The ACE CRC sea ice research group operates a helicopter-based remote sensing package dubbed ‘RAPPLS’ – for Radar, Aerial Photography, Pyrometer, Laser Scanner. Its main job is to determine the surface elevation of sea ice, in order to model sea ice thickness on regional scales. This system has evolved from a helicopter-mounted camera which has been part of the ACE-CRC and AAD sea ice group activities for some time.
In its current guise has been deployed on 5 voyages to date, in varying configurations. While the instrument package has shown great promise, underlying issues with instrument calibration and finding reliable reference data (eg sea surface) against which to measure sea ice elevation are still being solved.
The cartoon below illustrates some of the terms that aerial surveying over sea ice deals with. Dynamic reference points (dXYZ(t)) on the ship and the ice, a highly mobile airborne platform and a raft of ‘reference surfaces’ to identify. In this case, EGM2008 refers to a geoid model, assumed to be mean sea surface level in the open ocean. WGS84 refers to an ellipsoid surface used for GPS height reference, SSH(t) is dynamic sea surface topography and E(t) is ice elevation (or combined snow + ice freeboard). Put simply, the goal is to determine E(t)t relative to SSH(t) using points XYZ(t) – but it is not straightforward, since everything moves!
Dr Jan L Lieser is the project principal investigator; Adam Steer is a graduate student working on optimising the geophysical products returned by the RAPPLS system.