A Google Earth Engine Tool to Investigate, Map and Monitor Volcanic Thermal Anomalies at Global Scale by Means of Mid-High Spatial Resolution Satellite Data

Abstract

Several satellite-based systems have been developed over the years to study and monitor thermal volcanic activity. Most of them use high temporal resolution satellite data, provided by sensors like the Moderate Resolution Imaging Spectroradiometer (MODIS) that if on the one hand guarantee a continuous monitoring of active volcanic areas on the other hand are less suited to map thermal anomalies, and to provide accurate information about their features. The Multispectral Instrument (MSI) and the Operational Land Imager (OLI), respectively, onboard the Sentinel-2 and Landsat-8 satellites, providing Short-Wave Infrared (SWIR) data at 20 m (MSI) and 30 m (OLI) spatial resolution, may make an important contribution in this area. In this work, we present the first Google Earth Engine (GEE) App to investigate, map and monitor volcanic thermal anomalies at global scale, integrating Landsat-8 OLI and Sentinel-2 MSI observations. This open tool, which implements the Normalized Hot spot Indices (NHI) algorithm, enables the analysis of more than 1400 active volcanoes, with very low processing times, thanks to the high GEE computational resources. Performance and limitations of the tool, such as its next upgrades, aiming at increasing the user-friendly experience and extending the temporal range of data analyses, are analyzed and discussed.

The short life of the volcanic island New Late’iki (Tonga) analyzed by multi-sensor remote sensing data

“…Application of the Normalized Hotspot Indices (NHI) tool (cf. “ Multispectral satellite remote sensing monitoring ” 44 , 45 ) on Landsat-8 Operational Land Imager (OLI) and Sentinel-2 Multispectral Instrument (MSI) data resulted in the identification of a thermal anomaly on 16 October 2019 (Landsat-8, see the single hotspot pixel in Fig. 3 a), appearing more extended on 20 October 2019 (Sentinel-2, see hotspot pixels in Fig.…”

“…Furthermore, by combining the hotspots detected by Landsat-8 OLI and Sentinel-2 MSI, we estimated the total hotspot area. The main processing was performed using the Google Earth Engine Apps NHI Tool for volcanoes (version 1.4) 45 . In addition, we performed an offline processing of the Landsat-8 OLI and Sentinel-2 MSI scenes, for a more detailed analysis.…”

“…In addition, we performed an offline processing of the Landsat-8 OLI and Sentinel-2 MSI scenes, for a more detailed analysis. We performed this analysis by running the algorithm without using the spectral test implemented within the NHI tool to remove artefacts associated to the multispectral misregistration of Sentinel-2 MSI imagery (see 45 ).…”

Implementation of the NHI (Normalized Hot Spot Indices) Algorithm on Infrared ASTER Data: Results and Future Perspectives

“…Thus, the NHI algorithm considers pixels as “hot” if they have values of OR . It is capable, therefore, of successfully discriminating thermal anomalies from other targets, in spite of some limitations [ 18 , 19 ]. In particular, the algorithm should not detect thermal anomalies of a mid-low temperature (i.e., below 500 K [ 28 ]), which are less radiant in the SWIR band.…”

“…We previously tested the NHI algorithm in different volcanic areas using Multispectral Instrument (MSI) and Operational Land Imager (OLI) data [ 18 ]. The algorithm, which exhibited a good potential in mapping thermal anomalies in Thematic Mapper (TM) and Enhanced Thematic Mapper plus (ETM+) data, was then implemented within the Google Earth Engine (GEE) environment [ 19 ]. The GEE-based NHI tool enables the investigation and mapping of volcanic thermal anomalies at global scale, with low processing times, exploiting advantages of MSI and OLI data integration [ 19 ].…”