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What’s the value of data acquired from Landsat sensors when it comes to tracking toxic algal blooms in freshwater lakes? In monitoring vital habitat for threatened species? Or in regulating scarce water resources across drought-stricken landscapes?

Quite a bit, it turns out.

A U.S. Geological Survey (USGS) report released in November 2019 put the domestic and international economic benefits of the Landsat archive at roughly $3.45 billion in 2017—a substantial increase compared to the $2.19 billion calculated in 2011. Both the 2011 and 2017 totals were calculated by using what is called the contingent valuation method, a survey-based approach widely used to estimate the economic benefits of goods or services that are not bought or sold in markets.

Survey details aside, the $3.45 billion annual impact of Landsat’s archive is best captured in the stories of those using the imagery, and the societal benefits derived from it.

Here’s an example. NASA contractor Nima Pahlevan at the Goddard Space Flight Center in Greenbelt, MD, and several of his colleagues from the Carnegie Institute in Stanford, CA, did the first study of worsening algal blooms in freshwater lakes around the world using remotely sensed Landsat data. Their findings, released in Nature in 2019, revealed that harmful blooms have intensified in freshwater lakes across the planet between 1984 and 2013, resulting in $4 billion in economic losses annually just in the United States alone.

Tracking harmful algal blooms

Without access to the 31,000 Landsat images they used, Pahlevan said there was no way he and the others could have done this important work. While the 2017 USGS survey pegged the average economic benefit of a Landsat scene domestically at $183, Pahlevan said his team certainly couldn’t have paid that much per scene—or even much less for that matter.

satellite image of algal bloom
In September 2017, a Landsat 8 sensor acquired this natural-color image of a large phytoplankton bloom by Toledo in western Lake Erie.

In fact, having to pay anything for Landsat images today would have significant impacts on research, a reality confirmed by the Evaluation of a Range of Landsat Data Cost Sharing Models study done by the USGS Landsat Advisory Group and released in June 2019.

“This is becoming customary ... the use of satellite data for water quality monitoring and evaluating freshwater blooms,” Pahlevan said. “Having open access data, free data, is essential to enable this kind of activity, which overall is going to save the country a significant amount of money” through targeted and improved water management strategies, he said.

In the Pacific Northwest, Raymond Davis with the U.S. Forest Service uses Landsat data heavily in his work as the monitoring lead for old-growth forests and the northern spotted owl in Washington, Oregon, and Northwestern California. Under the Northwest Forest Plan, adopted in 1994 as a series of Federal policies and guidelines governing land use on Federal lands in the Pacific Northwest, Davis and his group are mandated to create a report every five years on what’s going on with northern spotted owl habitat, timber harvesting, wildfires, and other things causing changes in the old-growth forests.

“To monitor annual patterns of change across such a large area,” Davis said, “basically the only game in town is to use the remotely sensed data, the Landsat data.”

In these days of multiple remote sensing looks at Earth’s landscapes, Davis could use options like the European Space Agency’s Sentinel-2 satellite systems, which may in fact prove useful to what he’s doing going forward, he said. But Sentinel doesn’t provide the historical perspective needed for tracking old-growth forests and their changes going backwards over the decades, Davis added.

Assessing old-forest changes through time

As calibration techniques have advanced for Landsat, he said his group has been able to reprocess older maps and derive more consistency through the decades—a huge advantage as they create consistent time series for 50 million acres of forests going back to 1986.

So, where once they had just one map for the entire range in 2005, and then just bookend maps for the start and end of a reporting period, now their reports are filled with annual maps, thanks in large part to the opening of the Landsat archive to the availability of no cost imagery in 2008.

“That was a game changer for us,” Davis said. “It basically resulted in such a rich dataset that we were able to go back in time to 1986. We could use satellite information to see what the forests looked like back then, how they trended before the listing of the spotted owl (as a threatened species), and how they have trended since the implementation of the Northwest Forest Plan.”

Down in California, Senior Engineering Geologist Brent Vanderburgh with the California State Water Resources Control Board uses Landsat as part of his mission to protect the state’s water assets, and to monitor compliance with regulations.

