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Published October 25, 2013 | Published
Journal Article Open

Global monitoring of terrestrial chlorophyll fluorescence from moderate spectral resolution near-infrared satellite measurements: methodology, simulations, and application to GOME-2

Abstract

Globally mapped terrestrial chlorophyll fluorescence retrievals are of high interest because they can provide information on the functional status of vegetation including light-use efficiency and global primary productivity that can be used for global carbon cycle modeling and agricultural applications. Previous satellite retrievals of fluorescence have relied solely upon the filling-in of solar Fraunhofer lines that are not significantly affected by atmospheric absorption. Although these measurements provide near-global coverage on a monthly basis, they suffer from relatively low precision and sparse spatial sampling. Here, we describe a new methodology to retrieve global far-red fluorescence information; we use hyperspectral data with a simplified radiative transfer model to disentangle the spectral signatures of three basic components: atmospheric absorption, surface reflectance, and fluorescence radiance. An empirically based principal component analysis approach is employed, primarily using cloudy data over ocean, to model and solve for the atmospheric absorption. Through detailed simulations, we demonstrate the feasibility of the approach and show that moderate-spectral-resolution measurements with a relatively high signal-to-noise ratio can be used to retrieve far-red fluorescence information with good precision and accuracy. The method is then applied to data from the Global Ozone Monitoring Instrument 2 (GOME-2). The GOME-2 fluorescence retrievals display similar spatial structure as compared with those from a simpler technique applied to the Greenhouse gases Observing SATellite (GOSAT). GOME-2 enables global mapping of far-red fluorescence with higher precision over smaller spatial and temporal scales than is possible with GOSAT. Near-global coverage is provided within a few days. We are able to show clearly for the first time physically plausible variations in fluorescence over the course of a single month at a spatial resolution of 0.5° × 0.5°. We also show some significant differences between fluorescence and coincident normalized difference vegetation indices (NDVI) retrievals.

Additional Information

© Author(s) 2013. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 23 Mar 2013 – Published in Atmos. Meas. Tech. Discuss.: 22 Apr 2013 - Revised: 15 Aug 2013 – Accepted: 04 Sep 2013 – Published: 25 Oct 2013. Funding for this work was provided by the NASA Carbon Cycle Science program (NNH10DA001N) managed by Diane E. Wickland and Richard Eckman and by the Emmy Noether Programme (GlobFluo project) of the German Research Foundation. The authors are indebted to Phil Durbin and his team for assistance with the satellite data sets, particularly the GOME-2 data. We gratefully acknowledge the European Meteorological Satellite (EUMetSat) program, the GOSAT project, and the MODIS data processing team for making available the GOME-2, GOSAT, and MODIS data, respectively, used here. We also thank William Cook, Yen-Ben Cheng, Qingyuan Zhang, Jianping Mao, Rose Munro, Rüdiger Lang, Petya Campbell, Lawrence Corp, Wouter Verhoef, and Arlindo da Silva for helpful discussions, and Piet Stammes and an anonymous reviewer for comments that helped to improve the manuscript. This work was enabled by collaborations forged at the fluorescence workshop held at the California Institute of Technology Keck Institute for Space Studies, funded by the W. M. Keck Foundation. We gratefully acknowledge the organizers of this workshop including Joseph Berry, Paul Wennberg, and Michele Judd.

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August 19, 2023
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