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srtm30plus-na_pctshade.tif - SRTM30PLUS color-encoded shaded relief image of North America (approximately 1km) - GeoTIFF image

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Frequently-anticipated questions:


What does this data set describe?

Title:
srtm30plus-na_pctshade.tif - SRTM30PLUS color-encoded shaded relief image of North America (approximately 1km) - GeoTIFF image
Abstract:
Joseph J. Becker and David T. Sandwell at the Scripps Oceanographic Institute have generated a dataset of world-wide coverage combining NASA's Shuttle Radar Topography Mission (SRTM) obtained elevation data and Smith and Sandwell global 2-minute bathymetry. This data set provides a global composite of elevation that can be utilized to create elevation/bathymetry visualization.

The Shuttle Radar Topography Mission is a collaborative project between NASA, the National Imagery and Mapping Agency (NIMA), and the German and Italian space agencies to map the elevation of a large part of the globe. SRTM consisted of a specially modified radar system that flew onboard the Space Shuttle Endeavour during an 11-day mission in February of 2000. The instrument operated virtually flawlessly and imaged 99.96% of the targeted landmass at least one time, 94.59% at least twice and about 50% at least three or more times. The goal was to image each terrain segment at least twice from different angles (on ascending, or north-going, and descending orbit passes) to fill in areas shadowed from the radar beam by terrain. The 'targeted landmass' consisted of all land between 56 degrees south and 60 degrees north latitude, which comprises almost exactly 80% of the total landmass.

While SRTM30 has the same resolution as GTOPO30, it can be considered a more accurate global digital data set compared to GTOPO30 because of its seamless and uniform representation, due to the fact that it was created over a short period of time from a single source rather than from the numerous sources spanning many decades that went into creating the GTOPO30 data set.

This data set does not provide the high resolution SRTM elevation of the original one degree datasets. Sample spacing for the original individual data points is either 1 arc-second or 3 arc-seconds, referred to as SRTM-1 and SRTM-3, respectively. The user may visit <ftp://e0mss21u.ecs.nasa.gov/srtm/> or <ftp://e0mss21u.ecs.nasa.gov/srtm/> to obtain the higher resolution datasets.

Supplemental_Information:
While SRTM30 has the same resolution as GTOPO30, it can be considered a more accurate global digital data set compared to GTOPO30 because of its seamless and uniform representation, due to the fact that it was created over a short period of time from a single source rather than from the numerous sources spanning many decades that went into creating the GTOPO30 data set. However, it must be noted that the SRTM30 does not cover the poles north and south of approximately 60° latitude. Therefore, data for Antarctica, for example, must be obtained from the GTOPO30 data set.
  1. How should this data set be cited?

    Paskevich, Valerie, 200508, srtm30plus-na_pctshade.tif - SRTM30PLUS color-encoded shaded relief image of North America (approximately 1km) - GeoTIFF image: Open-File Report 2005-1001, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Poppe, L.J., Williams, S.J., and Paskevich, V.F., 2005, U.S. Geological Survey East-Coast Sediment Analysis: Procedures, Database, and GIS Data: Open-File Report 2005-1001, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.

    Online Links:

    Other_Citation_Details:
    Publication and data are released via DVD-ROM media. This digital publication may also be available via the web at pubs.usgs.gov

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -180
    East_Bounding_Coordinate: -30
    North_Bounding_Coordinate: 90
    South_Bounding_Coordinate: 0

  3. What does it look like?

    <http://pubs.usgs.gov/of/2005/1001/data/basemaps/srtm30plus/srtm30plus-na_pctshade-thumb.gif> (GIF)
    Thumbnail image showing extent and coverage of data layer.
    <http://pubs.usgs.gov/of/2005/1001/data/basemaps/srtm30plus/srtm30plus-na_pctshade.gif> (GIF)
    Overview showing image extent and coverage of data layer.

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

    Calendar_Date: 2005
    Currentness_Reference: publication date

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

    Geospatial_Data_Presentation_Form: remote-sensing image

  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 10804 x 18001 x 1, type Pixel

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

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.008333. Longitudes are given to the nearest 0.008333. Latitude and longitude values are specified in Decimal degrees.

      The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257224.

  7. How does the data set describe geographic features?


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?

    Please credit Joseph J. Becker, David T. Sandwell for the compilation of the Land and Ocean data used as the source.

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

    Valerie Paskevich
    U.S. Geological Survey
    Information Specialist, GIS Coordinator
    384 Woods Hole Road
    Woods Hole, MA 02543-1598
    USA

    (508) 548-8700 x2281 (voice)
    (508) 457-2310 (FAX)
    vpaskevich@usgs.gov


Why was the data set created?

