Nighttime Imaging Grows Landsat’s Science Value – NASA Science

By Earth Resources Observation and Science (EROS) Center 

For more than 50 years, Landsat has imaged Earth’s land and near-shore surfaces as the satellites descend in midmorning orbit, when daily sunlight is optimal. That’s just what they’ve always done. 

Currently, Landsat 8 and Landsat 9 circle the globe while also making better use of their ascending paths, peering into the darkness for special requests.

The visible spectral bands of Landsat—the same blue, green and red wavelength colors our eyes can see—are typically not that useful when collected on the ascending orbit node (also known as “nighttime imagery”). The exception is twilight or darkness at Earth’s poles, which can provide a surprisingly clear observation in the thermal infrared spectral bands where snow, ice and water temperatures can be retrieved when the sun is at or below the horizon. 

Through the dark, shortwave infrared (SWIR) bands within Landsat’s Operational Land Imager (OLI) instrument can detect intense heat sources such as volcanoes or active fires, while the Thermal Infrared Sensor (TIRS) measures surface temperatures that range from geothermal geysers to solid ice. 

There is a growing interest in seeing what Landsat can capture as it ascends over the dark side of Earth, according to Dr. Christopher Crawford, the Landsat Project Scientist at the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center. Crawford leads and oversees Landsat’s long-term Earth data acquisition strategy for the USGS.

“I’ve seen a noticeable uptick in the number of nighttime imaging special requests. That’s a very active and innovative measurement science area for Landsat right now,” Crawford said.

“We have active volcanoes, we’ve got an ice environment that’s changing, and wildfire occurrences are increasingly growing into hazards that threaten human safety, infrastructure and wildlife, among other issues. Nighttime imaging is an all-purpose solution, kind of like Jiffy Baking Mix.”

Keeping an Eye on Volcanoes and Yellowstone

A particular request for nighttime imagery that turned into a “systematic observation,” Crawford said, is Yellowstone National Park. The volcanic area’s 10,000 thermal features, such as geysers or hot springs or steam vents, can get hotter or colder, and they can appear or disappear. 

Crawford is fascinated by volcanoes in general and recognizes the value of imaging them day and night. After Landsat 9 launched in 2021, when two satellites with the same high-quality sensors would together yield an image of each area of land every eight days, it seemed like a good time to start a consistent annual campaign to capture active volcanoes at night, he said. 

R. Greg Vaughan of the USGS Astrogeology Science Center, who researches active volcanoes, gave him a list. Vaughan has used Landsat data and other remote sensing methods to monitor changing thermal features in his role as the remote sensing lead for the Yellowstone Volcano Observatory. 

Vaughan also taught Crawford something about imaging Yellowstone’s thermal features at night—that the best season for locating them is during winter. That’s when the contrast between the heated features and the colder surrounding area is greatest.

“The thing that I’ve probably taken away the most is that you have to acquire data to then understand what data to continue to acquire,” Crawford said.

Vaughan spotted an exciting surprise when reviewing Landsat 8 nighttime TIRS data of Yellowstone acquired in April 2017. Comparing warm areas in the imagery to previously mapped thermal features, he found a “big blob of bright, warm pixels” that didn’t match anything on the map.

After ruling out the possibility that it could be a thawing lake next to frozen land, he looked at the secluded area with daytime aerial imagery. The telltale signs of a new and growing thermal feature were there: bright hydrothermal-altered soil and dead and dying trees.

Vaughan discussed his find and his use of Landsat data in a recent Eyes on Earth podcast episode produced by USGS EROS.

“This is why I love Landsat 8 and 9 so much. These instruments acquire data regularly, not just during the day, but they can also be tasked to acquire data at night on a regular basis. And this is really critical for my work,” Vaughan said.

Vaughan has been named a member of the current Landsat Science Team, a group of scientific and technical subject matter experts who provide analysis and advice to the Landsat Program. His research in that capacity will focus on active volcanoes.

Fires, Flares and Urban Areas Among Requests

The fire community in the western United States also finds value in Landsat nighttime imagery, Crawford said—including the energy industry and its infrastructure.

The Department of Energy’s Pacific Northwest National Laboratory submits annual special requests for proactive nighttime imaging of seasonal wildfires to support on-the-ground decision making.

“We’ve done it three seasons in a row, and the results are pretty remarkable in terms of what we’re able to see,” especially with the SWIR bands, Crawford said. Those results compare well to airborne infrared sensing taken from low-altitude flights over the same wildfires.

Landsat can also detect gas flares that are useful to oil and gas industry functions. “There are regular special requests submitted to monitor global sites that produce Liquefied Natural Gas, or LNG,” Crawford said. 

In addition, he sees requests for nighttime images over particular cities to map urban temperature, which may be higher than cooler surrounding areas. 

One recent request went beyond the already routine monitoring of active volcanoes in Iceland to encompass the entire country and coastline in a large seasonal campaign to survey overall volcanic activity. 

Crawford weighs this type of request carefully, posing these questions: “Does this advance the science mission? Is it serving the user community?”

For Iceland, that was a yes.

“I look for areas where Landsat imaging data may be underutilized, as well as areas for strategic science mission advancement and societal benefits, and in many ways, these growth areas can be enabled through the data acquisition process,” Crawford said.

A LEAP Forward

A significant advancement in learning about Landsat’s nighttime capabilities came with the effort to monitor polar regions year-round, with leadership from former Landsat Science Team member Dr. Ted Scambos from the University of Colorado Boulder. 

The Landsat Extended Acquisition of the Poles (LEAP) campaign now routinely collects imagery over the polar regions, where few wintertime images had existed in Landsat’s data record before. The visible-to-shortwave infrared and thermal infrared spectral bands allow scientists to track changes in polar ice sheets, measure polar surface temperatures and examine the interaction of ocean water and ice shelves. 

The sun’s low angle is not much of a hindrance to imaging data quality, Crawford said in an Eyes on Earth episode about the LEAP campaign. “Snow and ice are still really bright mediums on the surface, and so even if the illumination is low, you can still see a lot of detail because of the high reflectivity.” 

Fortunately, nighttime imaging does not burden Landsat 8 and Landsat 9. “The instruments are always on, so it’s just a matter of whether we’re recording the data,” Crawford said.

The imagery’s darkness helps keep data volumes much lower than the daytime and allows sufficient time for the satellites to pass off the data to ground stations around the globe whose function is to downlink the recorded data. 

“We’re starting to leverage Landsat 8 and Landsat 9 observatory capabilities to maximum scientific and societal benefit returns,” Crawford said.

“We’re populating the Landsat archive with long-term image data records that are helpful for not only quantifying changes on the Earth’s surface right now, but in the past and in the future.”

Requesting and Accessing Imagery

To learn more about Landsat data acquisitions and to submit a special request for future nighttime imagery, visit the Landsat Acquisitions webpage.

All imagery collected by special requests is made available to the public through the USGS EarthExplorer website. Select the “Landsat Collection 2 Level-1” dataset, and then select “Night” under Additional Criteria.