According to the Daily Yomiuri, "Japan launched two satellites on Jan. 27
to strengthen its surveillance capabilities, including keeping a closer eye on North Korea which has vowed to stage another nuclear test. One of them was a radar-equipped unit to complete a system of surveillance satellites that will allow Tokyo to monitor any place in the world at least once a day. The other was a demonstration satellite to collect data for research and development." The Defense News version of the story
says "Japan developed a plan to use several satellites as one group to gather intelligence in the late 1990s as a response to a long-range missile launch by Pyongyang in 1998. The space agency has said the radar satellite would be used for information-gathering, including data following Japan’s 2011 quake and tsunami, but did not mention North Korea by name."