South Korea is seeking to improve its surveillance capabilities to deal with rising military threats, following the discovery of two drones that Seoul believes belong to Pyongyang near the border, military officials said Wednesday. A drone was found on Baengnyeong Island, located just south of the western maritime border, on Monday after the two Koreas exchanged artillery fire across the sea boundary during a live-fire drill by the North. A similar drone was discovered in Paju, south of the demilitarized zone, on March 24, and was found to contain photos of military installations and the residential quarters of Seoul's presidential compound. The South Korean military has concluded that the unmanned aerial vehicles are from North Korea, indicating holes in the air defense of the presidential office and border areas. Following the discovery, the Defense Acquisition Program Administration (DAPA) said it is pushing to resume a troubled blimp development project, which has been delayed over technical problems. "DAPA will hold a meeting later this week to approve a plan to restart the surveillance airship project," a DAPA official said. Seoul had pushed to build a surveillance airship to better monitor the North Korean military near the western maritime border, after North Korea shelled a border island in November 2010, killing four people. The 24 billion won (US$21.9 million) project initially aimed at deployment from 2012, but has since been delayed as arms makers struggled to make an airship suitable for the rapidly changing weather conditions in the western sea. The military is also considering purchasing advanced low-altitude surveillance radar to better monitor moving targets. The South Korean Army operates low-altitude surveillance radar, called TPS-830K, but military officials say it is not enough to detect small aircraft such as the drones recovered from the border region. "Although front-line troops have spotted unmanned aerial vehicles believed to be sent by North Korea several times recently, the low-altitude radar recognizes them as birds," an Army official said. The Air Force has placed Gap Filler radar systems with a range of about 100 km in areas with front-line troops, but they cannot effectively cover a wide range of mountainous border areas. As the North Korean drones fly autonomously according to a series of prearranged coordinates using the geographical positioning system (GPS), Seoul is seeking to develop GPS jamming devices, according to officials. North Korea is believed to have various types of unmanned aerial vehicles, including drones whose design is based on China's D-4 and R-3 Rey. The drones found here are considered prototypes and are equipped with cameras, designed to beef up a relatively weak aerial surveillance capability. "The two unmanned aerial vehicles are prime-type spy drones," a senior defense ministry official spoke on condition of anonymity. "While advanced spy drones can adapt their flight paths to different terrains, the North's drones cannot change their flight altitudes though they use the Global Positioning System."    The isolated communist regime is known to have bought several MQM-107D Streaker targeting drones used by the U.S. via Syria and modified the design to make unmanned attack aircraft, which were first unveiled during a military parade last year. The Streaker was first developed in the U.S. in the 1970s by Beech Aircraft and is used for testing various missiles. In light of the incident, the defense ministry pledged to work together with other related agencies to draw up measures to defend against such drones and other small aircraft that are hard to detect by radar and strengthen regulations on civilian drones.