Optical Imaging and Signals Intelligence

서울흥신소 Spy satellites roam the skies 100 miles above Earth, grabbing digital snapshots of places that the CIA and policymakers want to know about. They can even scour cell phone calls and other wired communications, says Baker.


While the details of most spy satellite programs remain classified, a few early programs—such as Corona, Zenit and Hexagon—have been declassified on occasion. These satellites overcome the limitations of spy planes.

Optical Imaging

Spy satellites fly 100 miles above Earth, grabbing digital snapshots of places the CIA (and policymakers and military officers it serves) want to see, from missile fields in Russia or China to environmental disasters in the Sahel. They have profoundly affected the course of the Cold War, though they were never revealed publicly until President Carter did so in 1978. Optical imaging is still one of the most important functions for spy satellites.

The earliest satellites, such as Corona and Zenit, took photographs, then ejected capsules of film that fell back down through Earth’s atmosphere. As technology improved, the satellites could take a wider range of images. Eventually they switched to digital photography, and later spacecraft downloaded their images via encrypted radio links.

Today, the National Reconnaissance Office’s satellites take a wide variety of pictures. The Keyhole series of satellites, for example, take images in visible and infrared light. They also examine bands of the electromagnetic spectrum, such as the radio waves used for communications.

Many countries launch spy satellites, although the U.S. and the 서울흥신소 Soviet Union are responsible for by far the largest numbers. Unlike airplanes, satellites can’t be shot down, so they are difficult to attack by air-to-air missiles. They also orbit at an altitude that’s too high for a country to shoot them down, though both the United States and Russia have developed anti-satellite weapons in case they ever need to.

Radar Imaging

While a few nations have used spy satellites equipped with cameras to take pictures in visible light, most use radar imaging. Radar is a powerful tool because it can detect objects at very long ranges and see through clouds or darkness. It also provides detailed information about the surface of the object or environment.

Unlike the photoreconnaissance satellites that preceded them, all Keyhole satellites use synthetic aperture radar (SAR), which creates high-resolution images of the Earth’s surface with an electromagnetic beam. Each pixel of a SAR image represents the amount of backscattered microwave energy it reflects. The intensity of this energy depends on a variety of factors, including slope, roughness, humidity and textural inhomogeneities.

Radar images can reveal a wide range of details, such as the type and location of a structure or its dimensional characteristics. They can also show how objects change over time. For example, a flood could cause a river to swell and alter the shape of its banks, which can be detected by SAR imaging.

Compared to cameras, radar can collect data more quickly and at lower costs. It also transmits digital information, which makes it easy to encrypt and send securely. This enables intelligence agencies to update maps of the Earth much more frequently. It can also provide useful information about moving targets, such as aircraft or ships. Umbra Satellite, a commercial company, has won a contract from DARPA to develop new collection modes on its SAR satellites.

Signals Intelligence

Signals intelligence (SIGINT) refers to the electronic collection of data sent through various communication channels. This includes all forms of non-human communication, as well as data from weapons systems or radar systems. SIGINT is divided into two broad categories: COMINT, or communications intelligence, and ELINT, or electronic intelligence.

A significant benefit of using satellites for signals intelligence is that it allows for a wide range of frequencies to be monitored. This can be helpful for detecting a range of potential threats, including terrorists and other armed groups. In addition, the use of satellites can also help to track the location of these threats.

SIGINT is a vital window into foreign adversaries’ capabilities, actions and intentions. The information obtained by the NSA is used for military operations, deterrence and diplomacy. It also helps guide policy makers in the US and around the world.

The recently declassified history of national reconnaissance programs offers insight into efforts to maximize all possible orbits for SIGINT collection. While details about programs launched into geosynchronous orbit are largely redacted, other information reveals the ingenuity and frugality of early national reconnaissance personnel and leaders.

Using satellites for signals intelligence also eliminates the need to install expensive, vulnerable hardware on the ground. Instead, spy satellites can “hoover up” hundreds of thousands of cell phone calls or scour the dark web for any signs of terrorist activity. This saves money and time, while providing valuable intelligence.

Relay Satellites

For countries that have geosynchronous satellites in orbit, intelligence agencies can watch a region for extended periods of time. This provides a more complete picture of activities in a particular area and can help identify potential threats before they become dangerous. It also allows nations to monitor their neighbors’ military capabilities and can serve as a form of deterrence.

The benefits of spy satellites are many, but they have their drawbacks too. The first problem is that the early spy satellites tended to die after three or four weeks, because they used up all of their film and then got dragged back down into Earth’s atmosphere by friction. The next problem is that the images captured by spy satellites are limited in resolution, so they cannot capture a lot of detail, and it’s often hard to interpret what’s on the ground.

One exception to this rule is the ability of a spy satellite to pick up electromagnetic signals that are transmitted through wires or wirelessly from cell phones and other devices. The ability to do this without cutting into the lines of communication can be a tremendous boon to governments that want to track terrorist activity or listen in on conversations.

A number of companies are developing relay satellites that will allow spacecraft in low-Earth orbit to send data directly to ground stations, rather than going through Earth’s atmosphere and then returning to space again. These include the Northern Virginia-based SpaceLink, which plans to launch its Aether data-relay constellation of four satellites this year. Other companies, including Kepler Communications and Capella Space, are using the Tracking and Data Relay Satellite (TDRS) network built by NASA to relay tasking instructions from the ground to its synthetic aperture radar constellation in low-Earth orbit.