After 20 years of continuous human presence, the International Space Station (ISS) has provided 241 visitors with an extraordinary view of Earth from outer space – one they have shared with the rest of the world.
Astronaut photography, formally called Crew Earth Observations (CEO), has resulted in more than 3.5 million photographs of the ever-changing blue planet. But camera-controlled astronauts are not the only ones looking down at Earth from their perch in the sky. An impressive package of Earth Science instruments has also visited the station to capture huge amounts of data about our planet.
However, the space around the station itself is limited and the spots are highly coveted. Instruments undergo a rigorous approval process and cycle through every few years, turning the station into a virtual Swiss army knife of interchangeable remote sensing tools. A particularly comprehensive package of Earth observation instruments is currently on board the station, with two more approved and several more proposing to become future ISS instruments.
These instruments complement each other to provide a more complete picture of the Earth’s systems, according to William Stefanov, branch manager of the Exploration Science Office at NASAJohnson Space Center and Chief Researcher for the Crew Earth Observations Facility at the International Space Station. “Therefore, it is serendipitously good that all these instruments are on the International Space Station and working at the same time,” Stefanov said.
The human crew member was particularly handy for the Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) instrument, which records the temperature of plants on the earth’s surface by measuring the heat they emit. The instrument required the addition of Wi-Fi modules to transmit its data to the station, which in turn required astronauts to complete a spacewalk to install them.
Since then, ECOSTRESS has provided new insights into the relationship between plant temperatures and water consumption. It can identify plant stress down to the individual farmer’s field when intervention and water management may still be possible to save crops.
Lead researcher Simon Hook says researchers have only just begun to scratch the surface of how the instrument can be used based on its frequent and high resolution temperature measurements. Work is underway to use the temperature data to observe forest fires, droughts, volcanoes and heat waves or even to identify heat patterns in urban cities.
From field to forest is another plant-focused instrument Global Ecosystem Dynamics Investigation (GEDI). Using lidar – a method of jumping a laser away from the planet and measuring how long it takes for the signal to return – GEDI creates an overview of the three-dimensional structure of the world’s tropical and temperate forests so that Earth’s canopies can be mapped and time tracked.
The vertical structure of the forest, which is essentially the height of the trees and how their leaves and branches are arranged vertically, can help determine how much carbon storage is lost by deforestation or gained by growing forests. GEDI lead researcher Ralph Dubayah, professor of geographic sciences at the University of Maryland, College Park, says this is the biggest uncertainty we have about the global carbon cycle and why so much emphasis is placed on understanding how deforestation and tree growth contribute to atmospheric carbon dioxide concentrations. GEDI is a collaboration between NASA and UMD.
To deliver its high-efficiency laser, GEDI takes advantage of the massive solar panels at the station. “Right now at the International Space Station, we have an amazing confluence of instruments that together are capable of observing ecosystem function, structure and plant composition,” Dubayah said. “And it became entirely possible because we have this incredible science platform in the ISS.”
Being high above the clouds also makes the station a great platform for observing the weather. NASA’s Lightning Imaging Sensor (LIS) detects time, energy output and locations of lightning events around the world in the lower atmosphere. It can provide information on when storms are growing or rotting, thereby helping to improve weather forecast models and safety precautions for aircraft / spacecraft.
It complements the Geostationary Lightning Mapper (GLM) aboard the Geostationary Operational Environmental Satellite (GOES-16), a collaboration between NASA, the National Atmospheric and Oceanic Administration (NOAA) and industry partners, and the European Space Agency (ESA) monitoring thunderstorms and lightning events in the upper atmosphere through the ASIM (Atmosphere Space Interaction Monitor) instrument on the ISS.
The data from ASIM and LIS are both able to record the effects of dust storms, pollution, fires and volcanic eruptions on cloud formation and electrification. This is just one example of how ESA and other international agencies, including the German Aviation Center (DLR) and the Japanese Aviation Agency (JAXA), also helps to promote a global understanding of our planet through ISS instruments with its own Earth observations.
