Images from the Landsat satellite series show the Aral Sea in central Asia shrinking significantly from 1977 to 2010 because of water diversion for agricultural use.
Image: USGS EROS Data Center
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The Best Science Writing Online 2012
Showcasing more than fifty of the most provocative, original, and significant online essays from 2011, The Best Science Writing Online 2012 will change the way...
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When Landsat 5 fell silent on 6 January, scientists across the globe mourned its passing but gave thanks for its fortitude. The satellite had lasted a record-breaking 28 years, snapping images of the changing planet from melting glaciers to burning rainforests, while its successors faltered. Landsat 6 failed during launch and Landsat 7, at 13 years old, is partially blind and has limited fuel. With the passing of Landsat 5, the future of the world’s longest-running — and perhaps most influential — set of data on global change rests with Landsat 8, which is scheduled to launch next week from Vandenberg Air Force Base in California.
“Landsat 8 is the most important NASA Earth-observing mission in over a decade,” says Greg Asner, an ecologist at the Carnegie Institution for Science in Stanford, California, who uses Landsat data to track tropical-forest trends. After making do for years with ageing and impaired orbiters, “we are getting our eyes back in the sky”, says Asner. “Those eyes are going to be extremely good.”
From the first launch in 1972, Landsat was designed to provide a global record of land-cover and land-use change. The earliest satellites captured images at several visible-light and near-infrared frequencies, all with a resolution of 80 meters. Landsats 4 and 5 reached 30-meter resolution and could see farther into the infrared, to aid studies of soil moisture and vegetation. Landsat 7 added a multi-spectral sensor that can achieve 15-meter resolution. Through careful calibration, the program has built up a continuous 40-year record of observations at the original frequencies, spanning a period of huge change for the planet.
The latest mission, commissioned in 2002, had a tortuous birth. NASA originally intended to buy data from a privately owned satellite, then formulated a plan to mount Landsat sensors on a separate set of polar-orbiting satellites. Only in 2005 did the administration of then-president George W. Bush call for an independent craft, formally known as the Landsat Data Continuity Mission.
The size of a large jeep, the US$855-million spacecraft will circle Earth at an altitude of about 700 kilometers, carrying sensors of even higher precision than its predecessors. Instead of scanning the terrain below it with a mirror and sending the signal to a few sensors, it will capture instantaneous views of a 185-kilometer swathe of Earth, using some 7,000 sensors for each bandwidth. The result is more data from each location and better image quality. “The data are much more sensitive to change across the landscape and over time,” says Jim Irons, project scientist for the mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Maybe we will be able to better differentiate corn from sorghum, for example, or maple trees from oak trees.”
The spacecraft will also be the first in the Landsat series to collect data in an ‘ultra-blue’ band, particularly useful for studying oceans and atmospheric aerosols. Another new data stream will be a shortwave infrared band that is sensitive to cirrus clouds, which are powerful players in Earth’s climate.
Landsat has endured major changes in ideology and organization during its lifetime, notably in the 1980s and 1990s, when Congress gave control of the satellites and all data to a private company. Images sold for several thousand dollars each, limiting analysis to an elite corps of scientists. The government regained control in 2001, however, and from 2008 the US Geological Survey, which oversees the data, opened up the archive as a free global resource. Access exploded. Whereas the agency once sold around 15,000 images a year, annual downloads now average about 3 million.
“It provided for data democracy,” says Mike Wulder, a research scientist at the Canadian Forest Service in Victoria and a member of the Landsat science advisory team. “Landsat really is a global resource.”
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7 Comments
Add CommentThe Aral Sea was artificially dessicated. This has nothing to do with Climate change, so why did SciAm use that particular image?
Reply | Report Abuse | Link to thisThe caption on the photo indicates that. Why do you comment about articles you haven't read?
Reply | Report Abuse | Link to thisGeologon, it was used as an example of the sorts of changes that can be seen when one has access to a continuous record over many years. It really had nothing at all to do with specific causes for those changes. You should be pleased to have a continuous record of the earth's surface, since even skeptics need good data as a basis for argument, right?
Reply | Report Abuse | Link to thisWhy shouldn't they use an image taken by Landsat satellites in an article about Landsat satellites? The only mention of climate change associated with this article is your comment.
Reply | Report Abuse | Link to thisA cynic would say that artificially drying up an inland sea due to short term greed is a good analogue for human induced climate change, however I don't think is anyone claiming that the Aral is not drying up or that it is due to natural causes.
Reply | Report Abuse | Link to thisAgreed, the artificial dessication of the Aral Sea was caused by many things people have done. Diverting its inlets towards agriculture caused a lot of the water loss, but human GHG emissions have raised the average temperature in the region too, diverting rainfall patterns and requiring MORE water for irrigation in the first place.
Reply | Report Abuse | Link to thisWhat really blows my mind is how control of the satellites and all the data was handed over to a private contractor in the 80's and 90's. What purpose did it serve? It OBVIOUSLY didn't help the advancement of science given that unfettered demand for LandSat data is 200 TIMES the actual "sales" while the data was privatized. Why should people have to pay for data whose existance was only made possible by an investment from the US government anyway? The focus on privatization deprived the scientific community of valuable data for decades and actually DIMINISHED the government's return on its investment in these satellites.
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