Abstract
In the last decade, significant progress has been made in estimating Solar-Induced chlorophyll Fluorescence (SIF) by passive remote sensing techniques that exploit the oxygen absorption spectral regions. Although the O2–B and the deep O2–A absorption bands present a high sensitivity to detect SIF, these regions are also largely influenced by atmospheric effects. Therefore, an accurate Atmospheric Correction (AC) process is required to measure SIF from oxygen bands. In this regard, the suitability of a two-step approach, i.e., first an AC and second a Spectral Fitting technique to disentangle SIF from reflected light, has been evaluated. One of the advantages of the two-step approach resides in the derived intermediate products provided prior to SIF estimation, such as surface apparent reflectance. Results suggest that errors introduced in the AC, e.g., related to the characterization of aerosol optical properties, are propagated into systematic residual errors in the apparent reflectance. However, of interest is that these errors can be easily detected in the oxygen bands thanks to the high spectral resolution required to measure SIF. To illustrate this, the predictive power of the apparent reflectance spectra to detect and correct inaccuracies in the aerosols characterization is assessed by using a simulated database with SCOPE and MODTRAN radiative transfer models. In 75% of cases, the aerosol optical thickness, the Angstrom coefficient and the scattering asymmetry factor are corrected with a relative error below of 0.5%, 8% and 3%, respectively. To conclude with, and in view of future SIF monitoring satellite missions such as FLEX, the analysis of the apparent reflectance can entail a valuable quality indicator to detect and correct errors in the AC prior to the SIF estimation.
Highlights
Remote sensing measurement of Solar-Induced chlorophyll Fluorescence (SIF) provides a new optical mean to track plant photosynthesis and gross primary productivity (GPP) of terrestrial ecosystems [1]
Two-step approaches have been used in the past to estimate SIF from airborne data [39,40], and a two-step strategy has been proposed in the context of the forthcoming Fluorescence Explorer (FLEX)/Sentinel-3 tandem mission [17,22]
In the particular case of the O2 –B and O2 –A bands, these are conveniently located in the SIF spectrum, i.e., close to each of the typical SIF emission peaks, being wider and deeper than the solar lines and more sensitive for SIF detection
Summary
Remote sensing measurement of Solar-Induced chlorophyll Fluorescence (SIF) provides a new optical mean to track plant photosynthesis and gross primary productivity (GPP) of terrestrial ecosystems [1]. Some SIF retrieval strategies exploit the Fraunhofer solar lines, which are generally weak and narrow but not as influenced by atmospheric effects as the oxygen bands [2,4,5,6,7,8]. First SIF maps were retrieved by the exploitation of the Fraunhofer lines from atmospheric chemistry satellite missions (e.g., [2,4,5,6,7,8,20]) Since these missions were not designed for vegetation monitoring, SIF was detected with a coarse spatial resolution e.g., ∼10 km for GOSAT-2 and 2.25 km for OCO-2. The paper is structured as follows: Section 2 introduces and assesses the impact of the mathematical assumptions considered in the FLEX AI, as well the steps to couple SF fluorescence retrieval with inverted Top-of-Canopy (TOC) apparent reflectance.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
