When it roared off into the blue California sky aboard an Atlas V rocket on February 11, 2013, Landsat 8 went with a mandate.
To image every continent during every season. To monitor the Earth’s farm fields, its precious water resources, its most endangered forests, and its fragile distant ice sheets. To provide key input to decision makers about agriculture and ecosystems, urban growth and water management, climate variability and human health.
And to do it all in ways that its six Landsat predecessors that reached orbit could not—with improved instruments with which to acquire large amounts of new and better measurements.
Mission accomplished, those who work closely with the satellite and its data insist five years after its launch.
“If we look back over the five years, have we hit our mark?” asks USGS EROS Chief Scientist Tom Loveland. “My answer would be that to date, almost all capabilities that we rely on for Landsat 8 are working superbly.”
Where to begin in corroborating that assessment? Start with the number of scenes acquired every day, and with the quality of those scenes, says John Dwyer, the USGS Landsat Project Scientist at EROS. The original requirement for Landsat 8 was to provide 400 scenes a day. In fact there are between 700 and 780 scenes acquired daily—much more than any of the Landsats that went before it.
“And I think that’s significant,” Dwyer says, “because there is a higher probability that we’ll have good, usable data.”
Not just more usable data, Loveland adds, but scenes from places that weren’t being imaged as well in the past, too.
“Persistently cloudy areas like the tropics are being imaged far more frequently. And very, very remote high latitude areas, the poles, are being imaged far more frequently,” Loveland says. “Those are two of the most changing parts of the Earth, and so our ability to understand some of the most fragile and dynamic parts of Earth are now being done with Landsat 8.”
More data is also better data because of significant technological advances that allow for improved radiometric performance over any of the previous Landsats, and better geometric performance, too. Both improvements have been important in such areas as tracking ice flow velocities with Operational Land Imager (OLI) data for cryospheric studies of ice dynamics, as well as with improved mapping of water quality.
“That’s really significant, I think, in terms of reaching aspects of the applications community that we couldn’t before,” Dwyer said.
With OLI, which is state-of-the-art in the civilian arena, Landsat 8 also benefited by a late decision in development to add the Thermal Infrared Sensor (TIRS) to its payload, says Jim Irons, NASA’s Landsat 8 Project Scientist. Though a short development schedule for TIRS led to a stray light problem that impacted the retrieval of absolute temperatures from the sensor’s data, an innovative processing algorithm implemented for operational TIRS data mitigated that issue.
As a result, ETM+ on Landsat 7 and TIRS on Landsat 8 now are the only on-orbit sensors capable of routinely collecting thermal images with resolutions of 60 or 100 meters. That ability, along with other new technologies onboard Landsat 8, allow us to:
- Identify cloud cover using a Cirrus band that detects thin clouds and their shadows, improving the overall quality of the imagery by removing artifacts that otherwise might not have been detected;
- Measure constituents in the water column using a shortwave blue coastal aerosol band;
- Increase understanding of the Earth’s energy budget using an additional thermal band that allows for the measuring of evapotranspiration, which is important for managing water use.
“There’s a lot of science that we’re able to achieve that wasn’t really possible before,” Dwyer says.
The performance and success of Landsat 8 led directly to the formulation of Landsat 9 as a clone copy of Landsat 8, Irons says. The fact is, Landsat 8’s role as a well-calibrated, consistent, operational, free source of land observations remains of high value in an era where other nations are launching similar systems, like the European Space Agency’s Sentinel-2 series, Irons adds. Or when a commercial company like Digital Globe is launching small sats that can provide a high-resolution image for an anchor national security customer. Or where commercial start-ups like Planet are launching swarms of cubesats providing frequent images.
At a time “where every other person, and his or her siblings, are flying drones with cameras, Landsat 9 will launch into this mix and continue to provide the stability and reliability necessary to systematically study Earth surface dynamics,” Irons says.
And Landsat 8 will have led it into that realm.
Based on its performance now at five years, it’s conceivable that Landsat 8 will not only be flying when Landsat 9 launches in the late 2020-early 2021 time frame, but also a decade from now, when some form of Landsat 10 is projected to go into space.
Certainly, one of the challenges for that to happen would be having the budget to operate three Landsats at once, Dwyer says. Decision makers would have to determine how three satellites would be spaced if, in fact, Landsat 10 ends up being similar to its predecessors, or is constellation of smaller satellites, or something else altogether.
But it’s an interesting possibility.
“We should have every expectation that Landsat 8 is going to go much longer than the five-year point we’re at now,” Loveland surmises. “That kind of stability meets one of the most urgent, most important parts of the overall Landsat mission, data continuity. So if (Landsat 8) gets us 10 more years, to the point where we can exchange it with a new generation, we’re meeting our requirement to have eight-day measurements around the globe. Without question, I think it can do it.”