This image provides a broad scale view of the world topography (elevation and bathymetry) on which other Geographic Information System (GIS) data layers may be co-located and viewed.

These data are intended for science researchers, students, policy makers, and the general public. The data can be used with geographic information systems (GIS) software to display geologic and oceanographic information.


How was the data set created?

  1. From what previous works were the data drawn?

    srtm30plus (source 1 of 1)
    Becker, Joseph J. , and Sandwell, David T. , 200412, SRTM30_PLUS: SRTM30, Coastal and Ridge Multibeam, Estimated Topography: Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA.

    Online Links:

    Type_of_Source_Media: disc
    Source_Scale_Denominator: 1:1000
    Source_Contribution:
    This data consists of 33 files binary of global topography (elevation & bathymetry; 16-bit signed values). The individual files were downloaded via the web and combined to create a single raster coverage of world coverage. The grid resolution of the source data is 30 second which is roughly one kilometer.

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

    Date: 02-May-2005 (process 1 of 8)
    Thirty-three zip archive files of global topography were downloaded. The files were unzipped to create raw 16-bit binary data files. Each of the thirty-three files were imported into a separate PCI Geomatics database file. Importing the files into PCI allowed the ability to swap the bytes from a 16-bit Most-Significant-Bit order (MSB: Sun/Motorola) to a 16-bit Least-Significant-Bit order (LSB: Intel/VAX). Georeferencing information were added to each of the thirty-three files.

    Person who carried out this activity:

    Valerie Paskevich
    U.S. Geological Survey
    Information Specialist, GIS Coordinator
    384 Woods Hole Road
    Woods Hole, MA 02543-1598
    USA

    (508) 548-8700 x2281 (voice)
    (508) 457-2310 (FAX)
    vpaskevich@usgs.gov

    Date: 02-May-2005 (process 2 of 8)
    A new PCI Geomatics database file was defined to combine the global dataset. The individual thirty-three files were mosaicked to create one world view.

    Person who carried out this activity:

    Valerie Paskevich
    U.S. Geological Survey
    Information Specialist, GIS Coordinator
    384 Woods Hole Road
    Woods Hole, MA 02543-1598
    USA

    (508) 548-8700 x2281 (voice)
    (508) 457-2310 (FAX)
    vpaskevich@usgs.gov

    Data sources produced in this process:
    • srtm30plus.pix

    Date: 04-May-2005 (process 3 of 8)
    The area of interest was extracted from the composite image. This was done to reduce the overall size of the image and to retain as much detail as possible. The 16-bit signed image data was transferred to the new database.

    Person who carried out this activity:

    Valerie Paskevich
    U.S. Geological Survey
    Information Specialist, GIS Coordinator
    384 Woods Hole Road
    Woods Hole, MA 02543-1598
    USA

    (508) 548-8700 x2281 (voice)
    (508) 457-2310 (FAX)
    vpaskevich@usgs.gov

    Data sources used in this process:
    • srtm30plus.pix

    Data sources produced in this process:

    • srtm30plus-na.pix

    Date: 05-May-2005 (process 4 of 8)
    Two additional 8-bit channel were added to the PCI database for future processing. The program REL was run to create an 8-bit shaded relief image based on the 16-bit signed image data.

    Person who carried out this activity:

    Valerie Paskevich
    U.S. Geological Survey
    Information Specialist, GIS Coordinator
    384 Woods Hole Road
    Woods Hole, MA 02543-1598
    USA

    (508) 548-8700 x2281 (voice)
    (508) 457-2310 (FAX)
    vpaskevich@usgs.gov

    Data sources used in this process:
    • srtm30plus-na.pix

    Data sources produced in this process:

    • srtm30plus-na.pix

    Date: 05-May-2005 (process 5 of 8)
    The shaded relief image was viewed in PCI Imageworks. A linear stretch enhancement was applied to the image and the resulting Look-up Table (LUT) saved in the database.

    Person who carried out this activity:

    Valerie Paskevich
    U.S. Geological Survey
    Information Specialist, GIS Coordinator
    384 Woods Hole Road
    Woods Hole, MA 02543-1598
    USA

    (508) 548-8700 x2281 (voice)
    (508) 457-2310 (FAX)
    vpaskevich@usgs.gov

    Data sources used in this process:
    • srtm30plus-na.pix

    Data sources produced in this process:

    • srtm30plus-na.pix

    Date: 05-May-2005 (process 6 of 8)
    The 8-bit shaded relief image had a linear stretch permanently applied to create a new, final image.

