The Landsat 7 satellite was launched in 1999, and data from the Enhanced Thematic Mapper Plus (ETM+) sensor onboard acquired data on the World Reference System-2 (WRS-2) for over 20 years before being lowered from the standard 705 kilometers (km) orbit to 697 km in April of 2022.
Background
After Landsat 7 was lowered to 697 km and all systems were deemed nominal, the ETM+ resumed imaging on May 5, 2022. Initial plans called for the satellite to continue to acquire data until the end of the 2022 Northern Hemisphere growing season, and then ‘orbit-in-waiting’ for the NASA's On-Orbit Servicing, Assembly, and Manufacturing-1 (OSAM-1) servicing mission. However, the health of the satellite and the ETM+ sensor remains steady, and the quality and usability of the data being receive remains nominal.
For the first time in Landsat Mission history, three Landsat satellites are providing valuable data for greater temporal coverage of Earth observations, and monitoring land changes from natural and human-induced events.
Below are important details about changes to the Landsat 7 satellite orbit, data acquisitions and available data products. Additional information about the Calibration/Validation efforts to ensure the data acquired during the Landsat 7 extended science mission remain high quality and usable are also provided.
Orbit
In the lower orbit, Landsat 7 is no longer on a repeating ground track, and acquisitions are not aligned to the World Reference System-2 (WRS-2) used by Landsat 8 and Landsat 9. Additionally, the Landsat 7 acquisition footprints are continually shifting in relation to the WRS-2 grid.
This animation displays the shifts in three Landsat 7 NDVI images acquired between May and June 2022. These scenes are all cataloged in the Landsat data archive as Path 38 Row 37.
Data Acquisition
Landsat 7 has added over 175,000 scenes to the USGS Landsat archive since May 5, 2022 in support of the extended science mission. The heatmap below displays the worldwide acquisitions.
Due to the variability in data acquisition, the best way to determine what Landsat 7 scenes will be collected on a given day is to access the pending acquisition files. These files are available up to one to two days in advance from the Landsat Acquisition Tool’s Pending Acquisitions tab. The ETM+ is currently acquiring about 450 images per day, and the satellite's current mean local crossing time at the equator is now earlier than 8:30 AM.
Data Products
It is important to note that while Landsat 7 data remains valuable, attention needs to be placed when searching for data from the mission. The data acquired during the Landsat 7 extended science mission are processed to Landsat Collection 2 Level-1 calibrated data products, and then to Level-2 surface reflectance and surface temperature science products. Like other Landsat products, they are available for download on USGS data access portals.
Reminder: No U.S. Landsat Analysis Ready Data (ARD) or Level-3 science products are created from the Landsat 7 extended science mission data.
The image to the right displays the EarthExplorer footprints of two Landsat 7 scenes from WRS2 path 25 row 28. The red footprint denotes a scene acquired March 27, 2022, at 705 km orbit; the green footprint denotes a scene acquired November 4, 2022, at the lowered 697 km orbit. Data in the right margin portion of the March scene is not included in the November scene.
Tip: When searching for Landsat 7 extended science mission scenes, the most accurate results will be returned by searching by region of interest (ROI), instead of specific WRS-2 path/row designations.
Calibration/Validation Results
Overall, the quality and utility of the Landsat 7 extended science mission data remains within its prior nominal performance. The USGS/NASA Calibration/Validation Team continually analyzes and quantifies the data collected by the ETM+ at the lower orbit. To date, no significant changes have been evident in the spectral bands, and the radiometric and geometric quality of the data remain stable within established thresholds. Data from the Landsat 7 extended science mission is still reliable for relevant global impact assessments.
Additional Calibration/Validation efforts regarding the extended science mission will be added to this page when they become available.
Science Analysis
Members of the USGS and the Technical Support Services Contract (TSSC) Landsat Science Office (LSO) team at USGS EROS performed analysis on the Level-2 science products created from Landsat 7 extended science mission data. As more analysis is completed, it will be added to this page.
CFMask Pixel Quality Assessment: Within the CFMask Pixel Quality Assessment (QA_PIXEL) data, reasonable agreement has been found between pixel classifications in clear Landsat 7 and Landsat 9 scenes (see the image below). Many of the differences were due to data acquisition timing (Landsat 7 scene center time: 15:34:19.8050354Z; Landsat 9: 17:01:43.1991100Z), the SLC-off artifact in Landsat 7,and orbit offset. There was stronger disagreement in cloudy scenes.
Underfly Activities Promote Data Quality
Even though Landsat 7 is no longer on WRS-2, the opportunity for the satellite to collect coincident data with Landsat 8 or Landsat 9 benefits the calibration of the ETM+ sensor, as well as the Operational Land Imagers and Thermal Infrared Sensors onboard Landsat 8 and Landsat 9. Analysis of Landsat 7’s underfly of Landsat 8 and Landsat 9 are being evaluated and will be added here when they become available.
Landsat 7 Extended Science Mission Images
