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 encounters 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 suffer 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 longwave infrared channels on currently operational satellites. Unfortunately, prior work on volcanic ash defection has not emphasised the dynamical interaction between the erupting volcano and the effects of overlying atmospheric Lr;ater vapor phreatic and phreatomagmatic water sources. Six volcanic ash eruptions from around the globe were chosen for study because they have wide variation in ambient atmospheric water vapor, available ground and surface water and different magma types. Results show that the present differencing technique is not uniformly effective in properly classifying volcanic ash pixels in the satellite scene and often falsely interprets meteorological clouds as volcanic ash clouds and conversely. Moreover it is not always a robust early detector, an operational aviation requirement. Seasonal variability in global integrated atmospheric water vapor coupled with the geographical distribution of currently active volcanoes, suggests the concerns discussed herein with regard to six specific eruptions, have applicability to 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.