The recent realization that explosive eruptions can be hazardous to people in the air as well as on the ground has gained greater attention following the eruptions of Mt. Redoubt (1989-1991) and Mt. Spurr (1992) in Alaska. There is a two-fold threat to aircraft, caused by the ingestion of ash into the jet engines (causing their failure as the ash turns to turbine-clogging volcanic glass) and the pitting of windows ( Casadevall, 1994). Using weather satellite data, Holasek and Rose (1991) and Schneider et al. (in press) have been able to develop plume identification techniques using the thermal infrared properties of the plumes. These same data have also been used to estimate particle sizes and total mass of particulates in volcanic clouds ( Wen and Rose, 1994).