Two of the three North Korean UAVs found in South Korea over the last five months have been traced back to a Chinese manufacturer (Taiyuan Navigation Technology). These two models were identical to the SKY-09P UAV offered for sale in China. North Korea modified the SKY-09P with a new paint job (to make it harder to spot), a muffler (to make it less detectable) and installed a different camera. The SKY-09P was used via its robotic mode, where the SKY-09P flew to pre-programmed GPS coordinates, taking digital photos over selected areas.
The SKY-09P is a 12 kg (26 pound) delta wing aircraft with a wingspan of 1.92 meters (6.25 feet) propeller in the front and a payload of three kg (6.6 pounds). It is launched via a catapult and lands via a parachute. Endurance is 90 minutes and cruising speed is 90 kilometers an hour. When controlled from the ground it can go no farther than 40 kilometers from the controller. But when placed on automatic it can go about 60 kilometers into South Korea and return with photos. These things cost the North Koreans a few thousand dollars each.
At first it was thought that the North Koreans built these using Chinese components. The other (straight wing) UAV found is probably also Chinese. The delta wing model was sold as a commercial item in China, where businesses, farms and government agencies are big users of UAVs.
UAVs this small are hard to spot with radar if they come in very low (under 100 meters/330 feet). Most importantly these UAVs appear to operate automatically and do not transmit photos back to the ground but store them onboard until the UAV comes back, completing its pre-programmed flight and using a parachute to land. Thus you cannot detect these UAVs via signals sent or received. They don’t make much noise, especially when equipped with a muffler, but when flying under the radar (under 100 meters altitude) you could see and hear it as it went by at about 100 kilometers an hour.
South Korea is now upgrading its aerial surveillance to handle this new (but not unknown) threat. Israel has a similar problem and has developed technology to deal with it. Since Israel sells a lot of military gear to South Korea, it was no surprise that ten Israeli radars were soon ordered. Meanwhile the government is considering offering rewards for civilians who find these UAVs since North Korea appears to be using a lot of them and for at least six months.