Comparing the Retrieval of Chlorophyll Fluorescence from Two Airborne Hyperspectral Imagers with Different Spectral Resolutions for Plant Phenotyping Studies

Abstract

Several studies have demonstrated the influence of the spectral resolution (SR) on the retrieval of solar-induced chlorophyll fluorescence (SIF) from ground-based sensors with different spectral configurations. However, research studying the implications of the SR of airborne hyperspectral imagers on the retrieved SIF is lacking, and its interpretation is critical for precision agriculture, plant stress detection and phenotyping studies. This work investigates the effects of SR on SIF performance through the Fraunhofer Line Depth (FLD) principle at the O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -A absorption feature (760.4 nm) using two airborne hyperspectral imagers with different spectral characteristics. A sub-nanometer hyperspectral imager with 0.1-0.2 nm full-width at half-maximum (FWHM) resolution and a broader-band hyperspectral imager of 5.8 nm FWHM were flown in tandem. The campaigns were conducted over a winter wheat field with randomized experimental design, with plots receiving different nitrogen rates to ensure SIF variability. Results showed a bias on the SIF levels quantified by both airborne imagers <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\text{RMSE} =3.7$</tex> mW/m <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> /nm/sr), but a strong relationship between both sensors at the O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -A absorption feature ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{R}^{2}=0.84,\ \mathrm{p} &lt; 0.001$</tex> ). Results confirm the utility of hyperspectral imagers ca. 5 nm FWHM resolution for stress detection and plant phenotyping where assessing the relative variability of SIF across experimental plots is sought.