Research / 2024
Sixty-one days under an ice sheet with no surface to return to and no second chance at recovery.
- Client
- Institute for Polar Bathymetry
- Vessel
- DRIFTER
- Duration
- 61 days
- Position
- 77.9310 N / 21.4405 E
0
Continuous deployment
Under fast ice
0
Hulls recovered
Both on schedule
0
Navigation error
Reset at each beacon pass
The brief
The institute needed water column structure beneath fast ice through the freeze season, in a place where a vessel cannot hold station and a moored instrument records one point and calls it a region.
The hard constraint was recovery. Under continuous ice there is no surfacing, no satellite pass, and no way to correct a drift error until the vehicle reaches the single hole cut for its return.
The approach
Two DRIFTER hulls deployed through the same hole, flying independent patterns, so that the loss of one would not end the season.
Navigation ran on dead reckoning corrected against a sparse array of acoustic beacons frozen into the ice above. Each beacon pass reset accumulated error to under 40 metres.
Both hulls were given a hard energy reserve that could not be spent on science. When the reserve was reached the vehicle abandoned its pattern and flew home, whatever it was in the middle of measuring.
What the returns showed
A warm intrusion at 180 to 260 metres persisted through the entire season rather than breaking down at freeze-up, which the standing model did not predict.
Under-ice topography varies by up to 14 metres over horizontal distances of 200 metres, which is enough to invalidate the flat-ceiling assumption used in earlier surveys.
Both hulls recovered. One arrived with 4 percent of usable energy remaining, which is a margin, but not a comfortable one.
They spent the first week arguing about the recovery plan and about ninety seconds on the science. In hindsight that was the correct ratio.
Similar water
Cold Survey 22 took 61 days and produced findings the client would rather not have had. That is the point of paying for a survey.