Abstract
Remote sensing is an established technological solution for bridging critical gaps in volcanic hazard assessment and risk mitigation. The enormous amount of remote sensing data available today at a range of temporal and spatial resolutions can aid emergency management in volcanic crises by detecting and measuring high-temperature thermal anomalies and providing lava flow propagation forecasts. In such thermal estimates, an important role is played by emissivity—the efficiency with which a surface radiates its thermal energy at various wavelengths. Emissivity has a close relationship with land surface temperatures and radiant fluxes, and it impacts directly on the prediction of lava flow behavior, as mass flux estimates depend on measured radiant fluxes. Since emissivity is seldom measured and mostly assumed, we aimed to fill this gap in knowledge by carrying out a multi-stage experiment, combining laboratory-based Fourier transform infrared (FTIR) analyses, remote sensing data, and numerical modeling. We tested the capacity for reproducing emissivity from spaceborne observations using ASTER Global Emissivity Database (GED) while assessing the spatial heterogeneity of emissivity. Our laboratory-satellite emissivity values were used to establish a realistic land surface temperature from a high-resolution spaceborne payload (ETM+) to obtain an instant temperature–radiant flux and eruption rate results for the 2001 Mount Etna (Italy) eruption. Forward-modeling tests conducted on the 2001 ‘aa’ lava flow by means of the MAGFLOW Cellular Automata code produced differences of up to ~600 m in the simulated lava flow ‘distance-to-run’ for a range of emissivity values. Given the density and proximity of urban settlements on and around Mount Etna, these results may have significant implications for civil protection and urban planning applications.
Highlights
As less than 10% of the ~1500 active subaerial volcanoes around the world are monitored regularly on the ground, remote sensing (RS) provides an opportunity to increase coverage
To extend the observable spectral range, two detectors (KBr at 0.66 to 2.50 μm and Mercury Cadmium Telluride (MCT) at 2.50 to 16.00 μm) were used, so that the data could be merged at 2.63 μm to provide the best signal-to-noise (STN) ratio result for the entire range from visible near-infrared (VNIR) to TIR wavelength
Our reflectance and emission Fourier transform infrared (FTIR) results at ambient/low temperature indicate that emissivity is wavelength-dependent. Both laboratory (FTIR) and spaceborne (ASTER Global Emissivity Database (GED)) data correspond well for the same target area, and show good correlation at specific TIR wavelengths by exhibiting an emissivity range/error of ≤0.03
Summary
As less than 10% of the ~1500 active subaerial volcanoes around the world are monitored regularly on the ground, remote sensing (RS) provides an opportunity to increase coverage. The prediction of lava flow ‘distance-to-run’ (ultimate length) is viewed as the key activity in support of risk mapping and planning the emergency response and crisis management of effusive volcanic events. The impact of volcanic eruptions and distances to which erupted lava will flow depend on several physical and chemical parameters [1,2,3,4]. It is widely recognized that RS data can be integrated with ground-based observations during volcanic crisis to facilitate the estimation of thermal anomalies and—depending on spatial and temporal resolutions—forecast the geographic extent of active lava flows. A developing lava flow is a complex surface to observe using remote techniques, due to the moving material exhibiting a range of temperatures, textures, vesicularities [5], and thicknesses. The evolution of thermal anomalies may involve continuous changes in energy emitted as surfaces cool, as well as variations that depend on viewing angles [6]
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