B081-0010
Improvement of Light Use Efficiency Estimation by Accounting for Sunlit and Shadowed Foliage

Monday, 14 December 2020
Poster
Paige Tatum Williams1, David J Harding2, Randolph Hamilton Wynne3, Valerie A Thomas4, Jon Ranson2, Karl Huemmrich5, Petya K. E. Campbell6, Elizabeth Middleton7 and Philip Dabney8, (1)Virginia Polytechnic Institute and State University, Blacksburg, United States, (2)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (3)Virginia Tech, Blacksburg, VA, United States, (4)Virginia Polytechnic Institute and State University, Blacksburg, VA, United States, (5)University of Maryland Baltimore County, Baltimore, United States, (6)UMBC, Greenbelt, MD, United States, (7)NASA Goddard Space Flight Cen., Greenbelt, MD, United States, (8)NASA Goddard Space Flight Cent, Greenbelt, MD, United States
Abstract:
Gross Primary Productivity (GPP) is the amount of carbon fixed during photosynthesis by all producers in the ecosystem. GPP is dependent on light use efficiency (LUE), photosynthetically active radiation (PAR), and fraction of absorbed PAR (fPAR). To estimate light use efficiency (LUE), which can vary based on the exposure of leaves to photosynthetically active radiation (PAR), we calculated the photochemical reflectance index (PRI) using 531 nm and 570 nm wavelengths. Our team examined the sensitivity of forest canopy PRI to canopy shadows using airborne hyperspectral data acquired in eastern North Carolina. Our study area was the area adjacent to a flux tower in a loblolly pine stand. We compared LUE derived from the reflectance data acquired in the morning, midday, and afternoon to LUE calculated using the flux tower observations. We computed PRI by thresholding a 2 m panchromatic image produced by averaging wavelength bands from 525 nm to 600 nm. We show that PRI for the sunlit canopy is substantially lower than for the shadowed components at all times of day, leading to an overestimate of LUE when using whole-canopy reflectance. Implications for estimating GPP using PRI reflectance as a surrogate for LUE were examined by comparing to the flux tower derivation of GPP. The results from this study will help refine measurement requirements for a diurnal constellation concept, the Structure and Function of Ecosystems (SAFE) mission.
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