Oxygen transmittance correction for solar-induced chlorophyll fluorescence measured on proximal sensing: application to the NASA-GSFC fusion tower

Since oxygen (O₂) absorption of light becomes more pronounced at higher pressure levels, even a few meters distance between the target and the sensor can strongly affect canopyleaving Solar-Induced chlorophyll Fluorescence (SIF) retrievals. This study was conducted to quantify the consequent error propagation and the impact of ignoring oxygen absorption effects on proximal sensing SIF measurements based on the O₂-A absorption band with field-acquired and simulated data. It was demonstrated that the uncorrected oxygen transmittance between target and sensor distance of 10 m can lead to SIF relative errors ranging from 66% to higher than 100% when using a Spectral Fitting (SF) technique or the 3FLD retrieval method, respectively. A proposed strategy to include oxygen transmittance effects on the well-known 3FLD and SF techniques is presented here and applied to the NASA-GSFC multi-angular spectral system known as FUSION over a field of corn plants (Zea mays L.) during the second half of the 2014 growing season. Daily averages of oxygen-corrected SIF measurements from FUSION were related to daily averages of heat and energy fluxes obtained from a nearby Eddy-Covariance (EC) flux tower, and showed a consistent behaviour with similar experiments performed at leaf level.