Spaceborne EO and a Combination of Inverse and Forward Modelling for Monitoring Lava Flow Advance

We aim here to improve the understanding of the relationship between emissivity of
the lava and temperature by carrying out a multi-stage experiment for the 2017 Mt Etna (Italy)
eruption. We combine laboratory, spaceborne, and numerical modelling data, to quantify the
emissivity–temperature relationship. Our laboratory-based Fourier-transform infrared (FTIR) results
indicate that emissivity and temperature are inversely correlated, which supports the argument that
emissivity of molten material is significantly lower than that of the same material in its solid state.
Our forward-modelling tests using MAGFLOW Cellular Automata suggest that a 35% emissivity
variation (0.95 to 0.60) can produce up to 46% overestimation (for constant emissivity 0.60) in
simulated/forecasted lava flow lengths (compared to actual observed). In comparison, our simulation
using a ‘two-component’ emissivity approach (i.e., di erent emissivity values for melt and cooled
lava) and constant emissivity 0.95 compares well ( 10% overestimation) with the actual 2017 lava
flow lengths. We evaluated the influence of variable emissivity on lava surface temperatures using
spaceborne data by performing several parametrically controlled assessments, using both constant
(‘uniform’) and a ‘two-component’ emissivity approach. Computed total radiant fluxes, using the same
spaceborne scene (Landsat 8 Operational Land Imager (OLI)), di er 15% depending on emissivity
endmembers (i.e., 0.95 and 0.60). These results further suggest that computed radiant flux using
high-spatial resolution data is bordering at lower boundary (range) values of the moderate-to-high
temporal resolution spaceborne data (i.e., Moderate Resolution Imaging Spectroradiometer (MODIS)
and Spinning Enhanced Visible and Infrared Imager (SEVIRI)), acquired for the same target area (and
the same time interval). These findings may have considerable impact on civil protection decisions
made during volcanic crisis involving lava flows as they approach protected or populated areas.
Nonetheless, the laboratory work, reported here, should be extended to include higher volcanic
eruptive temperatures (up to 1350 K).