Direct quantification of solar-induced chlorophyll fluorescence by solar-blind optical radiometry

Remote sensing of solar-induced chlorophyll fluorescence (SIF) can provide non-invasive in-situ insight into plant physiology in real-time. Ground-based SIF measurements have advanced our understanding of ecosystem behavior and biosphere-atmosphere interactions and offer new approaches to crop and ecosystem monitoring. However, current SIF measurement techniques rely on cumbersome instrumentation and excessively complex signal retrieval algorithms. This fundamentally limits the scalability of SIF measurements, and thus their widespread application in research and agriculture.We present a novel approach for proximal SIF remote sensing, in which SIF is measured directly, without the need for post-processing of the signal: The solar-blind optical radiometer for the quantification of SIF (SBR-SIF) measures the light intensity in a narrow spectral window (ca. 10 picometres width) inside a strong oxygen absorption line of the O2A-band. In this spectral window, SIF is the only natural light source, because all sunlight is absorbed by atmospheric oxygen before reaching the surface. SBR-SIF uses a Fabry-Pérot interferometer to achieve the required high spectral resolution and contrast in a compact and robust instrument [1].Proof-of-concept measurements with a first SBR-SIF prototype under real-world conditions demonstrate the feasibility of accurate, scalable, and real-time SIF quantification. [1] Kuhn, J., Bobrowski, N., Wagner, T., and Platt, U.: Mobile and high-spectral-resolution Fabry–Pérot interferometer spectrographs for atmospheric remote sensing, Atmos. Meas. Tech., 14, 7873–7892, https://doi.org/10.5194/amt-14-7873-2021, 2021.