# Satellite and Ground Based Thermal Observation of the 2014 Effusive Eruption at Stromboli Volcano
## 5 Discussion
### Added Value of TET-1 Data  
Monitoring of effusive volcanic activity at high temporal and high spatial resolution has not been possible until TET-1 became operational. TET-1 does not saturate in the MIR channel making it much more useful than other high resolution instruments like Landsat ETM+ or ASTER that tend to saturate in the case of intensive volcanic activity. Once BIROS is launched, the FireBird constellation will be able to provide data at least once per 3 days above the Equator. Figure 11 shows the analysis of lava flows observed by TET-1. Using the dual band method (Equation (1)), we estimated the effective temperature and the area covered by lava flows as well as their length. Please note, that the lengths are upper estimates, as we did not consider the point spread function of the instrument. A comparison between the TET-1 values and the observations from the boat reveal that the temperature and length of the flows are in a good agreement. However, the estimated areas of lava flows from the TET-1 and boat observations do not match on 19 September 2014. There are two possible explanations for this observation. (1) The observations of the flow from the boat simply did not capture the whole flow because of the low viewing angle. Looking at Figure 4 one can see that the lava flow seems to be coming from the left before it becomes visible to the camera. Field observations from a higher elevation on the slope show a big bulge of colder lava, which was built during the eruption. This bulge might hinder a direct view from the sea onto this large part of the flow. Above the bulge, the flow continued to the vent that is also not visible in Figure 4. This could well explain at least some of the differences detected between the boat and space based observations. (2) Comparing this one with other situations in Figure 5, we can see relatively cool lava flows covering a similar number of pixels as in other situations. Thus, the reasons of such an extreme large flow area must be related to the numerical solution of the dual band method. Figure 11: Analysis of the effective temperature, area and length of lava flows from TET-1 data; see Table 7 for exact values. In Table 7 we list the values of estimated temperature, area, and \(VRP\) computed with (a) dual band method; and (b) [PERSON]'s method for the cloud-free TET-1 data. Especially interesting is the comparison between both \(VRP\) results. We can see some differences, especially for the situation discussed above and for 27 September 2014. The mean dual band \(VRP\) value for the 11 datasets is 96 MW, for [PERSON]'s method \(VRP\) the mean value is 115 MW. Some of these differences can be ascribed to some steps in the processing chain. It is especially interesting to see that [PERSON]'s method, which results fits well with MODIS data (Figure 7), produces in general higher values. This deviation will be addressed in the future, as TET-1 data will be available for several volcanoes. In the past, the dual band method has been criticized for yielding unrealistic results [45; 46; 47; 48; 49]. Compared to older satellite instruments (for instance MODIS), TET-1 has an improved spatial resolution. Older instruments usually cover such a large pixel area that the assumption of only two endmembers in a pixel (hotspot and background) is unrealistic. This is nicely demonstrated by the fact that TET-1 can also see the separate flows on Stromboli, while in the MODIS images the whole flow covers only one pixel. This prevents a more detailed analysis on the extent of the lava flow from MODIS data, which is extremely important for modeling the evolution of the flow as well as for hazard assessment related issues. Applying the dual band method to the TET-1 data, which have a significantly higher spatial resolution than MODIS data, makes the solution of the dual band method much more reliable, as the two endmember model is better suited for smaller pixels.