One of the requests made to the modellers in order to demonstrate that they could produce a real-time forecast of the dispersing plume was to send a plot of the concentration distribution over the domain to the evaluation team at JRC Ispra, as soon as possible and within 6 hours from the communication of the release. The faxed maps were intended as basic evidence of the capability of the modellers to:

• collect the necessary weather information to run their dispersion models

• perform the dispersion simulation and forecast

• produce easy-to-interpret results within a limited amount of time.

While the concentration contour levels and the time of the forecasts were specified by the evaluation team, the different institutes were to send maps in different geographical projections and domain sizes. Furthermore, a check was made of whether the maps produced corresponded to the concentration data the modellers later submitted in numerical format for the statistical model evaluation.

In order to bring the faxed contour maps to a standard geographical projection, a specific computer procedure was developed at JRC Ispra. After the faxed maps were scanned and digitised, the procedure could be applied to interpret the contours produced on the various projections, and to reproduce them on the same reference projection for comparing the various predictions.