3. Quantitative measurements from space

Volcanic eruptions can have huge impacts on the economy, although they are relatively rare compared to other high-impact natural hazards. For instance, the eruption of the Eyjafjallajökull volcano in 2010 forced the cancellation of about 100 000 flights and generated a EUR 1.4 billion loss for airline operators.

It is actually very difficult for pilots to identify volcanic ash clouds, especially during nighttime, as airplanes are not normally equipped with instruments to detect ash. However, knowledge of the concentrations, vertical extent and particle size of ash is crucial for air traffic security like several incidents in the past have shown.

On 24 June 1982, British Airways Flight 009 en route from London Heathrow to Auckland was flown by the City of Edinburgh, a Boeing 747-236B registered as G-BDXH. The aircraft flew into a cloud of volcanic ash thrown up by the eruption of Mount Galunggung around 110 miles (180 km) south-east of Jakarta, Indonesia, resulting in the failure of all four engines. Partly because the event occurred at night, obscuring the cloud, the reason for the failure was not immediately apparent to the crew or air traffic control. The aircraft was diverted to Jakarta in the hope that enough engines could be restarted to allow it to land there. The aircraft glided out of the ash cloud, and all engines were restarted (although one failed again soon after), allowing the aircraft to land safely at the Halim Perdanakusuma Airport in Jakarta. Source: Wikipedia

If you want to know more about this incident, watch this documentary: https://www.youtube.com/watch?v=YYwN1R8hVsI

As a consequence of this and similar incidents, Volcanic Ash Advisory Centers (VAAC) have been created to monitor the propagation of volcanic ash clouds using satellite data as a primary source of information.

Currently, two types of passive satellite instruments provide quantitative measurements of trace gases such as SO2 emitted by volcanic eruptions. The first category of satellite sensors operates in the UV and visible spectrum (e.g., OMI, GOME-2 and TROPOMI) and the other type measures the infrared spectrum (e.g., IASI and AIRS). The tools best suited for volcanic ash cloud height assessment are active satellite instruments using lidar technology, such as CALIOP.

In the following section you will learn more about the categories of satellite sensors that are used to provide quantitative information on volcanic ash and SO2 clouds.