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John Hult: Hello everyone. Welcome to this episode of Eyes on Earth. We're a podcast that focuses on our ever-changing planet and on the people here at EROS and around the globe who use remote sensing to monitor and study the health of Earth.

My name is John Hult, and I will be your host for this episode. If you are a regular listener, you have surely heard us talk about how the Landsat satellite data archive represents the longest continuously collected record of the Earth's surface in existence. You have also heard about how scientists monitor the health of the planet by looking back through that nearly 50-year record to track change.

But how can data collected in 1972, by a satellite with 1972 technology, possibly align with data collected yesterday, by a satellite launched 40 years later? The answer, for the most part, is Collections. Landsat Collection 1 saw all that data calibrated to match up as closely as possible across all seven satellite systems. The work allowed scientists to track points on the surface of the Earth more easily and gave them more confidence in their conclusions.

The Landsat team at EROS has just released Collection 2 — an upgrade that improves accuracy and expands access to higher-level products like land-surface temperature. Collection 2 also makes Landsat data available in a cloud-friendly format.

Here with us to talk about Collection 2 is Dr. Chris Barnes, a contractor at EROS who supports the Landsat International Cooperator Network. Dr. Barnes, thank you for joining us.

Chris Barnes: Thank you very much. Great to be here.

Hult: Also joining us is Dr. Christopher Barber, a remote sensing scientist with the USGS Land Change Monitoring, Assessment, and Projection Initiative, also known as LCMAP. Dr. Barber, thank you for joining us.

Chris Barber: Not a problem. Happy to contribute.

Hult: Dr. Barnes and Dr. Barber, you both work in remote sensing. You are both named Chris. My guess is you have probably gone to the same conference once or twice. You guys must have had your luggage mixed up at the airport at least once, right?

Barber: We have had frequent-flyer miles mixed up.

Hult: Oh really? Who was the beneficiary of that?

Barnes: I'm pleased to say that it was me that took a trip to South America.

Hult: Oh, nice. Let's get into Collection 2 here. Dr. Barnes, we are going to start with you. Why don't you tell us what the word “collections” means in relation to satellite data? How does a collection help scientists study the Earth?

Barnes: Absolutely, that’s a great question. Back in 2016, USGS released the first collection — Landsat Collection 1 — which was a major shift in the management of the USGS archive. Before that, the Landsat archive was processed based on the most current calibration parameters that were available at the time, or the best-known updates. Users had to spend time and effort determining where that data came from and what system was used to process it. Not all Landsat instruments were processed using the same product-generation system. Recognizing these challenges, USGS worked with the Landsat user community and the joint USGS-NASA Landsat Science Team to provide a consistent archive of known data quality. The bonus was that it allowed users more time to conduct their scientific research using Landsat data.

Hult: If I can interject really quickly — I think what I heard was that in the past, before collections, the newest Landsat data had the best calibration and accuracy, while something from 20 years ago didn’t align as well with the rest of the data. There were issues, I guess?

Barnes: Yes. There was a little disconnect between what was being acquired today and what was acquired back in the 1970s and 1980s.

Hult: So in Collection 1, you fixed that. You aligned all of the data as well as possible, right?

Barnes: Absolutely. All the data going back to 1972 — from the days of Landsat 1 all the way to Landsat 8, the most current Landsat in orbit — over nine million scenes have all been processed to the same calibration and validation parameters. That allows users to go back and forth through the entire Landsat archive and conduct research knowing the most up-to-date parameters have been used to calibrate that data.

Hult: Now I want to jump over to Dr. Barber, because you worked with Landsat data before collections, in some remote parts of the world. Tell us about that work, and what it was like to use Landsat data before Collection 1.

Barber: Not all Landsat data was collected by U.S. ground stations. There was also a set called the “foreign ground stations,” scattered across countries worldwide. Each started with the U.S. version of the processing software, but they customized it to suit local needs. So when we worked in Southeast Asia or South America, using data from multiple foreign stations, each one had been processed differently — different software versions, algorithms, and physical formats. You had to adjust your workflow for each dataset depending on when and where it came from.

Hult: So, before the global consolidation — when all that international Landsat data was moved from those ground stations into the EROS archive and reprocessed into Collection 1 — you were relying on data processed differently in each country. It almost sounds like you were working with black-and-white versus color photography, or images with different zoom levels, trying to stitch them together. Is that fair?

Barber: That’s a rough but fair analogy. Even countries close together, like Thailand and Indonesia, would process data differently.

Hult: Interesting. Well, now if they’re looking at Collection 1, they’re looking at the same processing and standards, so things match up much more easily. Dr. Barnes, how do we make that possible? How can we compare a satellite image from 40 years ago to one collected yesterday? What are the steps involved in making those pixels align?

Barnes: The credit goes to a very intelligent team of calibration and validation engineers from both USGS and NASA. They constantly monitor the performance of instruments onboard the Landsat spacecraft and publish their findings in peer-reviewed journals. Feedback from the broader calibration/validation community helps refine those findings. It all comes down to daily monitoring of instrument performance and deciding when changes need to be applied — and that’s what triggers new collections like Collection 2.

