## 2 Background: Existing Space-Based Monitoring Systems
### SAR-Based Systems  
SARVIEWS, developed by the University of Alaska Fairbanks ([[http://sarviews-hazards.alaska.edu](http://sarviews-hazards.alaska.edu)]([http://sarviews-hazards.alaska.edu](http://sarviews-hazards.alaska.edu))), is a monitoring service based on the analysis of SAR imagery. The processing flow is triggered by an external alert system informing on an ongoing hazardous event, including volcanic eruptions, earthquakes, floods, or fires. By default it provides wrapped interferograms (6-day and 12-day) and Radiometric Terrain Correction (RTC) images computed over large spatial scales (\(\sim\)250 km wide). A Hybrid Pluggable Processing Pipeline (HyP3) allows on-demand higher level analysis, such as change detection algorithms. The derived products, although not available in open-access, have proven to be useful for operational volcano monitoring [50; 51].  
LiCS (Looking inside the Continents from Space) is developed by COMET (Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics). The InSAR portal ([[https://comet.nerc.ac.uk/COMET-LiCS-portal/](https://comet.nerc.ac.uk/COMET-LiCS-portal/)]([https://comet.nerc.ac.uk/COMET-LiCS-portal/](https://comet.nerc.ac.uk/COMET-LiCS-portal/))) is an interactive map which provides links to download interferograms and coherence maps computed from Sentinel-1 images on large spatial scales. Although the initial focus was the Alpine-Himalayan tectonic belt, the system has recently expanded to process volcanic areas globally. A volcano deformation database provides access to interferograms and coherence maps at several hundreds of volcanoes ([[https://comet.nerc.ac.uk/volcanoes/](https://comet.nerc.ac.uk/volcanoes/)]([https://comet.nerc.ac.uk/volcanoes/](https://comet.nerc.ac.uk/volcanoes/))), with the intention to be used for monitoring purposes in the future [26].  
The University of Miami Geodesy Laboratory developed a system which provides InSAR displacement time-series at a smaller number of selected volcano ([[https://insarmaps.miami.edu/](https://insarmaps.miami.edu/)]([https://insarmaps.miami.edu/](https://insarmaps.miami.edu/))). The system relies on automatic InSAR time series analysis of Sentinel-1 products, which allows visualization of the temporal evolution of deformation on a large number of points across the volcano. Such approaches can be useful to detect pre-eruptive inflation, which is often observed in closed volcanic systems [52].  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**System**} & \multicolumn{4}{c}{**Satellite/Sensor Characterization Used by the System**} & \multicolumn{4}{c}{**System Characteristics**} \\ \cline{2-10}  & \multicolumn{2}{c}{**Satellite (Sensor)**} & \multicolumn{2}{c}{**Work-Length**} & \multicolumn{2}{c}{**Onti.**} & \multicolumn{2}{c}{**Resolution**} & \multicolumn{2}{c}{**Algorithm**} & \multicolumn{2}{c}{**Key Products**} & \multicolumn{2}{c}{**_**Aveability**} & \multicolumn{2}{c}{**Notions**} & \multicolumn{2}{c}{**Web link**} \\ \hline \multirow{3}{*}{**MODVOIC**} & **Agent/Tears** & **Agent/Tears** & **plan-orbiting** & \multirow{3}{*}{1 km} & \multirow{3}{*}{spectral} & \multirow{3}{*}{-1 km} & \multirow{3}{*}{spectral} & \multirow{3}{*}{-1 km} & \multirow{3}{*}{-1 km} & \multirow{3}{*}{-1 km} \\  & **(MOOTS)** & & & & & & & & \\ \cline{5-10}  & **Agent/Tears** & **plan-orbiting** & \multirow{3}{*}{1 km} & & & & & & \\ \cline{5-10}  & **Agent/Tears** & **plan-orbiting** & & &