PUBLISHED: 22 JUNE 2017 | VOLUME: 1 | ARTICLE NUMBER: 0194 comment ISS observations offer insights into plant function E. Natasha Stavros, David Schimel, Ryan Pavlick, Shawn Serbin, Abigail Swann, Laura Duncanson, Joshua B. Fisher, Fabian Fassnacht, Susan Ustin, Ralph Dubayah, Anna Schweiger and Paul Wennberg In 2018 technologies on the International Space Station will provide ~1 year of synchronous observations of ecosystem composition, structure and function. We discuss these instruments and how they can be used to constrain global models and improve our understanding of the current state of terrestrial ecosystems. pace-based observations are index (a metric of vegetation greenness • How does land management interact increasingly central to global ecology, often used as a proxy for ecosystem with climate to control future disturbance Sopening windows to address questions productivity or carbon storage) influences regimes? pertaining to the carbon cycle, biodiversity, estimates of absorbed photosynthetic Common to all these questions is that productivity and disturbance. Until active radiation (fPAR) and leaf area they require multiple observations to test recently, satellite observations provided a index (a metric of one-side leaf area per specific hypotheses, and reject incorrect limited range of observations, albeit critical ground surface area)1. Thus, more direct model formulations. Fortunately, there are ones, relating light absorption to support observations of functioning and structure many exciting new developments in remote plant growth, disturbance and land use/ are needed to enable distinct testing and sensing that will provide key observations cover change. These observations have improvement of modelled representations of the land (for example, Sentinel series, revolutionized our knowledge of global of ecosystem processes. BIOMASS, NISAR). ecology, but have not addressed a series Questions include: Although new technology makes of critical questions about ecosystem • How sensitive are ecosystems to many key observations feasible, it’s process that must be resolved in order temperature and water availability and uncommon to have observing platforms to reduce uncertainty in future climate how will this affect future carbon and with multiple instruments collecting a and ecosystem service projections. These energy balances? variety of parameters at synergetic spatial key questions have been addressed in • Do diverse plant communities respond to resolutions and coordinated temporal local studies, but the findings of these climate change differently from simpler acquisition, particularly at scales needed local experiments cannot be tested across communities? for management. Yet this is exactly what broad landscapes with observations • Does diversity lead to ecosystems is needed to resolve how plant function from existing satellite technologies. For responding non-linearly to change, in affects ecosystem processes at landscape example, normalized difference vegetation ways we cannot predict now? scales in different regions across the globe. Box 1 | Description of ISS instruments. The instruments for deployment on ISS to produce observations in 25-metre OCO-3. A pointing instrument that are: GEDI, ECOSTRESS, OCO-3 and footprints along ten parallel tracks. The will use three high-spectral-resolution HISUI. Each instrument is being designed tracks are separated by ~600 m each, and grating spectrometers to measure solar- independently, but the nature of the footprints are separated by 25 m along induced fluorescence, a measure of observations offers an unprecedented the tracks. photon emission during photosynthetic opportunity to resolve regional and global partitioning that provides a direct proxy scale understanding of ecosystem process ECOSTRESS. Because transpiration for gross primary productivity, and and function. performs the same cooling function as atmospheric column CO2, with high sweat, when plants close stomata their precision (±1 ppm). GEDI. A geodetic-class LIDAR that leaf temperatures increase. This rise in will measure canopy heights and foliar temperature can be detected and such HISUI. Will provide contiguous visible vertical profiles to establish a baseline of observations at different hours throughout to shortwave infrared (400–2,500 nm) vegetation structure and global terrestrial the day are crucial for mapping vegetation surface reflectance at very high spectral biomass. GEDI observations leverage a water-use efficiency, represented by the resolution (400–979 nm at ~10 nm sampling scheme that is then interpolated ability of vegetation to close stomata in the average per band for 57 bands and to produce a map. The sample scheme afternoon to avoid transpiration that would 900–2,500 