Sea Ice Thickness

Sea ice thickness, harder to measure than extent, is retrieved from satellite altimeters that gauge the ice freeboard, the height standing above the waterline, then convert it to thickness using snow load and density assumptions. CryoSat-2 uses radar altimetry, ICESat-2 uses laser, and combining the two reduces the snow-depth error. Thickness times area gives ice volume, the quantity that best captures the long-term Arctic decline, since thinning continues even when extent fluctuates.