Another source of free elevation data is the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) mission, which was sponsored by NASA and Japan’s Ministry of Economy Trade and Industry (METI) and launched in December of 1999. Like the SRTM mission, elevation data were gathered in 1 arc-second intervals, the equivalent of approximately 30 meters (depending on latitude). Data are available for the entire world between 83ºN and 83ºS.
There are a whole slew of websites (including this one) where you can download the data in one degree lat/long tiles, which are in GeoTIFF format and georeferenced to the WGS84 geographic coordinate system. Version 2 was released in October of 2011.
For a long while, I always chose SRTM over ASTER. The Version 1 ASTER data weren’t very good when it came to accuracy, at least not compared to SRTM. However, the release of ASTER Version 2 has corrected some of the anomalies that characterized Version 1, which are due either to cloud coverage or to the “stack boundaries” in the original data. The anomalies may appear as “pits,” “bumps,” or curvilinear “mole runs.”
One reason to pick ASTER over SRTM is that it provides better resolution for areas outside North America. The Japan and U.S. teams estimate that the resolution of Version 2 data is about 72 meters (Tachikawa et al. 2011: 12).* Its accuracy is also much improved, with an overall vertical and horizontal accuracy of about 20 meters, depending upon the specific tile in question. Test results in the U.S. show it has an absolute vertical accuracy of 8.68 meters (Tachikawa et al. 2011: 6).
* You might be thinking, “Wait a minute. 72-meter resolution? I thought this was ’30-meter’ elevation data!” As it turns out, the resolution of the data released by the ASTER and SRTM missions is actually much coarser than the names imply. The 30-meter SRTM data (only available for the U.S.) varies between 45 and 60 meters (Farr et al. 2007:17)
A few studies have been done to compare the accuracy of SRTM and ASTER Version 1 data, like Nikolakopoulos et al. 2006 and Colosimo et al. 2009. The takeaway from these papers is that accuracy is variable and highly dependent upon the study area in question. Since Version 2 is still relatively new, it might be best to take some ground control points from your own region, then run your own analysis before settling on a dataset.
Colosimo, Gabriele, Mattia Crespi, Laura De Vendictis, and Karsten Jacobsen (2009). Accuracy evaluation of SRTM and ASTER DSMs. Paper presented at the 29th EARSeL Symposium, MAI Chania, 15-18 June 2009 (http://earsel29.maich.gr/).
Farr, T. et al. (2007). The Shuttle Radar Topography Mission. Review of Geophysics 45, RG2004, doi:10.1029/2005RG000183.
Nikolakopoulos, K. G., E. K. Kamaratakis, and N. Chrysoulaki (2006). SRTM vs ASTER Elevation Products: Comparison for Two Regions in Crete, Greece. International Journal of Remote Sensing 27(21): 4819-4838.
Tachikawa, T., et al. (2011). ASTER Global Digital Elevation Model Version 2 – Summary of Validation Results.(http://www.jspacesystems.or.jp/ersdac/GDEM/ver2Validation/Summary_GDEM2_validation_report_final.pdf)