Polar Radar for Ice Sheet Measurements

Special Report: Drifting Buoys

Hello all!

Another bit of science we are doing on this voyage - the Bureau of Meteorology asked us to deploy two buoys into the ocean at locations they specified. Or at least they said put the buoys into the water within 60 miles of the position we give you - at least they recognised the difficulty of trying to get to a specific spot with all the sea ice around.

Well, early Thursday morning we navigated our way to a position pretty near the first of the sites. It was an area in which there was quite extensive sea ice and a few hours before the deployment we were actually stopped in the ice for several hours waiting for proper daylight so we could better see what was around us. The crew took the buoy out of its packing crate, tied a rope and quick release to it and used a crane to lower it over the side of the ship into the water. It is about four metres long shaped a bit like a small rocket of the kind fired by hand held rocket launchers in the Army. You will have to wait for the pictures. OzGold and I sat on the buoy before it was dropped over the side.

A couple of days before the launch we removed a small shield around one part of the buoy to activate a beacon - the Bureau picked up the signal so we knew it was correctly transmitting.

OK, so what is it all about?

The drifting buoys are called FGGE/TOGA spar type buoys. They have sensors for air pressure, air temperature and sea surface temperature; some buoys also have optional sensors for wind speed and wind direction. Most of the buoys have a drogue attachment which allows the buoy to follow the prevailing sea surface currents. The buoys are powered by banks of ‘D’ size alkaline batteries stored at the bottom end. These allow enough power for up to two years transmissions. The hull is made of aluminium. Data from drifting buoys are collected using the Argos satellite based location and collection system, which is part of the NOAA polar orbiting satellite system. The data are received at a number of receiving stations including Casey, Melbourne, Perth and Darwin. The data are then relayed back to France for processing and insertion onto the Global Telecommunications system. The raw data gets back to the Bureau of Meteorology in Melbourne approximately 15 minutes after satellite collection, and the processed coded data from France anything up to an hour after collection. The data are used real-time for day-to-day operational forecasting, and in delayed mode for use in climate models. The in-situ sea surface barometer data from drifters in the southern oceans are in fact essential for climate related studies, e.g. for (a) validation/calibration of altimeters, (b) estimating fluxes - by deriving wind fields from surface pressure field, and (c) studies regarding Antarctic circumpolar waves.

Gordon got this information from the Bureau of Meteorology but I think there are some things in it you will need to follow-up from reference texts or the internet.

That’s all for now.