We meandered onto polar grid nav from discussions on drilling to the
sub-ice lake which appears to stretch 125 km or more near the S Pole.
I found it interesting that the folks associated with BAS (British
Antarctic Survey) apparently first identified these lake features by
considering echoes from 60 MHz pulses which find a window through cold ice.
On particular traverses, it was noticed that a bright echo feature
associated with the dielectric step from ice to water bearing rocks
under the ice, became sensibly horizontal - for which the only
reasonable explanation was a lake.
This observation later gave rise to intensive cooperative aircraft
traverses including NSF representation, and still later, Russian
drilled assays.