In 1979, the National Institute of Polar Research (NIPR) developed a 179 MHz airborne radio echo-sounder (NIPR-A), and installed it in a Pilatus Porter PC-6 aircraft. The peak power of the sounder is about lkW and the pulse width is 0.3 ys. Soundings were carried out in Antarctica on Shirase Glacier and the Yamato Mountains in January 1980. The total flight distance over the Shirase Glacier was about 500 km in six flights, while, on the Yamato Mountains area, about 80 km long, two north-south flights and three eastwest flights were carried out.
In spite of poor wave penetration, the presence of many sub-glacial uplands (1 000 to 2 000 m a.s.l.) near the Yamato Mountains area was revealed. Discussion is concentrated on the bedrock and surface topography of the bare ice area near Motoi Nunatak in the southeast Yamato Mountains, because the previous traverse party covered this area and many meteorites have been discovered here.
A high sub-ice ridge with three peaks extends east of Motoi Nunatak, and from 22 to 28 km east of Motoi Nunatak there is a short ridge with two peaks. From 12 to 20 km up-glacier from Motoi Nunatak, a long but comparatively low ridge surrounds Motoi Nunatak ridge like an arc. Finally, the sub-ice flow lines near Motoi Nunatak are deduced from new and earlier data.