ELEVATION AND DEPTH MAP - 30
ARC SECOND (ISciences)
[Status: Available on CD at TerraViva!. Note: ISciences also plans to release a 3 arc second global elevation map, date not set.]
THE PROBLEM
Productive analysis in many areas of earth and social science - climate, population, vegetation - requires accurate, complete global elevation data.
THE SOLUTION
ISciences' Elevation and Depth Map is a 900 million pixel image that shows the height of the Earth's land surfaces and the depths of its ocean floors for the entire world at a resolution of 30 seconds of arc. The ISciences map combines and corrects anomalies in three datasets: SRTM30 (NASA) for land areas, ETOPO2 (NOAA-NGDC) for ocean depths, and GTOPO30 (USGS) for for areas not covered by SRTM and for data voids in SRTM covered areas. |
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Area of Interest: Southeast Libya
Extent: 23°40'N to 24°07'N; 22°00'E to 23°36'E |
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THE STORY
The four images below help tell the story of how ISciences created an improved global elevation map by carefully blending and correcting data from several sources. Each image shows the same area of North Africa using different map data, and each is centered at 24° 28'N / 22° 10'E, with a scale of approximately 1:2,000,000. Scroll to the larger images for complete details. |
IMAGE 1: GTOPO30
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IMAGE 2: SRTM3
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IMAGE 3: SRTM30V2
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IMAGE 4: ISciences'
Elev
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| IMAGE 1: GTOPO30 (below) displays data from GTOPO30, an older standard elevation dataset created from numerous sources. Some of the GTOPO30 data are from digital elevation maps, while elevation for other land areas is interpolated from paper topographical maps of contour lines. Data for the center part of the image are derived from contour lines. The left edge and a block at the upper right are from digital terrain maps and show greater detail. Notice how the combination of contour and digital data results in a fairly conspicuous "seam" as well as an abrupt and unrealistic change in elevation. |
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| IMAGE 2: SRTM3 (below) displays data from the processed SRTM 3 data (3 seconds of arc). While the SRTM dataset is a great improvement over GTOPO30, notice the large dark areas indicating data voids (no data). |
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| IMAGE 3: SRTM30v2 (below) displays data from version 2 of NASA's SRTM30 product. SRTM30v2 is derived from SRTM3 (above). Voids in the SRTM data were filled by grabbing data from GTOPO30. The SRTM30v2 image is an improvement over GTOPO30 - boxed areas on the left and upper right are now "seamless." However, voids in SRTM data that were filled by GTOPO30 data (as indicated by the ellipses) exhibit a discontinuity with the surrounding data. |
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| IMAGE 4: ISciences' Elevation & Depth Map - 30 Arc Second (below) displays a well-integrated elevation image. To achieve this, we reconstructed areas that had formerly been filled with GTOPO30 data by using interpolated values from derived contour lines. The result, an image that exhibits no awkward "seams" between blended data, that more accurately reflects elevation of filled areas relative to the neighboring sensed SRTM data, and that provides the analyst with visual continuity. |
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NOTE: ISciences also plans to release a global 3 arc second Elevation & Depth Map. The 3 arc second map will be based on SRTM3. At present we are searching for reliable data to fill voids in SRTM data, clearly a data-blending challenge at 3 arc seconds of resolution. Watch for news of this upcoming release or register to receive email news.
NEED HELP TAMING YOUR DATA? Contact Dave Carson, Director
of
GeoSpatial
Solutions at ISciences: info@terraviva.net or
telephone +1.734.214.9810. |
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