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Landsat 9 enters orbit, improves and expands the Landsat open data mission

Pierre Potgieter 1 Oct 2021 - 23:15 SAST

Landsat 9 enters orbit, improves and expands the Landsat open data mission

Pierre Potgieter 1 Oct 2021 - 23:15 SAST

Compiled from NASA & USGS sources

The Landsat 9 Earth observation satellite has been launched on 27 September 2021 to continue the Landsat program’s repeat global observations for monitoring, understanding, and managing Earth’s natural resources.

The satellite will operate in its predecessor, Landsat 7’s near-polar, sun-synchronous orbit at an altitude of 705 km, replacing it as it reaches its end of life as a scientific instrument. Like its predecessor, it will work in tandem with Landsat 8 to collect images spanning the entire planet every eight days. (Landsat 7’s orbit will be lowered to prepare for NASA’s On-Orbit Servicing, Assembly, and Manufacturing-1 mission.)

Landsat 9 data products will, like other Landsat missions, continue to be made available for free download through the USGS Earth Resources Observation and Science Center.

Improved sensor specifications

The instruments aboard Landsat 9 – the Operational Land Imager 2 (OLI-2) and the Thermal Infrared Sensor 2 (TIRS-2) – measure 11 wavelengths of light reflected or radiated off Earth’s surface, in the visible and invisible spectrum. As the satellite orbits, these instruments will capture scenes across a swath of 185 kilometres, with each pixel in these images representing an area about 30 m across.

These instruments are improved replicas of those currently collecting data onboard Landsat 8. The OLI instruments (as well as the Thermal Infrared Sensors) on Landsat 8 were designed to produce 12-bit data. Landsat 9’s OLI-2 and TIRS-2 will have 14-bit resolution.

The latest satellite imagery will include nine spectral bands:

  • Band 1 Ultra blue – Coastal / Aerosol (0.43 – 0.45 µm) 30-m
  • Band 2 Blue (0.450 – 0.51 µm) 30-m
  • Band 3 Green (0.53 – 0.59 µm) 30-m
  • Band 4 Red (0.64 – 0.67 µm) 30-m
  • Band 5 Near-Infrared (0.85 – 0.88 µm) 30-m
  • Band 6 SWIR 1(1.57 – 1.65 µm) 30-m
  • Band 7 SWIR 2 (2.11 – 2.29 µm) 30-m
  • Band 8 Panchromatic (PAN) (0.50 – 0.68 µm) 15-m
  • Band 9 Cirrus (1.36 – 1.38 µm) 30-m

Landsat 8 and Landsat 9’s design make them more sensitive and more reliable than earlier Landsat satellites. Their “pushbroom” architecture (which uses a static array of sensors rather than a mechanical moving sensor) gives the satellites more dwell time over the ground, which leads to a better signal-to-noise ratio. That produces more nuanced details in the images for visual and computer inspections.

Creating a harmonised dataset for near real-time monitoring

Landsat satellites provide observations every 16 days, and having two satellites reduces that to every 8 days. The European Space Agency Sentinel-2 satellites collect data in similar wavelengths and at a similar spatial resolution, enabling the data to be combined for even more regular observations.

When harmonised into one dataset, the result is global observations every two or three days at 30 m resolution. This increased temporal resolution helps overcome challenges such as cloud cover that is associated with optical sensor data collection.

Applications looking at dynamic phenomena (e.g., crop conditions, burned area, surface water extent) where changes occur on the timescales of a few days or weeks, will benefit from the harmonised Landsat/Sentinel dataset. The harmonised dataset will also benefit applications where short-term environmental conditions (like drought) have a rapid impact on ecosystems.

In context of the Landsat programme

Landsat 9 is the first mission of the USGS-NASA Sustainable Land Imaging partnership, delivering the first instalment of a multi-decadal commitment to sustaining Landsat continuity for hundreds of thousands of users globally. After approximately 100 days after the launch, when NASA has ensured everything is working properly, it will turn the satellite over to the USGS.

The Landsat programme cemented its prominence in the geospatial community and beyond after making all Landsat images and the embedded data free and publicly available in 2008. This policy resulted in more than 100 million downloads since, and remains used to this day to make the case for the value of open data policies.

Since 1972, Landsat data have provided a unique resource for those who work in agriculture, geology, forestry, regional planning, education, mapping, and global-change research. Landsat images have also proved invaluable to the International Charter: Space and Major Disasters, supporting emergency response and disaster relief.