Automated Detection of Opaque Volcanic Plumes in Polar Satellite Data

Response to an explosive volcanic eruption is time sensitive, so automated eruption detection techniques are essential to minimize alert times after an event. Automated detection of volcanic ash plumes in satellite imagery is usually done using a variant of the split-window or reverse-absorption method. This method is often effective but requires among other things that an ash plume be translucent to allow thermal radiation to pass through it. In the critical first hour or two of an eruption, plumes are most often opaque, and therefore cannot be detected by this method. It has been shown that an emergent plume appears as a sudden cold cloud over a volcano where a weather system should not appear, and this has been applied to geostationary data that is acquired every 15 to 30 minutes and will be an integral part of the upcoming geostationary mission, GOES-R. In this study this concept is used on time sequential polar orbiting satellite data to detect emergent plumes. This augments geostationary data, and may detect smaller plumes at higher latitudes where geostationary data suffers from poorer spatial resolution. A series of weighted credits and demerits are used to determine the presence of an anomalously cold cloud over a volcano in time sequential advanced very high resolution radiometer (AVHRR) data. Parameters such as coldest thermal infrared temperature, time between images, ratio of cold to background temperature, and temperature trend are assigned a weighted value and a threshold used to determine the presence of an anomalous cloud. The weighting and threshold is unique for each volcano due to weather conditions and satellite coverage. Using the 20 year archive of eruptions in the North Pacific at the Geophysical Institute of the University of Alaska Fairbanks, explosive eruptions were evaluated at Karmsky Volcano (1996), Pavlof volcano (1996, 2007, 2013), Cleveland Volcano (1994, 2001, 2008), Shishaldin Volcano (1999), Augustine Volcano (2006), Fourpeaked Volcano (2006), Okmok Volcano (2008), Kasatochi Volcano (2008), and Redoubt Volcano (2009). All of the explosive events were successfully captured, with few false alerts (less than 5%). The false alerts involved either a smaller explosive event, typically at night or sudden change in weather common at stratocones. This method will be integrated into the automated volcano monitoring system at the University of Alaska Fairbanks Geophysical Institute and should permit more rapid response to a crisis.