Estimation of crop gross primary production (GPP): fAPAR_chl versus MOD15A2 FPAR

Authors

Qingyuan Zhang, NASA, Greenbelt, MDFollow
Yen-Ben Cheng, NASA, Greenbelt, MD
A. I. Lyapustin, NASA Goddard Space Flight Center
Yujie Wang, NASA, Greenbelt, MD
Feng Gao, USDA-ARS, Beltsville, MDFollow
Andrew E. Suyker, University of Nebraska-LincolnFollow
Shashi B. Verma, University of Nebraska-LincolnFollow
Elizabeth M. Middleton, NASAFollow

Date of this Version

2014

Citation

Remote Sensing of Environment 153 (2014) 1–6; doi: 10.1016/j.rse.2014.07.012

Comments

This article is a U.S. government work, and is not subject to copyright in the United States.

Abstract

Photosynthesis (PSN) is a pigment level process in which antenna pigments (predominately chlorophylls) in chloroplasts absorb photosynthetically active radiation (PAR) for the photochemical process. PAR absorbed by foliar non-photosynthetic components is not used for PSN. The fraction of PAR absorbed (fAPAR) by a canopy/vegetation (i.e., fAPAR_canopy) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) images, referred to as MOD15A2 FPAR, has been used to compute absorbed PAR (APAR) for PSN (APAR_PSN) which is utilized to produce the standard MODIS gross primary production (GPP) product, referred to as MOD17A2 GPP. In this study, the fraction of PAR absorbed by chlorophyll throughout the canopy (fAPAR_chl) was retrieved from MODIS images for three AmeriFlux crop fields in Nebraska. There are few studies in the literature that compare the performance of MOD15A2 FPAR versus fAPAR_chlin GPP estimation. In our studyMOD15A2 FPAR and the retrieved fAPAR_chlwere compared with field fAPAR_canopyand the fraction of PAR absorbed by green leaves of the vegetation (fAPAR_green). MOD15A2 FPAR overestimated field fAPAR_canopyin spring and in fall, and underestimated field fAPAR_canopyin midsummer whereas fAPAR_chlcorrectly captured the seasonal phenology. The retrieved fAPAR_chlagreed well with field fAPAR_greenat early crop growth stage in June, and was less than field fAPAR_greenin late July, August and September. GPP estimates with fAPAR_chland with MOD15A2 FPAR were compared to tower flux GPP. GPP simulated with fAPAR^chl was corroboratedwith tower flux GPP. Improvements in crop GPP estimation were achieved by replacing MOD15A2 FPAR with fAPAR_chlwhich also reduced uncertainties of crop GPP estimates by 1.12–2.37 g C m⁻² d⁻¹.