GNGTS 2022 - Atti del 40° Convegno Nazionale

90 GNGTS 2022 Sessione 1.2 LAND SURFACE TEMPERATURE (LST) DETECTED THROUGH LANDSAT 8 SATELLITE MISSION AT CAMPI FLEGREI CALDERA (SOUTHERN ITALY) A. Barone 1 , E. Bellucci Sessa 2 , S. Caliro 2 , T. Caputo 2 , R. Castaldo 1 , G. Chiodini 3 , S. Pepe 1 , M. Silvestri 4 , D. Stroppiana 5 , P. Tizzani 1 1 National Research Council (CNR), Institute for the Electromagnetic Sensing of the Environment (IREA), Naples, Italy 2 National Institute of Geophysics and Volcanology (INGV), Osservatorio Vesuviano, Naples, Italy 3 National Institute of Geophysics and Volcanology (INGV), Bologna, Italy 4 National Institute of Geophysics and Volcanology (INGV), Osservatorio Nazionale Terremoti, Rome, Italy 5 National Research Council (CNR), Institute for the Electromagnetic Sensing of the Environment (IREA), Milan, Italy Nowadays, volcanoes and geothermal fields are increasingly monitored using remote sensing technologies, which are useful tools to investigate these systems with the retrieval of the space-temporal distribution of several parameters. In particular, the increasing availability of Earth Observation (EO) missions has allowed the study of the thermal features of these areas by providing estimates of the Land Surface Temperature (LST). This last parameter is turning out to be crucial for understanding endogenous phenomena as an indicator of the distribution of thermally anomalous zones at the ground surface (Caputo et al. , 2019; Silvestri et al. , 2020). Nevertheless, the different acquisition time, i.e, daytime and nighttime, and spatial and temporal resolution of the consideredmissions can affect the performed analysis and the detection of local thermal anomalies becomes challenging (Wang et al. , 2019; Sekertekin and Bonafoni, 2020). In this framework, we show the preliminary results of a thermal study performed at Campi Flegrei caldera (CFc) by employing both daytime and nighttime imagery from Landsat 8 (L8) satellite mission and ground-based measurements related to 2013-2021 time interval. The CFc is a well-known volcanic area hosting processes of magmatic and hydrothermal natures, whose thermal anomalies may reflect both regional- and local-scale features in the space-time domain (Chiodini et al. , 2015; Caputo et al. , 2019; Castaldo et al. , 2021). In this framework, the thermal trends are derived from L8 thermal infrared (TIR) images that are characterized by a spatial resolution of 100 m (pixel size) and a frequency of acquisition of 16 days (Caputo et al. , 2019; Sekertekin and Bonafoni, 2020). Firstly, we estimate the LST time series by considering approaches based on Radiative Transfer Equations (RTE); specifically, the daytime LST dataset is retrieved by using a surface emissivity determination method based on the Normalized Difference Vegetation Index (NDVI) (Jimenez-Munoz et al. , 2014), while the nighttime one is estimated through surface emissivity values provided by the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Emissivity Dataset (ASTER-GED) distributed by United States Geological Survey (USGS) web site (Silvestri et al. , 2019; Caputo et al. , 2019; Silvestri et al. , 2020; https://earthexplorer. usgs.gov). Both the datasets are resampled with a spatial resolution of 30 m and have variable frequency of observation of surface conditions since the L8 images with high cloud cover have been discarded from the data. We emphasize the thermal anomalies related to endogenous phenomena by processing the retrieved LST time-series following these steps: (i) removal of spatial and temporal outliers; (ii) correction for adiabatic gradient of the air with the altitude; (iii) detection and removal of the seasonal component. We show the datasets of estimated LST through mean temperature maps over the time interval 2014 - 2020 in Fig. 1. In particular, the daytime LST dataset (Fig. 1a) shows several thermal anomalous zones related to exogenous processes (e.g., anthropogenic structures, water, vegetation, …), whereas the nighttime LST distribution (Fig. 1b) clearly highlights a single positive thermal anomaly at Solfatara crater, suggesting the occurrence of geothermal endogenous phenomena. At Solfatara area, we also observe similar spatial and temporal distribution of LST anomalies in the daytime and nighttime datasets suggesting that the time step of LST time series could be enhanced by integrating both the datasets, at least for this specific area. Then, we consider the ground-based measurements collected by the Osservatorio Vesuviano, National Institute of Geophysics and Volcanology (OV