An evaluation of volcanic cloud detection techniques during recent significant eruptions in the western ‘Ring of Fire’

We examined recent volcanic cloud events in the Western Pacific and Indonesian area, to validate the performance of remote sensing techniques used to support the International Airways Volcano Watch (IAVW). Five events were considered, during which eruptions from eight volcanoes injected ash into the upper troposphere or lower stratosphere. For one of the eruptions, at Miyakejima, Japan, at least five aircraft encountered volcanic ash clouds, and the cost to three operators alone exceeded US $12,000,000 in aircraft repairs, diversions, and lost operating time. We performed ‘reverse’ absorption and ‘pattern analysis’ using GMS-5/VISSR, MODIS and AVHRR data, and we examined TOMS SO2 and Aerosol Index data, surface-based observations, pilot reports, and dispersion model output. Our results verify that the introduction of ‘reverse’ absorption using the geostationary GMS-5 platform significantly enhanced our capacity to monitor volcanic ash clouds in the region. In one case, we tracked an eruption cloud for approximately 80 h. The primary impediment to remote monitoring is the presence of overlying cloud, or substantial amounts of ice within the volcanic clouds. TOMS data showed success in identifying volcanic clouds during these conditions, but was limited by the infrequency of observations. More effective future operation of the IAVW relies on developing complementary methods of volcanic cloud remote sensing, and greatly increasing the amount and quality of available surface and air observations, including observations of precursor activity. An understanding of the likely future limitations of remote sensing techniques will aid in the refining of IAVW procedures.