Every year around September, the question arises whether or not the sea ice extent in the Arctic Ocean will record its lowest ever level. Furthermore, sea ice extent in the Antarctic Ocean recorded its lowest ever level in March 2017. Remote sensing technologies by satellites support sea ice monitoring activities in the polar regions most sensitive to global warming and climate change, and of these, microwave scanning radiometers developed in Japan play an especially important role. With the rapid decrease in Arctic sea ice extent, increased use of the Northern Sea route for shipping and resource development makes sea ice remote sensing more important than ever.