the SRTM was a one-off mission, a once-only period of acquisition in February 2000, and there are no plans to fly the instrument again. Since 2000, the SRTM dataset has already become out-of-date at volcanoes where eruptive activity has significantly altered the terrain. For example, in 2000 alone, the topography at the following volcanoes changed significantly enough to outdate the SRTM data: Etna in Sicily, Soputa and Merapi in Indonesia, Usu and Miyake-jima, Japan, Arenal in Costa Rica, Santa Maria in Guatemala, Guagua Pichincha, Altar and Tungurahua in Ecuador, and Copahue, Argentina (Smithsonian Bulletins, 2000). The Terra ASTER instrument is still orbiting, and while SRTM is certainly impressive in terms of global coverage, the ASTER instrument still has an active role in producing up-to-date DEMs
at volcanoes provided that the amount of topographic
change exceeds the vertical accuracy of the ASTER DEM
data (i.e. a few tens of meters or more).