The use of radar measurements to monitor volcanic plumes in Iceland has proven to be invaluable. They have been conducted since January 1991, a few days after the installation of a C-band weather radar close to Keflavík international airport. Since November 2011 IMO, has had on loan from the Italian Civil Protection Agency a mobile X-band dual polarization radar. A combined system of fixed C-band radars and mobile X-band radars is a good solution to monitor volcanic plumes. They give valuable and accurate information of plume height used as input data into ash dispersion models. A fixed C-band radar is operational 24/7, thus it detects the initial state of the eruption. However, the accuracy is dependent on the distance from the volcano, e.g. for the Grímsvötn eruption located 260 km away from the C-band weather radar in Keflavík, the plume height accuracy is ± 2 km. In addition the radar does not detect plumes lower than 6 km height at this distance. There is less uncertainty in the plume height detected by the mobile X-band radar when stationed close to a volcano. In addition it detects the whole plume as long as there is no blocking of the radar beam due to mountains or other obstacles. A mobile X-band radar needs to be transported close to the volcano site, which can take time. During that time, it is not measuring. This makes the combination of fixed C-and mobile X-band radars the preferred solution in providing data for ash dispersion models.

In the Grímsvötn eruption in May 2011, the use of Lidar measurements at Keflavík airport and in-situ measurements in the surroundings was demonstrated. Due to their support, in addition to satellite information, IMO was able to assist Isavia (Icelandic aviation service provider) in decisions of opening of the Keflavík international airport, which would have been closed otherwise based on forecasts from dispersion models only. Substantial savings were made due to these extra measurement efforts.