Simulated Volcanic Ash Satellite Imagery
Millington, Sarah1; Saunders, Roger1; Beckett, Frances1; Stevenson, John2; Webster, Helen1
1Met Office, UNITED KINGDOM; 2School of GeoSciences, The University of Edinburgh, UNITED KINGDOM
The London Volcanic Ash Advisory Centre (VAAC), operated by the Met Office UK, makes extensive use of satellite data and atmospheric dispersion model forecasts to provide guidance on the presence of airborne volcanic ash in its area of responsibility. Simulated volcanic ash imagery was developed to enable easy comparison between model forecasts and satellite imagery. A radiative transfer model, RTTOV, is used to forward model the radiances measured by the SEVIRI instrument on Meteosat. Inputs to RTTOV are taken from the Met Office’s NWP model and the ash mass concentration data from the NAME atmospheric dispersion model. The simulated radiances are used to create simulated volcanic ash images. Forecasters operating the VAAC service are then able to compare the simulated image to the real image during a volcanic event to help validate the model forecast.
The simulated imagery is also proving a useful tool in understanding the limitations and sensitivities of real volcanic ash satellite imagery to factors such as ash particle size and ash composition. For example, images simulated with large ash particles shows a much weaker (or non-existent) ash signal compared with images simulated with small ash particles suggesting large volcanic ash particles will not be seen in satellite imagery. The development of the simulated imagery and its applications in improving our knowledge of the physical properties of volcanic ash will be presented.