Thermal Activity Monitoring of an Active Volcano Using Landsat 8/OLI-TIRS Sensor Images: A Case Study at the Aso Volcanic Area in Southwest Japan

Abstract

Thermal remote sensing is currently an emerging technique for monitoring active volcanoes around the world. The study area, the Aso volcano, is currently the most active and has erupted almost every year since 2012. For the first time, Landsat 8 TIRS thermal data were used in this study area to evaluate and monitor the recent thermal status of this volcano, situated in Southwest Japan, from 2013 to 2016 using four sets of images. The total heat discharged rate (HDR), radiative heat flux (RHF), land surface temperature (LST), and land cover (LC) were evaluated, and the relationship between them was determined, to understand the thermal status of the study area. We used the NDVI (normalized difference vegetation index) for land cover, the NDVI-threshold method for emissivity, the split-window algorithm for LST, and the Stefan–Boltzmann equation for radiative heat flux estimation in this study. The total heat discharge rate was computed using a relationship coefficient of RHF and HDR here. The highest HDR was obtained in 2013, at about 4715 MW, and was the lowest in 2016, at about 3819 MW. The total heat loss showed a declining trend, overall, from 2013 to 2016. The highest pixel RHF was in 2013 and the lowest was in 2014; after that, it increased gradually until 2016, coinciding with the LST of this study area. LC showed that, with decreasing heat loss, the vegetated coverage increased and bare land or mixed land decreased, and vice versa. From the spatial distribution of RHF, we saw that, within the Nakadake craters of the Aso volcano, Crater 1 was the most active part of this volcano throughout the study period, and Crater 3 was the most active after 2014. We inferred that the applied methods using the continuous Landsat 8 TIRS data showed an effective and efficient method of monitoring the thermal status of this active volcano.