Probabilistic Inverse Method for Source Localization Applied to ETEX and the 2017 Case of Ru-106 including Analyses of Sensitivity to Measurement Data

Kasper Skjold Tølløse,Jens Havskov Sørensen,Eigil Kaas

doi:10.3390/atmos12121567

Kasper Skjold Tølløse, Jens Havskov Sørensen + Show 1 more

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https://doi.org/10.3390/atmos12121567

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Abstract

In recent years, cases of unexplained, elevated levels of radioactive particles have demonstrated an increasing need for efficient and robust source localization methods. In this study, a Bayesian method for source localization is developed and applied to two cases. First, the method is validated against the European tracer experiment (ETEX) and then applied to the still unaccounted for release of Ru-106 in the fall of 2017. The ETEX dataset, however, differs significantly from the Ru-106 dataset with regard to time resolution and the distance from the release site to the nearest measurements. Therefore, sensitivity analyses are conducted in order to test the method’s sensitivity to these parameters. The analyses show that the resulting source localization depends on both the observed temporal resolution and the existence of sampling stations close to the source. However, the method is robust, in the sense that reducing the amount of information in the dataset merely reduces the accuracy, and hence, none of the results are contradictory. When applied to the Ru-106 case, the results indicate that the Southern Ural region is the most plausible release area, and, as hypothesized by other studies, that the Mayak nuclear facility is the most likely release location.

Highlights

IntroductionIntroduction and Susan JLeadbetterIn the case of an accidental release of a substance to the atmosphere, the time and location of the release may be unknown, in which case, only indirect information about the source location is available
Introduction and Susan JLeadbetterIn the case of an accidental release of a substance to the atmosphere, the time and location of the release may be unknown, in which case, only indirect information about the source location is available
We found that the third approach gives the overall best results, while the second approach leads to systematic underestimation of the release rates for the European tracer experiment (ETEX) case

Summary

Introduction

Introduction and Susan JLeadbetterIn the case of an accidental release of a substance to the atmosphere, the time and location of the release may be unknown, in which case, only indirect information about the source location is available. There is no unambiguous way of calculating the source location from this information; instead, inverse problem theory is needed in order to relate the measurements to possible release scenarios. The aim of this study is to develop and illustrate a method suitable for operational usage, and the focus is on efficiency and robustness. Examples of previous work on source localization include different applications of adjoint dispersion modelling, i.e., running the model backwards in time, such as the methods by Pudykiewicz [1], Wotawa et al [2], Seibert et al [3,4], and Sørensen [5]. One of the main challenges in inverse dispersion modelling is that model predictions are subject to large unknown errors, which complicate direct comparison of model and measurements

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