Abstract
The amount of energy emitted from basalt at high temperatures has been measured by collecting simultaneous thermal and multispectral images of an active lava lake at night. In this study, we attempt to constrain the component of the VNIR (visible to near-infrared approximately 475-842nm) spectrum is due to thermal emission to evaluate the usefulness of multispectral data for detecting changes in crystallinity. Reflectance in the VNIR has proven to increase with increasing crystal abundance in solidified basalt. However, the high temperatures of molten basalt can cause glowing in the visible range which influences the absolute reflectance as well. In this study, we present side-by-side thermal and VNIR imagery of the Halema'uma'u lava lake in the evening of February 22nd, 2021 to evaluate the effect of temperatures ranging from approximately 400-1100 degrees C on the brightness of the reflectance in the five bands, blue, green, red, red edge, and near-IR. Radiance values ranged from 0.001-0.008. We present emissivity values of these five bands over a range of temperatures for molten and recently solidified basalt. These values will provide greater accuracy when interpreting VNIR satellite images of hot volcanic deposits, a necessary step towards potentially providing constraints on crystal content, glass content, proportion of altered material, and chemical compositional data for dangerous or difficult to access eruptions.