The IMOS Rottnest Coastal Shelf (RCS) hydrophone in the Perth Canyon has been key to discovering acoustic triangulation details in the CTBTO Cape Leeuwin hydrophone data. New details have been revealed about RCS. Two hydrophones were retrieved, but the focus has been on the one that detected an event. It was retrieved last year from 31°52.447’S; 115° 0.068’E. Both hydrophones were programmed to be active only 1/3 of the time on a 15 minute cycle to extend battery life, but the timing was staggered to capture more marine life sounds. A previously reported 4 second uncertainty in the RCS timing has been estimated to now be within a second, because the hydrophones are checked against GPS time at deployment and retrieval to account for timing drift.
The revised location change of 2.1 km caused an 8 km shift in the resulting triangulation search path where it intersects the 7th Arc. The better timing info has reduced the error limit width of the search path from 63 km to 42 km. This limit will be further reduced by determining an accurate local sound speed over the predicted paths. The error range is now a generous 1460-1516 meters/s, though it is probably within a few m/s of the current value of 1488. This can be calibrated by experimental detonations in the SOFAR channel, or more certain estimates from historical data.
Requests have been made for additional hydrophone and infrasound data for discovery of additional events based on the new location and timing estimates. This will hopefully provide a third intersect to narrow the search region around the 7th Arc to an even smaller area.