Comparison of measurements and FluorMOD simulations for solar‐induced chlorophyll fluorescence and reflectance of a corn crop under nitrogen treatments

Abstract

Laboratory and field measurements previously acquired from foliage and canopies of corn (Zea mays L.) under controlled nitrogen (N) fertilization were used to parameterize and evaluate a new spectral vegetation Fluorescence Model (FluorMOD) developed to include the effects of steady‐state solar‐induced chlorophyll fluorescence (SIF) on canopy reflectance. These data included biophysical properties, fluorescence (F) and reflectance spectra for leaves; reflectance spectra of canopies and soil; solar irradiance; plot‐level leaf area index (LAI); and canopy SIF emissions determined using the Fraunhofer line‐depth (FLD) principle for the atmospheric telluric oxygen absorption features at 688 nm (O₂β) and 760 nm (O₂α). FluorMOD simulations implemented in the default mode did not reproduce the observed magnitudes of leaf F, canopy SIF, or canopy reflectance. However, simulations for all of these parameters agreed with observations when the default FluorMOD information was replaced with measurements, although N treatment responses were underestimated. The observed shift in the red/far‐red SIF ratio (from <1 to ∼2) that occurred in scaling from leaves to canopies, partially attributed to the paucity of abaxial leaf information incorporated in the model, was not expressed in the simulations. Recommendations were provided to enhance the potential utility of FluorMOD in support of SIF field experiments and studies of agriculture and ecosystems.

Acknowledgements

We thank Craig S. T. Daughtry, Andrew Russ and James E. McMurtrey (retired) of USDA, Milton Hom (SSAI) for ASD calibration, Maryn Butcher (formerly, SSAI) for assistance with measurements, and Diane Wickland (NASA HQ) for funding support.