Retrieval of Sun Induced Fluorescence Using Advanced Spectral Fitting Methods from Radiative Transfer Simulations and Hyplant Imagery

In the framework of the candidate EE-8 ESA/FLEX mission, different Solar-Induced Fluorescence (SIF) retrieval algorithms are under implementation and testing. The Spectral Fitting Method is the baseline for the fluorescence retrievals for FLEX, since it is a powerful technique to decouple canopy reflected radiance and SIF by exploiting the high-resolution observations in the red/far-red spectral regions. Two main approaches are investigated in this work: i) the SIF retrieval around the oxygen absorption bands (O2-A and O2-B); ii) the SpecFit algorithm to retrieve the full SIF emission spectrum in the 670-780 nm spectral range. The accuracy of the retrieval algorithms is assessed by employing radiative transfer simulations representing the FLEX/FLORIS radiances. The proposed algorithms are under testing on “real datasets” collected by the novel airborne HyPlant imaging spectrometer, which is well suited as airborne demonstrator of the FLEX mission. Currently, the results on radiative transfer simulations show that the relative root mean square error (RRMSE) of the fluorescence retrieval at the O2-A and O2-B bands is about 3%; the RRMSE for the full spectrum retrieval (integral of fluorescence emission) is around 7%. The preliminary map of fluorescence derived from HyPlant imagery over an agriculture area in Germany is presented. The accuracy of the fluorescence maps is assessed by comparison to groundbased measurements collected simultaneously to the airborne surveys.