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ESA
     
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Retrieval of vegetation chlorophyll fluorescence from FLEX spaceborne measurements in the O2A and O2B absorption bands

Luis Guanter(1) and Jose Moreno(2)

(1) GFZ Potsdam, Telegrafenberg, A17, 14473, Potsdam, Germany
(2) University of Valencia, Dr. Moliner, 50, 46100, Valencia, Spain

Abstract

Solar-induced chlorophyll fluorescence (ChF) is a key variable to constrain dynamic vegetation models. A typical ChF emission spectrum covers roughly the 630-770 nm spectral range, and has an intensity of about 100 times less than the reflected solar radiation at the top-of-atmosphere (TOA) level. This low intensity interposes a scientific and technical challenge when the ChF signal is to be monitored from a space-borne sensor. The emitted ChF signal must then be decoupled from the radiation reflected by the surface and from the atmospheric effects at the same spectral range. ChF retrieval algorithms are usually based on the exploitation of atmospheric absorption features, where the emitted signal is enhanced with respect to the reflected radiation. The FLuorescence EXperiment (FLEX) mission concept presents a Fluorescence Imaging Spectrometer (FIS) as the main instrument. With the aim of ChF retrieval, it samples the O2-A and O2-B atmospheric absorption features at 0.1 nm intervals. The methodology developed for the ChF retrieval from FLEX/FIS-like data will be presented in this contribution. Such a methodology deals with the normalization of those environmental and instrumental factors with the largest potential impact on ChF retrieval. Radiative transfer simulations at high spectral resolution considering a range of atmospheric and scene parameters, as well as realistic instrument radiometric and spectral specifications, are used to generate a data base of FLEX/FIS-like images. This has been used in the development of the algorithm and in the derivation of approximate error figures for the retrieval of ChF from space. The performance, accuracy and limitations of the method will be discussed in the presentation.

 

Workshop presentation