Ice Floe Survey

 
Ice floe coordinate system 'origin point', set up using a GPS receiver and a robotic total station

Ice floe coordinate system ‘origin point’, set up using a GPS receiver and a robotic total station

Adam Steer, Petra Heil, Rob Massom, Roger Stevens, Jennifer Hutchins, Olivier Lecomte, Takenobu Toyota, Barry Giles, Ted Maksym, and Ernesto Trujillo-Gomez.

On SIPEX-2, spatial datasets for both physical and biological attributes of sea ice will be collected using above, on, and under-ice instruments. Each of these are collected in different reference frames, but to build a complete and coherent picture at a ‘whole floe’ scale, each dataset needs to be co-registered in a single reference frame with confidence.

The ice floe survey project aims to provide the spatial backbone to SIPEX-2 measurements. It will configure and monitor a floe-centric local surface coordinate system which is co-registered with the under-ice acoustic coordinate system. It will also provide high precision GPS positions in order to determine ice floe drift, rotation and dynamic sea surface topography during ice stations. Time is a critical element, since time stamps provide the link between GPS based ice floe drift and rotation, and total station measurements of local floe coordinates.

Together, these data will provide the basis for:

  • precise local level coordinates to allow ‘same day’ visits on the ice surface to locations-of-interest determined by under-ice instruments.
  • precise local-level tracking for snow and ice thickness survey grids, and a means for precise geolocation
  • precise ice floe orientation data for airborne LiDAR calibration
  • precise ice floe geolocation with respect to time, for airborne + terrestrial LiDAR and airborne imagery coregistration
  • dynamic sea surface topography
  • precise data on ‘ridge tectonics’

…and many opportunities not yet foreseen.

False north site, looking back toward the ship and the 'origin' site

False north site, looking back toward the ship and the ‘origin’ site

The main surveying setout consisted of two GPS sites, one defining a coordinate system origin and the other defining a ‘false north’ point. Reflector prisms were mounted beneath GPS antennae at each point and a robotic total station was used to define the local coordinate system. These were monitored on a half-daily basis for any site motion. The total station was used to determine the on-floe locations of science projects underway on the ice, registration of terrestrial LiDAR targets, and recording the position of snow probe measurements. Since no underwater robots were lost or stuck, it was not required for SAR purposes.

Two additional GPS sites were deployed on the ice in a ‘ridge tectonics’ experiment. They were placed on each side of an ice pressure ridge to investigate differential motion across ridges. These also proved useful as backup sites for geolocation as the ‘false north’ reference GPS failed to record any data for two ice stations.

Precise processing for ice drift, rotation and deformation is underway. Local ice station maps with survey points and rectified aerial imagery are available, georeferenced snapshot maps (at time of image capture) will be released in the last quarter of 2013