A multifrequency laboratory investigation of attenuation and scattering from volcanic ash clouds

Interest in remote monitoring of volcanic activity has increased in the last several years partly as a result of several powerful eruptions and partly as a result of satellite-borne spectrometers with thermal IR bands with which to monitor the physical makeup and effects of the volcanic inputs to the atmosphere. The authors consider the first wide-bandwidth laboratory experiments intended to improve our understanding of the spectral response of volcanic ash important for remote sensing of volcano eruption ejecta, making comparisons between data from the laboratory of ash suspensions and Mie theory for scattering and attenuation from spheres. Described are the experimental configuration, the sample preparation techniques and the results obtained. The results indicate a general sphere-like behavior of the ash, however the levels indicate effective radii that lie at the extremes of the actual particle size ranges. The data presented are unique in their multispectral character as well as their control over ash particle size distributions. They should be useful in the process of selecting appropriate remote sensing datasets and for improving models for retrieving estimates of particle size distribution, concentration, total mass of ash ejected, cloud drift, and fall-out rate from that data. They should also be useful for designing and assessing performance of ash hazard sensors for flying aircraft