A SLSTR (Sea and Land Surface Temperature Radiometer)-based system for the near-real-time monitoring of active volcanoes on a global scale from space.

The Sea and Land Surface Temperature Radiometer (SLSTR), aboard Sentinel-3A/3B satellites, thanks to SWIR (shortwave infrared), MIR (medium infrared) and TIR (thermal infrared) bands, and a temporal resolution up to about 12 hours, may be used to detect, monitor and characterize thermal volcanic activity. In particular, the SWIR bands (500 m spatial resolution) may enable a more accurate identification of high-temperature volcanic features (e.g., lava flows/lava lakes), which could be then quantified also in terms of radiative power. Recently, the NHI (normalized hotspot indices) system, originally developed to map these features on a global scale through the analysis of Sentinel-2 and Landsat 8/9 imagery, has been extended to SLSTR SWIR observations to monitor active volcanoes in near real time. In this work, we present the updated NHI system, along with the outcomes of first months of operation. The results show the successful identification of several eruptive activities with a very low false positive rate, in both daylight and night-time conditions, as well as their effective characterization in terms of relative intensity level. The study demonstrates that SLSTR SWIR observations may provide valuable support to the surveillance of active volcanoes from space.