Dr Phil Sutton of NIWA explains how Argo scientific floats are deployed and how they work in the water. He describes their cycle of floating at depth, collecting measurements as they rise to the surface and transmitting data to satellites before sinking again. The deployment of floats from the NIWA research ship Kaharoa is also explained.
DR PHIL SUTTON
Floats measure temperature and salinity through the water column, so despite the fact they are called floats they actually sink. The first thing that happens is you put the float in the water. It then sinks down to 1,000 metres, it floats around for 9 days, it then sinks down to about 2 kilometres of depth before it comes up to the surface, and on its way up, it measures temperature and salinity through the water column. Once it's on the surface, it transmits that data off to satellite and then repeats the process, sinks back down to a 1,000 metres, spends another 9 days drifting around.
So basically, what you get is temperature and salinity through the top 2 kilometres of the ocean. You get it every 10 days from each float, and the floats have a lifetime of about 5 years.
The measurements of temperature, and salinity, and pressure are made using electronic sensors. In fact, it measures conductivity, not salinity, and then uses the conductivity of the water to calculate the salinity. And pressure, of course, basically gives you depth, because the amount of water above you determines the pressure, and that tells you how deep you are. So those are all measured electronically, stored on board, and then once the float is on the surface, it transmits that data off to satellite through an antennae that is on the top of the float.
There are 2 different sorts of, or manufacturers for Argo floats that we deploy off Kaharoa. There are yellow ones that are made by Webb Research for the University of Washington, and those are just deployed naked. So basically the float is picked up out of a wooden box, carried to the stern and then just lowered into the water, and because Kaharoa is so low to the water, you can almost just lean over and place the float right directly into the sea rather than dropping it.
The other ones are manufactured by Scripps Institution of Oceanography and those are deployed in cardboard boxes, and basically the boxes are held together with a tape that dissolves in the water, and the boxes, after a few minutes in the water flop open, and the float just gently floats out of that. And the idea of those is that the sensors are protected through the process of getting the float into the water.
Public domain Scripps Institution of Oceanography, UCSD
Southampton Oceanography Centre, UK
Alan Blacklock, NIWA