Retrieval of red solar-induced Chlorophyll fluorescence with TROPOMI on the Sentinel-5 precursor mission

Authors: ZHAO, FENG - Beihang University; MA, WEIWEI - Beihang University; KOHLER, PHILLIP - California Institute Of Technology; MA, XINXIN - Beihang University; SUN, HAOCHEN - Beihang University; VERHOEF, WOUT - University Of Twente; ZHAO, JUN - Beihang University; Huang, Yanbo; LI, ZHENJIANG - Beihang University; RATUL, ADIB - Beihang University

Submitted to: IEEE Transactions on Geoscience and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2022
Publication Date: 3/28/2022
Citation: Zhao, F., Ma, W., Kohler, P., Ma, X., Sun, H., Verhoef, W., Zhao, J., Huang, Y., Li, Z., Ratul, A.K. 2022. Retrieval of red solar-induced Chlorophyll fluorescence with TROPOMI on the Sentinel-5 precursor mission. IEEE Transactions on Geoscience and Remote Sensing. 60:1-13. https://doi.org/10.1109/TGRS.2022.3162726.
DOI: https://doi.org/10.1109/TGRS.2022.3162726

Interpretive Summary: Remotely sensing plant leaf chlorophyll fluorescence signals induced by sun light has been investigated as an innovative approach to relating to plant photosynthesis status. The scientists of Beihang University, California Institute of Technology, University of Twente and USDA ARS collaboratively developed a new approach to extraction of the plant leaf chlorophyll fluorescence signals from the data obtained from the recently launched TROPOspheric Monitoring Instrument (TROPOMI) on board of Sentinel-5 satellite precursor. The extracted fluorescence signals are around the signal peak within the red spectral band at around 685 nm. The signal extraction was conducted over land and ocean and the results indicated that the distribution of extracted plant leaf chlorophyll fluorescence signals matches well with the NASA's corresponding product globally with the uncertainty around 10%. This is acceptable for the data to be used practically for ecological decision support.

Technical Abstract: Solar-Induced chlorophyll Fluorescence (SIF) is a signal emitted by chlorophyll molecules after the absorption of solar radiation. Because of the close relationship between SIF and the photosynthetic apparatus, remote observation of SIF could be used as an indicator of photosynthetic status. SIF retrieved from spaceborne measurements can provide a synoptic perspective of the surface targets. The recently launched TROPOspheric Monitoring Instrument (TROPOMI) on board of Sentinel-5 precursor provides dataset for the retrieval of SIF with an unprecedented resolution in spatial and temporal dimensions. In this study, we propose an approach for the retrieval of the red SIF peak value (at around 685 nm) over both the land and ocean from TROPOMI measurements. This approach makes use of the Fraunhofer lines located in the spectral window of 669 - 686 nm to disentangle SIF from the solar radiation reflected by the surface and atmosphere system. Through simulated TROPOMI-like datasets, we determine the proper parameter settings and demonstrate the feasibility of the approach for the red SIF retrieval from TROPOMI. The approach is then applied to real TROPOMI measurements. The red SIF retrieved with the proposed approach for two months’ TROPOMI data is compared with another TROPOMI red SIF dataset and marine nFLH (normalized fluorescence line height) product of Aqua MODIS (moderate resolution imaging spectroradiometer). They display similar spatial distributions over both the land and ocean for the weekly global composites. Especially the comparison of the two red SIF datasets demonstrates overall good agreement, indicating consistency of the two retrievals. The retrieval uncertainty for the weekly global composite is about 13% and 10% of the peak SIF value over the land/ocean, respectively, which can be considered as a desirable error threshold for global composites of SIF.