Different levels of surface reflection

Arctic sea ice as seen by Envisat's MERIS instrument overlaid with data acquired by CryoSat-2 as it orbited over the same area a few hours after Envisat. The coloured lines in the CryoSat data indicate different levels of surface reflection. The darker blue represents the open ocean and sea ice where the surface is rough while the green show smooth mirror-like reflection representing the cracks, or leads, between the sea ice floes.

These data are used for Level 2 processing to help discriminate between the sea ice and leads and ultimately to determine sea-ice freeboard and hence ice thickness.