CyroSat-2 does not measure snow depth
CryoSat-2 seeks to determine the freeboard of floating ice. The primary instrument is a synthetic aperture interferometric X-band radar altimeter. Precise altimetry alone has been found not to give accurate ice thickness -- hence the other 31 companion files (such as ice density)
in the netCDF under discussion. These are not taken from generic FYI/MYI climatology, as follows already from the map mismatch with snow depth and density (and good agreement with precip-modeled RASM-ESRL). Here we can benefit from recent papers such as:
Effect of Snow Salinity on CryoSat-2 Arctic First-Year Sea Ice Freeboard Measurements
V Nandan et al
http://onlinelibrary.wiley.com/doi/10.1002/2017GL074506/fullA weekly Arctic sea-ice thickness data record from merged CryoSat-2 and SMOS satellite data
R Ricker et al
https://www.the-cryosphere.net/11/1607/2017/https://www.ifm.uni-hamburg.de/en/institute/staff/kaleschke/publicationskaleschke.htmlThin Sea Ice, Thick Snow, and Widespread Negative Freeboard Observed During N-ICE2015
A Rösel et al
http://onlinelibrary.wiley.com/doi/10.1002/2017JC012865/fullNote the radar reflection horizon is not necessarily the top surface of the ice nor the top surface of the snow. Locally, there may have been extruded or deposited brine salinity, snow on refrozen rain on snow, or snow melt in the dead of winter from advected semi-tropical moisture and abnormal temperatures.
Whatever, it adds to the mass afloat, though snow (granulated ice) lacks other mechanical, thermal, dynamical and volumetric properties of ice. We are not after freeboard per se but a more nuanced understanding of the heterogeneously distributed composite out there.
The question here is where does
this netCDF file get its snow depth, snow depth uncertainty, snow density, snow density uncertainty from and how good are they. It is a near-real time winter product under active development, not a static journal article.
In the meantime, the companion files themselves are instructive even though we don't have a lot of people here who will click on them. The two uncertainty maps are shown below: