1"/3" SRTM Files

Shuttle Radar Topography Mission data was first  released in early 2002, two years after the ten day mission flew on the space shuttle. By early 2004, 3" data for North America, South America, Eurasia, Africa, Australia, and islands was available. Only the polar regions are missing. 1" data for the US was also universally available initially, and has now being released worldwide after initially being available only for the US military.  The mission did not cover the poles, leaving 20% of the landmass vacant.

The biggest problem with SRTM is holes, which occur mostly in two settings: very steep mountains, like the Himalyas, when steep canyons and ridge sides often were not seen by the sensors; and dry sand in the regions like parts of the Sahara where there were no radar reflections.

Recommended sources, in order to try:

• OpenTopography
• EarthExplorer  has global 1" data (now version 3)  and the version 3, hole filled in Geotiff format.  You will have to create an account and log in.
  • "Click here to export your results" gives a list of tiles that is not useful.
  • If you download files one at a time, you can get DTED or GEOTIFF in addition to BIL, but each download takes multiple clicks.
• MERIT DEM
• HydroSHEDS:  also has drainage basins. Select files by name; the Lat/Long are for the SW corner of the data set, and each covers 5ºx5°.  Has not been recently updated.
• SRTM ftp download for version 2.1, with US 1", and global 3" and 30". 
• CGIAR with holes removed (tends to annoyingly slow)
• SRTM version 3 from NASA: http://opentopo.sdsc.edu/gridsphere/gridsphere?gs_action=lidarDataset&cid=geonlidarframeportlet&opentopoID=OTSRTM.042013.4326.1
• LP DAAC - SRTMGL1 (usgs.gov) SRTM version 3, to eliminate voids; HGT format

Other Global DEMs

SRTM hole filling projects.  Noble goal, but remember that you cannot easily turn lead into gold.  But for visualization or hydrology, removing the holes is important.  These are probably now replaced by the Other Global DEMs

• HydroSHEDS:  Probably the best option if you need the holes filled.  These are 5 degree tiles; you want the BIL format.  You can also get stream networks and drainage basin shapefiles.
• http://srtm.csi.cgiar.org/  Slow downloads.
• http://www.viewfinderpanoramas.org/dem3.html  Some DEMs in mountainous regions, from Jonathan de Ferranti.

Small scale, merged with bathymetry

• SRTM 30+
• SRTM 15+

Using  SRTM data:

• Map library can graphically open and merge tiles on the fly 
• Open and merge DEMs on the File, Open submenu.
• Do automatic filling of the voids; pick this, and set the maximum size void to fill, on the Import/Export tab of the Options form. This will remove smaller holes, but not the large "Swiss cheese" DEMs in many mountainous regions.

• MICRODEM does not perform a vertical datum shift for this data, which you must consider when comparing SRTM data to other DEMs.

SRTM References:

• jpl_nasa siteindex.html
• srtm factsheet
• factsheet_technology

Point is area

Relation of SRTM3 (DTED 1) to SRTM1 (DTED 2):

• "SRTM DTED® is a uniform matrix of elevation values indexed to specific points on the ground. The horizontal datum is the World Geodetic System 1984 (WGS84) and the vertical datum is mean sea level as determined by the WGS84 Earth Gravitational Model (EGM 96) geoid. The elevation data are with respect to the reflective surface, which may be vegetation, man-made features or bare earth. DTED® Level 2 elevation values are spaced one arc second apart between 0 degrees and 50 degrees latitude, and spaced one arc second apart in latitude and two arc seconds apart in longitude between 50 degrees and 60 degrees latitude. SRTM DTED® Level 1 values are derived from the SRTM DTED® 2 values such that the DTED® 1 values are identical to the DTED® 2 values at coincident points."

Last revision 7/19/2021