Regional and seasonal variability in Antarctic sea ice and snow thickness: surface and airborne LiDAR validation of estimates from ICESat laser altimetry

Satellite remote sensing offers the only means of providing routine global coverage of the Antarctic sea-ice zone, but until recently the retrieval of sea-ice and snow-thickness data has not been possible from satellite-based instruments. While routine thickness products are still some way off, ESA’s ERS-1/2 missions and NASA’s ICESat mission have yielded results from radar and laser altimeters, respectively, which suggest that these could be obtained from improved measurements of freeboard combined with buoyancy theory. However, a number of important challenges are still to be resolved in the interpretation of altimetry data, including examination of the validity of the assumption of constant ice and snow thickness and density (and therefore a constant isostatic relationship) across all regions and for all seasons. This paper will investigate the relationships between sea-ice and snow thickness from two major Antarctic field experiments conducted in 2007 and relate the results to near-coincident satellite and aircraft data, including ICESat laser altimetry, airborne laser altimetry, aerial photography and the AMSR-E snow-thickness product. The Sea Ice Physics and Ecosystem eXperiment (SIPEX) was conducted in the narrow band of East Antarctic sea ice near 120° E while the Sea Ice Mass Balance of Antarctica (SIMBA) program was conducted in the more consolidated ice cover of the Bellingshausen Sea at 90° W. During SIPEX 15 ice stations were occupied at which extensive in situ measurements were made in addition to underway ship-based observations of sea-ice and snow-cover thickness. Additionally, airborne laser altimetry was conducted in some regions yielding a valuable source of intermediate resolution data that was calibrated over drilled transects across ice floes. During SIMBA, which was predominantly a Lagrangian drift experiment, a single ice floe was occupied and sampled for almost 30 days. Repeated transects were taken over three different ice- and snow-thickness regimes on the floe and ice mass-balance buoys provided point measurements of snow- and ice-thickness changes during the experiment. Thus temporal changes in the springtime characteristics of this floe can be assessed. Limited spatial variability in SIMBA was also measured using the same methodology as SIPEX for underway ship-based observations of sea-ice and snow-cover thickness. Similarities and differences between the two regions and comparisons to the ICESat altimetric results using algorithms generated from the field data are expected to yield better estimation and quantification of errors in generating Antarctic snow- and ice-thickness fields from satellite altimetry.