Landsat 7’s nominal science mission ended in April 2022 after nearly 23 years of acquiring Earth imagery from 705 kilometers above the Earth. Landsat 7 is now in an extended science mission after having its orbit lowered by about 8 kilometers to make way for Landsat 9.
Landsat 7 Extended Science Mission
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. The satellite acquired science data until January 19, 2024.
Background
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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, since the health of the satellite and the ETM+ sensor remained steady, and the quality of the data remained nominal, data acquisitions continued.
Since being lowered in orbit, the satellite has continued to drift within its orbit, exposing it to periods of full sunlight and earlier imaging times, impacting imaging opportunities and the ability to process valid science data.
On January 19, 2024, Landsat 7 imaging was suspended due to the satellite’s transition into full sunlight, which caused issues with the batteries. Imaging was suspended to retain the health and safety of the batteries. The satellite will remain in full sunlight until mid-April 2024. Visit the January 19th News page describes more about how being in full sunlight affects the satellite, and why data imaging was suspended.
Below are details about the Landsat 7 extended science mission, including Calibration/Validation efforts to ensure the data acquired during the Landsat 7 extended science mission remain high quality and usable.
Orbit
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In the lower orbit, Landsat 7 was no longer on a repeating ground track, and data acquisitions were not aligned to the World Reference System-2 (WRS-2) used by Landsat 8 and Landsat 9. Additionally, Landsat 7 acquisition footprints continually shifted 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
The ETM+ acquired about 450 images per day and the satellite's current mean local crossing time at the equator moved to earlier than 8:30 AM.
The map below displays the location of over 175,000 Landsat 7 scenes added to the USGS Landsat archive during the during the extended science mission.
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Data Products
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No U.S. Landsat Analysis Ready Data (ARD) or Level-3 science products were 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.
Calibration/Validation Results
Overall, the quality and utility of the Landsat 7 extended science mission data remained within its prior nominal performance. The USGS/NASA Calibration/Validation Team continually analyzed and quantified the data collected by the ETM+ at the lower orbit. No significant changes were evident in the spectral bands, and the radiometric and geometric quality of the data remained stable within established thresholds. Data from the Landsat 7 extended science mission was deemed reliable for relevant global impact assessments.
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.
CFMask Pixel Quality Assessment: Within the CFMask Pixel Quality Assessment (QA_PIXEL) data, reasonable agreement was 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.
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Landsat 7 Extended Science Mission Images
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Eyes on Earth Episode 85 - Landsat 7 Extended Science Mission
Landsat 7’s nominal science mission ended in April 2022 after nearly 23 years of acquiring Earth imagery from 705 kilometers above the Earth. Landsat 7 is now in an extended science mission after having its orbit lowered by about 8 kilometers to make way for Landsat 9.
Landsat 7’s nominal science mission ended in April 2022 after nearly 23 years of acquiring Earth imagery from 705 kilometers above the Earth. Landsat 7 is now in an extended science mission after having its orbit lowered by about 8 kilometers to make way for Landsat 9.