Source term estimation of a volcanic ash cloud using a genetic algorithm

Volcanic eruptions can create large clouds of ash which pose a major threat to aircraft. The ash has the potential for damage so great that the aircraft are generally rerouted to avoid the cloud entirely. Atmospheric transport and dispersion (AT&D) models are employed to forecast cloud movement. These models require accurate knowledge of the volcanic clouds source term, including the amount of ash released into the atmosphere as well as the representative meteorology. Determining these quantities is difficult but could be accomplished if one had concentration observations available. In this study, a genetic algorithm is applied to determine the amount of aerosols pumped into the atmosphere. In addition, the wind observations available to drive the transport and dispersion model may not be representative so the GA will be used to back-calculate the relevant wind speed and wind direction. The emission rate and meteorological information can then be used to update the AT&D forecast and better inform emergency responders. Observed concentration data are derived from satellite data to determine the observed ash concentrations. A case study is made of the March 2009 eruption of Mt. Redoubt in Alaska.