Atmospheric transport modelling
and data fusion

Atmospheric transport modelling

Co-locating radionuclide detections with waveform events through atmospheric transport modelling (ATM) is one way of performing data fusion. Since the radionuclide technology does not provide any information on the probable location of an event, ATM is used to obtain this information.

Based on high-quality global meteorological data and using ATM, it is possible to trace the various three-dimensional travel paths of any selected radionuclide from any station where it was measured back to the area where it may have originated. This process is called source region attribution.  The aim is to obtain the best possible estimation for the source area, i.e. to identify an area as the release area that would best match the observations.

ATM can backtrack the movement of radionuclides from the point of detection to identify a possible release area or predict the travel path of radionculides based on a known emission location.

The backtracking method is most suitable when there is no advance knowledge of a possible release location. If it is known, however, the processing can be turned around. This means that ATM can provide forward calculations and predict where emitted radionuclides may be transported to, using meteorological data. This was the case when the Democratic People’s Republic of Korea announced its nuclear test in October 2006. The predicted results of the forward ATM calculations closely resembled the levels and timing of radioactive xenon detected at a radionuclide monitoring station in Canada.

Cooperation with WMO

It has been shown that the quality of the meteorological data utilized is crucial in atmospheric transport modelling (ATM), for both forward modelling and backtracking. In order to assess and reduce the uncertainties of its ATM results, CTBTO works closely with the World Meteorological Organization (WMO) in the area of dispersion modelling.

CTBTO cooperates successfully with the WMO in the area of dispersion modelling.

Several experiments have already been carried out to test the inclusion of ATM calculations provided by WMO. The results were very promising.  It was shown that WMO’s contribution could markedly enhance the ability of the CTBTO to identify source locations for possible releases of radionuclides.

Data fusion is a term used to describe the process of combining observations from the different monitoring networks which may originate from the same event. Data fusion includes correlating events that were located using waveform data with radionuclide observations.

Data fusion is used to correlate waveform analysis results with radionuclide observations.

Fusion of waveform and radionuclide events

For example, if an event that was recorded and located using data from the seismic network were indeed a nuclear explosion, then this could only be confirmed by recording anthropogenic radionuclides at one or more of the radionuclide stations. Using atmospheric transport modelling (ATM), it then needs to be shown that these observations are consistent with a radioactive release at the time and place of the located event.

In the case of a partly contained nuclear explosion, it may be expected that several stations would detect the radioactive debris released into the atmosphere.  With the benefit of ATM a source area can be calculated, based on data from all these stations.  This information is then overlaid with information from waveform data.

A software tool called WEB-GRAPE (web connected graphics engine) has been developed to assist in the performance of this task.  It includes a graphic display of the field of regard, which defines the regions from which the radionuclide observations could have originated, superimposed upon a map showing the seismic-acoustic events.

The software tool WEB-GRAPE has been developed to perform the overlay of waveform and radionuclide source locations.

The overlay of waveform and radionuclide source locations is crucial for two reasons.  Firstly, the radionuclide analysis can provide conclusive evidence as to the nuclear nature of the event.  Secondly, the event location information can be utilized to dramatically reduce the geographic region under scrutiny.

The results of all ATM computations are made available to Member States. In addition, experimental data fusion bulletins are provided during small scale test exercises that take place regularly.

Member States have access to the WEB-GRAPE software, which enables them to generate their own customized ATM and data fusion results.

Along with all relevant data, Member States are given access to the WEB-GRAPE software, which enables them to generate their own customized ATM and data fusion results. In the case of any ambiguities that still remain, Member States will, after the Treaty enters into force, be able to request additional data or analysis to clarify outstanding questions on specific events. It is their prerogative to make the final assessment of an ambiguous event based on data analysis provided by the CTBTO.

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Operations Centre and Computer Centre