Many aspects of volcanic activity such as thermal emission, gas emission, and the changing shape of a volcano can be studied remotely (see Mouginis-Mark et al., 2000). This chapter, however, limits discussions of remote sensing to techniques also available in the study of volcanism on Io.

Remote sensing of volcanic activity on Earth

Remote sensing has become an essential tool for terrestrial volcanologists since its origins in the data collected in the mid 1960s by the High-Resolution Infrared Radiometer (HRIR) on Nimbus 1. Those data were used to show that the Hawaiian volcano Kilauea had a higher infrared radiance than Mauna Loa, its then-inactive neighbor (Gawarecki et al., 1965). More than four decades later, Earth-orbiting platforms are now being used to detect and monitor volcanic activity at different temporal, spatial, and spectral resolutions (Plate 3). Reviews of the development of spacecraft, orbits, sensor capabilities, and data analysis techniques up to the launch of the first Earth Observing System (EOS) spacecraft (Earth Observing 1 [EO-1], Terra and Aqua) are summarized in a series of papers collected in the monograph Remote Sensing of Volcanic Activity (Mouginis-Mark et al., 2000). The reader is specifically directed to Mouginis-Mark and Domergue-Schmidt (2000) for their comprehensive appraisal of the strengths and limitations of terrestrial satellite remote sensing capabilities. More recent EOS spacecraft observations of active volcanism are described by Ramsey and Flynn (2004) and references therein, and by Davies et al. (2006a).