nm at ~12.5 average per band uses three lasers (at 242 pulses per second) exceed water uptake from the soil. for 128 bands). NATURE ECOLOGY & EVOLUTION 1, 0194 (2017) | DOI: 10.1038/s41559-017-0194 | www.nature.com/natecolevol 1 ©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved. comment Table 1 | A list of high-level data products that will provided by each instrument expected for deployment to the ISS starting in 2017. Data ECOSTRESS OCO-3 GEDI HISUI product (40–60 m pixels, 20–30 samples (5 km2 footprint, capable of (~500 m2 footprint spaced (30 m pixels with 20 km swath and 10 nm spectral level per hour of the day collected mapping up to one hundred 60 m along a track with no resolution over 0.4–2.5 μm spectral range) throughout the year) 1,000 m2 areas per day) temporal repeat) 2 Surface temperature Atmospheric column CO2 Height metrics Atmospherically corrected surface reflectance with Emissivity Solar-induced fluorescence Canopy metrics quality assurance (not validated) 3 Evapotranspiration Gridded level 2 Gridded level 2 4 Water-use efficiency Aboveground biomass Evaporative stress index (footprint and gridded) Fortunately, with a coordinated strategy, dynamics questions that cannot be answered on investment. Coordinated observations such an opportunity will arise for ecologists from any one instrument and that have can include using aircraft versions of these in the next few years. the ability to substantially enhance our spaceborne instruments (for example, understanding of ecosystem responses to LIDAR for GEDI, PhyTIR for ECOSTRESS, Novel Earth observations global change. For example, an estimation CFIS for OCO-3, and AVIRIS for HISUI) The International Space Station (ISS) will of carbon sink potential (Fig. 1) can be both before and after launch. Airborne host four instruments from JAXA (Japan estimated using observations of carbon campaigns with instruments analogous to Aerospace Exploration Agency) and NASA flux (OCO-3) and carbon storage (LIDAR- those deployed for space are frequently used (Box 1) in 2018 that will advance our ability derived biomass from GEDI), both of which for calibration and validation activities of to monitor and model terrestrial ecosystems can be affected by the efficiency of individual delivered data products both leading up between latitudes ~50° North and South. plant species (HISUI) to sequester carbon to and after launch. Furthermore, these Three of the instruments are from NASA and under variable access to water (ECOSTRESS). instruments may help to scale understanding include: the Global Ecosystem Dynamics Despite added information value from of ecological processes between ground-based Investigation (GEDI), the Ecosystem synergistic observations, the protocols and and spaceborne observations. Additional Spaceborne Thermal Radiometer Experiment measurement strategies for any one of these consideration for integration with airborne on Space Station (ECOSTRESS), and the instruments do not currently consider the (high spatial resolution) and ISS (unique Orbiting Carbon Observatory 3 (OCO-3). other instruments. Thus, there is an argument temporal acquisition) observations is the All three are being developed for deployment and need for collaboration during mission use of other spaceborne observations (for to the ISS in 2018 and will distribute the free development to coordinate observation example, Sentinel series and Landsat), as data products listed in Table 1. The fourth strategies and maximize scientific returns these can provide additional information for instrument, also for deployment in 2018, is the Hysperspectral Imager Suite (HISUI) ECOSTRESS GEDI from JAXA1,2. Complementing HISUI is the German Aerospace Agency (DLR) EnMAP3, OCO-3 HISUI Land surface Height Volume for which the observational plan has already temperature Leaf area index been established, thus it is not the focus Emissivity Surface of the imaging spectroscopy discussion Surface reflectance Spectral Water-use eciency henceforth. These four instruments will absorption roughness make observations of three-dimensional Biomass Species structure (GEDI) that can be used to scale biochemical signals4–6 to the canopy level Solar-induced fluorescence Canopy Live vs dead (HISUI) and derive estimates of ecosystem Root depth functional composition, productivity (solar-induced traits Canopy water fluorescence from OCO-3), and water-use Atmospheric Carbon sink content efficiency (a product of ECOSTRESS) at column CO2 potential landscape scales. This instrument suite offers Nutrients a unique opportunity because the drifting Disturbance ISS platform and pointing capabilities of Carbon ecology Evapo- some of the instruments enable co-location residence transpiration time of high-spatial-resolution