Toward an Observation of Volcanic Ash: which kind of Observation can be Made by Different Instruments and How to Design a Network
London Volcanic Ash Advisory Center (VAAC) was responsible for providing information about the ash plume to the relevant civil aviation authorities in the form of Volcanic Ash Advisories (VAA). On this basis, the authorities made decisions about when and where airspace should be closed due to the safety issues.
It was difficult for the VAAC to provide accurate information about the size and concentration of the volcanic particles. As a result, Toulouse VAAC asked Météo-France to find solutions to detect volcanic ashes from the ground to a 12km altitude and to assess their concentration.
Météo-France conducted an intercomparison campaign between several lidars and ceilometers during summer 2012 in order to assess their ability to detect aerosols dust for lack of volcanic ashes. The observations produced by the instruments are obtained thanks to several algorithms: STRAT from SIRTA and BASIC from the LOA (both French laboratories). It turns out it was difficult to compare the data with one another for several reasons: there is no aerosol measurement reference, instruments have different wavelengths, they can be dual-polarized. Results show the aerosols lidar technology may be a good mean to meet the VAAC requirements. Moreover, having the desire to built an efficient network in terms of number and location of sites over metropolitan France, Météo-France has run a model of pollutant dispersion, named MOCAGE, in retro-plume mode with different configurations in order to define the network which provides the best coverage.
This presentation describes how the intercomparison was conducted, the processing algorithms used, the difficulties encountered and the method used to design an optimum volcanic ash detection network.