Source: NIWA – National Institute of Water and Atmospheric Research
“You put everything together and then put the units through some rigorous testing, so that when they’re deployed, we have complete faith in the system.”
Each buoy comprises two main components – a Bottom Pressure Recorder (BPR) that sits on the sea floor, and a large, yellow float on the surface above.
Deploying both components requires a sophisticated mix of precision positioning on the high seas, sophisticated marine mapping below and a deep understanding of ocean currents. NIWA’s flagship research vessel Tangaroa and Brewer’s deployment team onboard are fully equipped to deliver.
A bathymetric survey of the seafloor using multibeam echosounders checks to ensure the gradient is less than 5 degrees, with no obstructions to interfere with signals travelling through the ocean.
Current and wave conditions are also assessed. Once the site has been cleared, the two components are lifted off the ship, and their separate moorings are carefully positioned hundreds of metres below.
The BPR and the float communicate with each other through the water column. Every 15 seconds the BPR records the height of the ocean above and sends that information to the surface buoy once an hour. From there the data goes via satellite to the server based at GNS Science’s National Geohazards Monitoring Centre back in Wellington.
“Tsunami are very long period waves, with some having wave lengths of up to an hour,” says Brewer.
“Wind and swell waves are short period waves, so by measuring every 15 seconds we are cutting out those short waves and concentrating on the big differences.”