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Landsat Mission Underfly Opportunities

Throughout the Landsat Program’s long mission history, calibration and characterization of data are of paramount importance. One of the best methods for cross-calibration between instruments is imaging near-coincidentally in tandem using an underfly with an earlier mission sensor. 

These opportunities are once-in-a-lifetime as the satellite continues its way to final orbit on the Worldwide Reference System-2 (WRS-2). These cross-calibration activities benefit Landsat Collections processing by providing an opportunity to standardize all Landsat sensors to the same radiometric scale.

Landsat 5 was the first satellite to perform an underfly with another Landsat satellite. Landsat 4 and Landsat 5 flew in tandem during an underfly campaign on March 15-16, 1984, that collected nearly 100 coincident scenes. Data for both the Multispectral Scanner (MSS) and Thematic Mapper (TM) sensors were acquired during this underfly effort. Later in their missions and for the well-being of the archive, the USGS/NASA Calibration and Validation team used the under flights to improve cross calibration efforts.

Landsat 5 Underfly with Landsat 4 over Huntsville, Alabama
Images acquired over Huntsville, Alabama during the Landsat 5 underfly with Landsat 4. On the top is the Landsat 4 TM image, and on the bottom is the Landsat 5 TM image. Both image composites are shown as a natural color composite using the red, green, and blue bands (Bands 3|2|1)

Landsat 7, early in its mission, also collected tandem images in an underfly with Landsat 5 to establish sensor calibration and characterization. During the orbits from June 1-4, 1999, 791 pairs of near-coincident scenes were used in cross-calibration efforts by USGS and NASA engineers for Landsat 5 and Landsat 7. In April 2022, Landsat 7 was lowered from the Worldwide Reference System-2 (WRS-2) orbit to allow Landsat 9 to take its place. 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.

Landsat 7 Underfly Image with Landsat 5
Landsat 7 underfly with Landsat 5 over the Niobrara River, Nebraska on June 2, 1999. The left image shows the Landsat 5 TM image and the right image is from Landsat 7 ETM+. Both images are shown as a false color image using the near infrared, red, and green bands (Bands 4|3|2).

On March 29-30, 2013, Landsat 8 was in position under the Landsat 7 satellite. This underfly provided opportunities for 916 near-coincident data collects from both satellites. Landsat 8 was the first of the Landsat satellites with the ability to take off-nadir collects. An additional 15 images were off-nadir contributing to an increase in number of underfly collects by this satellite. 

On March 29-30, 2013, the Landsat Data Continuity Mission (later named Landsat 8) was in position under the Landsat 7 satellite. This provided opportunities for near-coincident data collection from both satellites.  These images (Path 38 Row 35), were both acquired on March 29, 2013 by Landsat 7 (left) and Landsat 8 (right), near Peach Springs, Arizona. Both images are shown as a false color image using the shortwave infrared, near infrared, and red bands (Landsat 7 Bands 5|4|3; Landsat 8 Bands 6|5|4).

The underfly legacy continues calibration excellence with the Landsat 8 and Landsat 9 underfly as Landsat 9 continued its journey to its nominal orbital altitude in WRS-2. This tandem collection opportunity extended to about 5 days, collecting 2,396 images from November 12-16, 2021, with 100 percent overlap on November 14. 

Landsat 9 Underfly with Landsat 8 over Puerto Vallarta, Mexico
Images from the Landsat 9 underfly with Landsat 8 over Puerto Vallarta, Mexico on November 11, 2021. The left image shows the Landsat 8 OLI image and the right image is from Landsat 9 OLI. Both images are shown as a true color image using the red, green, and blue bands (Bands 4|3|2).



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