NASA’s Newest Map of the World

By Rebecca Lindsey Design by Robert Simmon November 18, 2009

In June 2009, NASA and the U.S. Geological Survey put the finishing touches on a new collection of mapped images covering the entire land surface of the Earth and made them available to anyone, anywhere in the world, absolutely free.

The result of a collaboration between NASA, the U.S. Geological Survey, and the U.S. National Geospatial Agency, the Global Land Survey 2005 features around 9,500 images from NASA’s Landsat satellites captured between 2004–2007.

The images are detailed enough to make out features as small as 30 meters (about one-third the length of an American football field), they have been carefully screened for clouds, and each one shows the landscape during its growing season.

Some of the images are as striking as a piece of artwork. Stitched together into a single mosaic, the collection paints the most detailed picture of Earth’s land surface a person can get for free.

Global Land Survey image of Algeria.
Sand dunes deep in the Sahara Desert align parallel to the prevailing winds. This natural-color image was obtained on March 11, 2006, by the Landsat 7 satellite. (NASA Earth Observatory image by Robert Simmon, based on 2005 Global Land Survey data.)

Before you think about ordering it, however, consider this: to view the entire thing at full size, your computer screen would need to be as big as the Hoover Dam.

More than a pretty picture

The survey’s pretty pictures are just a fringe benefit, though. The real motivation for the project, explains remote-sensing scientist Jeff Masek, the NASA lead on the project, was the increasingly urgent need among Earth and climate scientists for a detailed global image of the land surface in which the latitude, longitude, and elevation of every pixel had been mapped.

Scientists need this view in order to understand the extent and pace of changes people are making to Earth’s surface. Landscape changes affect the climate, but perhaps more significantly, they will determine whether Earth’s natural and managed ecosystems are able to sustain the human population as it grows to a projected 9 billion people in the next 40 years.

Satellite image of Tehran, 1985.
Satellite image of Tehran, 2009.
Tehran, Iran, is one of the fastest-growing cities on Earth. These false-color satellite images show downtown Tehran on August 2, 1985 (top), and July 19, 2009 (bottom). Urban areas appear gray and black, vegetation is bright green, and barren areas are brown. (NASA Earth Observatory images by Robert Simmon, based on Landsat 5 data.)

Of course, scientists could have used this detailed, global view several decades ago, and in theory, the earliest Landsat missions could have provided it. But only recently have scientists been able to handle the expense and the technical challenges of mapping the world with Landsat images.

A $36 Million Map

When the first Landsat launched in 1972, virtually every piece of technology that we think of as essential for viewing, sharing, or analyzing digital images either hadn’t been invented (like the World Wide Web and DVDs) or hadn’t been commercialized (like the microprocessor that runs desktop computers).

Photograph of Landsat 3 in a clean room.
Two technicians examine Landsat 3 during its assembly in 1977. The earliest Landsat satellites predate most contemporary computer technology. (Photograph courtesy the Landsat Program.)

Each Landsat image is several hundred Megabytes. Until recently, it would have taken a super computer to sort, join, and geolocate (map the latitude and longitude of) the thousands of images needed to make a global picture. “For decades, the computing challenge was huge,” says Masek.

The challenge of handling the data translated into prices that few researchers could afford. “For a number of years in the 80s and early 90s,” said Masek, when the satellites were being operated by a commercial company, “it cost about $4,000 for a single Landsat image, and it takes about 9,000 of them to map the land area of the globe.” To make a global image for just one time period would have cost $36 million.

When the government resumed satellite operations in 2000, the price per scene dropped to about $600, says Masek. And since late last year, all the Landsat scenes in the USGS archive have been free. With prices dropping, in the late 1990s, NASA began working on Landsat image mosaics centered on 1975 and 1990, and a 2000-era collection came out a few years ago.

Price may have been the primary obstacle to global Landsat mosaics for many years, but according to John Dwyer, the USGS lead on the Global Land Survey 2005 project, “monumental” technical challenges remained.

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