Obama surveys Korean DMZ close up WASHINGTON, South Korea, March 25 (UPI) -- President Barack Obama Sunday looked out over the demilitarized zone separating South Korea from North Korea after speaking to U.S. troops. Obama used field glasses to survey the DMZ for about 10 minutes at Observation Post Oullette. He asked his military escorts where the demarcation line was in various directions, and the size of a North Korean village about 7 1/2 miles away. At about 100 yards away, the outpost is the closest observation post to the North-South demarcation line. Shortly before, at a dining hall at Camp Bonifas, the U.S. base near the DMZ, Obama told a gathering of about 50 troops they are part of a "long line" of soldiers who have helped South Korea to prosper. "You guys are at freedom's frontier," said the president, sporting a dark windbreaker given him by Gen. James Thurman, commander of the joint forces in Korea. The contrast between South Korea and North Korea could not be clearer, could not be starker. I could not be prouder of what you do. The troops cheered him. He also said South Korean President Lee Myung-bak once told him he was able to rise from a poor childhood to his position of power thanks, in large part, to America's military aid and support. Obama reached South Korea following a 17 1/2-hour trip aboard Air Force One from Washington. After a brief stop in Seoul, he took a 16-minute flight by helicopter from Yongsan air base in Seoul to Camp Bonifas. Besides speaking to the U.S. troops, Obama was to meet separately with several South Korean soldiers in a break room at Observation Post Ouellette. Obama, who is in South Korea for a nuclear summit amid tensions over North Korea's vow to launch a missile into space, arrived on Korean soil at Osan Air Base just before 6:30 a.m. local time. On a sunny-but-crisp morning, the U.S. president was greeted by a contingent of dignitaries that included U.S. Ambassador Sung Kim, Gen. James D. Thurman, commander of U.S. forces in South Korea and South Korean Deputy Chief of Protocol Chang Jae-bok. From the base, Obama flew by helicopter into Seoul by helicopter, touching down at an athletic field at 7:05 a.m. From there, he went by motorcade through Seoul's mostly empty streets to his hotel, located on a hill with a sweeping view of the city. Obama is to discuss goals of the Nuclear Security Summit in a meeting Sunday afternoon with Lee. The summit begins Monday. North Korea is moving forward with plans to launch a rocket carrying a satellite next month despite opposition from the United States and other countries. If North Korea goes ahead with the launch, the United States said it would not honor a Feb. 29 agreement to provide U.S. food aid to the North in exchange for its freezing its nuclear programs and putting a moratorium on long-range missiles. North Korean leader Kim Jong Un has called the summit a "childish farce" and said denouncing the North would amount to a "declaration of war." Obama is to discuss Iran's nuclear program with Russian President Dmitry Medvedev.