    Person who carried out this activity:

    Valerie Paskevich
    U.S. Geological Survey
    Information Specialist, GIS Coordinator
    384 Woods Hole Road
    Woods Hole, MA 02543-1598
    USA

    (508) 548-8700 x2281 (voice)
    (508) 457-2310 (FAX)
    vpaskevich@usgs.gov

    Data sources used in this process:
    • srtm30plus-na.pix

    Data sources produced in this process:

    • srtm30plus-na.pix

    Date: 05-May-2005 (process 7 of 8)
    The final 8-bit grey-scale, shaded relief image was exported to a GeoTIFF image

    Person who carried out this activity:

    Valerie Paskevich
    U.S. Geological Survey
    Information Specialist, GIS Coordinator
    384 Woods Hole Road
    Woods Hole, MA 02543-1598
    USA

    (508) 548-8700 x2281 (voice)
    (508) 457-2310 (FAX)
    vpaskevich@usgs.gov

    Data sources used in this process:
    • srtm30plus-na.pix

    Data sources produced in this process:

    • srtm30plus-na.tif
    • srtm30plus-na.tfw

    Date: 05-May-2005 (process 8 of 8)
    The two source images were brought into Corel PhotoPaint. The color-encoded elevation image (strm30plus-na_color.tif) was overlaid ontop of the shaded relief image (srtm30plus-na_shade.tif_. The color image was made 60% transparent to allow shading to be seen through the image. The two images were combined to create a single 24-bit image showing elevation based on color.

    Person who carried out this activity:

    Valerie Paskevich
    U.S. Geological Survey
    Information Specialist, GIS Coordinator
    384 Woods Hole Road
    Woods Hole, MA 02543-1598
    USA

    (508) 548-8700 x2281 (voice)
    (508) 457-2310 (FAX)
    vpaskevich@usgs.gov

    Data sources used in this process:
    • srtm30plus-na_shade.tif
    • srtm30plus-na_color.tif

    Data sources produced in this process:

    • srtm30plus-world_pctshade.tif
    • srtm30plus-world_pctshade.tfw

  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?

    Elevation Data - Each SRTM data tile contains a mosaic of elevations generated by averaging all data takes that fall within that tile. Since the primary error source in synthetic aperture radar data is speckle, which has the characteristics of random noise, combining data through averaging reduces the error by the square root of the number of data takes used. In the case of SRTM the number of data takes could range from a minimum of one (in a very few cases) up to as many as ten or more.

  2. How accurate are the geographic locations?

  3. How accurate are the heights or depths?

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

    Land data are based on the 1-km averages of topography derived from the USGS SRTM30 grided DEM data product created with data from the NASA Shuttle Radar Topography Mission. GTOPO30 data are used for high latitudes where SRTM data are not available. Ocean data are based on the Smith and Sandwell global 2-minute grid between latitudes +/- 72 degrees. Higher resolution grids have been added from the LDEO Ridge Multibeam Synthesis Project and the NGDC Coastal Relief Model. Arctic bathymetry is from the International Bathymetric Chart of the Oceans (IBCAO) [Jakobsson et al., 2003].

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


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:
Bathymetry is not to be used for navigational purposes.

Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information.

All source data are derived from public domain sources and these data are also in the public domain.

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

    U.S. Geological Survey
    384 Woods Hole Road
    Woods Hole, MA 02543-1598
    USA

    (508) 548-8700 (voice)
    (508) 457-2310 (FAX)

  2. What's the catalog number I need to order this data set?

    Downloadable Data

  3. What legal disclaimers am I supposed to read?

    Although this data set has been used by the U.S. Geological Survey (USGS), no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and/or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Trade, firm, or product names and other references to non-USGS products and services are provided for information only and do not constitute endorsement or warranty, express or implied, by the USGS, USDOI, or U.S. Government, as to their suitability, content, usefulness, functioning, completeness, or accuracy.

  4. How can I download or order the data?

  5. What hardware or software do I need in order to use the data set?

    This image is available as a GEOTIFF image with an accompanying world file. To utilize this data, the user must have an image viewer, image processing or GIS software package capable of importing a GeoTIFF image.


Who wrote the metadata?

Dates:
Last modified: 12-May-2005
Last Reviewed: 12-May-2005
Metadata author:
U.S. Geological Survey
c/o Valerie Paskevich
Information Specialist, GIS Coordinator
384 Woods Hole Road
Woods Hole, MA 02543-1598
USA

(508) 548-8700 x2281 (voice)
(508) 457-2310 (FAX)
vpaskevich@usgs.gov

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:


Generated by mp version 2.8.6 on Wed Aug 24 06:51:46 2005