Measuring Ice Pressure
Ice pressure primarily determines successful navigation through pack ice. High ice pressure not only reduces the maneuverability of ships but also increases the risk of ships and fixed platforms being crushed.
Ice stresses in 3 directions and ice stress for a single direction were measured in the pack ice to see if there was a dependence of ice stress on wind, ice temperature, and air temperature. Complex multi-variate regression analysis was performed on the data to test this dependence.
In a second experiment, ice beacons to which Global Positioning System (GPS) sensors had been added were deployed on mobile pack ice as vertices of a polygon to measure ice convergence/divergence. The relation of the site-specific, measured, ice stress to converging and diverging pack ice was investigated with correlation analysis. The hypothesis was that increases/decreases in the areal size of a GPS polygon was related to decompression/compression of the pack ice. The GPS sensors improved location accuracy of transmitted positions and increased sampling frequency from irregular satellite pass intervals to hourly intervas.
High Arctic pressure sensors filled with mercury were tested on land-fast ice along the Labrador coast (Prinsenberg et al, 1997) but have since been replaced by sensors filled with environmentally-friendly oil (eg. canola oil). The new sensors were developed at the Bedford Institute of Oceanography in Dartmouth, Nova Scotia. The expendable pressure sensor beacon was connected by a cable to a Service Argos transmitter such that hourly data were transmitted to ARGOS satellites. The pressures measured in three directions were converted to major and minor principal stresses. The major stress and the uni-directional ice pressure were used in separate regression analyses with observed/gridded wind data and ice/air temperatures.
At each ice station, GPS location beacons were deployed as corners of a triangle/quadrangle. Pressure sensor ice beacons were deployed at the centre of each polygon. The GPS-derived location data were transmitted to satellites. In 1997 five GPS beacons were deployed to form quadrangles in the pack ice off Labrador and off the coast of Prince Edward Island. The area of the polygon was calculated for each hourly transmission and an attempt to relate the ever-changing area to the measured ice pressure was made using correlation analysis.
- Aside from the ice pressure beacon mentioned above, other satellite-tracked ice beacons were used in both experiments.
- Miniaturization in electronic design and optimization of battery requirements have led to the development of the new generation of compact GPS location beacons by both Seimac Ltd. and MetOcean Data Systems Ltd. of Dartmouth, Nova Scotia.
- In an effort to partition atmospheric and ocean ice drift forcing, an ice beacon equipped with sensors to measure atmospheric properties (atmospheric ice beacon) was deployed on the pack ice by helicopter (1993, 1994, and 1997). The beacon's anemometer collected hourly wind speed and direction, air temperature, and air pressure at 2 m above the ice surface. It contained an ARGOS transmitter which transmitted the last six, hourly atmospheric data to the ARGOS satellites.
- A temperature staff/probe collected hourly temperature profiles from the surface water, ice, and atmosphere (1995, 1996, and 1998). Ice temperatures were monitored at 5 cm intervals in depth in 1995 and 1996 and were used for checking ice temperature at the depth of the pressure sensors. In 1998, ice temperatures were measured at 4 depths at 5 m intervals.
- Canadian Meteorological Centre (CMC) 10 m gridded wind data
- observed wind data supplied by
- Institut Maurice-LaMontagne
- Atlantic Climate Centre, for stations in Labrador: Cartwright and Hopedale
- Peterson I., S. J. Prinsenberg, and G. A. Fowler. 1995. Newfoundland Shelf Sea Ice Program, 1993 and 1994
- Prinsenberg, S. J., G. A. Fowler, A. van der Baaren, and B. Beanlands. 1997. "Ice stress measurements from land-fast ice along Canada's Labrador Coast"
- Prinsenberg, S. J., A. van der Baaren, G. A. Fowler, and I. K. Peterson. 1997. "Pack Ice Stress and Convergence Measurements by Satellite-Tracked Ice Beacons"
- Prinsenberg, S. J., G. A. Fowler, and A. van der Baaren. 1998. "Pack Ice Convergence Measurements by GPS-ARGOS Ice Beacons"
- van der Baaren, A. and S. J. Prinsenberg. 2000. Labrador Shelf and Gulf of St. Lawrence Sea Ice Program, 1995-1998
- van der Baaren, A. and S. J. Prinsenberg. 2001. Satellite-tracked Ice Beacon Program, 1999-2001
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