Long-Term Radiometric UAS–TIR Monitoring at Pisciarelli Hydrothermal System, Campi Flegrei Caldera

Thermal monitoring is a key tool for tracking the evolution of active volcanic and hydrothermal systems, although ground observations are spatially limited and satellite data may not resolve small thermal anomalies. Here, we analyze 55 radiometric UAS–TIR surveys acquired at the Pisciarelli hydrothermal area, Campi Flegrei caldera, between September 2019 and May 2025. The surveys were geometrically controlled using PPK positioning, GCPs, and independent CPs, and processed within a common radiometric and spatial framework. The dataset reveals a warming phase at an average rate of about +1.7 °C yr−1 from September 2021, with a faster initial increase of about +5.5 °C yr−1 until April 2023. Thermal classification shows that warming involves a progressive contraction and heating of the background temperature zone together with an expansion of transition and anomalous thermal domains. Satellite-derived LST shows a comparable warming evolution during the common observation interval, while increasing seismicity and InSAR-derived ground deformation characterize the post-2021 interval. These observations indicate a temporal co-evolution of independent parameters during the ongoing Campi Flegrei unrest. The almost six-year radiometric UAS archive highlights the value of systematic UAS-TIR for resolving long-term thermal changes in small and hazardous hydrothermal targets and for complementing volcanic monitoring.