Retrieval and global assessment of terrestrial chlorophyll fluorescence from GOSAT space measurements

• Published in: Remote sensing of environment Vol. 121; pp. 236 - 251
• Main Authors: Guanter, Luis, Frankenberg, Christian, Dudhia, Anu, Lewis, Philip E., Gómez-Dans, José, Kuze, Akihiko, Suto, Hiroshi, Grainger, Roy G.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.06.2012; Elsevier
• Subjects: Animal, plant and microbial ecology; Applied geophysics; Biological and medical sciences; Chlorophylls; Confidence intervals; Earth sciences; Earth, ocean, space; Exact sciences and technology; Feasibility; Fluorescence; Fluorescence retrieval; Fraunhofer lines; Fraunhofer-line approach; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; GOSAT-FTS; Gross primary production; Internal geophysics; Inversions; Retrieval; Singular vector decomposition; Spectral lines; Teledetection and vegetation maps; Vegetation indices; Gross primary production; GOSAT-FTS; Singular vector decomposition; Fluorescence retrieval; Vegetation indices; Fraunhofer-line approach; atmosphere; spectra; Fourier transformation; Inversion; decomposition; global; Modeling; greenhouse gas; platforms; evaluation; Field; fluorescence; Sciences; radiance; satellites; models; inverse problem; chlorophyll; carbon cycle; windows; Spectrometer; Sun; Singular vector; techniques; Alternative method
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2012.02.006

The recent advent of very high spectral resolution measurements by the Fourier Transform Spectrometer (FTS) on board the Greenhouse gases Observing SATellite (GOSAT) platform has made possible the retrieval of sun-induced terrestrial chlorophyll fluorescence (Fs) on a global scale. The basis for this retrieval is the modeling of the in-filling of solar Fraunhofer lines by fluorescence. This contribution to the field of space-based carbon cycle science presents an alternative method for the retrieval of Fs from the Fraunhofer lines resolved by GOSAT-FTS measurements. The method is based on a linear forward model derived by a singular vector decomposition technique, which enables a fast and robust inversion of top-of-atmosphere radiance spectra. Retrievals are performed in two spectral micro-windows (∼2–3nm width) containing several strong Fraunhofer lines. The statistical nature of this approach allows to avoid potential retrieval errors associated with the modeling of the instrument line shape or with a given extraterrestrial solar irradiance data set. The method has been tested on 22 consecutive months of global GOSAT-FTS measurements. The fundamental basis of this Fs retrieval approach and the results from the analysis of the global Fs data set produced with it are described in this work. Among other findings, the data analysis has shown (i) a very good comparison of Fs intensity levels and spatial patterns with the state-of-the-art physically-based Fs retrieval approach described in Frankenberg et al. (2011a), (ii) the overall good agreement between Fs annual and seasonal patterns and other space-based vegetation parameters, (iii) the need for a biome-dependent scaling from Fs to gross primary production, and (iv) the apparent existence of strong directional effects in the Fs emission from forest canopies. These results reinforce the confidence in the feasibility of Fs retrievals with GOSAT-FTS and open several points for future research in this emerging field. ► We present a method for the retrieval of chlorophyll fluorescence from GOSAT-FTS data. ► The potential of GOSAT-FTS data for global fluorescence retrievals is demonstrated. ► Results are highly consistent with other state-of-the-art retrieval methods. ► A biome-dependent linear relationship between fluorescence and GPP observed. ► Strong directional effects are apparent in the fluorescence emission.