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Completing the jigsaw

By on 5 December, 2018

NASA’s ECOSTRESS mission will use environmental data collected by TERN’s nation-wide network of ecosystem observing sites, including TERN’s OzFlux station in the NT’s Sturt Plains (photo courtesy of Lindsay Hutley).

The sophisticated remote Australian data collection infrastructure helping to calibrate and validate heavyweight satellite-derived data products. This article was written by Mark Grant of TERN, and first appeared in issue 96 of Position magazine.

As the saying goes, ‘the quality of a decision is only as good as the information used to make it’. 

So, when it comes to collecting environmental observation data for management, modelling and ecological forecasting – one should never underestimate the importance of good quality data.

Terrestrial Ecosystem Research Network (TERN), Australia’s terrestrial ecosystem observatory, provides the Australian and international earth observation communities with the high quality, on-the-ground data required to properly calibrate and validate their observations and predictions.

Data from TERN’s ecosystem field observatory, including plot data on soil and vegetation; gas, energy, and water exchange data; remote sensing data; and modelled data products about soil, climate, and landscape attributes, are being used on the international stage by Europe’s, America’s and India’s space agencies to improve the accuracy of global biogeophysical satellite products.

Here are four of the ways in which TERN’s ecosystem observation data are being used to ensure the accuracy of some of the most important environmental prediction tools:

1. More accurate climate variables from space

Fernando Camacho is CEO at  The Earth Observation Laboratory (EOLAB). “Basically, validation aims to answer one simple question,” he said, “How good (accurate, precise, stable) is an earth observation dataset?”

Camacho is working with the Committee on Earth Observation Satellites (CEOS) to identify a global set of on-ground monitoring sites that can be used by space agencies, including the ESA and NASA, to validate their bio-geophysical, satellite derived products.

“TERN’s ecosystem processes monitoring SuperSites meet all our criteria for suitable sites. They’re part of a long-term supported network, and the measurements are regular and highly appropriate for satellite validation,” he said.

Based on these factors, CEOS’s Land Product Validation (LPV) subgroup has selected TERN SuperSites in their first selection of 55 global supersites for the calibration and validation of satellite derived bio-geophysical products, such as LAI and FAPAR.

High-tech equipment on the OzFlux tower at TERN’s Alice Mulga SuperSite in the Northern Territory collects data on the exchanges of energy and water between the land and the atmosphere, which are used by NASA to validate their satellite collected measurements (photo courtesy of James Cleverly, TERN).

LAI (Leaf Area Index) and FAPAR (Fraction of Absorbed Photosynthetically Active Radiation) are biophysical variables that characterise vegetation cover and photosynthetic activity. Satellite based estimates of the variables are used in models to predict changes in primary productivity, plant growth and the absorption of carbon dioxide by vegetation.

On-the-ground data on LAI, soil moisture and phenology collected at TERN Ecosystem Processes SuperSites will be used by CEOS agencies in addition to micrometeorological observations of energy, carbon and water exchanges between the atmosphere and key Australian ecosystems collected by OzFlux towers at each site.

Terrestrial and airborne laser scanning (LIDAR) and hyperspectral data collected by TERN’s Landscape Assessment platform will also be used in the validation process.

“The availability of integrated, open-access data complete with documented calibration and validation protocols presented the ideal data package for our global validation work,” said Camacho.

Sites belonging to TERN’s global partner observatories including America’s National Ecological Observation Network (NEON) and Europe’s Integrated Carbon Observation System (ICOS) were also chosen by the CEOS LPV subgroup.

TERN’s Great Western Woodlands SuperSite, Credo Station, one of 12 TERN Ecosystem Processes monitoring SuperSites across the country selected for their ability to improve our understanding of how Australia’s ecosystems respond to environmental change (photo courtesy of Suzanne Prober, TERN).

2. A better understanding of water stress and water use by plants

A new collaboration has blasted off between NASA and TERN that’s set to dramatically improve global climate monitoring. NASA’s ECOSTRESS (Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station) mission to the International Space Station launched from Cape Canaveral at the end of June, providing critical climate data to scientists, helping them have a better understanding of how crops, the biosphere and the global carbon cycle respond to water availability and drought.

