Abstract
Using thermal infrared (TIR) data from multiple instruments and platforms for analysis of an entire active volcanic system is becoming more common with the increasing availability of new data. However, the accuracy and uncertainty associated with these combined datasets are poorly constrained over the full range of eruption temperatures and possible volcanic products. Here, four TIR datasets acquired over active lava surfaces are compared to quantify the uncertainty, accuracy, and variability in derived surface radiance, emissivity, and kinetic temperature. These data were acquired at Kīlauea volcano in Hawai’i, USA, in January/February 2017 and 2018. The analysis reveals that spatial resolution strongly limits the accuracy of the derived surface thermal properties, resulting in values that are significantly below the expected values for molten basaltic lava at its liquidus temperature. The surface radiance is ~2400% underestimated in the orbital data compared to only ~200% in ground-based data. As a result, the surface emissivity is overestimated and the kinetic temperature is underestimated by at least 30% and 200% in the airborne and orbital datasets, respectively. A thermal mixed pixel separation analysis is conducted to extract only the molten fraction within each pixel in an attempt to mitigate this complicating factor. This improved the orbital and airborne surface radiance values to within 15% of the expected values and the derived emissivity and kinetic temperature within 8% and 12%, respectively. It is, therefore, possible to use moderate spatial resolution TIR data to derive accurate and reliable emissivity and kinetic temperatures of a molten lava surface that are comparable to the higher resolution data from airborne and ground-based instruments. This approach, resulting in more accurate kinetic temperature and emissivity of the active surfaces, can improve estimates of flow hazards by greatly improving lava flow propagation models that rely on these data.
Highlights
Using remote sensing data to monitor volcanic eruptions has improved our understanding of the precursory activity, eruptions dynamics, and eruptive products [1,2]
A primary goal was to constrain the relationship between the derived emissivity and acquired surface radiance to improve the accuracy of the surface temperatures derived from the Thermal infrared (TIR) data [1,3]
The TMP separation analysis appears to provide a consistent and reasonable method for extracting the higher temperature fractions and allows more accurate values of surface radiance, kinetic temperature, and emissivity to be extracted from the lower spatial resolution datasets
Summary
Using remote sensing data to monitor volcanic eruptions has improved our understanding of the precursory activity, eruptions dynamics, and eruptive products [1,2]. Multi-instrument, multi-platform TIR data of an entire volcanic system must be properly integrated and cross-calibrated to understand the thermal regime An orbiting instrument such as the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) acquiring moderate spatial (90 m) and spectral (5 TIR channels) resolution data will provide lower temporal frequency observations (~16 days) of the larger volcanic system and the ongoing eruption [6]. Near-daily broadband helicopter-based TIR camera data were acquired to produce lava inundation maps, but no thermal lava flow propagation forecasts were calculated, mostly due to the lack of an available robust and reliable modeling approach With these recent large flow-producing eruptions, there is an increasing need to develop rapidly implementable lava flow propagation models to aid in volcanic hazard response. A primary goal was to constrain the relationship between the derived emissivity and acquired surface radiance to improve the accuracy of the surface temperatures derived from the TIR data [1,3]
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