Technical Development
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New Methods to Measure Photosynthesis from Space

Reducing uncertainties in the carbon budget of the terrestrial biosphere will require new methods for estimating the overall rate of ecosystem carbon uptake. In August 2012, the KISS workshop on "New Methods to Measure Photosynthesis from Space" convened international scientists to discuss the use of Solar Induced Fluorescence (SIF) emitted from plants because SIF is a novel measure of photosynthetic activity and can be measured globally from space.

Figure 1 Global fluorescence retrievals from the GOSAT satellite.

While SIF has been measured from space using GOSAT and other platforms such as GOME-2, many important issues remain poorly quantified mostly with respect to leaf-canopy scaling, influences of environmental conditions, stresses (water, temperature, nutrients), radiative transfer and the relation of SIF to GPP across plant functional types. Field measurements using the new retrieval paradigm would greatly help to bring us to the next level but mature, robust and field-deployable instruments that enable SIF measurements based on the Fraunhofer line principle are so far lacking.

In essence, with fluorescence we have been given the keys to a Ferrari but now need to obtain the appropriate drivers license to exploit the full potential. This technology project has two primary objectives

  1. Develop a set of robust and accurate field-deployable SIF spectrometer systems, with the spectral resolution and signal-to-noise ratios to enable Fraunhofer line bases SIF retrievals.
    (year 1)
  2. Deploy the spectrometers for both long-term monitoring (entire growing season) and short-term field campaigns in different environments, followed by data analysis and publications in peer reviewed literature
    (year 2)

This investigation builds greatly on our foundational work since the KISS workshop and will provide the first step towards a robust SIF monitoring network. Only ground-based stations can achieve continuous data records that can be compared against CO2 flux measurements. We will perform both long-term measurements at selected flux-tower sites as well as intensive field campaigns in crucial biomes (agricultural test facilities, tropical rainforest) to fully characterize the relationship of photosynthesis and SIF across different biomes, canopy structures and environmental conditions.

For questions contact: Paul Wennberg, Christian Frankenberg, Joseph Berry or Michele Judd


Photosynthesis

Image credit: Pat Rawlings/
Keck Institute for Space Studies.