The Spacecraft Tarot: Landsat
Temperance teaches us how to strike a balance.
We are living in times of excess. Excess of information, excess of waste, excess of stimulation. In a world where it’s easy to overdose on fake news or feel genuine fear of “missing out,” it’s important to remember the value of patience and moderation. In many tarot decks, temperance is personified in the image of a person with one foot on land, the other in water — finding balance between both worlds.
Streaking across both the landmasses and bodies of water of our home planet is Landsat, one of a series of Earth-observing satellites that provides us with invaluable information about our planet’s natural resources: forest abundance, water supplies, and agricultural fertility. In many cases, what Landsat is telling us are more stories of excess — too many resources are dwindling for the long-term sustainability of our systems.
Landsat not only exemplifies temperance in its fifty-year history of gradual improvements and enhanced observations, it also calls for our societal need of temperance in our daily lives.
Ironically, the idea for an Earth-observing satellite was conceived during NASA’s Moon-bound programs. As Mercury, Gemini, and Apollo missions captured photos of the Earth from space for the very first time, U.S. Geological Survey (USGS) director William Pecora realized the potential of a satellite that could regularly capture terrain data.
The path from fruition to execution was a long one. Although weather satellites had been in operation since 1960, it wasn’t until 1965 that the idea behind Landsat began to take form. Due to budget concerns, as well as geopolitical concerns about photographing other countries from space, it wasn’t until July 23, 1972, that the first in the Landsat series — known then as Earth Resources Technology Satellite (ERTS) — launched onboard a Delta 900 rocket from Vandenberg Air Force Base, California.
To make its observations, ERTS used two instruments: a camera system and the Multispectral Scanner System, which used an oscillating mirror to sweep across four spectral bands. Each of these bands picked up a different wavelength of light, which could used be used for monitoring different things, such as aerosols or vegetation, as the satellite orbited the planet 14 times a day.
The idea of using satellite data to monitor the Earth was a foreign concept at the time. To develop techniques to apply the data, 300 scientists across various disciplines came together to form the organization of Landsat principal investigators. Early Landsat data was used to identify regions for oil exploration, monitor deforestation in the Amazon rainforest, and create accurate and up-to-date maps of the world.
ERTS outlived its design life by five years by the time it was officially decommissioned in 1978. By then, the second in the series — known as Landsat 2 — had been in operation already for three years, and Landsat 3 would launch into orbit just two months later. The operational Landsat program soon shifted from NASA to the National Oceanic and Atmospheric Administration, the agency responsible for managing weather satellites, although NASA still continues to build and launch spacecraft in the series.
Each craft saw improved instrumentation, which enhanced the detail of their observations. Landsat 4 and 5, launched July 16, 1982 and March 1, 1984, respectively, could observe the Earth with a higher portion of the electromagnetic spectrum and at a higher resolution using a new instrument called the Thematic Mapper. Both satellites lasted much longer than expected. When Landsat 5 was given the final command to power off the transmitter on June 5, 2013, it had survived in Earth’s orbit for 28 years and 10 months, outliving its expected lifespan of three years and setting a Guinness World Record for the longest-living Earth observation satellite.
However, Landsat was not without its challenges. Landsat 6 failed to reach orbit on Oct. 5, 1993 due to an explosion in its liquid fuel system.
When Landsat 7 successfully launched on April 15, 1999, the satellite carried an Enhanced Thematic Mapper Plus, which included additional features that could map larger areas more efficiently. Landsat 7 is also the most accurately calibrated Earth-observing satellite, which means that the measurements it makes are extremely accurate when compared to the same types of measurements on the ground. Landsat 7 continues to serve as a standard for cross-calibrating other Earth satellites.
Landsat 7 is so well-calibrated, in fact, that the data is still useful even after the Scan Line Corrector (SLC) failed on May 31, 2003. Without a working SLC, the sensor’s line of sight creates a zig-zag pattern instead of what is supposed to be straight lines. When the data is processed and the duplicate areas are removed, the satellites pick up only 78% of the ground then it did before — but still enough to be incredibly useful for the scientific community.
Perhaps most importantly, as of Oct. 1, 2008, all Landsat 7 data became free for the public to use, and soon after, the entire Landsat USGS archive followed suit.
Today, scientists all over the world have free access to over fifty years of data to assist in a diversity of different research applications.
Launched on Feb. 11, 2013, Landsat 8 is the most recently launched spacecraft in the Landsat series. Between the Operational Land Imager and Thermal Infrared Sensor, the satellite picks up 11 different bands in the electromagnetic spectrum — more than any other Landsat satellite before.
Landsat 7 and 8 are currently in near-polar orbits of our home planet. Every spot on Earth is measured by one or the other every eight days.
Today, Landsat data does not cease to find useful applications. Imaging hurricanes, forest fires, droughts, volcano eruptions, and disease outbreaks from space can assist disaster responses by pointing recovery efforts in the right direction or providing communities with up-to-date information.
Most recently, scientists are using Landsat data to track how the environment has been impacted by the COVID-19 pandemic. For example, less planes in the air and less cars on the road could mean less urban pollutants in our environment, which could in turn affect the cycle of warming and cooling on our planet. In addition, with lockdown policies preventing the U.S. Department of Agriculture from traveling to collect information on crop conditions, scientists are supplementing the missing pieces with Landsat data. Forecasts can help anticipate food shortages or inform farmers about good planting times.
Landsat data can even be used to track the biodiversity of our planet, like the Bureau of Land Management is currently doing in Alaska with freshwater fish species. Teams measure the amount of specific kinds of fish DNA in the water and cross-check where they find certain populations with data collected from Landsat, such as land surface temperature or vegetation. Knowing what environmental conditions help native species thrive can influence land management decisions. Landsat data is also being used in a similar fashion to assist chimpanzee conservation efforts.
Just as Temperance teaches us to strike a balance, the legacy of Landsat is one of careful observation and measured responses. With the human population expected to swell to 9 billion by 2050, we need to keep careful track of the resources we are expending to ensure we have enough for future generations. And as climate change continues shift weather patterns, melt glacial ice, and raise sea levels, Landsat data will continue to monitor the fluctuating environment to help inform mitigation efforts.
Just as Landsat data is shared by government agencies, research institutions, and citizen scientists, the data communicates a message of sharing Earth’s resources as well.
Temperance encourages us to seek accurate information, make science-based decisions, and practice balance wherever you can.
Every week I will be sharing a new card from the Spacecraft Tarot. For more information about the series, read this.