# Help understanding radar data in subglacial lake complex beneath Devon Ice Cap

The BBC News article Isolated lakes found beneath Canadian ice sheet links to the open access Science Advances article Discovery of a hypersaline subglacial lake complex beneath Devon Ice Cap, Canadian Arctic.

The discovery is based on radar "soundings" of the Devon Ice Cap in Nunavut, Canada.

I'm having trouble understanding the nature of the evidence for liquid water as stated in the article. I understand that there will be a relatively strong reflection at an interface where the dielectric constant changes, and that this is expressed in dB in some of the plots, but I don't understand the blue "blobs" or the axis label Spec. content shown.

I've cropped some of the plots and rearranged them below to help highlight the "blue blobs" below.

Also it looks like the potential lakes are associated with dips in the underlying bedrock contour, but I can't tell if the lakes are sitting on top of the bedrock, or at an intermediate elevation above it with ice both above and below them, and I don't understand at all what the axis label Hydrolic head (m) in other plots means. And why does the top surface of the ice look relatively flat in the radar images, but rise and fall hundreds of meters in the ice surface and bed plots? Did the plane fly at a fixed distance with respect to the top ice surface rather than a fixed elevation?

below: Figure 1 from here.

• – uhoh Apr 15 '18 at 8:35