The 30-acre pear orchard in the Sacramento-San Joaquin River Delta has been in Brett Baker’s family since the end of the California Gold Rush. After six generations, though, the most precious resource in California is no longer gold — it’s water. And most of the state’s freshwater can be found in the delta.
Because so much of California now depends on that water, around 2010 the state mandated that all landowners in the delta monitor and report the water they use on their land. What sounded like a simple requirement, however, was not. Equipment to measure water diversion is expensive, and the estuary’s twice-daily rise and fall with the tides makes measurements inaccurate, said Baker, who added that the data also is only reported for the previous year, further limiting its usefulness. Meanwhile, the state has calculated water consumption in the area using an outdated equation that doesn’t reliably account for local weather, groundwater flows, or runoff into the delta. “The utility of that data is minimal, if any,” Baker said.
In the last few years, though, accurate, near-real-time measurement of actual water use in the delta has become possible, not with meters on the ground but with satellite instruments in space. The OpenET platform, created by a consortium including NASA, the U.S. Geological Survey (USGS), and several other partners, can calculate the total amount of water transferred from the surface to the atmosphere through evapotranspiration. This is the combined moisture evaporating from soil and transpired, or “exhaled,” by plants. Evapotranspiration is a key measure of the water that’s actually being removed from a local water system. And it’s calculated based on imagery from Landsat and other satellites in low-Earth orbit.
OpenET is only one of the latest practical uses that researchers and businesses continue finding for Landsat imagery, 50 years after the program’s first satellite launched.
On July 23, 1972, months before the last Apollo astronauts went to the Moon, NASA launched the Earth Resources Technology Satellite, later renamed Landsat 1, from Vandenberg Air Force Base in California. The world’s first space-based land observatory carried two imaging sensors — a television-style camera, initially considered the primary imager, and an experimental multispectral scanner (MSS).
The MSS was conceived by Virginia Norwood, one of the first female engineers at Hughes Aircraft Company. Many involved in the project were initially skeptical of the imager, but its detectors were digital, making its imagery open to precise calibration and computer analysis, and it collected light in specific visible and infrared wavelengths selected for their ability to reveal characteristics like plant health and soil moisture.
After seeing the first images from orbit, the Landsat team designated the MSS the primary imager, and subsequent Landsat imagers, through Landsat 9, launched in 2021, have all been advances to the basic MSS concept. Norwood became known as “the Mother of Landsat.”
The original satellite exceeded expectations, successfully improving crop-yield predictions, spotting deforestation, monitoring lake and river levels, discovering uncharted islands, and much more. It paved the way for a multitude of other Earth-imaging satellites from NASA, other space agencies, and, later, private companies. Today, even the commercial satellites capturing high-resolution Earth imagery typically rely on Landsat for the precise calibration that makes their data useful for science.
With the advent of high-speed internet and high-performance computing, access to — and applications of — Landsat data exploded in the 2010s. More recently, cloud computing has enabled products built using the entire Landsat archive, a dataset most users simply couldn’t have downloaded.
Maps became one of the most widespread uses for Landsat data, especially after 2008, when the Department of the Interior made all the imagery available free of charge. (Landsat is a joint mission between NASA and the USGS, which owns and distributes the data.)
While driver navigation software usually does not use satellite imagery, applications for hikers, runners, and bikers, for example, rely on it heavily. “For apps like Strava and AllTrails, satellite imagery is a significant enhancement for their users,” said Alistair Miller, who heads imagery products and partnerships for Mapbox Inc., naming two of the company’s prominent customers. Mapbox, based in Washington, D.C., provides a platform and map data that enable developers to create customized map-based applications. “Our main purpose is using imagery to enhance the context of the maps our customers create with our platform,” Miller said.
As a small startup in 2010, he said, the company couldn’t spend millions on proprietary images and instead integrated data from Landsat. The global coverage and regular updates — capturing images of the same areas every 14 days — enabled the company to build huge, cloud-free images of Earth.
The company eventually started purchasing commercial, high-resolution images, and today Mapbox blends these with data from one of Landsat’s direct descendants, NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) to let users seamlessly zoom in and out of views.
“We have an appreciation for NASA essentially starting the Earth-observation industry,” Miller said. “If it weren’t for Landsat, we wouldn’t be where we are in terms of understanding our Earth.”
Some of the most pressing questions people ask about Earth are about the food it’s producing. Agriculture and adjacent industries like farm equipment manufacturers and grain futures traders are among the heaviest users of Earth-imaging satellite data, which can help assess crop health and predict yields.
Even in this well-established niche, though, new capabilities continue to emerge. One up-and-coming company, Boulder, Colorado-based Perennial Inc. — formerly Cloud Agronomics — was founded in 2018 to validate sustainable farming practices by measuring carbon stored in the earth. To do this, the company relies on Landsat, as well as the European Space Agency’s Sentinel satellites.
Perennial is working to enable the emerging markets for carbon credits, through which farmers can get paid for using practices that maximize their land’s storage of carbon, explained CTO David Schurman. These might include reducing soil tillage, planting cover crops during the off season, reducing fertilizer usage, and changing grazing practices. Satellite images can determine not only whether a farm is using these techniques but also the carbon content of the ground.
The company is also discovering interest among food companies that want to reduce their environmental impact, letting them audit suppliers’ carbon footprints and make informed decisions about where to buy food and who to reward with incentives.
Landsat provided the scientific-grade images that enabled all this, but Perennial had to figure out how to use that data to determine soil carbon content. While it’s not unusual for a company to put in this kind of work, NASA and the USGS also continually work to create tools and practical applications for Landsat. OpenET, the tool calculating water use at Baker’s pear farm, for example, is the product of years of work by scientists at multiple universities and agencies.
“Many of the scientists and software engineers on the OpenET team have been working on these models and approaches for more than a decade,” said Forrest Melton, NASA’s Project Scientist for OpenET. The platform uses Landsat data to essentially determine how much energy from the sun is reflected from Earth’s surface, versus how much is absorbed by the surface and the air.
Reprocessing and uploading the entire Landsat archive to the cloud was the biggest effort of the last several years at the USGS Earth Resources Observation and Science Center, and the researchers are constantly working to extract more information from Landsat data.
With a data user community that keeps growing, scientists and engineers are already looking forward to the next mission. NASA and USGS are developing options for the next iteration of Landsat, currently called Landsat Next.
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