USGS, EROS Process ‘First Light’ Images from Landsat 9

USGS, EROS Process ‘First Light’ Images from Landsat 9

Landsat 9 carries two instruments designed to work together to capture a broad range of wavelengths: the Operational Land Imager 2, or OLI-2, which detects nine different wavelengths of visible, near-infrared and shortwave-infrared light; and the Thermal Infrared Sensor 2, or TIRS-2, which detects two wavelengths of thermal radiation to measure slight changes in temperature. Data from both instruments are shown in the two pairs in this image.The top left shows snow and glaciers in the Himalayan mountains, leading to the flat Tibetan Plateau to the north. The top right shows the same area in thermal data from the TIRS-2 instrument. Blue-white color indicates relatively cooler surface temperatures, while orange-red indicates warmer surface temperatures.The bottom left shows the brown and green rectangles of farm fields in southern Ontario, sandwiched between Lake Erie and Lake St. Clair. The white and grey rectangles in the bottom of the image are produce greenhouses, which show up as blue-ish (relatively cooler) spots in the TIRS-2 image on the right. (Public domain.)

The images acquired Oct. 31 over the Florida panhandle, Lake Erie, the Navajo Nation, Australian mangroves, and the Himalayas highlight the value of the Landsat program to the monitoring of natural resources, water use, climate-related land change and more.

The images didn’t arrive from Landsat 9 in their final form, however. The raw X-band data was transmitted in a series of zeros and ones to USGS and international partner ground stations, then pushed through the USGS Earth Resources Observation and Science (EROS) Center’s Data Processing and Archive System (DPAS). The “first light” images are the final product, representing the data that will be available to users once the mission reaches operational status. 

The USGS EROS role is critical to data quality. NASA builds and launches each Landsat satellite and leads the mission through a 100-day check-out period. The USGS, meanwhile, builds the ground system to capture, process and archive the data. The agencies work together closely throughout check out and commissioning to ensure the DPAS is ready to turn that raw data into the science products relied upon for monitoring the health of the planet.

“When we talk about this data, it’s not just that pretty picture that you see. It takes a lot of work to get there. A lot of the data is what we call ancillary data—everything from spacecraft attitude and ephemeris to the individual temperatures of components within the instruments,” said Chris Engebretson, the USGS EROS Data Processing and Archive Systems Manager. “All of that has a very specific format that has to be read and interpreted correctly, then run through some very complicated algorithms in order to make the imagery that people are accustomed to seeing out of Landsat.”

Landsat 9 has two sensors: the Operational Land Imager-2, which captures nine wavelengths of the electromagnetic spectrum; and the Thermal Infrared Sensor-2, which records surface temperature data in two wavelengths.

Landsat 9 is similar to Landsat 8, but features several improvements. The new data have higher radiometric resolution and detect more subtle differences, especially over darker areas like water or dense forests. For example, Landsat 9 can differentiate more than 16,000 shades of a given wavelength; Landsat 7, the satellite being replaced, detects only 256 shades.

The first light images arrived about a month after the observatory made first contact with the Landsat 9 ground stations in Svalbard, Norway; Gilmore Creek, Alaska; and Sioux Falls, SD.

Those contacts, which came shortly after launch on Sept. 27, 2021, involved the transmission of test data stored on board the spacecraft. The test transmissions were later downlinked by the two other primary ground stations for Landsat 9: Neustrelitz, Germany, and Alice Springs, Australia.

“They’ve all successfully downloaded and delivered the test pattern imagery at this point,” said Ryan Brown, the USGS Landsat Ground Network Manager at EROS.

All five ground stations will continue to collect data throughout the 100-day commissioning phase for Landsat 9. The work of collaboration and preparation will continue through the end of 2021, with Landsat 9 data expected to be available through USGS platforms like EarthExplorer in early 2022.

USGS News: Landsat MissionsRead More