Remote IR detection of volcanic ash hits headlines

Easyjet have announced that they are trialling a system to detect volcanic ash from their aircraft. Most of the coverage I've seen refers to this as radar but it is an infrared system not centimetric and it is also passive not active.

AVOID (Airborne Volcanic Object Identifier and Detector) has been developed by a Norwegian academic spin-off called Nicarnica led by Anglo-Australian climate scientist Dr Fred Prata. It is presumably a specialised development of their CyClops Infrared Imaging Camera which uses an uncooled bolometer (a type of radiant energy detector invented in 1878) to detect heat radiation in five separate but adjustable wavelengths. The company say that their camera can identify volcanic ash particles and sulphur dioxide gas (a common part of volcanic eruptions) at a distance that is presumably only limited by line-of-sight.

This isn't strictly an imaging system (it does not show recognisable objects) but it does produce an image analogous to radar, showing cloud boundaries mapped against distance. Using spectroscopic analysis CyClops can differentiate between ordinary water/ice clouds and more hazardous types. AVOID will presumably offer similar facilities to allow pilots to navigate around hazardous clouds even if they are invisible to the naked eye.

Dr Prata (together with Ian Barton) produced what looks like their first patent in the field (Detection system for use in an aircraft United States Patent 5602543) in 1991 where the abstract says that the "system is able to detect the presence of volcanic ash cloud ahead of the aircraft". So this is something of which Dr Prata and his team have long experience. Incidentally, the associated advance detection of clear air turbulence from aircraft using infrared goes back even further, to at least the 1960s.

To go back even further, we find bolometers used on ships back towards the start of the 20th Century to try to detect icebergs; at a time when the Titanic was a recent memory.