Helicopter CTD – transportable CTD with autonomous winch
Fig. 1: A-frame with CTD and 5-l bottle. The support gear near the edge hosts the frame and spreads the mechanical forces.
High resolution profiles of typical physical parameter of seawater such as temperature, conductivity/salinity, and pressure can only be measured in the water column, including the bottom boundary layer, by means of a single wire cable.
In ice covered regions this is only possible aboard a ship or from an ice floe. The latter requires autonomous instrumentation able to handle long cable lengths to reach the bottom. In shelf areas of less than 500 m deep water but also for greater depth along the continental shelf break full-depth data acquisition needs a cable length of more than 1500 m.
Such self-sustaining system has the advantage of being independent from ship operations and gives a wider range for data collection not consuming expensive and rare ship time. This is even more important, when the ship is immoveable due to heavy ice conditions.
Therefore AWI decided to develop a special device, which can be carried by a helicopter (type BO-105) as outside payload to ice floes. The operation radius around the ship is up to 100 km. The only requirements are stable ice floes more than 0.5-m thick and some open leads around to lower the instrument. The latter saves drilling devices and thus space and weight during the air lift. The rack consists of a special lift-off frame, which combines two aluminum sledges, carrying the generator and the mobile winch. The whole system weighs 525 kg.
The instrument rack includes a CTD-probe, an altimeter, and up to two 5-liter bottles, which can be fixed to the cable and closed by a messenger. This allows for tracer sampling in the bottom layer.
The CTD probe is a Seabird 911 plus with double sensor pairs for temperature and salinity to achieve the same accuracies as the ship system.
Fig. 2: Flying with the total pay load. To shelter the system all components are covered by a tarpaulin.
Fig. 3: Dropping off the system at the edge of an ice floe.
After intensive flight tests in Bremerhaven, this equipment was first used successfully during the international drift experiment ISPOL (2004-2005) in the western Weddell Sea. Here, the outflow of very cold shelf waters from the Larsen ice shelf into the deep basin of the Weddell Sea was observed (http://www.ispol.de).
Fig. 4: Fully assembled measuring system, consisting of a tent, a winch, and an A-frame. Inside the tent a laptop computer samples the data while the CTD-probe descend. The A-frame can be lifted up and down to move the instrument over the ice floe edge. It can be dismantled into 4 pieces of 1.2 m length each. The generator is located in the back (not seen on the picture).
Fig. 5: Helo-CTD with A-frame in measuring mode.
Fig. 6: Complete helo-CTD-station seen from above the air.
Fig. 7: Rack during a test flight. The lift-off frame carries two combined sledges, the winch (left side), and the generator (right side). On the ice the two sledges can be separated.
