Abstract
In the presented work, the spectral emissivity of basaltic melts at magmatic temperatures was retrieved in a laboratory-controlled experiment by measuring their spectral radiance. Granulated bombs of Etnean basalts were melted and the radiant energy from the melting surface was recorded by a portable spectroradiometer in the short wavelength infrared (SWIR) spectral range between 1500 and 2500 nm. The Draping algorithm, an improved algorithm for temperature and emissivity separation, was applied for the first time to SWIR hyperspectral data in order to take into account the non-uniform temperature distribution of the melt surface and, at the same time, solving the two temperatures and the spectral emissivity. The results have been validated by comparing our results with the emissivity measured at a "lava simulator". Basalt spectral emissivity does not vary significantly at magmatic temperature, but shows an absorption feature in the range 2180–2290 nm, an atmospheric window pivotal for the IR remote sensing of active volcanoes.
Highlights
Surface emissivity is a pivotal parameter for contactless remote temperature measurements [1,2].The emissivity represents the material’s ability to absorb and radiate energy
In the presented work, the spectral emissivity of basaltic melts at magmatic temperatures was retrieved in a laboratory-controlled experiment by measuring their spectral radiance
Multispectral satellite data recorded in the short wave infrared (SWIR) region of the spectrum have been used to estimate the temperature of hot volcanic features, such as basaltic lava flows, e.g., [3,4,5,6], domes and silicic lava flows, e.g., [7,8,9,10] and lava lakes, e.g., [11,12,13,14]
Summary
Surface emissivity is a pivotal parameter for contactless remote temperature measurements [1,2].The emissivity represents the material’s ability to absorb and radiate energy. The spectral radiance emitted by a radiating surface R(λ, Ts) at a given temperature Ts is a function of the spectral radiance emitted by a blackbody B(λ, Ts) and the emissivity of the material’s surface ε at the same temperature, described by Equation (1): R(λ, Ts) = ε(λ) × B(λ, Ts), (1). The SWIR radiation emitted by volcanic features depends on both the temperature and the material’s emissivity. Non-weathered, cold basaltic surfaces have a uniformly high emissivity of 0.96–0.98 [20,21] The application of these “cold” emissivity values to the analysis of active lavas has become common in volcano remote sensing, e.g., [4,5,8,12,13,18,19,22,23]. The TIR spectral range is most commonly used for land surface estimation, numerous studies have studied the simultaneous estimation of temperatures and emissivity from hyperspectral data [26,27,28,29,30,31,32,33,34,35,36,37]
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