Concurrent observation of CO2 fluxes, hyperspectral reflectance, and solar-induced fluorescence for improved understanding of rice photosynthesis: progress and challenges
Will P Richardson, University of Arkansas, wprichar@uark.edu (Presenter)
Kaiyu Guan, University of Illinois, kaiyug@illinois.edu
Michele L Reba, USDA-ARS, Delta Water Management Unit, michele.reba@usda.gov
Benjamin Runkle, University of Arkansas, Dept of Biological & Agricultural Engineering, brrunkle@uark.edu
Information on carbon input via photosynthesis is important for understanding a number of processes in rice ecosystems including crop development and response to stress as well as methane production and emission. Eddy covariance (EC) observations of CO2 fluxes provide the best current estimates of ecosystem photosynthesis (i.e., Gross Primary Production, or GPP) but are still subject to some uncertainties. Near-surface remote sensing of hyperspectral reflectance and solar-induced chlorophyll fluorescence (SIF) provide unique information on canopy structure and function, which can be combined with EC GPP to overcome some of its uncertainties.
In this work, we present an ongoing campaign to make hyperspectral reflectance and SIF observations at AmeriFlux site US-HRC, a commercial rice production field in the U.S. Mid-South region. We show the key details of our instrument system including protection from the ambient environment, radiometric calibration methodology, as well as measurement and processing techniques. Additionally, we present results from tests of the system over grass, as it is not yet robust enough for long-term deployment at US-HRC. During these tests, common vegetation indices such as NDVI remained within plausible ranges of values, indicating stable performance of the spectrometer which measures hyperspectral reflectance. While the instrument system remained thermally stable, ambient humidity caused significant interferences with SIF observations. Furthermore, the method we used for radiometric calibration induced additional uncertainties in the spectra used to retrieve SIF. We discuss a number of possible modifications to the system to increase its robustness including changing the internal temperature of the SIF spectrometer, using an integrating sphere for radiometric calibration, and exploring different fiber optic attachments for measuring incoming radiation. We plan to deploy our instrument system during the 2024 growing season to examine the impacts of various stresses (e.g., high air temperature and vapor pressure deficit, soil moisture deficits) on SIF, hyperspectral reflectance, and GPP.
Associated Project(s):
Poster Location ID: 40
Presentation Type: Poster
Session: Poster Session 1
Session Date: Wednesday (9/27) 1:15 PM