RN measurement scenario Plot

Summary of Field of Regard and geo-temporal source correlation results

According to the PTS results as well as the joint computations the source receptor sensitivity field of the major detection at NZP46 emerges backward (upflow) from the collection stop (CS) date & time (22 Jan, 0 UTC) towards the North Island of New Zealand. Due to the flow patterns surrounding this Island the SRS field turns first northward, than westward and finally south-west ward, thus also surrounding New Zealand. 4 days backward from CS the increased sensitivity emerges further towards south-west. It is noticable that the SRS field remains fairly compact for the first 3 days backward from CS. Later on the pattern is first elongated (in west east direction) and lateral dispersion is not prominent within the first 5 days of backward transport.

It is remarkable that the level of congruence in the SRS summary display (Multiple Model FOR's) remains high the first 4 days of the backward dispersion. This shows that all participating models fairly agree on the first half of their computations. The Agreement and Overlap Values resulting from the inter-comparison statistic (as shown in the table being part of this report) do not fully reflect this congruence, since not only the first 4 but allways the first 6 days in 3 hourly frequency are compared. However, an agreement of 50% can still be regarded as a very good result.

The Source Location Estimation results based on the PTS SRS fields indicate an elongated pattern covering New Zealand and reaching more than 5000 km south-westward into the southern Indian Ocean. However if information on the release date is additionally taken into account (January 18 between 15:00 and 18:00 UTC), the Source Location Estimation is confined substantially towards the west coast of of the Southern and the East coast of the Northern Island of New Zealand. Such timing information would in a real case be available from the isotopic ratios of the radionuclides detected and can thus be regarded as independent information.

The results obtained with the PTS source location estimation algorithm fed with the data from the experiment participants are in very good agreement with the initial PTS results. Hence in general they also feature the aforementioned elongated pattern for the Source Location Estimation performed without event time information. Introducing this timing information confines the estimate again to New Zealand and the immediate surrounding.

Finally the PTS put together all results by calculating the average of all 12 participants source location estimates (in terms of their correlation). It is of interest that this product, even without utilizing the event time information, confines the most likely source region toward the North Island of New Zealand.

Taking finally the event time information into account, the source location algorithm reveals a very confined possible source region over New Zealand, centered across the southern part of the North Island and in the Tasman Sea facing the western coastline of the South Island.

From this jointly computed results we have to conclude that this VIRTUAL nuclear event occured within or close to New Zealand.