ISS Utilization: ECOSTRESS (ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station)
Background: In July 2014, NASA has selected proposals from the second Earth Venture Instrument (EVI-2) Pathfinder Program for two new instruments that will observe changes in global vegetation from the International Space Station. The sensors will give scientists new ways to see how forests and ecosystems are affected by changes in climate or land use change. 1) 2) 3)
The new projects are:
• GEDI (Global Ecosystem Dynamics Investigation), a laser-based system from the University of Maryland, College Park, to observe the structure of forest canopy. This instrument is expected to be launched in 2019.
- Ralph Dubayah, of the University of Maryland, is the principal investigator for the GEDI Lidar. This project will use a laser-based system to study a range of climates, including the observation of the forest canopy structure over the tropics, and the tundra in high northern latitudes. This data will help scientists better understand the changes in natural carbon storage within the carbon cycle from both human-influenced activities and natural climate variations.
- The GEDI team has extensive experience in observing and modeling forest and vegetation dynamics. Dubayah has led numerous vegetation lidar observations from sub-orbital platforms throughout his career. The team includes partnerships with NASA's Goddard Space Flight Center, Greenbelt, Maryland; Woods Hole Research Center, Woods Hole, Massachusetts; the U.S. Forest Service, Ogden, Utah; and Brown University, Providence, Rhode Island.
• ECOSTRESS (ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station), a high-resolution multiple wavelength imaging spectrometer from NASA/JPL (Jet Propulsion Laboratory) in Pasadena, CA, to study the effectiveness of water use by vegetation.
- Simon Hook of JPL is the PI (Principal Investigator) for ECOSTRESS. This project will use a high-resolution thermal infrared radiometer to measure plant evapotranspiration, the loss of water from growing leaves and evaporation from the soil. These data will reveal how ecosystems change with climate and provide a critical link between the water cycle and effectiveness of plant growth, both natural and agricultural.
- The ECOSTRESS team has extensive experience in development and analysis of thermal infrared spectroscopic images of the Earth's surface. Hook has served as project scientist for the ASTER (Advanced Spaceborne Thermal Emission Reflection Radiometer) instrument on NASA's Earth Observing System Terra satellite and has been involved in numerous sub-orbital field campaigns. The team includes partnerships with the U.S. Department of Agriculture, Beltsville, Maryland, and Maricopa, Arizona; Princeton University, Princeton, New Jersey; and University of Idaho, Moscow, Idaho.
The International Space Station provides several in-orbit capabilities useful to both instruments. The space station orbit is inclined relative to the poles, providing more observation time of forests and vegetation over temperate land masses than possible from the polar orbits commonly used for other types of Earth observations. The GEDI laser requires significant power resources, which the space station can provide. Also, the relatively low altitude of the station's orbit, about 400 km up, benefits GEDI by ensuring a higher return energy for laser pulses reflected from the ground.
NASA/LaRC (Langley Research Center) in Hampton, Virginia, manages the Earth System Science Pathfinder program for NASA's Science Mission Directorate. The missions in this program provide an innovative approach to address Earth science research with periodic windows of opportunity to accommodate new scientific priorities.
Figure 1: Two new spaceborne Earth-observing instruments will help scientists better understand how global forests and ecosystems are affected by changes in climate and land use change. This image of the Amazon rainforest is from a 2010 global map of the height of the world's forests based on multiple satellite datasets (image credit: NASA Earth Observatory)
ECOSTRESS will monitor one of the most basic processes in living plants: the loss of water through the tiny pores in leaves. When people lose water through their pores, the process is called sweating. The related process in plants is known as transpiration. Because water that evaporates from soil around plants also affects the amount of water that plants can use, ECOSTRESS will measure combined evaporation and transpiration, known as evapotranspiration (ET). ECOSTRESS will address 3 science questions: 4)
• 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 consumptive use and improved drought estimation?
Three science objectives have been identified to address these questions:
• Identify critical thresholds of water use and water stress in key climate sensitive biomes (e.g., tropical/dry transition forests, boreal forests)
• Detect the timing, location, and predictive factors leading to plant water uptake decline and/or cessation over the diurnal cycle
• Measure agricultural water consumptive use over CONUS (Contiguous United States) at spatiotemporal scales applicable to improving drought estimation accuracy.
ECOSTRESS will meet these objectives by measuring the thermal infrared brightness temperatures (BT) of plants and using that information to derive their evapotranspiration (ET). These measurements will be made CONUS-wide and over key climate sensitive biomes around the world as well as in European and South Asian agricultural zones, and selected FLUXNET validation sites. Figure 2 shows the sites the ECOSTRESS will measure. The instrument is capable of measuring additional sites, provided the sufficient downlink capability is provided by the International Space Sation.
