Earth Imaging Glossary
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" W "
WGS 72--World Geodetic System 1972
The definition of DMA DEMs, as presently stored in the USGS data base, references the WGS 72 datum. WGS 72 is an Earth-centered datum. The WGS 72 datum was the result of an extensive effort extending over approximately three years to collect selected satellite, surface gravity, and astrogeodetic data available throughout 1972. These data were combined using a unified WGS solution (a large-scale least squares adjustment).
WGS 84--World Geodetic System 1984
The WGS 84 datum was developed as a replacement for WGS 72 by the military mapping community as a result of new and more accurate instrumentation and a more comprehensive control network of ground stations. The newly developed satellite radar altimeter was used to deduce geoid heights from oceanic regions between 70 degrees north and south latitude. Geoid heights were also deduced from ground-based Doppler and ground-based laser satellite-tracking data, as well as surface gravity data. This system is described in "World Geodetic System 1984," DOD DMA TR 8350.2 September 1987. New and more extensive data sets and improved software were used in the development.
DIFFERENCE BETWEEN WGS 84 and WGS 72 GEODETIC COORDINATES
Difference (Meters)
Degrees Latitude Longitude Height
90 N 0.0 0.0 4.1
85 0.4 1.5 4.1
80 0.8 3.0 4.0
75 1.3 4.4 3.9
70 1.7 5.9 3.8
65 2.1 7.2 3.6
60 2.4 8.6 3.4
55 2.8 9.8 3.2
50 3.1 11.0 3.0
45 3.4 12.1 2.7
40 3.6 13.1 2.4
35 3.9 14.0 2.0
30 4.1 14.8 1.7
25 4.2 15.5 1.3
20 4.4 16.1 1.0
15 4.4 16.5 0.6
10 4.5 16.5 0.2
5 N 4.5 17.1 -0.2
0 4.5 17.1 -0.6
5 S 4.4 17.1 -1.0
10 4.4 16.9 -1.4
15 4.2 16.5 -1.8
20 4.1 16.1 -2.1
25 3.9 15.5 -2.5
30 3.7 14.8 -2.8
35 3.5 14.0 -3.1
40 3.3 13.1 -3.4
45 3.0 12.1 -3.7
50 2.7 11.0 -3.9
55 4.2 9.8 -4.2
60 2.1 8.6 -4.3
65 1.7 7.2 -4.5
70 1.4 5.9 -4.7
75 1.1 4.4 -4.8
80 0.7 3.0 -4.8
85 0.4 1.5 -4.9
90 S 0.0 0.0 -4.9
Applies only when proceeding directly from WGS 72 coordinates to WGS 84 coordinates; does not contain the effect of the WGS 84 Earth gravitational model and geoid, nor the effect of local geodetic system-to-WGS 84 datum shifts being better than local geodetic system-to-WGS 72 datum shifts.
WRS--Worldwide Reference System
The WRS is a global indexing scheme designed for the Landsat program based on nominal scene centers defined by path and row coordinates.
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Initial content for this Glossary of terms has been graciously supplied by RADARSAT International - www.rsi.ca
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