So there I was, with five others, standing on a small boat in the Gulf of Oman. The air temperature was an unbearable 47 degrees, and the boat was fiercely rocking side to side, enough to make even the hardiest of sailors question their choice of profession. All eyes were focused on the horizon, as though any distracting glance away from the sea could jeopardise all efforts. Until suddenly, out of the deep, a yellow metallic body was spotted glistening under the midday sun. This was exactly what we were searching for.
As soon as the object was spotted, the ship was brought to an abrupt stop by the captain, whilst the crew organised themselves accordingly. An extended catching device was lowered into the water, plucking the object carefully out of the water below.
This yellow metallic object is in fact a Sea Glider! This particular sea glider had been circumnavigating around the Gulf of Oman for over three months. A Sea Glider (figure 1) is an autonomous underwater vehicle (AUV), capable of recording a range of variables, such as temperature, salinity, oxygen, and more. They are completely automatic; requiring at most times one person to remotely operate, but most importantly, they enable scientists to analyse detailed oceanic information, making it possible to gain new insights on the state of our oceans.
“A sea glider is a completely automatic underwater vehicle that enables scientists to analyse detailed oceanographic information”
How does a sea glider work?
Sea gliders are a love child of engineering and innovation. A set of wings and a rear rudder helps to guide the glider horizontally through the water, whilst an external bladder (figure 2) moderates the glider’s buoyancy in relation to seawater, causing it to move vertically in the water. The pitch (slope) of the glider is controlled by redistributing the glider’s buoyancy using internal volume and the battery. A satellite antenna is positioned at the rear end, which sticks out of the water between consecutive dives. This is used to receive new commands and to send back any retrieved data via satellite to keen scientists (or desperate PhD students) back on land.
The glider reads the commands from a simple text file, containing a list of variables that it needs to process in order to carry out successful dives. Sea Gliders can typically last for months at end in the ocean, however this particular glider now had to be retrieved as it was starting to run out of battery power.
"Sea gliders are a love child of engineering and innovation”
So that’s how a Sea Glider works. But why was it deployed in the Gulf of Oman?
This Sea Glider had been chosen specifically to investigate the physical and biogeochemical variability of the ocean in the Gulf of Oman. In fact, it was the first time data has ever been retrieved from this region with such high temporal and spatial quality, and reaching depths of up to 1000 m.
The Gulf is particularly interesting to study as the ocean is influenced by both the Northeast and Southwest monsoons, and some regions are considered extremely productive due to a nearly continuous upwelling of nutrients. As well as this, a number of important coral reef ecosystems can be found in shallower parts of the Gulf.
Deployment, Retreival, Replacment
Now that the glider was retrieved, the next step was to deploy its replacement. A glider was prepared and tested to check that everything was working accordingly, and most importantly, that a reliable signal existed between the gliders antenna and our computers. As without this, the gliders position would be unknown and future retrieval would be close to impossible.
The following day we were once again on board the ship, this time prepared with a year’s supply of seasickness tablets and a fridge full of ice-cold water. The initial period of deploying a glider is prone to things going wrong, and requires a good deal of communication between us and the team back at the University of East Anglia.
However, after some shoving here, and some fiddling there, the replacement glider was deployed successfully.
Now all we had to do was sit back, relax, and wait for highly detailed data to roll in.
Crew onboard the ship enjoying one of the many spectacular sunsets in the region.
References Sharp, G.D. 1995. Arabian Sea Fisheries and their Production Contexts In The Arabian Sea: Living Marine Resources and the Environment. (Eds.) Thompson, M. F. and Tirmizi, N.M. A.A. Balkema, Rotterdam. p. 239-264. Rudnick, D.L. 2015. Ocean Research Enabled by Underwater Gliders. Annual Reviews of Marine Science. Vol. 8, p 9.1 – 9.23. Eriksen, C.C., Osse, T.J., Light, R.D., Wen, T. Lehman, T.W., Sabin, P.L., Ballard, J.W., and Chiodi, A.M. 2001. Seaglider: A Long-Range Autonomous Underwater Vehicle for Oceanographic Research. J. of Oceanic Engineering. Vol. 26, p 424 – 436.