If your remote sensing techniques sometimes fail to distinguish between snow, ice, and water, how can you reliably calculate the volume of Arctic ice?

Pen Hadow to measure allegedly retreating Arctic ice - Times Online

Scientists have a great deal of data on ice thickness, mostly gathered through remote sensing by satellites, aircraft and submarines. This has enabled them to construct models aimed at forecasting the fate of the icecap. However, they produce a range of predictions, partly because the climate is variable but also because remote sensing techniques sometimes fail to distinguish between snow, ice and water. Hadow’s survey is designed to correct these errors.

His data will be used to test the accuracy of a model used by the American navy’s postgraduate school in California, which has calculated that the Arctic could be ice-free in the summer as early as 2013.

Hadow will set out in February from the Canadian side of the Arctic. The short days mean much of the trip will be undertaken in darkness in temperatures as low as -50C, while the break-up of the icecap means the team will have to put on immersion suits and swim. Hadow said: “Hitherto our skills and experience have been largely socially redundant, but now we have the chance to deploy them for the benefit of everyone.”

Arctic ice volume allegedly lowest "ever" as globe allegedly warms

GENEVA (Reuters) - Ice volume around the Arctic region hit the lowest level ever recorded this year as climate extremes brought death and devastation to many parts of the world, the U.N. weather agency WMO said on Tuesday.

And if we can't reliably figure the Arctic ice volume today, how can we compare today's volume to that of 1999, 1899, 1099, etc?