# Satellite and Ground Based Thermal Observation of the 2014 Effusive Eruption at Stromboli Volcano
## 2 Thermal Observations of Active Volcanoes
### Characteristics of Instruments Suitable for Observing Volcanic Thermal Anomalies  
The most important source of uncertainties in thermal monitoring of active volcanoes from space stems from the lack of dedicated satellite instruments. A perfect instrument dedicated to monitoring thermal anomalies should have the following characteristics:  
* high spatial resolution (width of an average lava flow <20 m),
* short revisit time (<15 min),
* numerous spectral channels, or at least an appropriate combination of channels [27],
* high radiometric accuracy (<0.1 K), and
* automatic adjustment of gain settings, _i.e._, being able to observe high and low temperature events using the same sensor.  
Considering the currently available technology, such instruments are not available. This leads to compromises between spatial and temporal resolution--if the data were available at high temporal resolution (from geostationary instruments), it is impossible to provide high spatial resolution data. The most promising solution seems to be a constellation of small satellites, as proposed by ESA [28], for they can provide data at high spatial resolution and provide a short revisit time as there is a high number of satellites in the constellation.  
In addition, it is difficult to provide narrow spectral channels at high radiometric accuracy for monitoring high and low temperatures at the same time. Instruments designed for meteorological applications are usually used in remote sensing of volcanic thermal anomalies. These instruments also contain a MIR channel, which provides crucial data for monitoring active volcanoes. However, the settings of meteorological instruments are optimized for monitoring low temperatures, which results in often saturated data over active volcanoes. The saturation level depends on the temperature of the observed anomaly and its size, as well as on the instrument's settings. Taking 1500 K as the upper limit for volcanic thermal anomalies, the saturation of the instrument's signal depends on the size of the anomaly. This means that instruments with coarser spatial resolution are less prone to saturation than high resolution instruments. However, high resolution instruments are necessary in order to observe the exact position of the anomaly and precisely quantify its amplitude.  
The currently operational instruments suitable for monitoring volcanic thermal anomalies with spatial resolution of no more than 100 m are: (1) the Operational Land Imager (OLI) accompanied by the Thermal Infrared Sensor (TIRS) on-board Landsat-8; and (2) the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on-board Terra satellite. The latter has a malfunction in its short-wave infrared channels since spring 2008, which limits its use for the quantification of thermal anomalies. An alternative is represented by the Visible Infrared Imaging Radiometer Suite (VIIRS) on board the Suomi National Polar-orbiting Partnership satellite, which provides a suitable spectral channel (VIIRS I4) also at 375 m spatial resolution, but this channel becomes saturated already at 367 K [29]. Another option could be the Chinese small satellite HJ-1B (spatial resolution of 150 m in the MIR channel), however its data are not available in an open access web archive.