Note: FLUXNET is a "network of regional networks," integrating worldwide water and energy flux measurements.
Figure 2: Planned coverage of ECOSTRESS measurements (image credit: NASA/JPL)
One of the core products that will be produced by ECOSTRESS team is the ESI (Evaporative Stress Index). ESI is a leading drought indicator - it can indicate that plants are stressed and that a drought is likely to occur providing the option for decision makers to take action. Figure 3 illustrates the ESI for the United States during the 2012 drought. The red areas indicate regions of high water stress.
Figure 3: Map of the 2012 drought in the United States showing differences in water stress. Red areas indicate high water stress (drought conditions) and green areas indicate low water stress (non-drought conditions), image credit: NASA
Launch: The ECOSTRESS radiometer will be launched with a SpaceX Dragon cargo spacecraft to the ISS, planned for the summer of 2018 on the SpX-15 flight (Dragon trunk) of SpaceX from KSC (Kennedy Space Center), FL. 5)
Orbit: Near-circular orbit, altitude of ~400 km to ISS, inclination =51.6°.
ECOSTRESS will be implemented by placing the existing space-ready PHyTIR (Prototype HyspIRI Thermal Infrared Radiometer) onto the ISS and using it to gather the measurements needed to address the science goals and objectives. PHyTIR was initially developed under the ESTO (Earth Science Technology Office) Instrument Incubator Program (IIP) to support testing and assessment for the HyspIRI (Hyperspectral Infrared Imager). — The 2007 National Research Council's (NRC) 2007 Decadal Survey report, 'Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond,' identified HyspIRI as a Tier-2 priority. 6)
From the ISS, PHyTIR will provide data with a spatial resolution of 38 m x 68 m (science requirement is 100 m) and a predicted temperature sensitivity of ≤ 0.1 K (science requirement is 0.3 K). The ISS orbit allows excellent coverage of the selected targets including diurnal coverage. The existing hardware was developed to reduce the cost and risk for the thermal infrared radiometer on the future HyspIRI (Hyperspectral Infrared Imager) mission.
ECOSTRESS consists of a cross-track, push-whiskbroom, scanning, multiband filter radiometer . A double-sided scan mirror, rotating at a constant 23.3 rpm, allows the telescope to view a 51º wide nadir cross-track swath as well as two internal blackbody calibration targets every 1.29 seconds (Note that the two-sided mirror rotating at 23.3 rpm provides 46.6 sweeps per minute). The optical signal is focused by a telescope onto the 60 K focal plane containing a custom 13.2 µm cutoff MCT (Mercury Cadmium Telluride) infrared detector array. Spectral filters on the focal plane define 5 spectral bands in the 8-12.5 µm range. The focal plane is cooled by two commercial Thales cryocoolers.
Electronics consist of six build-to-print and four commercial boards. Heat rejection for the ECOSTRESS cryocoolers and electronics is provided by the cooling fluid loop on the ISS Japanese Experiment Module External Facility (JEM-EF). ECOSTRESS can fit any of the nine JEM-EF payload locations but will be deployed at Site 10 (one of the two end locations).
Table 1: Science requirements and expected capability for ECOSTRESS
The ECOSTRESS instrument is a push-whiskbroom 5 channel cross-track scanner with the following accommodation parameters: 7)
- Mass = 266 kg
- Average on-orbit power = 527 W
- Volume: 1.3 m3 (1.85 m L x 0.88 m H x 0.80 m W)
- Data rate = 4.5 Mbit/s, 2.32 Mbit/s (average)
- Design life = 5 years
- Typical revisit of 90% of CONUS every 4 days at varying times over the diurnal cycle.
The TIR instrument will acquire data from the ISS with a 38 m in-track by 68 m cross-track spatial resolution in five spectral bands, located in the TIR part of the electromagnetic spectrum between 8 and 12.5 µm. The positions of three of the TIR bands closely match the first three thermal bands of ASTER, while two of the TIR bands match bands of ASTER and MODIS typically used for split-window type applications (ASTER bands 12–14 and MODIS bands 31, 32). It is expected that small adjustments to the band positions will be made based on ongoing engineering filter performance capabilities. 8)
The TIR instrument will operate as a push-whisk mapper, similar to MODIS but with 256 pixels in the cross-whisk direction for each spectral channel (Figure 4), which enables a wide swath and high spatial resolution. As the ISS moves forward, the scan mirror sweeps the focal plane ground projection in the cross-track direction. Each sweep is 256-pixels wide. The different spectral bands are swept across a given point on the ground sequentially. From the 400±25 km ISS altitude, the resulting swath is 402 km wide. A wide continuous swath is produced even with an ISS yaw of up to ±18.5º. The scan mirror rotates at a constant angular speed. It sweeps the focal plane image 53º across nadir, then to
Figure 4: ECOSTRESS TIR scanning details (image credit: NASA/JPL)
Figure 5: Illustration of the ECOSTRESS radiometer in container (image credit: NASA/JPL)
The ECOSTRESS radiometer will be flown to the ISS and accommodated on the JEM-EF (Japanese Experiment Module - External Facility) site 10. At this location, the radiometer scan is perpendicular to the ISS velocity. 9)
Figure 6: Japanese Experiment Module on International Space Station (image credit: NASA)
Figure 7: Overview of Earth science instruments on the ISS (installed or planned) in the second decade of the 21st century (image credit: NASA) 10)
In summary, ECOSTRESS will provide the highest spatial resolution thermal infrared data ever from the International Space Sta1on. HyspIRI (Hyperspectral Infrared Imager) is planned for the 2023+ timeframe.
