Walt sent me this essay unsolicited, and I think it is very useful for establishing some baseline techniques. There’s more useful information on techniques here than in the entire Catlin Arctic Survey website. UPDATE, a response has been posted at the end of the article. – Anthony
Dr. Walt Meier
There have been several recent posts on sea ice thickness, particularly in regards to the Catlin expedition. I don’t have any direct connection to Catlin and in my research focus, I don’t anticipate using the Catlin data. I’m not responding to defend them or their methods. Thus, I can’t address details of their operation. However, from reading the posts and comments it seems like some basics on how sea ice thickness is estimated might be of interest.
Sea ice floats in the ocean. Because sea ice is a lower density than unfrozen water, it floats and a portion (~10-15% depending on density) rises above the water line, while most of the ice (~85-90%) is below the surface. The part of the ice cover above the water line is called the “freeboard”; the portion below is called the “draft”. The sum of the freeboard and the draft is the total ice thickness. There may or may not be snow on top of the ice which can add to the “snow+ice freeboard” and the “snow+ice thickness”.
A variety of techniques have been developed to obtain information about sea ice thickness. Most of these methods don’t actually directly measure thickness but estimate thickness from a related measurement. Here are some examples: Read the rest of this entry »
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