Hult: Collection 1 sounds pretty great. You calibrated and validated all the data. You’ve taken it from Betamax to DVD, essentially. So now we’re looking at Collection 2 — how much better could it possibly be? What’s new?

Barnes: Some of the main improvements are substantial gains in absolute geo-location accuracy using updated global ground-control reference datasets. That means each Landsat scene is now pinpointed more accurately on the Earth’s surface, which also improves interoperability with the European Space Agency’s Sentinel-2 satellites.

Hult: That seems like a big deal — each 30-meter pixel aligning even more precisely than before. There were slight offsets even in Collection 1, right?

Barnes: A little bit, yes. But improving interoperability allows users to get more frequent observations of the same area by combining data from the Sentinel-2 satellites with Landsat.

Hult: So it’s not just aligning Landsat pixels but also synchronizing with Sentinel 2 to increase observations. Interesting.

Barnes: Exactly. Other major highlights include updated global digital-elevation models used in processing and, for the first time, global surface-reflectance and surface-temperature products from the early 1980s. These will all be distributed as part of Collection 2.

Hult: And when you say “distributed,” you mean they’ll be available right there in EarthExplorer, without special requests, right?

Barnes: Correct. Previously, surface-reflectance data was only available on demand, and surface-temperature data only for the U.S. Now both are processed and available globally.

Hult: Dr. Barber, tell us about LCMAP. My understanding is that it uses Collection 1. What does LCMAP do, and how might Collection 2 improve it?

Barber: Twenty years ago, monitoring land cover with Landsat was expensive — both data and storage. You might handle 20 images, maybe 100 for a big project. Today, data is free and storage is cheap, so we can look at every image across the United States. Before collections, inconsistent data made time-series analysis unreliable. Collection 1 standardized it — like keeping your thermometer in one spot instead of measuring temperature all over the neighborhood. Collection 2 further refines that accuracy and will be even more impactful globally, where earlier calibration was weaker. Eventually, we hope to take LCMAP global — that’s where Collection 2 and beyond become crucial.

Hult: So LCMAP tracks every pixel back through time, and that’s only possible because of collections. Collection 2 improves accuracy, and it also makes the data globally usable. Is there also interplay with other datasets in your algorithms?

Barber: Definitely. The European Space Agency’s Copernicus program, with Sentinel-2, produces data similar to Landsat. We’re learning to “harmonize” those datasets — to make measurements comparable. It’s an exciting era for Earth observation; the next decade will bring many new satellites. Integrating all those sensors is the way forward.

Hult: NASA’s also working on a harmonized Landsat/Sentinel product. So Collection 2 is part of enabling that future — more systems, more interoperability.

Barber: Exactly. We’ve unified data from eight Landsats. The next step is applying that same rigor across multiple satellite systems so researchers can use it seamlessly without worrying about the engineering behind it.

Hult: Dr. Barnes, that sounds like good news for your team. But you also mentioned the new surface-temperature and surface-reflectance products. What kind of research will those advancements enable?

Barnes: The biggest benefit is that preprocessing is already done. Surface-reflectance products correct for aerosols, water vapor, and ozone — allowing more accurate mapping of surface change. The surface-temperature product enables global energy-balance studies, hydrological modeling, crop monitoring, vegetation-health assessments, and tracking extreme heat events, wildfires, and urban-heat-island growth.

Hult: Because it’s available globally and cloud-ready, researchers will be able to automate analysis or study urban heat in cities worldwide — say, comparing temperatures in India now versus 1994.

Barnes: Exactly. And making Collection 2 available in a commercial cloud means researchers can bring their algorithms to the data instead of downloading terabytes locally. It saves time, money, and effort — really expanding what’s possible.

Hult: That cloud access also levels the playing field for researchers without high-end local computing, doesn’t it?

Barnes: Absolutely. USGS has processed the archive to the highest standard yet and made it more accessible than ever, giving researchers everywhere equal opportunity to use it.

Hult: And just to clarify, the data is freely available, but users still pay their own cloud-compute costs, right?

Barnes: Correct. The data itself remains free under the 2008 Open Data Policy, but users handle their own commercial-cloud compute or storage costs.

Hult: To wrap up — how does it feel to have this project completed? Any final thoughts?

Barnes: This is the second major reprocessing of the Landsat archive in about five years, and it’s a huge accomplishment. The improvements in data quality, access, and new global products mark a major leap forward. Migrating processing and distribution to the cloud demonstrates just how far USGS has come since Collection 1 — delivering the most accurate Landsat archive ever.

Hult: We’ve been talking with Dr. Chris Barnes and Dr. Chris Barber about Collection 2 and the improvements to the Landsat archive. Doctors, thank you for joining us.

Barnes: Thanks, John.

Barber: Thanks, John. Exciting times ahead.

This podcast is a product of the U.S. Geological Survey, Department of the Interior.