Several instruments currently on board the station are not the first of their kind. As the name suggests, the Orbiting Carbon Observatory-3 (OCO-3) is a third iteration instrument for long-term monitoring of atmospheric carbon dioxide distributions across the globe that complements long-term terrestrial observations. It provides insight into regional carbon sources and sinks and monitors changes in the carbon cycle associated with human activity.
Together with GEDI and ECOSTRESS, OCO-3 contributes to a more complete picture of terrestrial ecosystems. While its predecessor, the OCO-2 satellite, followed a polar orbit, the OCO-3’s path aboard the station offers a denser data set for areas with large carbon streams, including Earth’s most biologically diverse regions such as the Amazon rainforest.
The orbit also allows measurements at different times of the day, which particularly benefits ECOSTRESS and OCO-3, as plants and their contribution to the carbon cycle fluctuate with the time of day due to variations in sun, temperature and water availability.
Like the OCO-3, the Stratospheric Aerosol and Gas Experiment (SAGE) III is a third generation instrument. The successive SAGE instruments have continuously detected the Earth’s upper atmospheric water vapor, aerosol and ozone – which form the protective “sunscreen” layer for the planet.
As sunlight passes through the upper atmosphere, its unique blend of particles and gases creates the picturesque colors of spectacular sunsets and sunrises. To replicate a sunset or sunrise from the space station, SAGE III sees the Earth from a side angle and captures a similar view of the atmosphere on its edge as someone watching the sunset from Earth. But from its vantage point of space, SAGE III can see all of these atmospheric layers, according to project researcher Dave Flittner, and sees 15 sunrises and sunsets each day.
Science leader Marilee Roell says the lifetime of these observations has been crucial for monitoring and maintaining the protective ozone layer in the upper atmosphere. CASE II closely monitored the previous ozone depletion from common aerosols in hair sprays and flame retardants that degraded the layer, and its data informed the Montreal Protocol, which phased out the use of these harmful chemicals.
“It’s one of the biggest success stories in science that informs politics,” Roell said. “And not only is this a leading scientific instrument, but it is also on the International Space Station – an occupied platform. We are a little bit about getting the best out of both sciences and becoming part of the human space program in a peripheral way. ”
Additional atmospheric measurements of the sun come from the Total and Spectral Solar Irradiance Sensor (TSIS-1) – which is actually made of two instruments: the Total Irradiance Monitor (TIM) and the Spectral Irradiance Monitor (SIM).
TSIS-1 continues work on NASA’s satellite radiation and climate experiment satellite by measuring the amount of sunlight reaching the earth and how it is distributed in wavelength.
These measurements of solar energy, together with model-based calculations of its absorption and reflection of the Earth’s atmosphere and surface, provide insight into the sun’s influence on climate, the ozone layer, atmospheric circulation and ecosystems. The data are critical inputs for modeling the Earth’s climate and atmospheric systems.
Coming soon: EMIT & CLARREO-PF
There is still more to learn about the Earth, and new instruments that can further contribute to our understanding such as. The Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder and Earth Surface Mineral Dust Source Investigation (EMIT) are already scheduled to reach the station within the next few years.
CLARREO Pathfinder measures sunlight reflected from the earth and takes direct measurements of the sun unparalleled accuracy. The data can then help calibrate other sensors starting in 2021. EMIT is scheduled to start the following year in 2022 to map dust source regions on the Earth’s surface and assess the impact of dust on global warming and cooling.
“It has been really satisfying to see the range of things we have had on the space station,” Stefanov said. From imaging systems to lasers and radars and recently hyperspectral instruments, Stefanov believes that the limit of what they can do in the future is limited only by what scientists and engineers are capable of designing, and the number of instrument ports available.
“There will be opportunities for new sensors to go up to the station,” he said. “And I think it will continue to evolve as a very useful remote sensing platform for Earth observations in the future.”