Volcanic ash is a serious hazard to aviation even thousand of miles from an eruption.
At least 15 aircraft have been damaged since 1980 by flying through volcanic ash. Very little is known about how much ash a jet engine can tolerate before failure. This limit could be determined by ground testing, but some real time information about the ash density and particle sizes in actual volcanic clouds would be necessary. One of the problems is that ash particles are notoriously irregular in shape, but most scattering theories and retrieval algorithms have assumed spherical particles. First, the particle shape measurements of the ash fallout samples were analyzed as well as the measurements of the index of refraction at TOMS wavelengths.