National scale decision support systems. Rapporteur's report: Pt. 1

National scale decision support systems are used to aid decision makers in taking the appropriate corrective actions to minimise public exposure to radiation during a nuclear accident. These systems couple environmental radiation measurements and meteorological data with atmospheric and radioecological models for predicting the potential public health impacts. The session on Atmospheric Dispersion Modelling and Related Aspects focused on a wide spectrum of atmospheric dispersion models used to support the systems being developed within the US, Japan, Russia, UK and Germany. One of the limitations of these decision support systems is their inability to quantify the uncertainties associated with the dispersion model predictions, particularly when simulating flows over complex terrain, as well as estimating the heterogeneous deposition patterns resulting from wet deposition processes. This limitation, however, is being addressed by the use of data from both local and regional scale tracer experiments for evaluating model performance and the development of numerical techniques for more effectively integrating the environmental radiation measurements with the model predictions. (author)