The ongoing melt of Alaska's Columbia glacier is revealed in these images captured by the US government's Landsat satellites in 1986, 1999 and 2017.Credit: Landsat/EO/NASA

The US government is considering whether to charge for access to two widely used sources of remote-sensing imagery: the Landsat satellites operated by the US Geological Survey (USGS) and an aerial-survey programme run by the Department of Agriculture (USDA).

Officials at the Department of the Interior, which oversees the USGS, have asked a federal advisory committee to explore how putting a price on Landsat data might affect scientists and other users; the panel’s analysis is due later this year. And the USDA is contemplating a plan to institute fees for its data as early as 2019.

Some scientists who work with the data sets fear that changes in access could impair a wide range of research on the environment, conservation, agriculture and public health. “It would be just a huge setback,” says Thomas Loveland, a remote-sensing scientist who recently retired from the USGS in Sioux Falls, South Dakota.

The Landsat programme began with one satellite in 1972, and has launched seven since. Together, they have produced the world’s longest-running data set of satellite images and documented decades of global change. The current pair of satellites takes pictures at a resolution of 30 metres up to every 8 days.

Until 2008, researchers had to buy Landsat images — and they often designed studies to hold down data costs, Loveland says. “You would buy as few images as you possibly could to get an answer.”

Popular pictures

Since the USGS made the data freely available, the rate at which users download it has jumped 100-fold. The images have enabled groundbreaking studies of changes in forests, surface water, and cities, among other topics. Searching Google Scholar for “Landsat” turns up nearly 100,000 papers published since 2008.

A USGS survey of Landsat users released in 2013 found that the free distribution of Landsat imagery generates more than US$2 billion of economic benefit annually — dwarfing the programme’s current annual budget of roughly $80 million. More than half of the nearly 13,500 survey respondents were academics, and the majority lived outside the United States.

In July 2017, officials at the Department of the Interior asked a committee of external advisers to study whether Landsat’s costs could be recovered from users. The panel is now preparing a white paper for release this year. “It’s a serious discussion,” says committee member Rebecca Moore, director of engineering at Google’s Earth Engine, which hosts a continuously updated copy of the entire Landsat archive.

Snow cover on Mount Shasta in California has been shrinking over the last two decades, as shown here by images from the US government's Landsat probes.Credit: Landsat/EO/NASA

Loveland says that trying to make the Landsat programme pay for itself could backfire: charging for data would probably lower usage, and the administrative costs of handling payments would eat into any revenue. “It costs a lot of money to charge money,” he says.

The last time the federal advisory committee examined whether to reinstate fees for Landsat data, in 2012, it concluded that “Landsat benefits far outweigh the cost”. Charging money for the satellite data would waste money, stifle science and innovation, and hamper the government’s ability to monitor national security, the panel added. “It is in the U.S. national interest to fund and distribute Landsat data to the public without cost now and in the future,” it wrote.

Eyes in the sky

Then there is the USDA's National Agricultural Imagery Program. Since 2003, it has hired companies to gather images of Earth’s surface using aeroplanes, with the goal of covering the entire United States at least once every three years. The resulting pictures have a resolution of 1 metre, enabling scientists to detect individual trees and buildings.

The data are “a critical component to [land] management here in the West”, says April Hulet, an ecologist at the University of Idaho in Moscow who uses images from the programme to study invasive plant species and fire risk. If the USDA began charging for the information, Hulet says, she would probably pay — if she could afford it.

The USDA is considering whether to license the data for a fee starting in 2019, according to minutes from a November 2017 meeting of an interagency panel that oversees US geospatial policy. The USDA hopes to have a plan ready by the end of summer, after which it would post any proposed changes for public comment, says Denny Skiles, director of the department's Aerial Photography Field Office in Salt Lake City, Utah, who is leading the review of the imagery programme.

There are no perfect substitutes for images from Landsat or the USDA programme. Companies such as Planet and DigitalGlobe collect high-resolution satellite images and give scientists free access to some, but not all, of their data. Buying commercial imagery that covers large areas or long periods can cost tens of thousands of dollars — too expensive for many researchers.

And although the European Space Agency’s Sentinel-2 satellites provide free global imagery that is updated as often as every 5 days, at resolutions up to 10 metres, they cannot match Landsat’s 46-year record, says Martin Herold, a remote-sensing expert at Wageningen University in the Netherlands.

Having access to data over such a long period is crucial for determining how things such as ecosystems, farmland, bodies of water and cities have changed over time. “The longer and more dense the archive,” Herold says, “the more valuable it becomes.”