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Landsat 8 to the rescue

NASA prepares to launch satellite that will continue historic record of global change.

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    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.

    USGS EROS Data Center

  2. Diverson of water has also shrunk the Dead Sea, where water levels have dropped about 30 metres in the past 50 years. From 1972 to 2011, the southern portion of the sea has been converted into evaporation ponds for extracting minerals.

    Robert Simmon/Landsat/USGS/NASA

  3. In 1974, Mount St Helens in Washington state was surrounded by forests. An image taken three months after the volcanic eruption on 18 May 1980  reveals the devastation caused by the blast, which directed its energy northwards. By 2011, much of the damaged region had started to regrow.

    L1 MSS, L2 MSS, L5 TM/USGS

  4. Between 1986 and 2011, the terminus of the Columbia Glacier in southeastern Alaska retreated by 20 kilometres. Icebergs that broke off the glacier's edge can be seen floating south of the terminus.

    Jesse Allen and Robert Simmon/Landsat 5/USGS Global Visualization Viewer/NASA

  5. An image of Rondônia in the Brazilian Amazon shows little human impact on the forest in 1975. By 2001, large sections of the forest had been cleared, creating bright patches on the Landsat image.

    Goddard Space Flight Center Scientific Visualization Studio/NASA

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 metres. Landsats 4 and 5 reached 30-metre 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-metre resolution. Through careful calibration, the programme 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 kilometres, 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-kilometre 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.”

The data helped to spark a digital revolution among remote-sensing specialists, who have developed tools to exploit massive computing resources and stitch together high-resolution records of global change over time and space. Other space-borne imagers, such as the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites, can take snapshots of larger areas at a single pass, but with much lower resolutions.

With Landsat, “we can get the detail and the enormous geographic coverage”, says Asner. “This alone puts Landsat at the very forefront in land-cover and land-use change monitoring.”

Landsat 8 is scheduled to begin operations 90 days after entering orbit, although the first images could arrive within three or four weeks. The satellite might not live as long as its predecessor, which NASA engineers have put forward as a candidate to Guinness World Records, but Irons believes that Landsat 8 will make its own mark. “I do not think it hyperbole to suggest that all seven billion of us will benefit from the Landsat continuity mission.”

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