• ECOSTRESS is possible because of the development of the PHyTIR (Prototype HyspIRI Thermal Infrared Radiometer) instrument for HyspIRI-TIR supported by ESTO
• ECOSTRESS will address a subset of the science associated with HyspIRI
• The ECOSTRESS mission will help answer three key 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 consumptive use and improved drought es1ma1on?
• ECOSTRESS has a clearly defined set of data products and mature algorithms
• Opportunity for combined HyspIRI-like datasets using the European EnMAP and ECOSTRESS with GEDI (Global Ecosystems Dynamics Investigation Lidar) for structure.
Table 2: ECOSTRESS science data products 11)
• The ORR (Operational Readiness Review) of ECOSTRESS is scheduled for February 7, 2018 at JPL (Jet Propulsion Laboratory).
• May, 2016: JPL selected an upgraded Thales LPT9310 COTS (Commercial Off The Shelf) cryocooler for the ECOSTRESS instrument. The LPT9310's proven reliability has resulted in interest from JPL in using this cooler for cost-sensitive space applications. This instrument provides nominally over 4 W of cooling capacity at 80 K. - However, this capability has only been proven in terrestrial (commercial) applications. In order to provide sufficient justification for using an off-the-shelf cooler for a flight application, additional tests have been performed on the delivered flight coolers, to attain a sufficiently controlled level of quality while leveraging the heritage of the COTS cooler. 12)
- A qualification test campaign was completed successfully, with the upgraded design meeting qualification-level robustness requirements after being subjected to fatigue cycling as well as providing the required efficiency increase. Flight models are currently in production and will be delivered to JPL July 2016.
Figure 8: Photo of the LPT9310 pulse tube cryocooler (image credit: Thales Cryogenics B. V.)
Figure 9: EM cryocooler installation for ECOSTRESS (image credit: NASA/JPL)
1) Steve Cole, "NASA Selects Instruments to Track Climate Impact on Vegetation," NASA, Release 14-199, July 30, 2014, URL: https://www.nasa.gov/press/2014/july/nasa-selects-
2) Alan Buis, "NASA's ECOSTRESS Will Monitor Plant Health," NASA, October 27, 2014, URL: https://www.nasa.gov/jpl/nasas-ecos
3) Lacey Young, Alan Buis, "New NASA Insights into the Secret Lives of Plants," NASA/JPL, Nov. 2017, URL: https://www.jpl.nasa.gov/news/news.php?release=2017-298
7) "NASA Earth Science Division Update," NASA, November 12, 2014, URL: http://www.wmo.int/pages/prog/sat/meetings
8) Glynn Hulley, Simon Hook, Joshua Fisher, Christine Lee, "ECOSTRESS, a NASA Earth-Ventures instrument for studying links between the water cycle and plant health over the diurnal cycle," Proceedings of IGARSS 2017 (IEEE International Geoscience and Remote Sensing Symposium), Fort Worth, Texas, USA, July 23–28, 2017
10) Julie A. Robinson, William L. Stefanov,"Earth Science Research on the International Space Station," Committee on Earth Science and Applications from Space (CESAS) Space Studies Board National Academies of Science, Engineering, Medicine, 29 March 2016, URL: http://sites.nationalacademies.org/cs
11) Simon J. Hook and the HyspIRI and ECOSTRESS Teams, "ECOSTRESS Update," JPL/ Caltech, June 1, 2016, URL: https://hyspiri.jpl.nasa.gov/downloads/2016_
12) R. Arts, J. Mullié, D. Johnson, I. McKinley, J. Rodriguez, T. Benschop, "LPT9310 COTS cooler for ECOSTRESS," ICC (International Conference on Communications), Kuala Lumpur, Malaysia, May 23-27, 2016 , URL: http://www.thales-cryogenics.com/wp-content/uploads
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).