Landsat Missions

Using Landsat 7 Data

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Landsat 7 satellite in space

The Landsat 7 satellite (launched April 15, 1999) images the Earth every 16 days in an 8-day offset with Landsat 8. Data collected by the instruments onboard the satellites are available to download at no charge from GloVis, EarthExplorer, or the LandsatLook Viewer within 24 hours of acquisition.

Landsat 7 Instrument

Landsat 7 carries the Enhanced Thematic Mapper Plus (ETM+) sensor, an improved version of the Thematic Mapper instruments that were onboard Landsat 4 and Landsat 5. A panchromatic band with 15-meter spatial resolution, full aperture, 5% absolute radiometric calibration, and an onboard data recorder all allow for versatile and efficient imaging for global change studies, land cover monitoring and assessment, and large area mapping.

Landsat 7 Data Products

Landsat 7 data products are consistent with all Landsat standard Level-1 data products, using the specifications described on the Landsat Processing Details page.

Landsat 7 Scan Line Corrector (SLC) Failure

On May 31, 2003, the Scan Line Corrector (SLC), which compensates for the forward motion of the satellite, failed. Subsequent efforts to recover the SLC were not successful, and the failure is permanent. Without an operating SLC, the sensor’s line of sight traces a zig-zag pattern along the satellite ground track (Figure 1).

As a result, the imaged area is duplicated, with a width that increases toward the edge of the scene.  When the Level-1 data are processed, the duplicated areas are removed, leaving data gaps. Although these scenes only have 78 percent of their pixels remaining after the duplicated areas are removed, these data are still some of the most geometrically and radiometrically accurate of all civilian satellite data in the world.

Scan Line Corrector (SLC) Failure Depiction
Figure 1.  Scan Line Corrector (SLC) Failure Depiction

Filling Landsat 7 SLC-off Data Gaps

A number of methods have been developed to fill the gaps of Landsat 7 data. The following links contain useful tools, documents, and other items to assist users in creating a usable gap-filled image. The links below provide information about SLC-off data, as well as additional tools to help users best utilize Landsat 7 data.
What is Landsat 7 SLC-off data?
How do Landsat 7 ETM+ SLC-off data products compare to previous Landsat 7 data?
SLC-off Gap Mask Files - These files help users identify the location of the pixels affected by the original data gaps in the primary SLC-off scene.
Usability Assessments - These documents evaluate the scientific usability of Landsat 7 SLC-off data products.
Which images will work best to fill in the gaps?
Gap Phase Estimator  - This tool allows users to enter the Gap Phase Statistic (found in the scene metadata) from two Landsat 7 scenes to calculate the approximate area that will be filled if the selected scenes are combined.

Filling Landsat 7 SLC-off data: Approaches and Data Sources

Several methods allow users to fill the gaps of Landsat 7 SLC-off data for display purposes only. Other methods better maintain the integrity of the data to create an image more suited for scientific interpretation and analysis. These methods contained within the links below have proven useful and are provided for informational purposes only. Many image-processing packages may have capabilities such as those described on these pages. (NOTE: References to non-USGS products do not constitute endorsement by the U.S. Government.)
Filling the Gaps for Display
Filling the Gaps to use in Scientific Analysis

Landsat 7 End of Life Plans

On February 7, 2017, the twentieth and final Delta-I (inclination) maneuver took place. Delta-I maneuvers keep the spacecraft in the correct orbit to ensure the satellite maintains its 10:00 am local mean time (LMT) acquisitions.  After this maneuver, the satellite will drift in its inclination over the next four years, falling back to 9:15 by early 2020.

By the time the Landsat 9 satellite launches in late 2020, Landsat 7 will be at a lower orbit, allowing Landsat 9 to move into the 705-kilometer standard orbit altitude after launch.  Once Landsat 7 reaches a 9:15 am (LMT) acquisition time, it will no longer be providing valid science data and the satellite will be decommissioned.  Landsat 9 will allow the continuance of an 8-day offset for acquisitions with Landsat 8.

NASA Restore_L Mission

Landsat 7 is a candidate for the NASA Restore_L Robotic Servicing Mission. The mission - the first of its kind in low-Earth orbit - will provide Landsat 7 with the needed fuel for a successful decommissioning. This added fuel could also provide other possibilities: Landsat 7 could be turned into a transfer radiometer; it could fly below Landsat 8 and Landsat 9, as well as the European Space Agency’s Sentinel-2A and 2B satellites; or it could serve as a calibration instrument. The additional fuel could also potentially extend its science mission.

Landsat 7 Data Documentation and Information

The Landsat 7 Data User's Handbook provides information about the Landsat 7 data products.
The Frequently Asked Questions include all necessary information about Landsat 7 and available data products.
Landsat 8/LDCM’s Underfly with Landsat 7: In March 2013, the Landsat 8 satellite (then known as LDCM) was in position under Landsat 7 to collect near-coincident data for calibration activities.
The Landsat Project Documentation page contains policy and technical documents, as well as Data Format Control Books (DFCB).

 

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Landsat represents the world's longest continuously acquired collection of space-based moderate-resolution land remote sensing data. Four decades of imagery provides a unique resource for those who work in agriculture, geology, forestry, regional planning, education, mapping, and global change research. Landsat images are also invaluable for emergency response and disaster relief.

 

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