Etna woke up again in the evening of 15 March 2017, spewing ash and SO2, and forming a nice looking plume.
09 August 2021
15 March 2017
By Djordje Gencic (RHMSS), HansPeter Roesli (Switzerland) and Jose Prieto and Jochen Kerkmann (EUMETSAT)
After a few hours the plume consisted of mixture of ash (seen as red) and SO2 (seen as green). This process of mixing continued in next few days as it can be seen in the Meteosat-10 Ash RGB, Figure 1 and animation.
On next day, the hot melted rocks from inside of Earth (lava) could be seen flowing onto the slopes of Mount Etna. This four panel image (Figure 2) which consists of VIIRS and SEVIRI data shows lava very well. Three of them are VIIRS images, and only the lower left is SEVIRI.
The spatial resolution difference (375 m for VIIRS and 3 km for SEVIRI) is very obvious. Lava can be seen in two right-hand side images (IR 3.74 µm for top and 11.45 µm for the lower one) as a yellow/orange area, which in this colour table represent very high temperatures.
Top left image is the S-NPP Natural Color RGB. On it, the side slopes of Mount Etna which were still covered with snow appear as cyan, while the lava is red/brown.
The lower left image shows more or less the same as the top right, just from the Meteosat-10 SEVIRI instrument.
The Meteosat-10 Near-Infrared Channel 3 (1.6 µm) animation shows the evolution during the night, in synchrony with fresh lava eruptions. In the 1.6 µm imagery the lowest meaningful counts were enhanced, less than 3% equivalent reflectivity, if compared with the Sun. But the source is emitted energy, and not reflection, still well detectable at this solar wavelength.
The Meteosat-10 Infrared Channel 4 (3.9 µm) animation shows a similar evolution during the night, with values frequently saturating the Meteosat sensor at 336 K, and highly correlated to the values at channel 3.
As discussed in this Portuguese fire case from 2006, in SEVIRI imagery the saturation of the IR3.9 channel causes some kind of ring structures (ripples) around the hot lava spot, as is very clearly seen in the Night Microphysics RGB (Figure 3). The users of MSG data should be aware that these ring structures are artefacts coming from the digital filter that is applied to the data. For lower wavelengths (0.8µm or 0.6µm), Meteosat is not sensitive to lava.
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