"North Korea’s ICBM Intrigue: Is Latest Missile New or Old Technology?" by Timothy W. Martin, Dasl Yoon and Nancy A. Youssef for The Wall Street Journal

High orbiting satellites, which can monitor as much as one-third of the earth's surface, use infrared sensors that could pick up more intense heat signatures, if Pyongyang had launched its newer and more powerful missile, said Xu Tianran, an analyst at the Open Nuclear Network, a research group based in Vienna. Similar reads could come from surveillance aircraft. And ground-based radar could detect a bulkier-sized ICBM based on a bigger return signal.

"Over time, they should have established some sort of baseline," Mr. Xu said.