Optimising airborne LiDAR surveys in the Antarctic pack ice zone

Understanding the influence on Antarctic sea ice in the planetary system is confounded by a critical under-sampling of its third dimension: thickness. Satellite altimetry seeks to overcome the problem of reliably estimating Antarctic sea ice thickness on appropriately vast spatial scales, but requires a method for validation which ties pinpoint in-situ drill hole measurements to the larger scales of satellite ground altimeter footprints over the ice surface. Airborne scanning Light Detection and Ranging [LiDAR] instruments offer a critical link, providing surface elevation data with vertical resolution at the few centimetre level, a horizontal resolution comparable to drill hole measurements, and a regional coverage comparable to the area captured by satellite altimetry. The Achilles’ heel of airborne LiDAR in very remote areas is its reliance on GPS for accurate positioning and therefore accurate determination of surface elevation. This is exacerbated in the Antarctic pack ice zone where ground control points cannot be established, and reference GPS receivers are distant, moving, or both. In this environment, the sub-decimetre GPS positioning accuracy required for sea ice thickness estimation is generally considered difficult, if not impossible. We determined the best-case scenario for positioning a LiDAR instrument using GPS from both static and moving base stations then investigated the integration of instrument positions from aerial triangulation using coincident aerial photography. This paper describes the possibilities, potential and pitfalls of long range, large scale aerial surveying in remote areas, details our approach to calibration and validation, and provides initial estimates of sea ice thickness using airborne and satellite measurements.