Failures in detecting volcanic ash from satellite-based technique

Immediate and accurate detection of airborne volcanic ash is an operational imperative of the aviation industry, especially jet aircraft. Ash encounte rs place passengers aboard these aircraft at severe risk and significantly impact, via forced rerouting, both the safety and profit margins of freight carriers due to their limited fuel supply. Moreover the airlines can suffe r high economic costs for repair and -replacement of equipment. Operational detection. and tracking of volcanic ash by most national weather services has relied heavily on a split window differencing technique of thermal long wave infrared channels on currently operational satellites. Unfortunately, prior work on volcanic ash defection has not emphasised the dynamical inter action between the erupting volcano and the effects of overlying atmospheri c Lr;ater vapor phreatic and phreatomagmatic water sources. Six volcanic as h eruptions from around the globe were chosen for study because they have w ide variation in ambient atmospheric water vapor, available ground and surf ace water and different magma types. Results show that the present differen cing technique is not uniformly effective in properly classifying volcanic ash pixels in the satellite scene and often falsely interprets meteorologic al clouds as volcanic ash clouds and conversely. Moreover it is not always a robust early detector, an operational aviation requirement. Seasonal vari ability in global integrated atmospheric water vapor coupled with the geogr aphical distribution of currently active volcanoes, suggests the concerns d iscussed herein with regard to six specific eruptions, have applicability t o the global aviation industry. Operational implications are discussed and a strategic proposal is presented on necessary steps to improve detection. (C) Elsevier Science Inc., 2000.