Detection of thermal features from space at Indonesian volcanoes from 2000 to 2020 using ASTER

Routine analysis and detection of volcanic thermal features (VTFs) are available globally for low spatial resolution (>1 km/pixel) thermal infrared (TIR) sensors. However, medium resolution (90 m/pixel) ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) TIR data, which is sensitive to smaller and cooler VTFs, have yet to be systematically examined at all active Indonesian volcanoes. We manually examined cloud-free nighttime images at 136 potentially active volcanoes from 2000 to 2020 CE and found at least 71 volcanoes with VTFs, despite the low proportion (26.5%) of cloud-free images. Of these, 34 volcanoes have VTF detections from space published for the first time (to our knowledge) and at least 44 volcanoes have non-eruptive VTFs (fumaroles, heated volcanic lakes and open vent systems). The inclusion of hotspots detected by ASTER in this study increases the percentage of Indonesian volcanoes with recorded satellite-detectable thermal features from 27% to 52%, larger than in Latin America (27%) and the US (33%) which were surveyed in the same way and is possibly due to a higher frequency of eruptions in Indonesia. The distribution of VTFs across sub-regions in Indonesia is not uniform but may be correlated with the number of volcanoes with eruptions. This multi-decadal country-wide survey highlights the potential of TIR monitoring and detection of low-temperature volcanic features that may be eruption precursors, but also the limits of the available datasets since many volcanoes only have a few cloud-free nighttime images per year.