Radar-altimeter data from ERS-1 allow detailed topographic mapping of
Antarctica to 82-degrees-S to be carried out, revealing several notabl
e surface features. Among these is the large subglacial lake near Vost
ok which is mapped here in detail. The central part of the lake is fou
nd to have an exceptionally smooth surface with r.m.s. elevation varia
tions of less than 0.2 m. A search for other large Antarctic lakes in
the data is made based on the smoothness and low gradient of the surfa
ce. A number of other flat areas are identified with lake locations pr
eviously determined from radio-echo sounding observations. However, ra
dar-altimeter observations show that a minimum lake size of 20 km is r
equired for a surface above a lake to become flat. Numerous bowl-like
features can be seen in the surface topography, and these may be assoc
iated with intermediate-sized subglacial lakes. It is determined that
high spatial-resolution radar altimetery could be used to identify sub
glacial lakes greater than 10 km in lateral extent. Flat regions of th
e ice sheet are particularly useful as they may be used as height-refe
rence surfaces to help fix the orbits of radar-altimeter satellites.