The United States, Canada, and 22 European nations signed the Treaty on Open Skies on March 24, 1992. The treaty entered into force on January 1, 2002, and now has 34 members. Each participant must permit unarmed observation aircraft to fly over its entire territory to observe military forces and activities. The treaty is designed to increase transparency, build confidence, reduce the chances of military confrontation, and encourage cooperation among European nations.
According to the U.S. State Department, the parties have conducted more than 1,200 observation flights since 2002. While the United States has conducted more flights over Russia than Russia has conducted over the United States, Russia recently conducted flights over both the Washington DC area and Bedminster, New Jersey. Some Pentagon officials have questioned Russia's plan to upgrade cameras and sensors on the aircraft it employs for U.S. overflights, and some in Congress have questioned U.S. continued participation in the treaty.
President Eisenhower proposed an Open Skies agreement in 1955 to reduce the risk of war. Before satellites existed, aerial overflights provided information for both intelligence and confidence-building purposes. The Soviet Union rejected the proposal because it considered overflights equal to espionage and believed the United States had more to gain than it did. President George H. W. Bush revived the proposal in May 1989. By this time, both the United States and Soviet Union collected intelligence with satellites and remote sensors. But as Europe emerged from the East-West divide of the Cold War, the United States supported increased transparency to reduce the chances of military confrontation. The Open Skies Treaty was one of three arms control arrangements—including the Vienna Document and the Conventional Armed Forces in Europe Treaty (CFE)—which could serve, as then-Secretary of State Baker noted, as "the most direct path to greater predictability and reduced risk of inadvertent war."
Open Skies participants make all their territory accessible to overflights by unarmed fixed-wing observation aircraft. They can restrict flights for safety concerns, but cannot impede or prohibit flights over areas, including military installations that would otherwise be off-limits. In most cases, the nation conducting the observation flight provides the aircraft and sensors. Nations can also conduct joint overflights to share costs or use aircraft and sensors provided by other nations.
The treaty specifies that a nation conducting an observation flight provide 72 hours' notice before arriving in the host country. This provides the host with time to suspend sensitive military exercises or activities. The observation team presents a mission plan, specifying details including the route and altitude for the flight. The host nation can propose changes to the mission plan, due to weather or flight safety considerations, but it cannot deny access to any area of its territory.
Open Skies aircraft can be equipped with four types of sensors: optical panoramic and framing cameras (cameras for still photography) with a ground resolution of 30 centimeters (around one foot); video cameras with a ground resolution of 30 centimeters; infrared line-scanning devices with a ground resolution of 50 centimeters (around 20 inches); and sideways-looking synthetic aperture radars (SARs) with a ground resolution of 3 meters (around 8 feet). This equipment allows collection of basic information on military forces and activities, but would not provide detailed technical intelligence. It also allows monitoring of military and civilian infrastructure, such as industrial plants, airports, roads, and railway lines, but would not allow recognition of sensitive details about items such as electronic equipment. Both the observing nation and observed nation have access to the data from each flight; other parties can purchase copies of the data, so all can share information collected during all flights.
The treaty allows the participants to upgrade cameras and sensors as technology advances, as long as the capabilities remain within treaty parameters. The party using the new technology must demonstrate that technology to the others participants and receive consensus approval before they can transition to new cameras.
According to the U.S. State Department, Russia has refused access for Open Skies observation some areas of southwestern Russia. It has also limited access to a region over Moscow and along the border of Russia with the Georgian regions of South Ossetia and Abkhazia. Russia has reportedly also failed to provide priority flight clearance for Open Skies flights on a few occasions. The United States has raised these issues, without resolution, in the Open Skies Consultative Commission.
When the United States first signed Open Skies, most analysts agreed that the treaty would provide little information not already available from observation satellites. Nevertheless, some have identified benefits not related, directly, to the value of the information collected during the overflights. For example, most other participants in the treaty do not have observation satellites, so, as former Secretary of State George Schultz has noted, "Open Skies is their only means of alleviating security concerns through timely overhead imagery." This reduces the risk of misunderstandings or crises that could involve the United States and also contributes to "a more stable and secure European continent." The treaty has been particularly useful in recent years, as an increased number of flights have provided the parties with added information about Russian military forces near the border with Ukraine.
In 1992, analysts also asserted the treaty would create few risks for the United States because Russia could collect more detailed information with its observation satellites. Recently, however, U.S. military and intelligence officials have expressed concerns about U.S. vulnerabilities if Russia were to employ new electro-optical cameras. Admiral Cecil Haney, the former Commander of U.S. Strategic Command, noted that better optical technology would allow Russia to overcome weaknesses in its satellite surveillance capabilities. Others have questioned these conclusions, however, noting that Russia will operate commercially available cameras, with resolutions that are both within the bounds established by the treaty and also less precise than those offered by commercial satellites.