Landsat: An Earth-Observing Trailblazer
By Michael Moraniec
The Landsat series of satellites has revolutionized the field of Earth observation. Seven satellites have provided a detailed record of Earth’s landmasses for nearly four decades, providing vital information to experts in such fields as agriculture, disaster response and relief, climate change, water management and cartography. An eighth satellite is being built and launched to provide even more data to study Earth’s ever-changing global landscape.
What is Landsat?
Landsat is an Earth observation satellite series that uses remote sensing to take images of the world’s landmasses. The instruments aboard Landsat, known as radiometers, passively measure electromagnetic energy reflected and emitted from the Earth’s surface and transmitted through the atmosphere. Collected data are processed and converted to images (Short 1). Figure 1 shows a false-color image of the Bonneville Salt Flats of the Great Salt Lake Desert.
Landsat: The Experimental Phase
The idea of Earth observation was conceived when early satellite experiments proved that it was possible to capture images of the Earth from outer space. These experiments included Explorer 6 in 1959, the Television Infrared Remote Observation Satellite in 1960, and the Gemini and Apollo missions in the 1960s and early 1970s (Williams 1173). In 1965, William Pecora, then director of the USGS, proposed a satellite to measure Earth’s natural resources. At first, various government agencies opposed the idea because it was viewed as too expensive and too risky. But, with the help of the Secretary of the Interior, Stewart Udall, NASA was able to start building the first Landsat satellite in 1970 (NASA & Rocchio 1).
There have been seven satellites in the Landsat series, with an eighth due to launch in 2012. The first Landsat satellite, originally called the Earth Resources Technology Satellite (ERTS), launched on July 23, 1972, and featured two instruments to collect data. The Return Beam Vidicon (RBV) produced a television-like picture of the Earth and was supposed to be the main image collector. However, it failed early in the mission and the Multispectral Scanner System (MSS) became the primary instrument. Landsat 1 operated five years past its design life until January 1978. In that time, it collected more than 300,000 images. To explore the applications of this data, NASA selected 300 investigators to understand how the data could be used in different scientific fields (NASA & Rocchio 1).
Landsat 2 was very similar to Landsat 1 in that it was still deemed an experimental satellite, and was designed and operated by NASA. It launched on Jan. 22, 1975, and also carried the RBV and MSS until February of 1982, when it was decommissioned (NASA & Rocchio 2).
It was discovered early in the life of Landsat how significant vegetation imaging would be. By viewing the foliage density in vegetation-rich images, scientists could describe sunlight absorption, photosynthetic capacity, and evaporation rates. This helped in the understanding of how land characteristics modulate the processes and systems of Earth (Williams 1172).
Landsat 3 was originally considered experimental at the time of its launch on March 5, 1978. The following year President Carter assigned management responsibility for “civil operational land remote sensing activities” to NOAA (NOAA took over day-to-day operations of Landsat in 1983).
Landsat 3 carried the RBV and MSS, but the MSS was upgraded to capture images for a thermal band, in addition to the red, green, and two near-infrared bands sensed by the earlier MSS sensors. Unfortunately, the new, thermal band failed soon after launch (NASA & Rocchio 3). As more Landsat data was collected, more capabilities of the Earth observation system were discovered. This led to the realization that the same kind of remote monitoring could be applied to Earth’s oceans and atmosphere, creating an integrated network of global examination (Williams 1172). Landsat 3 was decommissioned in March of 1983 (NASA & Rocchio 3).
Landsat 4 was launched on July 16, 1982, and carried a new instrument, the Thematic Mapper (TM) in addition to an MSS. The TM offered a better spatial resolution and additional bands compared to the MSS. In 1983, Landsat 4 experienced a significant problem with two of its solar panels and both downlink transmitters, which allowed its data to be received at a ground station. Once the first Tracking and Data Relay Satellite System (TDRSS) satellite (TDRS-East) was launched and operational Landsat 4 was able to use its working transmitter (Ku-band).
Landsat Becomes a Private Enterprise
Landsat 5 was built at the same time as Landsat 4 and carried the same instruments. It was launched on March 1, 1984, with a three-year design life and is still in operation today (2011). The USGS recently reported that it is “acquiring data normally.” The year it was launched saw a radical change in the operations of the Landsat program. The Land Remote Sensing Commercialization Act of 1984 mandated that all land remote-sensing satellites be maintained and operated by the private sector. The Landsat contract was awarded to the Earth Observation Satellite Co. (EOSAT). EOSAT was now responsible for operating Landsats 4 and 5, archiving and distributing their data, and building and operating the next two satellites in the series (Williams 1172).
