Coming Soon from a Space Station Near You

Two new innovative instruments aboard the International Space Station (ISS) are bringing a wealth of vital Earth observing data to NASA’s Earth Observing System Data and Information System (EOSDIS) collection, and a third instrument will soon be on the way.

The ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS), installed on July 5, 2018, globally monitors and measures evaporation and plant transpiration, collectively known as evapotranspiration. NASA's Global Ecosystem Dynamics Investigation (GEDI) mission uses a light detection and ranging (lidar) laser system (installed in December 2018) to create 3D images of forest and canopy structure. Finally, the Orbiting Carbon Observatory-3 instrument (OCO-3)—scheduled for launch in April 2019—will continue the global data record of atmospheric carbon dioxide (CO₂) measurements and provide a better understanding of the regional sources and sinks of CO₂.

Along with being valuable individual datasets, data from these three missions complement each other. For example, OCO-3 CO₂ data can be combined with evapotranspiration and biomass measurements from ECOSTRESS and GEDI in studies of terrestrial ecosystem processes and carbon storage. The result is a data collection that will add to the global climate data record. As with all EOSDIS data, these data are (or, in the case of OCO-3, will be) fully and freely available through EOSDIS Distributed Active Archive Centers (DAACs) for use by a diverse worldwide user community.

Humans need to regulate their body temperature to survive. When body temperature begins to increase beyond a certain threshold, a mixture of water, salt, and other minerals (what we call sweat) is released through pores in the skin. As sweat evaporates, it exchanges heat with the atmosphere, which results in overall cooling that helps reduce body temperature.

Plants, like people, also need to regulate their temperature to survive, and accomplish this in a similar manner.Plants release water through tiny pores on their leaves called stomata in a process called transpiration. As this transpired water evaporates and exchanges heat with the atmosphere, it lowers the plant’s temperature. When plants have sufficient water, they can maintain a steady temperature. If water resources are insufficient or if relative humidity gets too high, plant stomata close and the plant can heat up and become stressed. Orbiting sensors like radiometers, which sense radiated energy, can measure this vegetative temperature rise over large areas. These temperature data, in turn, can be used to calculate how much water plants use and can help pinpoint areas of potential drought or areas with developing drought.

Over the course of its one-year mission, ECOSTRESS is using a multispectral thermal infrared radiometer to sense and globally measure the temperature of plants, giving scientists a better understanding of how much water plants need and how plants respond to stress.

ECOSTRESS launched June 29, 2018, aboard a SpaceX cargo resupply mission that docked at the ISS on July 2. Ground controllers extracted ECOSTRESS on July 5, robotically transferred it to the station’s Japanese Experiment Module-Exposed Facility (JEM-EF), and installed it. After a few days of testing and start-up activities, ECOSTRESS acquired its first data image of Egypt and the Nile River on July 9.

The ECOSTRESS radiometer is producing the most detailed global surface temperature images ever acquired from space, and is so sensitive it can even measure the temperature of individual fields. These plant-temperature data are addressing three primary science questions:

• How is the terrestrial biosphere responding to changes in water availability?
• How do changes in diurnal vegetation water-stress impact the global carbon cycle?
• Can agricultural vulnerability be reduced through advanced monitoring of agricultural water consumption and improved drought estimation?

One of the core data products produced by the ECOSTRESS science team is the Evaporative Stress Index (ESI). ESI is a leading drought indicator, and can show when plants are stressed and areas where drought is likely to occur. These data enable decision-makers to know where and when resources (such as supplemental water) might need to be allocated to mitigate potential risks.

ECOSTRESS data products are still in development, but will be available through the Land Processes DAAC (LP DAAC). LP DAAC is responsible for NASA land cover and land use data in the EOSDIS collection, and operates as a partnership between the U.S. Geological Survey (USGS) and NASA.

Our world exists in three dimensions, yet data depicting this 3D structure is a gap in Earth observations. The GEDI (pronounced "jedi") mission is helping to fill this gap.

Launched on December 4, 2018, aboard a SpaceX Falcon-9 rocket, GEDI’s primary mission is to produce high-resolution laser ranging observations of Earth in 3D. From its mounting on the ISS, GEDI can observe nearly all tropical and temperate forests. These data allow for precise measurements of forest canopy height, canopy vertical structure, and surface elevation. In addition, these data will greatly advance our ability to characterize carbon and water cycling processes, biodiversity, and habitat by quantifying the amount of carbon stored in Earth’s vegetation and estimated carbon fluxes resulting from land use and climate change. GEDI’s data on surface structure also will aid weather forecasting, forest management, glacier and snowpack monitoring, and help enable the generation of more accurate digital elevation models (DEMs).

The GEDI instrument is a geodetic-class lidar laser system comprising three lasers producing eight parallel observation tracks. Each laser fires 242 times per second and illuminates a 25-meter spot on the surface over which 3D structure is measured. Each illuminated spot is separated by 60 meters along track, with an across-track distance of about 600 meters between each of the eight tracks. GEDI is led by the University of Maryland in collaboration with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and is expected to produce about 10 billion cloud-free observations during its two-year mission.

