**Preface to "Remote Sensing of Volcanic Processes and Risk"**

Remote sensing data and methods are increasingly implemented in assessments of volcanic processes and risk. This happens thanks to their ability to provide a spectrum of observation and measurement opportunities to accurately sense the dynamics, magnitude, frequency, and impacts of volcanic activity in the ultraviolet (UV), visible (VIS), infrared (IR), and microwave domains.

This book includes research papers published in the Special Issue "Remote Sensing of Volcanic Processes and Risk" of the journal Remote Sensing.

Launched in mid-2018, the Special Issue comprises 1 editorial and 19 research papers on the use of satellite, aerial, and ground-based remote sensing to detect thermal features and anomalies, investigate lava and pyroclastic flows, predict the flow path of lahars, measure gas emissions and plumes, and estimate ground deformation.

The strong multi-disciplinary character of the approaches employed for volcano monitoring and the combination of a variety of sensor types, platforms, and methods that emerge from the papers testify the current scientific and technology trends toward multi-data and multi-sensor monitoring solutions.

The research advances presented in the published papers are achieved thanks to a wealth of data including but not limited to the following: thermal IR from satellite missions (e.g., MODIS, VIIRS, AVHRR, Landsat-8, Sentinel-2, ASTER, TET-1) and ground-based stations (e.g., FLIR cameras); digital elevation/surface models from airborne sensors (e.g., light detection and ranging (LiDAR), or 3D laser scans) and satellite imagery (e.g., tri-stereo Pleiades, SPOT-6/7, PlanetScope); ´ airborne hyperspectral surveys; geophysics (e.g., ground-penetrating radar, electromagnetic induction, magnetic survey); ground-based acoustic infrasound; ground-based scanning UV spectrometers; ground-based and satellite synthetic aperture radar (SAR) imaging (e.g., TerraSAR-X, Sentinel-1, Radarsat-2).

Data processing approaches and methods include change detection, offset tracking, interferometric SAR (InSAR), photogrammetry, hotspots and anomalies detection, neural networks, numerical modeling, inversion modeling, wavelet transforms, and image segmentation. Some authors also share codes for automated data analysis and demonstrate methods for post-processing standard products that are made available for end-users, and are expected to stimulate the research community to exploit them in other volcanological application contexts.

The geographic scope is global, with case studies in Chile, Peru, Ecuador, Guatemala, Mexico, Hawai'i, Alaska, Kamchatka, Japan, Indonesia, Vanuatu, Reunion Island, Ethiopia, Canary Islands, ´ Greece, Italy, and Iceland.

The added value of the published research lies in the demonstration that remote sensing technologies can improve our knowledge of volcanoes that pose a threat to local communities; back-analysis and critical revision of recent volcanic eruptions and unrest periods; and improvement of modeling and prediction methods. Therefore, this Special Issue provides not only a collection of forefront research in remote sensing applied to volcanology, but also a selection of case studies demonstrating the societal impact that this scientific discipline can potentially have in volcanic hazard and risk management.

#### **Francesca Cigna, Deodato Tapete , Zhong Lu, Susanna K. Ebmeier**

*Editors*
