Polar Ice Motion Monitors

Additional local (SOC) support for ARCICE was successfully sought. We were awarded 50K pounds to design and build a new type of cheap expendable surface-following ice-capable drifter with ORBCOMM communications, GPS and SST/SAT sensors. These floats are called PIMMs - Polar Ice Motion Monitors. Test floats were trialed on the James Clark Ross 1999 summer cruise - Cats-Miaow, and the full set were deployed from the Jan Mayen 2000 winter cruise, SCORESBY.

PIMMs Photos

Background and Objectives:

Float Specifics:

Hull design:

The main considerations were for the float to be surface following - ie of similar profile to ice pancakes; strong - to withstand surface ice conditions; stable - to rise rather than sink if squeezed by ice. This last point uses the same idea as for Nansen's Fram all be it on a smaller scale.

Communications:

Orbcomm satellite communications were used to allow buoys to transmit position, air and sea temperature to SOC in the form of an email. ORBCOMM is a commercial provider of global low-Earth orbit satellite data communication services. The system uses LEO satellites instead of terrestrial fixed site relay repeaters. This provides worldwide geographic coverage and allows two-way packets to be sent and recieved - ie e-mail. The PIMMs floats communicate with the satellites via a data communicator (microprocessor based VHF transceiver) with inbuilt GPS to establish position.

Sensors:

Platinum resistance thermometers were used for the measurement of air and sea temperature. Air temperature measurements could be made over a range of -20 to +20 degrees C. Sea temperature measurements were constrained to a range of -2 to +10 degrees C, for greater accuracy.

Trials on Cats-Miaow:

The test buoys were deployed on an opportunistic basis in the marginal ice zone in various ice conditions. On-board stowage became a trade off between finding a position with clear sky view to maximise the number of good satellite passes and position for ease of deployment. A total of 28 hours of deployment were made in a mixture of open water; open ice, small flows; ice edge in thick Brash; ice.

Hull design:

The buoys behaved well in the ice. There was a tendency to drift off relative to the ice flow when in open water, but this relative drifting stopped when the buoy was in ice or brash. As hoped the hull design was successful in that the buoy popped out or was lifted up, rather than pushed under, when caught in ice or squeezed by large floes.

Communications:

As the ship moved further north the buoys were only in range of near polar orbiting satellites. This limited the number of satellite passes seen - typically 3 to 4 good passes per day.

Deployments on SCORESBY:

Deployments:

10 deployments were made using PIMMs with two different makes of satellite communicator (Stellar and Panasonic). The absence of the Odden ice tongue meant that deployments were made either on ice floes in the East Greenland Current, or with a drogue in the open ocean.

Communications:

Of the 10 apparently successful deployments, only 5 floats made successful satellited communications. Two communicators were used. The Stellar had a more sophisticated interface allowing multiple records to be assembled in one message - reducing the total number of messages to be sent. In contrast the Panasonic had less buffer storage capacity and produced more messages, however it was both lower powered and could comunicate with more satellites thus allowing more messages to be sent per day. On initial consideration, perhaps the Panasonic communicator was more successful.

Poster

PIMMs on Ice: A new type of float - Pancake Ice Motion Monitors. (pdf 671K)

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