There is no way that a secondary (to this mission) air search radar in Chiba would have the first look at any North Korean missile launch.
Leave it to the professionals on the dedicated land-based platform up north, the two sea-based platforms with a look from the Sea of Japan, and the field radars out with the deployed defenses.
Don't blame yourselves, but look to this as a learning experience.
...because it is obvious from the media and local government authorities that there is a limited amount of good-will on this matter...
...and when the real launch comes, all this is something you *have to* get right.
UPDATE - SAT 0430 (time as reported on this'blog; U.S. Pacific time)
Here is where the fumble happened, as per Kyoudou wire service:
According to the Defense Ministry, the ground-based FPS-5 radar at the ministry's Iioka research and development site in Asahi, Chiba Prefecture, picked up a trace over the Sea of Japan on the radar screen.Very well then. Learn from it, and don't do it again.
The information was immediately conveyed to the ASDF's Air Defense Command in the suburbs of Tokyo, but the person who received it mistook the information for satellite early warning information provided by the U.S. military.
The satellite early warning information is based on data sent by the U.S. Air Force's Defense Support Program satellite orbiting the Earth. Equipped with an infrared telescope, it is normally the quickest means to detect ballistic missile launches.
The erroneous information then got passed onto the SDF's Central Command Post at the Defense Ministry headquarters, from which it was conveyed to the crisis management center at the prime minister's office, according to the ministry.