What Satellites See

This IKONOS photo shows the town of Muzaffarabad, Pakistan, prior to (left) and following (right) the 2005 earthquake and subsequent landslide.

Disaster management
Each year, the world's governments spend billions of dollars and countless man-hours assisting regions devastated by natural disasters such as hurricanes, volcanic eruptions, blizzards, and wildfires. With lives hanging in the balance, emergency workers rely on the most accurate and timely information available, often using satellite photographs to assess large-scale damage. For example, in 2005, a 7.2-magnitude earthquake and resulting landslides in Kashmir caused more than 70,000 fatalities in Pakistan, India, and Afghanistan. The landslides buried entire villages and left millions of survivors homeless. Images from the satellite IKONOS allowed responders to evaluate the damage and plan rescue efforts, preventing much higher casualties.

This MODIS instrument image from NASA's Aqua satellite shows Hurricane Frances over Florida on September 5, 2004.

Weather forecasting
Until NASA launched the TIROS-1 satellite in 1960, forecasting the weather accurately was next to impossible, with virtually no advance warning of major storms and little chance to evacuate if necessary. Today, satellites can alert us days in advance of dangerous weather patterns and save countless lives, as with the highly destructive Hurricane Frances in 2004 (see image). After hearing forecasts of Frances' path and strength, Florida Governor Jeb Bush declared a state of emergency, and 41 counties containing nearly 3 million residents received evacuation orders, the largest evacuation in Florida's history. The rest of the world benefits as well from storm tracking, with satellites from Europe, Russia, India, China, and Japan contributing to a continuous global weather watch.

Translucent lines radiating from the ancient Syrian village of Tell Brak indicate the presence of once-vital roads.

Archeology
By analyzing newly declassified images from a Corona spy satellite, University of Chicago researchers recently discovered a series of Bronze Age roadways. Spanning modern Syria and Iraq, these roads pointed to a long-ago center of commerce important to the development of ancient Persia. Once up to two feet deep and 400 feet wide, the now-buried thoroughfares remain visible as slight depressions in the landscape—so slight, in fact, that they went unnoticed by archeologists until the images were released, offering a broader view. Similarly, in 2006, scientists used satellites to uncover Mayan ruins hidden beneath vegetation in the Guatemalan jungle. In 2007, another research team mapped the ancient city of Angkor, Cambodia, which at 1,150 square miles is said to have been the world's largest pre-industrial city.

Telstar 1 ushered in a new era of commercial telecommunications.

Communications
It may not look like much, but AT&T and NASA literally launched a communications revolution with the beach-ball-sized Telstar 1. On July 10, 1962, the same day the satellite reached orbit, Telstar 1 received television signals from the planet's surface and bounced them back, allowing viewers worldwide to watch footage from the United States. Later satellite technology would allow half a billion people to watch the 1969 Apollo moon landing. Today, everything from international phone calls and text messages to digital television and radio are transmitted by dozens of satellites orbiting Earth. During the 1990s, they brought high-speed Internet access to consumers, many of whom lived in areas too remote to receive conventional connections to the Web.

Different light spectra can tell us more than the naked eye about vegetation growth. Here, vigorous crops are seen in red; bright blue indicates bare soil.

Traditional industries
Satellites' commercial applications extend far beyond your cell phone and television set. Information gathered from orbit can determine the best spots for commercial fishing based on climate and water temperatures, and it can tell forestry officials how well wooded areas are growing. Images depicting vegetation and soil conditions can even indicate to farmers how their crops will likely fare in the coming season. In 2006, the European Union's Joint Research Centre, studying such images, warned farmers to ready themselves for an unusually light harvest. Many farmers worldwide use such satellite data to determine which crops need the most attention, allowing them to save money in the long run.

A map depicting temperature peaks and humidity in the U.S. tells scientists how West Nile virus could migrate. Black dots indicate bird populations infected by mosquitoes with the disease.

Disease tracking
By looking at vegetation and analyzing climatic data to calculate future weather conditions, scientists can predict and potentially control the spread of disease. In 2002, NASA researchers released a report indicating that increased rainfall and subsequent plant growth in Africa had led to the spread of Rift Valley Fever, a lethal mosquito-born virus. Since vegetation varies with rainfall, it is a good indicator of conditions necessary for disease-carrying insects to thrive. In recent years, scientists have used such data in the U.S. to track the spread of the West Nile virus.

This Landsat image of Washington, D.C. shows current urban development in yellow. Projected growth appears in red.

Urban planning
Multispectral images like the one seen here capture light frequencies beyond what is visible to humans. While archeologists may use this technology to uncover ancient sites hidden beneath years of undergrowth, it has also proved beneficial to urban planning, with different colors depicting the extent to which cities have developed. The Indian government is currently using satellite data to assist in the planning and monitoring of 137 cities. In Bhopal, for instance, such images have demonstrated the rapid conversion of agricultural to urban land, enabling planners to observe related social problems such as displacement of agricultural workers and unauthorized development.

Blue and purple areas represent low ozone levels over Antarctica.

Environmental assessment
Since 1979, satellites measuring Earth's atmosphere have gathered data on the ozone hole, which measured less than 4 million square miles before 1985, but reached 10 million square miles during the following decade. In 2005, the NASA Aura satellite's onboard Ozone Monitoring Instrument gave scientists the ability to map the hole, as seen here. Researchers use Aura's sister satellites, Aqua and Terra, to study air pollution and atmospheric humidity. Aqua and Terra also help assess environmental issues on the ground, such as deforestation. Together, these and other satellites give scientists information to help monitor the health of our planet.

In Yellowstone National Park, specialists use GPS receivers (blue circles) in concert with seismographs to pinpoint the location of small earthquakes.

Navigation
Your car may have more in common with a cruise missile than you may think. Passenger cars and missiles, as well as ships, airplanes, and military vehicles, all use the same Global Positioning System (GPS) satellites to literally pinpoint their own location on Earth—the latest GPS receivers are accurate to the nearest centimeter. This precision is made possible when a receiver locates four or more satellites and calculates its distance from each to deduce its own location. Civilian vehicle and cell-phone GPS units communicate with the same 27 satellites that keep airplanes on their paths and even guide ballistic missiles to their targets.