Landsat images help to verify compliance with water use permits, and to show if someone might be bypassing rules put in place to protect other water users and the environment, Vanderburgh said. If fields not covered by appropriate water use permits suddenly green up, he added, Landsat sensors can also see that.

Color photo of Northern Spotted Owl
Northern Spotted Owl (U.S. Forest Service)

“Recent advancements in cloud computing also gives us the ability to track plant water use through Landsat-based models that look at evaporation from the soil and transpiration from vegetation—called evapotranspiration,” Vanderburgh said. “This has become an important tool for public and private water managers to better understand consumptive water use at the field, watershed, or statewide scale.”

Landsat enables defensible decision-making

Other free imagery services they were using to look at different areas were comprised of stitched or “mosaicked” imagery titles that may have been collected on different dates or at different resolutions, he said. Although Landsat imagery may be lower resolution than the mosaicked data, its strict formatting and metadata requirements for each image make it far more defensible for data-driven decision-making and policy development, Vanderburgh said.

Plus, the fact that Landsat is free often proves very valuable to government entities that may not have the technical knowledge or finances to manage full-fledged satellite data contracts, he said.

“Landsat provides a way to improve agency services to the public without having to go through complicated budget maneuvers to accommodate large contracts,” Vanderburgh said. “Agencies small or large can simply hit the ground running using Landsat data and free open-source GIS tools.”

To no one’s surprise, once the California State Water Resources Control Board had free access to Landsat data, it began to institutionalize and operationalize that data, Vanderburgh said. “Now,” he added, “we’re dependent on a very useful technology.”

Leif Olmanson, a research associate at the University of Minnesota who has worked on monitoring the water quality of lakes and rivers in Minnesota for over 20 years, said that same institutionalization and operationalization of Landsat is now part of what he does. Olmanson, who participated in the 2017 survey on the economic value of Landsat data, uses that imagery to make water clarity assessments for over 10,000 lakes in Minnesota that can then be viewed online.

The LakeBrowser, which includes water quality data for those 10,000 lakes from 1975 to 2018, gets several thousand unique visitors every month, Olmanson said. The Minnesota Department of Natural Resources and Pollution Control Agency tap into it. County and City administrators do, too. Management agencies use Olmanson’s work to look at everything from the current status of lake water quality to how it has changed and how those changes, along with warming temperatures, impact cold water fish.

“For citizens, it is a big thing because anyone can look at the site and get information about ‘their’ lake and surrounding lakes,” he said. “We have just started talking to realtors and how they use it. They’ve been using it for helping their clients know what the water quality is before they buy.”

Landsat enables near real-time monitoring

Without Landsat images, Olmanson said any hope of near real-time water quality assessments would be significantly decreased. And having to pay for those images, he added, would likely mean having to charge for the products produced.

“We probably would not be able to do assessments in near real time,” he said. “We would go back to five-year assessments but would have to find funding to pay for the imagery and image processing.

The LakeBrowser is very popular now because Landsat data are available at no cost, and he’s been able to secure Federal and State funds to complete the research and image processing, Olmanson said. “So, what we do is freely available to users,” he said. “I expect if we had to charge for that, our usership would go down significantly.”

That’s a concern that echoes across the Landsat-using landscape. With the availability of free and open Landsat data, there’s been a dramatic paradigm shift from intermittent mapping to continuous monitoring in the last decade—a shift that is a key reason why the economic benefits of Landsat continue to grow, and why the benefits to society are expanding.

Whether it involves monitoring natural resources or implementing operational programs that help with the management of those resources, Landsat has really become invaluable, Pahlevan, Vanderburgh, Olmanson, and Davis say.

And if Landsat becomes cost prohibitive, Davis with the U.S. Forest Service believes that in his case, it will take away a powerful piece of information that allows for not just monitoring, “but for adapting to doing a good job of managing the forests out there instead of doing it blindly.”

“We’re supposed to be stewards of all the natural resources that the forests provide,” he said. “To be a good steward, you’ve got to have a good understanding of what your management is doing.”

A good understanding, he added, that is exactly what Landsat gives them.

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