Remote sensing of volcanic ash plumes from thermal infrared: a case study analysis from SEVIRI, MODIS and IASI instruments

The Eyjafjallaj kull eruption during May 2010 is used as a case study to evaluate the consistency of retrievals from different thermal infrared instruments for the detection and characterization of volcanic ash plumes. In this study, the split window technique is used to estimate the optical thickness, the effective particle size and the mass concentration of volcanic particles from brightness temperatures measured in the infrared atmospheric window (8–12 μm). Retrievals are obtained for several mineral compositions whose optical properties are computed using Mie theory accounting for spectral variations of the refractive index. The method is applied similarly to data from MODIS, SEVIRI and IASI space-borne instruments, using two channels at 11 μm and 12 μm. Despite different instrumental characteristics, the results are in good agreement, which denotes the robustness of the retrieval method and the consistency of the observations. Nevertheless, the refractive index data and altitude used for the plume in the inversion may lead to large uncertainties in retrieved effective size and mass concentration in dense plumes and makes it difficult to estimate its composition. While it brings additional constrains, the use of a third channel (8.7 μm) does not allow determining the nature of the particles. As confirmed with high spectral resolution radiative transfer simulations, hyperspectral sensors, such as IASI, are well-suited to study the particle composition of volcanic plumes.