# An Overview of Infrared Remote Sensing of Volcanic Activity
## 6 Prospects for the Future
One of the chief disadvantages of small satellites is that, given their size, and hence narrow swaths, their revisit frequencies are usually sub-optimal for monitoring phenomena that change on short timescales (such as volcanic activity). Small satellites, however, open the possibility that more can be constructed for the same cost as their expensive relatives, resulting in constellations of satellites [127]. Should such constellations be equipped with infrared sensing capabilities, then it would provide the potential for high spatial and temporal resolution observations of thermally-anomalous volcanic surfaces. China launched one such system, the Small Satellite Constellation for Environment Protection and Disaster Monitoring in 2008, and with its 30-m resolution infrared imaging capabilities, this system has proven useful in observing wildfires [128]. The DLR has also instigated a fire monitoring constellation, FireBIRD, with the first satellite, TET-1, having already shown utility in providing high resolution MIR and TIR imagery of a Strombolian lava flow [75]. The second satellite of the FireBIRD constellation, the Bi-spectral InfraRed Optical System (BIROS), was launched in 2016, and it is envisaged that in total, the FireBIRD constellation will have a three-day revisit period for locations at the Equator [75]. A constellation of multi-spectral infrared VISible-to-thermal IR micro-SATellites (VISIR-SAT) has also been proposed by the DLR, with a spatial resolution of potentially less than 30 m and with one of its aims being: \"To predict... volcanic hazards through detection of transient thermal phenomena\" (p. 1286) [74]. In the last decade, one development in the field of volcanic remote sensing (other than by satellite) has been the use of unmanned aerial vehicles (UAVs) mounted with infrared cameras (e.g., [129]). The chief advantage of such an approach, over that of using satellites, is a higher spatial resolution, given that the UAVs may be a few metres from the surface of interest. However, problems with payload weight, battery power and distance between operator and the hazardous surface have slowed progress in this promising field of study. In the future, an ideal strategy is for a multi-scale approach, combining the use of high temporal resolution, wide swath spectroradiometers (e.g., MODIS or AVHRR) with higher spatial resolution imagers that focus on high-risk areas. If such systems communicate with each other, events noted at high temporal resolution could be used to trigger higher spatial resolution observations; and the precedence of this has been discussed. One significant prospect in this regard is an ESA Sentinel Convoy, whereby [74] suggests that the VISIR-SAT could be flown with the Sentinel-3 satellites, thus providing high spatial resolution observations of thermal anomalies detected by the coarser resolution, but more widely-viewing, Sentinel range. Infrared remote sensing of volcanoes has made much progress in little more than half a century. It is essential that this progress is maintained to ensure areas of potential or imminent volcanic hazard are identified for scientists and decision makers. If investment continues in the development of Earth-orbiting infrared remote sensors, then improvements in what scientists can visualize and interpret will continue. Such developments will aid in the understanding of the actual geological phenomena on the ground and in the management of the associated hazards posed to vulnerable communities globally. The authors declare no conflict of interest.