The GEDI Science Operations Center (SOC) receives the Level 0B data from the GEDI Mission Operations Center (MOC) located at Goddard Space Flight Center. The Level 0B science data will be sent from the GEDI SOC to the LP DAAC for archiving and will be processed by the SOC in four EOSDIS data processing levels. Lower level GEDI products—Level 1B, Geolocated Waveforms (which also contains Level 1A, Waveform Fitted Parameters); Level 2A, Footprint Elevation and Height Metrics; and Level 2B, Footprint Cover and Profile Metrics—are acquired from the SOC, and will be distributed through the LP DAAC. Higher level products—Level 3A, Gridded Land Surface Metrics; Level 4A, Footprint Aboveground Biomass; and Level 4B, Gridded Aboveground Biomass—come from the GEDI science team and Principal Investigators (PIs) and will be distributed through the Oak Ridge National Laboratory DAAC (ORNL DAAC), which is responsible for biogeochemical and ecological data and models. A summary of GEDI data products is available on the GEDI mission website.

GEDI data will complement several NASA missions, including the upcoming joint NASA-Indian Space Research Organisation Synthetic Aperture Radar (NISAR) mission and NASA’s recently-launched Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) mission. GEDI data also will be incorporated with Landsat maps of vegetation change to provide high spatial resolution estimates of vegetation height and change in aboveground carbon stocks at annual to five-year time scales. The result will be some of the most accurate estimates of carbon emissions from deforestation. Additionally, GEDI lidar data will be incorporated with data from the German Aerospace Center (DLR) TanDEM-X SAR interferometry mission to produce wall-to-wall maps of canopy heights and other structure metrics.

Precise measurements of atmospheric concentrations of CO₂, methane (CH₄), and other greenhouse gasses have been collected from orbit since 2009 and the launch of the Greenhouse gases Observing Satellite "Ibuki" (GOSAT). GOSAT was developed by the Japan Aerospace Exploration Agency and is still in operation. NASA’s first mission to precisely measure atmospheric CO₂ from orbit, the 2009 Orbiting Carbon Observatory (OCO) mission, suffered a launch vehicle failure and never reached orbit.

NASA’s OCO-2 satellite, described as a “carbon-copy” of the original OCO satellite in the OCO-2 Data Product User’s Guide, successfully launched in 2014 to collect space-based measurements of atmospheric CO₂ with the precision, resolution, and global coverage necessary to characterize the sources and sinks of CO₂ and quantify CO₂ variability over seasonal cycles. Originally designed as a two-year mission, OCO-2 is still providing valuable data from orbit.

OCO-3, which is tentatively scheduled for launch in April 2019 on a SpaceX Falcon-9 rocket for a planned three-year mission, is a complete stand-alone payload built using the spare OCO-2 flight instrument with additional elements added to accommodate installation and operation on the ISS. Unlike OCO-2, a free-flying satellite in a 705 km Sun-synchronous polar orbit that observes locations at nearly the same time every day, OCO-3 will monitor CO₂ concentrations throughout the day from approximately 400 km at an inclination of 51.6 degrees (which provides coverage of about 80 percent of Earth’s surface north and south of the equator, but not the poles).

OCO-3 data will address four principal science questions:

• What is the magnitude, distribution, and variability of surface-atmosphere CO₂ fluxes and what are their uncertainties in time and space?
• What are the inter-annual, seasonal, and diurnal changes in uptake and release of CO₂ on sub-regional and regional scales in the terrestrial biosphere?
• How do the regional oceanic sources and sinks of atmospheric CO₂ change with sub-seasonal to inter-annual variability, such as from synoptic forcing or the El Niño/Southern Oscillation (ENSO)?
• How are urban population growth and changing patterns of fossil fuel combustion influencing atmospheric CO₂ distributions? Can regional trends of human-created CO₂ emissions be compared against the backdrop of natural variability?

Like OCO-2, OCO-3 will not measure CO₂ directly, but rather will measure the intensity of sunlight reflected from the presence of CO₂ in a column of air. The OCO-3 instrument uses a diffraction grating (like the back of a compact disk) to separate incoming sunlight into a spectrum of multiple component colors. CO₂ and molecular oxygen (O₂) molecules in the atmosphere absorb light energy at very specific wavelengths. The intensity of these wavelength bands is analyzed, with the absorption levels indicating the presence of specific gasses. By simultaneously measuring gases over the same location and over time, OCO-3 will be able to track surface changes.

The OCO-3 instrument will acquire data in three different measurement modes. In Nadir Mode, the instrument views the ground directly below the space station. In Glint Mode, the instrument tracks near the location where sunlight is directly reflected on Earth’s surface (which enhances the instrument’s ability to acquire highly accurate measurements, particularly over the ocean). In Target Mode, the instrument views and tracks a specified surface target continuously as the ISS passes overhead. Target Mode provides the capability to collect a large number of measurements over sites where ground-based and airborne instruments also measure atmospheric CO₂. The OCO-3 Science Team will compare Target Mode measurements with those acquired by ground-based and airborne instruments to validate OCO-3 mission data.

OCO-3 data will be available through the Goddard Earth Sciences Data and Information Services Center (GES DISC). GES DISC is the EOSDIS DAAC responsible for NASA Earth science satellite and modeling data products related to global precipitation, atmospheric composition, atmospheric dynamics, hydrology, and solar irradiance, and archives and disseminates OCO-2 data.

Together, OCO-3, ECOSTRESS, and GEDI will provide further insight into Earth’s complex systems, especially the cycling of carbon and CO₂. Data from these new missions, coming from Earth’s largest orbiting observing platform, will contribute significantly to the climate data record being compiled by space-based instruments—data that are fully and freely available to support interdisciplinary global investigations and research.