SlashGeo has a post up asking for feedback and info about the various version of SRTM-90 data. SRTM was the Shuttle Radar Topography Mission, an instrument package aboard a 2000 flight of the Endeavour space shuttle that mapped the earth’s topography at a resolution of 30 meters using radar. While one of the most inclusive and comprehensive worldwide topographic datasets, SRTM has a few drawbacks:
- The original data had many voids, holes and other irregularities
- The SRTM radar registered buildings and vegetation as terrain, and added their height to the actual terrain height
- Radar mapping has problems with dry sand (e.g. sand dunes)
- 30-meter data has only been released for the US; for the rest of the world, the 30-meter data was re-sampled to 90 meters (hence, SRTM-90)
NASA has released SRTM Version 2, a “cleaned-up” version of the original SRTM data with holes and voids filled, and the data irregularities supposedly cleaned up; this data is available from the USGS Seamless Server. There are still problems with this cleaned data, like the mountain I viewed in Mexico that had a hole in its summit that went all the way down to sea level. I’ve been using my own version of SRTM-90, with holes in the original data patched using GTOPO30 data. But since GTOPO30 data has a resolution of 1 km, my solution was less than ideal.
The SlashGeo post and comments mention two attractive-sounding alternative versions of SRTM-90 data:
- The CGIAR Consortium For Spatial Information has released Version 3 of their cleaned-up SRTM-90 data, using contour interpolation and alternate data sources to fix voids and holes. I looked at CGIAR’s Version 2 before, and wasn’t satisfied with it. I’ve taken a cursory look at some of their Version 3 compared to NASA’s Version 2, and while the CGIAR data still isn’t perfect, it looks better than the NASA Version 2 data (and also better than my patched data). But be prepared to have the downloads timeout on you, as happened to me on multiple occasions on the main site (haven’t tried the mirror download sites yet). There’s also a Google Earth file that offers a more convenient interface for viewing and downloading the data.
- The USGS has developed their own “cleaned-up” version of the SRTM-90 data for use with the WWF’s HydroSHEDs program. Haven’t looked at these yet, but more information and download links are available from their website (I wasn’t able to successfully download any data – curse you, ArcIMS). Also, data is currently only available for Central and South America, a small part of the US, and parts of Asia and Oceania.