PACK ICE CONVERGENCE MEASUREMENTS BY GPS-ARGOS ICE BEACONS

Satellite-tracked ice beacons containing Global Position System (GPS) location sensors were field tested for their reliability and their pos ition accuracy (both relative and absolute) before being deployed on t he mobile pack ice to monitor pack ice motion. On flat lake ice, a sin gle beacon on average provided hourly data 87% of the time with a posi tion accuracy of 20 m. In ice nibble, data availability was reduced to 83% and position accuracy decreased to 35 m. Between pairs of beacons , relative distance accuracy depended on whether the positions of the beacons were derived using the same satellite constellation. For all a vailable position data, the data availability for relative distances b etween beacons was 78% for the short 1-day data set of the lake ice si te and 69% for the longer 25-day data set of the ice rubble site. Rela tive distance accuracies were respectively 15 and 20 m using all posit ion data. When positions were derived using the same satellite constel lation for beacon pairs, the data availability reduced to 60% for the lake site and 52% for the ice rubble site while the relative accuracy increased respectively to 1.5 m (lake) and 10 m (ice rubble). The beac ons proved their durability by monitoring the ice motion for an additi onal 60 days in an offshore experiment in which three flees forming a triangle were tracked until the flees the beacons were on melted. (C) 1998 Elsevier Science B.V. All rights reserved.