.5 degree minute size).

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 {0.01 meter]) per each profile. The last physical record of the DEM is an accuracy record (C-record).

The 1 degree (60-minute) DEMs (3 arc second x 3 arc second data spacing) is cast on the geographic coordinate system (no projection). It provides coverage in 1 degree square blocks. Each product contains over edge data. Coverage is available for the many estuaries of the conterminous United States, but is not complete.

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.

Supplemental_Information:
The datum for these bathymetric DEMs (Mean Low Water) is not the same as that used by the United States Geological Survey (USGS) for land based DEMs (NAV29), which results in a discontinuity of about 1/2 the tidal range. Moreover, the shoreline for the USGS DEMs is indeterminate and not the same as that used for the Bathymetric DEMs. Furthermore, the vertical resolution is smaller and accuracy of the Bathymetric DEMs is better than USGS DEMs. Because of these differences, extreme care should be used in merging NOAA and USGS DEM data.

One degree bathymetric DEMs have profiles (north-south lines) containing 1201 soundings. Missing values (over land as defined by the Mean High Water Line) are filled with null values represented by the value -32676. Profiles within the 1 degree square, which contain only null values, are omitted.

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.

  1. How should this data set be cited?

    Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Special Projects (SP), 19980606, Estuarine Bathymetric Digital Elevation Models (30 meter and 3 arc second resolution) Derived From Source Hydrographic Survey Soundings Collected by NOAA: NOAA's Ocean Service, Special Projects (SP), Silver Spring, MD.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -125.00
    East_Bounding_Coordinate: -65.00
    North_Bounding_Coordinate: 50.00
    South_Bounding_Coordinate: 24.00

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date:
    Ending_Date: 1989
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: raster digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Raster data set. It contains the following raster data types:

      • Dimensions, type Grid Cell

    2. What coordinate system is used to represent geographic features?

  7. How does the data set describe geographic features?

    Entity_and_Attribute_Overview:
    The digital elevation model is composed of an elevation value linked to a grid cell location representing a gridded form of a bathymetric map overlay. Each grid cell entity contains a 6-character integer value between -32,767 and 32,768. The grid is generated from profiles of data each containing header information (profile identifier, starting point, relative datum for profile values (deepest value within the DEM), number of values, etc) followed by profile values relative to the relative datum for the profile. All non-null values in the profile are positive.
    Entity_and_Attribute_Detail_Citation:
    U.S. Department of the Interior, U.S. Geological Survey, 1992, Standards for digital elevation models: Reston, VA, is available at: <http://rockyweb.cr.usgs.gov/nmpstds/demstds.html>


Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Special Projects (SP)
    Chief, Integrated Planning and Technical Services (IPTS)
    1305 East West Highway N/MB7
    Silver Spring, MD 20910-3281
    U.S.

    301-713-3000 (voice)
    301-713-4384 (FAX)
    special.projects@noaa.gov


Why was the data set created?

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).


How was the data set created?

  1. From what previous works were the data drawn?

    GEODAS vol 2 ver 3.3 (source 1 of 3)
    National Oceanic and Atmospheric Administration (NOAA), National Environmental Satellite, Data and Information Service (NESDIS), National Geophysical Data Center (NGDC), 1997, National Ocean Service- Hydrographic Survey Data: NOAA, National Environmental Satellite, Data and Information Service (NESDIS), National Geophysical Data Center (NGDC), Boulder, CO.

    Online Links:

    Type_of_Source_Media: CD-ROM
    Source_Contribution: Hydrographic Soundings

    NOAA (source 2 of 3)
    National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), 1994, Medium Resolution Vector Shoreline: NOAA's Ocean Service, Boulder, CO.

    Type_of_Source_Media: CD-ROM
    Source_Contribution: Shoreline position

    CONTROL1 (source 3 of 3)
    United States Geologic Survey (USGS) or NOAA's National Geodetic Survey (NGS), 19920503, Project control: U.S. Geological Survey, Reston, VA.

    Type_of_Source_Media: magnetic tape
    Source_Contribution: Ground control points

  2. How were the data generated, processed, and modified?

    Date: 1989 (process 1 of 1)
    The production procedures, instrumentation, hardware, and software used in the collection of standard National Oceanic and Atmospheric Administration (NOAA) Bathymetric Digital Elevation Models (DEM's) vary depending on systems used at the time of the survey.

    Logsheets 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 & Chesapeake Bays only), soundings were digitized from 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 into 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% 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 points. 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.

    Creating DEM files: The MapInfo grid files were converted to a public domain USGS format DEM files using the NOAA DEM maker software. Both Untiled (large grid) DEMs and Tiled (7.5 degree minute cells) DEMs were generated. The formats available for downloading are 30 meter & 3 arc second DEMs in USGS DEM format.

    DEM's are viewed on interactive editing systems to identify and correct blunder and systematic errors. DEM's are verified for physical format and logical consistency.

  3. What similar or related data should the user be aware of?


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

    The accuracy of a DEM is dependent upon the level of detail of the source soundings and the grid spacing used to sample that source. The primary limiting factor for the level of detail of the source is the scale of the source survey, the technology used to collect soundings, and the resolution of the source soundings. Additional complications in describing accuracy are the ages of the surveys used to collect sounding in a given area. Care was used to use the most recent surveys covering a given area but in some instances adjacent surveys may be decades apart in age. In some regions, the only source data were at fathom (6 feet) resolution. In general, most source surveys were certified to one foot or better by the National Ocean Service.

