Polar Profiling Floats: Overview
PIs: Breck Owens and Peter Winsor, WHOI
Engineers: James Valdes and Robert Tavares, WHOI
The Argo program is a global array of 3,000 free-drifting profiling floats that will measure the temperature and salinity of the upper 2000 m of the ocean (http://www.argo.ucsd.edu/). This will allow, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all data being relayed and made publicly available within hours after collection. However, the “global” array is not global at this point, as high-latitude ice-covered oceans are not represented. The main problem with using profiling floats in ice-covered regions is that the floats need to surface through a lead or other open water to be able to transmit data back to shore.
We have developed techniques that allow profiling floats, which we named Polar Profiling Floats (PPFs), to successfully find open water within the sea ice, and transmit data back to shore via Iridium satellite communication.
We have gratefully received funding from NSF OPP to conduct a field test of our PPFs in 2005 during leg 3 of the Beringia 2005 expedition, crossing the Arctic Ocean from Barrow Alaska to Svalbard Norway. In order to achieve a representative picture of Arctic sea ice conditions we deployed the floats at three different locations (marked A-C in Fig. 1). We programmed each float to drift in the core of the Atlantic Layer (~300 m depth) for a week after deployment after which it will descend to ~900 m depth and make a full profile to the surface (~10 m depth). The float will then go into its transmitting mode, cycling between 50 m and the surface to try to find open water and send data to shore. Each time the float comes to the surface (or under ice) it will look for Iridium satellites, and if detected, transmit its stored data within a minute or two. If no satellite is detected, the float will go down to 50 m again, wait for a predefined time period and try again. This pattern will be repeated until the float transmits its data successfully, with a cycling limit of ~100 tries. If the float is unsuccessful after 100 repetitions, it will go down to its pre-set drift depth (~300 m) and continue its mission for another year. In our field test, we simulated this cycle by letting the float drift for one week, profile, and then go into its cycling/transmitting mode again, thereby simulating a mission over several years.
All three floats deployed during the Beringa 2005 expedition have reported back their position and multiple vertical profiles containing hydrographical data (pressure, temperature, conductivity and salinity). They all show that the technique to find open water during sever ice conditions works very well.
|Support from the National Science Foundation is gratefully acknowledged.