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NGDC Digital Elevation Model Frequently Asked Questions


U.S. CRM

What is the horizontal datum of the model?

The horizontal datum of the U.S. CRM is NAD 83 geographic. This datum is effectively identical to WGS 84 geographic at the scale of the 3 arc-second (~90 meter cell size) CRM; the horizontal differences between the two datums are less than a meter across most of the U.S. All source elevation data used in building the CRM were transformed to NAD 83 geographic prior to CRM development.

What is the vertical datum of the model?

The vertical datum of the U.S. CRM is “sea level”. Source elevation data were not converted to a common vertical datum due to the large cell size of the CRM (3 arc-second; ~90 meters). This means that the vertical uncertainty of CRM elevations (greater than one meter) exceeds the differences between vertical datums (usually less than a meter). Source bathymetric data retained their original vertical datum of either mean lower low water (MLLW) or mean low water (MLW), while source topographic data remained in either NAVD 88 or NGVD 29 prior to CRM development.

What are the vertical units of the model?

Elevations of the CRM are in meters.

Are there any restrictions on using this model?

Just two: The U.S. CRM cannot be used for navigation, and products derived primarily from NGDC data are not subject to copyright protection in the United States (see http://www.ngdc.noaa.gov/ngdcinfo/privacy.html#copyright). We do ask that you acknowledge NGDC as source.

How do I cite the model?

NOAA National Geophysical Data Center, U.S. Coastal Relief Model, Retrieved date goes here, http://www.ngdc.noaa.gov/mgg/coastal/crm.html

How can I extract a specific area of the CRM?

You can extract a part of the CRM by using the 'Grid Extract' tool that can be found on the various CRM web pages. It allows you to define the boundaries of the data you want, and what file format you want the CRM in (dependant upon what formats your software can read).

Are there metadata records for the CRM?

Are there plans to update the CRM volumes?

Yes. As resources allow, all 10 volumes of the U.S. CRM will be updated, starting with Southern California, though no time frame has been set.


ETOPO1

What is the horizontal datum of the model?

The horizontal datum of ETOPO1 is WGS 84 geographic. All source elevation data used in building ETOPO1 were transformed to WGS 84 geographic prior to ETOPO1 development.

What is the vertical datum of the model?

The vertical datum of ETOPO1 is “sea level”. Source elevation data were not converted to a common vertical datum due to the large cell size of ETOPO1 (1 arc-minute; ~2 km). This means that the vertical uncertainty of ETOPO1 elevations (greater than 10 meters) exceeds the differences between vertical datums near sea level (usually less than a meter). Except for the Caspian sea bathymetric data, all source data retained their original vertical datum prior to ETOPO1 development.  

What are the vertical units of ETOPO1?

Elevations in ETOPO1 are in meters.

Are there any restrictions on using this model?

Just two: ETOPO1 cannot be used for navigation, and products derived primarily from NGDC data are not subject to copyright protection in the United States (see http://www.ngdc.noaa.gov/ngdcinfo/privacy.html#copyright). We do ask that you acknowledge NGDC as source..

Do I need permission to use ETOPO1 or its color images?

It is not necessary to obtain written permission to use ETOPO1 or other NOAA products that are in the public domain, nor are there any fees for using them. We ask only that you cite NGDC as source.

How do I cite the model?

Amante, C. and B.W. Eakins, 2009. ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis. NOAA Technical Memorandum NESDIS NGDC-24. National Geophysical Data Center, NOAA. doi:10.7289/V5C8276M [access date].

What is the difference between various global datasets? Which one should I use?

Most, if not all, current global bathymetric models use bathymetry estimated from satellite altimetry for unsurveyed ocean areas. Model cell size and completion date vary slightly, though restrictions on model use can vary significantly. Choose the one that best fits your intended use.

What happened to ETOPO2v2 and ETOPO5?

Both of these older models have been deprecated but can still be accessed from the ETOPO1 web page.

What should I do if GDAL has difficulties reading the netCDF files?

Older versions of GDAL improperly invert the ETOPO1 netCDF files (south pole at top). Please use the latest version of GDAL, which has resolved this issue.

Where can I find the color palette used to create the ETOPO1 color images?

The color palette used by NGDC can be found at cpt-city:  http://soliton.vm.bytemark.co.uk/pub/cpt-city/ngdc/index.html


Great Lakes Bathymetry

What is the horizontal datum of the data?

The horizontal datum of the Great Lakes bathymetric contours and grids is NAD 83 geographic. This datum is effectively identical to WGS 84 geographic at the scale of the data; the horizontal differences between the two datums are less than one meter in the Great Lakes region. All source elevation data used in creating the Great Lakes bathymetric contours and grids were transformed to NAD 83 geographic prior to development.

What is the vertical datum of the data?

Bathymetric data for each lake is referenced to its own low water datum (LWD). Information on the individual Lake Datums can be found at NOAA’s Tides and Currents pages (http://tidesandcurrents.noaa.gov/gldatums.html). Grids extracted using NGDC’s ‘Grid Extract’ tool are referenced to a vertical datum of Mean Sea Level.

What are the vertical units of the data?

Elevations of Great Lakes bathymetric data are in meters.

Are there restrictions on using these data?

Just two: The Great Lakes bathymetry cannot be used for navigation, and products derived primarily from NGDC data are not subject to copyright protection in the United States (see http://www.ngdc.noaa.gov/ngdcinfo/privacy.html#copyright). We do ask that you acknowledge NGDC as source.

How do I cite these data?

NOAA National Geophysical Data Center, U.S. Great Lakes Bathymetry, Retrieved date goes here, http://www.ngdc.noaa.gov/mgg/greatlakes/greatlakes.html

When will Lake Superior be completed?

No time frame has been set for completing bathymetric contours of Lake Superior, though a 3 arc-second (~90 meter cell size) grid is available.

Do you have fishing maps for the Great Lakes?

No. Fishing maps of U.S. coastal and offshore waters are available at: http://www.ngdc.noaa.gov/mgg/bathymetry/maps/nos_intro.html If the area you are interested in is not available from NGDC you might try NOAA’s nautical charts: http://www.nauticalcharts.noaa.gov/staff/chartspubs.html