A North Korean drone that crashed on a remote mountain near the border last week had been spying on the site of a Terminal High-Altitude Area Defense battery in southeastern Korea.
While South Korean politicians were bickering over the deployment of the THAAD, North Korea sent a drone 270 km south of the heavily fortified border to snoop around the base in Seongju, North Gyeongsang Province.
"It looks like it took detailed photos of the THAAD base and surrounding area using pre-programmed coordinates," a military source said Tuesday.
The source added North Korea "probably figured out the coordinates quite easily because the deployment was broadcast live and TV stations use drones and helicopters to film the base."
The Joint Chiefs of Staff announced their analysis of the 64GB memory card found in the digital camera fitted in the drone. It started snapping pictures several kilometers north of Seongju, flew over the THAAD base and continued to take photos as it headed back north.
Between 200 and 300 photos were found on the memory card, of which 10 were images of the THAAD battery, according to the JCS.
The resolution was good enough for the THAAD launcher and radar to be distinguishable as well as the overall layout of the battery, a spokesman said. The commercial Sony Alpha 7R camera has a resolution of 36.3 megapixels, which is adequate for semi-professional photography.
Asked when the surveillance photos were taken, the spokesman said, "The camera was reset so we couldn't assess the exact date." But since a drone can operate for only a few hours at a time, the photos showed relatively recent activities. As it was discovered last week, they were likely taken in last two weeks."
One military source said, "Although the drone was discovered in a remote area, it was probably not too long after it crashed."
The drone is believed to have been launched from North Korea's Kangwon Province, where the North's first and fifth divisions are stationed. The most probable causes of the crash are lack of fuel or engine problems.
Seongju is around 270 km south of the inter-Korean border, so the drone flew at least 500 km. The North Korean drones that were discovered in Paju north of Seoul and Samcheok, Gangwon Province and on Baeknyeong Island in 2014 had ranges of between 180 and 300 km.