EOSAT’s main objective was to turn a profit, in contrast to NASA, USGS, and NOAA, which were more concerned with future research studies. The cost of images went up dramatically due to constraints in the Commercialization Act, from $650 to $4,400 (NASA & Rocchio 5). Many of Landsat’s data users were unable to afford the higher prices.
Because of problems experienced with the privately owned Landsat, Congress passed the Land Remote Sensing Policy Act of 1992 that mandated the seventh Landsat satellite be built by a government agency.
Landsat 7 was launched on April 15, 1999, and is the other satellite in the series that is still in operation today. It collects data using an Enhanced Thematic Mapper Plus (ETM+) system. Per the Remote Sensing Policy Act of 1992, NASA built and launched Landsat 7. Since the launch, USGS has been responsible for operating the satellite as well as collecting and archiving its data (Williams 1174). ETM+ is the most accurately calibrated sensor in the Landsat series and has helped set a standard for other Earth observing satellites. However, in May of 2003 the Scan Line Corrector (SLC), a component of the ETM+ optical system, failed. The purpose of the SLC is to compensate for the rotation of the Earth under the Landsat 7 orbit. Without the SLC, the scanning mirror instantaneous field-of-view traces a zigzag pattern across the image swath causing wedge-shaped gaps at both edges of the swath.
Applications of Landsat Data
Despite all its issues, Landsat missions have been funded for nearly 40 years. The reason for its continued funding is simple: The images it returns are extraordinarily useful in managing a wide range of terrestrial activities, projects and programs. The Science Citation Index has recorded more than 10,000 peer-reviewed articles that have used Landsat data since 1972.
Some common applications include mapping urban growth, monitoring carbon in forests and deforestation, monitoring crop acreage, and surveying disaster aftermath. During the Deepwater Horizon oil spill and aftermath, Landsat images provided clean-up crews with initial and up-to-date images of the spill.
Landsat data has even found previously uncharted land and led to the discovery of new species. During a survey of Canada’s coast in 1976, imagery from Landsat 1 showed a number of small islands off the northeast coast of the Labrador region. Once the existence of the islands was confirmed in person, the largest was named for its discoverer, “Landsat Island” (Rocchio 1). And in 2005, Dr. Julien Bayliss used Landsat images to inventory forests in Mozambique. After finding good candidate sites on the images, he explored the areas and discovered a forest with three new species of butterflies and one new species of snake (Kew 1).
Landsat data has been used to study the impact of Hurricane Katrina. The deadly hurricane wiped out nearly five million acres of forestland while on its path of destruction. The trees were a major source of carbon dioxide removal and storage in the area. Before and after images of the area collected by Landsat 5 were used with data collected from MODIS, another remote sensing Earth observation instrument, to estimate the change in forest area and change in carbon dioxide storage (Cook-Anderson 1).
Landsat data is also being used in the restoration of the Chesapeake Bay, the largest estuary in the United States and staple in the area’s fishing industry. The Chesapeake Bay Program is comparing Landsat images taken in 1984, 1992, 2001, and 2006 to determine the changes in land cover that might contribute to pollution and runoff into the bay. Scientists included the land cover data in a computer model of the Chesapeake watershed, which is used to help determine daily pollution loads into the Bay and its rivers (Lutz 1).
But Landsat data isn’t just for observing Earth’s complex systems and mankind’s ecological impact. One surprising area it is being used in is cancer research. Since many cancers have been linked to exposure to agricultural chemicals, the USGS, National Cancer Institute, and Colorado State University are working together to classify land cover characteristics that could cause exposure. These characteristics, such as crop type, irrigation methods, and animal feeding grounds, are used with data on the use and spread of chemicals to predict exposure to human populations (Maxwell 1).
USGS made the entire Landsat archive available for free in 2009. Since that time the amount of downloaded Landsat scenes have dramatically increased— the 7 millionth free scene was distributed this October. New ways to use Landsat data have emerged because of this easy data access and new applications are being explored.
— Landsat imagery courtesy of NASA Goddard Space Flight Center and U.S. Geological Survey.
Bidwell, Steven. Personal interview. 18 Jan. 2011.
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