## 4 Discussion and Conclusion: Lessons Learned and Future Perspectives
**Acknowledgments:** We thank the OVPF team for their tireless commitment to Piton de la Fournaise volcano monitoring, research, education, and information of scientists, decision makers, media, and the interested public. We also thank [PERSON] and three anonymous reviewers for very valuable suggestions and comments on the manuscript. Seismic data shown on Figure 1 were collected and processed by the Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris (OVPF-IFGP), and raw seismic data can be downloaded from the [[http://volobsis.ipgp.fr/](http://volobsis.ipgp.fr/)]([http://volobsis.ipgp.fr/](http://volobsis.ipgp.fr/)) website. All SAR data except those shown in Figure 4c, Figure 9, and Figure 10 (which were processed using DIAPASON) were processed using the SARproZ software. We would like to thank the European Space Agency (ESA) for providing ENVISAT ASAR data through the AO-ENVISAT project #746, and ALOS1 data through the ALOS-ADEN project #3622. We also thank the Sentinel-1 ESA team, especially Mr. [PERSON] and Mr. [PERSON] for facilitating routine Sentinel-1 StripMap acquisitions over La Reunion Island. We thank the German Aerospace Center (DLR) for providing TerraSAR-X and TanDEM-X data through the LAN0237, GEO3602, and XTI_GEOL_NR0224 data proposals. ASI provided us with CSK scenes through the CSK AO 2080 project, for which we are thankful. Likewise, we thank JAXA for providing us with ALOS2 data through the 4 th ALOS RA 1287, as well as the 6 th ALOS RA 3187 projects. We thank the Canadian Space Agency, MacDonald, Dettwiler & Associates Ltd., and the SOAA program for providing RADARSAT-1 and RADARSAT-2 data, as well as the SEAS-OI (Survey of Environment Assisted by Satellite in the Indian Ocean) receiving station that provided RADARSAT-2 data at no cost (www.seas-oi.org). Developing the SAR \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mission Name** & **Country/Space** & **Launch Date** & \begin{tabular}{c} **Number of** \\ **Satellites** \\ \end{tabular} & **Wavelength** & **Notes** \\ \hline ICEYE & Finland & \begin{tabular}{c} ICEYE-X1 launched \\ January 2018 \\ \end{tabular} & \begin{tabular}{c} 18 SAR \\ microsatellite \\ \end{tabular} & X-band & \\ \hline PAZ & Spain & launched January 2018 & 1 & X-band & \begin{tabular}{c} Operated in \\ constellation with \\ Germany’s \\ \end{tabular} \\  & & & & & TerraSAR-X and \\  & & & & TanDEM-X satellites \\ \hline HRWS (High Resolution Wide Swath) & Germany & 2023 & \begin{tabular}{c} 1 active, \\ 3 companions \\ \end{tabular} & X-band & \\ \hline COSMO-SkyMed & Italy & 2018–2020 & 2 & X-band & \\ \hline RCM (RADARSAT Constellation Mission) & Canada & \begin{tabular}{c} in phase of planning, \\ uncertain launch date \\ \end{tabular} & 3 & C-band & Canada focused only \\ \hline NISAR & USA-India & \begin{tabular}{c} not before \\ 31 January 2022 \\ \end{tabular} & 1 & \
\begin{tabular}{c} L-band, \\ S-band \\ \end{tabular} &
\begin{tabular}{c} Left-looking; \\ free and open \\ data policy \\ \end{tabular} \\ \hline TanDEM-L & Germany-Japan & uncertain & 2 & L-band & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Overview of future SAR satellite missions. database for Piton de la Fournaise volcano was supported by the French Space Agency (CNES) through the TOSCA and Kalideos programs, by the French National Institute for Earth Sciences and Astronomy (CNRS-INSU) through the PNTS and SNOV programs, by the French National Research Agency through ANR-10-EQPX-20 (GEOSUD) and ANR-16-CE04-0004-01 (SlideVOLC) projects, and by the French Government Laboratory of Excellence initiative ANR-10-LABX-0006. The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.