| Summary: | Progress Code: completed Statement: The quality of this dataset is affected by the vertical movement of the airframe: the helicopter provides a vibrating mounting point for the laser scanner and associated instrumentation. The Inertial Motion Unit (IMU) was not able to capture the full spectrum of small-scale vibrations. Hence the derived total freeboard is affected by some instrument associated noise. Consequently: * The data exhibit approximately 0.2 m vertical scatter due to uncharacterised vibration at the LIDAR head (compared to the same instrument in a fixed-wing aircraft); * In 2007, a single frequency GPS was used to position the helicopter, limiting absolute point elevation accuracy to no better than 30cm (combined GPS + IMU); * From 2008 onwards a dual-requency GPS was used to position the helicopter, enabling nadir point elevation accuracies in the sub-decimetre range. Purpose Derive combined sea-ice and snow elevation as intermediate step to sea-ice thickness data. The dataset submitted here is 'Sea-ice freeboard derived from airborne laser scanner'. Between 2007 and 2012, the Australian Antarctic program operated a scanning LiDAR system and other scientific instruments for sea-ice geophysical surveys in East Antarctica. For example see Lieser et al. [2013] for the 2012 survey. The dataset here provides the sea-ice freeboard (i.e. elevation above sea level) along various helicopter flight lines of the 2012 survey in the sea-ice zone between 113 degE and 123 degE. The data collection was based on: - Riegl LMS Q240i-60 scanning LiDAR, measuring sea ice elevation above the WGS84 reference ellipsoid; - Hasselblad H3D II 50 camera, taking aerial photographs at about 13 cm resolution every 3-5 seconds (older digital camera used in 2007); - inertial navigation and global positioning system, OxTS RT-4003. The following geophysical corrections were applied to the sea-ice elevations to derive the sea-ice freeboard: - geoid correction (from the EGM2008 Earth gravity model); - mean ocean dynamic topography ...
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