Improving the accuracy of SIF quantified from moderate spectral resolution airborne hyperspectral imager using SCOPE: assessment with sub-nanometer imagery

• SIF 760 quantified at 1 nm FWHM from standard 5.8 nm hyperspectral imagery using SCOPE. • Validation carried out with sub-nanometer hyperspectral imagery (≤0.2 nm FWHM) • Strong agreement between estimated and reference airborne SIF 760. • TOC SIF simulations carried out with plant traits retrieved from narrow-band reflectance imagery. • SIF 760 from standard resolution hyperspectral imagers can be scaled via RT modelling. Hyperspectral imaging of solar-induced chlorophyll fluorescence (SIF) is required for plant phenotyping and stress detection. However, the most accurate instruments for SIF quantification, such as sub-nanometer (≤1-nm full-width at half-maximum, FWHM) airborne hyperspectral imagers, are expensive and uncommon. Previous studies have demonstrated that standard narrow-band hyperspectral imagers (i.e., 4–6-nm FWHM) are more cost-effective and can provide far-red SIF quantified at 760 nm (SIF 760 ), which correlates strongly with precise sub-nanometer resolution measurements. Nevertheless, narrow-band SIF 760 quantifications are subject to systematic overestimation owing to the influence of the spectral resolution (SR). In this study, we propose a modelling approach based on the Soil Canopy Observation, Photochemistry and Energy Fluxes (SCOPE) model with the objective of enhancing the accuracy of absolute SIF 760 levels derived from standard airborne hyperspectral imagers in practical settings. The performance of the proposed method was evaluated using airborne imagery acquired from two airborne hyperspectral imagers (FWHM ≤ 0.2-nm and 5.8-nm) flown in tandem on board an aircraft that collected data from two different wheat and maize phenotyping trials. Leaf biophysical and biochemical traits were first estimated from airborne narrow-band reflectance imagery and subsequently used as SCOPE model inputs to simulate a range of top-of-canopy (TOC) radiance and SIF spectra at 1-nm FWHM. The SCOPE simulated radiance spectra were then convolved to match the spectral configuration of the narrow-band imager to compute the 5.8-nm FWHM SIF 760 . A site-specific model was constructed by employing the convolved 5.8-nm SR SIF 760 as the independent variable and the 1-nm SR SIF 760 directly simulated by SCOPE as the dependent variable. When applied to the airborne dataset, the estimated SIF 760 at 1-nm SR from the standard narrow-band hyperspectral imager matched the reference sub-nanometer quantified SIF 760 with root mean square error (RMSE) less than 0.5 mW/m 2 /nm/sr, yielding R 2 = 0.93–0.95 from the two experiments. These results suggest that the proposed modelling approach enables the interpretation of SIF 760 quantified using standard hyperspectral imagers of 4–6 nm FWHM for stress detection and plant physiological condition assessment.