Dr. Joshua Fisher, Science Lead for the ECOSTRESS mission from NASA’s Jet Propulsion Laboratory (JPL), is thrilled to have access to data collected and made openly available by TERN.

“This is an exciting new data sharing collaboration between NASA and TERN, which will lead to a better understanding of water stress and water use by plants from different biomes, and the implications for agricultural and natural ecosystems,” Dr. Fisher said.

“ECOSTRESS will do this by measuring plant temperatures in various locations at different times of day, in a number of locations, using a multispectral thermal infrared radiometer on the International Space Station.”

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The temperature images of Earth’s surface from ECOSTRESS will be the most detailed ever acquired from space and will make it possible to measure the temperature of individual farm paddocks.

Meanwhile, in Australia, TERN will be collecting key southern hemisphere data at sites in a wide range of major Australian biomes, such as Tasmania’s eucalypt forests and Western Australia’s woodlands, which will then be used by NASA to verify the validity of data collected from the mission.

Specifically, NASA will use data on the exchanges (fluxes) of carbon, energy and water between the land and the atmosphere collected by TERN’s nation-wide network of instrumented OzFlux towers. TERN is also supplying weather data on soil moisture data collected from the sites.

NASA’s collaboration with TERN on the ECOSTRESS mission follows the success of TERN’s role in NASA’s soil moisture active passive (SMAP) mission to map global carbon.

3. High resolution 3D models of the world’s forests

When it launched later this year, NASA’s Global Ecosystem Dynamics Investigation (GEDI) will be the first space-borne laser instrument to measure the structure of Earth’s tropical and temperate forests in high resolution and three dimensions.  Data from GEDI will be used to measure and monitor change to the world’s vegetation and its impact on carbon storages and biodiversity.

This giant leap for ecosystem science wouldn’t be possible without some equally high-tech, but more down-to-Earth, data collection. To validate the space-borne LIDAR data collected by GEDI, similar ground and airborne-based LIDAR data is required.

Dr. John Armston of the GEDI Science Definition Team at the University of Maryland has been working with the University of Queensland Joint Remote Sensing Research Program (JRSRP) to collect airborne (ALS) and terrestrial laser scanning (TLS) data around Australia including selected TERN SuperSites for calibration and validation of GEDI algorithms and data products.

“So far we’ve collected and made available TLS and biomass plot data from eight TERN SuperSites,” said Dr. Armston.  “Together with the ALS data, the plot level data we’re collecting across a wide range of major Australian biomes, such as Queensland’s dry eucalpyt forests or Tasmania’s temperate wet forests, play an important role in making sure that GEDI’s southern hemisphere data are valid and accurate.”

“There are very few sites in the southern hemisphere where airborne and ground-based scans have been collected together with traditional inventory data across a range of biomes, so the TERN sites fill an important information gap for NASA.”

Data from TERN’s nation-wide network of flux monitoring sites, including from TERN’s Dry River OzFlux station near Katherine in the Northern Territory (above), are being used by NASA to calibrate and validate their global Earth observation products (photo courtesy of Jason Beringer, TERN).

4. Detailed information on the Earth’s most complex processes

Unlike GEDI, which uses light to monitor the Earth, the NASA-ISRO Synthetic Aperture Radar (NISAR) space-borne instrument will use radar sensors working in microwave wavelengths to observe and take measurements of some of the planet’s most complex processes, such as changes of vegetation biomass at the seasonal to annual cycles, ecosystem disturbances, ice-sheet collapses, and earthquakes.

Despite their differences in approach; underlying technology and required processing, GEDI and NISAR have one important thing in common, they both require on-the-ground data for validating the accuracy of their outputs.

Dr. Sassan Saatchi of NASA, who is organising the NISAR mission ecosystem science products on forest biomass jointly with the Indian Space Research Organisation (ISRO), is working with Australian-based researchers, including John, to collect the required data at TERN sites around the nation.

“We’re planning on colleting airborne laser scanning [ALS] data at a number of TERN SuperSites and at TERN’s smaller one-hectare ecosystem surveillance monitoring sites,” said Dr. Saatchi.  “We need data across a variety of biomes, so the large number and excellent distribution of TERN sites makes this possible.”

“Even though NISAR doesn’t launch until 2021 at the earliest, the ALS data we collect at the TERN sites are vital for pre-launch preparation activities within the next year.”

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