  2. How accurate are the geographic locations?

    The horizontal accuracy of the DEM is expressed as an estimated root mean square error (RMSE). The estimate of the RMSE is based upon horizontal accuracy tests of the source soundings used to generate the DEM. As a first approximation the locational accuracy of the source soundings are 0.0015 m at source "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 plotted on them.

  3. How accurate are the heights or depths?

    The vertical RMSE statistic is used to describe the vertical accuracy of a DEM. It encompasses both random and systematic errors introduced during production of the data. The RMSE is encoded in element number 5 of record C of the DEM. This accuracy estimate includes components related to quantization of the source soundings (1.3 to 0.15 m), the systematic editing of the source data (1% or 0.10m), un-sampled bathymetric features (estimated at less than 5% of depth), time related changes (erosion, deposition, and seismic shifts), and dredging operations (cut and fill).

    It is estimated that the accuracy of the Bathymetric DEMs is 2% of depth or 1 meter for depths grater than 20 meters and 2 % of 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 but cannot be completely eliminated. Blunders are errors of major proportions and are easily identified and removed during interactive editing. Systematic errors follow some fixed pattern and are introduced by data collection procedures and systems. Systematic error artifacts include vertical unsampled elevation shifts, relative spacing of the source soundings, misinterpretation of terrain surface caused by softness or poor reflectivity and by the resolution of the collected soundings (feet, feet & fractions, fathoms, fathoms & fractions, meters, tenths of meters etc.). Random errors result from unknown or accidental causes. The 1 degree (DSQ) DEMs are generated from 30 m grids on UTM projection. The RMSE difference between these surfaces is an estimate of the vertical accuracy of the DSQ DEMs.

  4. Where are the gaps in the data? What is missing?

    The DEM is visually inspected for completeness on a DEM view and edit system for the purpose of performing a final quality control and if necessary, edit of the DEM. The physical format of each DEM is validated for content completeness and logical consistency during production quality control.

    Due to the variable orientation of the 7.5 minute quadrilateral in relation to the Universal Transverse Mercator (UTM) projection grid, profiles that pass within the bounds of the DEM quadrilateral may be void of elevation grid points and are not represented in the DEM. This condition occurs infrequently and is always the first or last profile of the dataset.

    DEM's may contain void areas caused by elevations being above Mean High Water or on non-tidal land. Void elevations are assigned the value of -32,767. In addition, suspect elevation areas may exist in the 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 holes in the bathymetric data set, but was not available at the time this project was completed. No additional updates or error corrections are planned for this data set.

  5. How consistent are the relationships among the observations, including topology?

    The fidelity of the relationships encoded in the data structure of the DEM are automatically verified using a NOAA-NOS software program upon completion of the data production cycle. The test verifies full compliance to the DEM specification.


How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: none
Use_Constraints:
Not to be used for Navigation.

Acknowledgment of the National Oceanic and Atmospheric Administration- Nation Ocean Service would be appreciated in products derived from these data.

The datum for these bathymetric DEMs (Mean Low Water) is not the same as that used by the US Geological survey (USGS) for land based DEMs (NAV29) which results in a discontinuity of about 1/2 the tidal range. Moreover, the shoreline for the USGS DEMs is indeterminate and not the same as that used for the Bathymetric DEMs. Furthermore, the vertical resolution is smaller and accuracy of the Bathymetric DEMs is better than USGS DEMs. Because of these differences, extreme care should be used in merging NOAA and USGS DEM data.

  1. Who distributes the data set? (Distributor 1 of 1)

    National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Special Projects
    Chief, Integrated Planning and Technical Services (IPTS)
    1305 East West Highway N/MB7
    Silver Spring, Maryland 20910
    U.S.

    301-713-3000 (voice)
    301-713-4384 (FAX)
    special.projects@noaa.gov

    Hours_of_Service: 0800-1600 Monday -Friday, EST
  2. What's the catalog number I need to order this data set?

    Downloadable Data

  3. What legal disclaimers am I supposed to read?

    Not to be used for navigation. Although these data have been processed successfully on a computer system at the National Oceanic and Atmospheric Administration, no warranty expressed or implied is made by NOAA regarding the utility of the data on any other system, nor shall the act of distribution constitute any such warranty. The National Oceanic and Atmospheric Administration will warrant the delivery of this product in computer-readable format and will offer appropriate adjustment of credit when the product is determined unreadable by correctly adjusted computer input peripherals, or when the physical medium is delivered in damaged condition. Requests for adjustment of credit must be made within 90 days from the date of this shipment from the ordering site.

  4. How can I download or order the data?


Who wrote the metadata?

Dates:
Last modified: 20-Dec-2012
Last Reviewed: 10-May-2010
Metadata author:
National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Special Projects (SP)
Chief, Integrated Planning and Technical Services (IPTS)
1305 East West Highway N/MB7
Silver Spring, MD 20910-3281
U.S.

301-713-3000 (voice)
301-713-4384 (FAX)
special.projects@noaa.gov

Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)


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