In total the tapes contain something over an hour of sound recordings which the Swedish Armed Forces have asked FOI to analyse. Aspects of particular interest include a sonar-like signal and where it originates from.
 
The analyses of the very brief sonar-like signal recorded on 11 October 1982 are continuing. The question is whether the signal originated from a Swedish helicopter sonar or from a sonar transmitter deployed by a foreign power.

“It is not possible to say anything definite at present, but some new tests suggest a strengthening of the helicopter theory,” says Matts Gustavsson, Head of Department for underwater research at FOI.

Among other things, this is to do with the positions of the hydrophones which probably do not agree with the earlier positions that FOI’s scientists have had to base their analysis on. FOI will be re-examining the data on which the earlier positioning of the hydrophones was based and they will attempt to determine new positions that correspond more closely with the data and its associated uncertainties.

These uncertainties are inevitable in this context. They mean that it is only possible to locate the source as being within a fairly large area. And this in turn means that the fact that the signal can be heard, but not the helicopter’s rotor noise, does not necessarily rule the helicopter theory out. FOI will very shortly be carrying out helicopter sonar trials at sea for comparison purposes and this may then lead to further conclusions.

Full results of the analysis will be contained in a report to be submitted to the Swedish Armed Forces on 12 May.