ASTER GDEM vertical units inconsistent with SRTM???

RGEarleyRGEarley Global Mapper UserPosts: 29Trusted User
edited May 2014 in Elevation Data
I'm having trouble reconciling the vertical units when I use the ASTER GDEM online data (I'm running GM 14.2).

The elevations seem to be low by a factor of about 3.28. The SRTM sources seems to be more correct, at least based on the World Topo online source. I have a some independent data with elevations, and was unsure of the units (ft. or meters) and went to compare to ASTER.

If I set my vertical units of my data to ft., and I display an elevation profile along the path using ASTER data, they seem to match.

ASTER_GDEM_elev_profile.PNG


When I do the same with SRTM data (leaving my elevations in ft.), my elevations seem to be low by 1/3.2808, which would indicate my elevations are actually in meters not feet.

SRTM_elev_profile.PNG

When I look at the World Topo map, and find a marked elevation which is labeled meters, it is much closer to the SRTM elevation. (World topo: 420m; SRTM: 366m; ASTER: 110m).
WorldTopo.PNG
All of the online downloaded have been left in the default vertical units. It is as if the ASTER data were in meters and divided by 3.2808.

Any idea what is going on?

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