Blog entry by Sariaka Ramarherison with Ria Oelerich
Gliders are autonomous underwater vehicles that sample the ocean, driven by changes in their buoyancy — which enables them to float in water. Equipped with an oil pump that adjusts their density, they descend and ascend the water column in sawtooth motions. One down- and upcast is called a “yo”.
On this expedition, the glider team’s main focus was to test an adaptive sampling algorithm for studying and repeatedly tracking frontal systems in a specified location. The algorithm is designed to detect sharp horizontal transitions in temperature regimes which are accompanied by sharp horizontal density changes, known as fronts.
We deployed two deep gliders with a maximum dive depth of 1000 m provided by GEOMAR: the Slocum G1 and G3. Both gliders are equipped with various sensors specific to each glider summed up in the table below.
The most essential aspects of preparing a glider for deployment are well-established glider communication, ballasting of the glider and preparing mission files. One of the first steps is setting up our communication system, which includes one radio frequency antenna (Freewave) for each glider. They are usually positioned high up on the ship’s mast, in clear sight of the gliders. The Freewave antennas are then connected via a serial port to a computer representing our local communication base. In addition to this, the gliders can also communicate via satellite, using a shared antenna with the GPS. The next step is to adjust the weights of the gliders to ensure proper control over their movement in the water—and, of course, to avoid sinking. To ensure accurate ballasting of the gliders, we tested their buoyancy during a pool test: this involved lowering the gliders into a tank filled with seawater from the area of interest. The gliders’ positions in the water were then tested in sinking, neutral and buoyant configurations.
Once accurate ballasting of both gliders was confirmed, communication was established, the Microriders were mounted and the oxygen sensors were calibrated; the gliders were ready for deployment.
