“…Techniques used include visual observations (ASPeCt protocol; Worby et al, 2008a), drilling transects (e.g., Jeffries et al, 1998), and electromagnetic sounding from the surface, ships, or helicopters (e.g., Haas, 1998) (Laxon et al, 2003) and the ICESat laser altimeter (Kwok et al, 2009). In the Antarctic, however, the thick snow cover shields the ice below from direct measurement (Giles et al, 2008;Zwally et al, 2008;Yi et al, 2011), requiring independent information on snow thickness (and density) to determine ice thickness.…”