How accurate are the Arctic sea ice thickness numbers?

NERC - Arctic sea ice is allegedly getting thinner as well as receding

The team of researchers, including Dr Seymour Laxon and Andy Ridout, used satellites to measure sea ice thickness over the Arctic from 2002 to 2008. Winter sea ice in the Arctic is around two and half metres thick on average. Ice thickness can be calculated from the time it takes a radar pulse to travel from a satellite to the surface of the ice and back again.
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The Envisat satellite that provided the UCL scientists with their data doesn't cover the whole of the North Pole. Because of the satellite's orbit, there's a hole north of 81.5 degrees, which is about 600 miles shy of the North Pole. But a team, including Laxon, at the Centre for Polar Observation & Modelling has designed a satellite - CryoSat-2 - to plug this hole.