Mackie, S & Watson, M, 2015, Atmospheric dependency of the sensitivity of infrared satellite observations to volcanic ash clouds. Journal of Applied Remote Sensing, vol 9.
Volcanic ash can travel great distances and sometimes persist for several weeks, necessitating the monitoring of large areas for potential aviation hazards. Ash can affect aircraft in several ways, from engine failure to manageable impacts if the ash concentration is low. The location and properties of even low levels of ash are, therefore, required in order to make informed safety decisions. Infrared (IR) satellite-borne sensors are vital to this monitoring because of their high spatial coverage day and night. Interpretation of IR ash observations generally relies on exploiting the difference between an observation and the observation anticipated for the same scene under ash-free conditions, the so-called ash signal. We apply forward-model observations of andesitic ash with a fixed particle size distribution to investigate the sensitivity of ash signals to the ambient atmosphere. The variability in the ash signals attributable to atmospheric effects is found to be at least as high as the variability attributable to differences in ash concentration and altitude, implying that different concentrations could be retrieved if atmospheric effects were ignored. Ash with different optical properties is likely to correspond to a slightly different ash signal and may exhibit a different sensitivity to atmospheric effects to that presented here.