SAN FRANCISCO — Researchers eagerly awaiting access to data from the Landsat Earth observation mission launched Feb. 11 say the new satellite will offer far more detailed imagery than its predecessors, enhancing their ability to observe subtle changes in environmental characteristics such as water quality.
“Our ability to detect subtle changes on the surface of the Earth, changes in the amount of water stored in vegetation or whatever variable we are trying to measure, should be done with significantly improved accuracy and precision,” said Thomas Loveland, senior scientist for the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center and senior scientist for the Landsat Data Continuity Mission.
The NASA-USGS Landsat Data Continuity Mission, renamed Landsat 8 after launch, carries two sensors — the Operational Land Imager built by Ball Aerospace & Technologies Corp. of Boulder, Colo., and the Thermal Infrared Sensor built by NASA’s Goddard Space Flight Center in Greenbelt, Md. — on a spacecraft built by Orbital Sciences Corp. in its Gilbert, Ariz., facility.
Unlike the electromechanical sensors flown on previous Landsat missions, Landsat 8’s sensors feature thousands of photosensitive detectors designed to provide higher-resolution imagery. Instrument testing conducted before launch showed that, as expected, the new sensors will measure 4,096 different levels of reflected light, compared with 256 levels measured by the Enhanced Thematic Mapper Plus, the primary instrument on Landsat 7, Loveland said.
Landsat 8 is designed to produce far more data than its predecessors. The spacecraft’s two instruments will provide a total of 400 daily images, compared with 250 images per day captured by Landsat 7. In addition, Landsat 8 features a solid-state data recorder designed to store all imagery and relay it daily to the EROS ground station near Sioux Falls, S.D., the central repository for Landsat data. Since data recorders carried by previous Landsat spacecraft were unable to store a full day’s worth of data, each satellite sent as much data as possible to the EROS ground station and relayed the rest to ground stations around the world. Much of the data initially sent to other ground stations eventually was transferred to the EROS archive, but not all of it, Loveland said.
By sending all data to EROS every day, the Landsat 8 mission is designed to offer researchers a comprehensive data set and swift access to imagery. These features of the Landsat program will benefit many Landsat data customers, “particularly those involved in global-scale monitoring of forests and agriculture,” Loveland said.
Although one of the primary goals of Landsat 8 is to extend the Landsat program’s four-decade record of moderate-resolution Earth imagery, the mission also is poised to offer new types of data. The Operational Land Imager features nine spectral bands. Seven of those bands are similar to those of Landsat 7’s Enhanced Thematic Mapper Plus. The two additional channels are designed to improve observations of ocean color as well as high-altitude cirrus clouds.
One of the most difficult aspects of studying water quality using space-based sensors is eliminating the confusing signals produced by aerosol particles in the atmosphere, said John Schott, a professor at the Chester F. Carlson Center for Imaging Science at the Rochester Institute of Technology in New York. By measuring light reflected in the shortwave ultra-blue band, the Operational Land Imager will enable researchers to detect variations in atmospheric aerosols and use that information to make more accurate observations of suspended particles or chlorophyll in the lakes, rivers and coastal waters below, said Schott, who began working with NASA in 1981 to develop instruments for Landsat 4.
Cirrus clouds are another environmental feature that sometimes obscures Earth imagery. EROS officials plan to use Landsat 8’s cirrus channel to remove thin clouds from Landsat imagery and improve the quality of the data provided to customers, Loveland said.
For decades, Landsat missions have gathered data on land surface temperatures. Those measurements have been used extensively by water resource managers in the western United States to identify irrigated fields, said Tony Morse, managing partner of the Spatial Analysis Group in Boise and former geospatial technology manager for the Idaho Department of Water Resources. Well-irrigated plants release more water into the atmosphere through transpiration than dry grass, crops and trees. In thermal imagery, transpiring plants appear cooler than plants without adequate water.
Catching Heat
To cut costs, NASA officials originally planned to fly Landsat 8 without a thermal imaging capability. Morse and his colleagues spent years urging government officials to include a thermal instrument on Landsat 8 to provide ongoing observation of water use. “The combination of Landsat’s thermal data, its 30-meter-by-30-meter pixel size and its extensive data archive makes it an ideal satellite for water resources applications,” Morse said. “No other satellite has those three factors.”
In 2009, NASA approved plans to develop Landsat 8’s Thermal Infrared Sensor, which is designed to obtain data in two thermal bands compared with one on Landsat 7. The additional band “will allow us to measure surface temperature far more accurately,” Loveland said. With Landsat 8, water resource managers will be able to observe crop irrigation on a field-by-field basis, Morse said.
Now, Morse and his colleagues have turned their attention to the satellite’s launch. “It will be a success as long as the little rascal makes it into the proper orbit,” he said.
NASA launched Landsat 8 into polar orbit on a United Launch Alliance Atlas 5 rocket from Vandenberg Air Force Base, Calif.
After launch, NASA and USGS officials plan to spend approximately 100 days confirming the satellite and its instruments are functioning properly. Then, EROS officials plan to begin processing Landsat 8 imagery and making it available free of charge to customers within 24 hours.
Researchers who rely on Landsat data are anxious to see Landsat 8’s successful launch because Landsat 5 stopped collecting imagery in January and Landsat 7 produces images with significant data gaps due to the failure of the satellite’s scan line corrector. Landsat 6 was launched in 1993 but an on-board propulsion system failed and it never reached orbit.
