Simplified Physically Based Retrieval of Sun-Induced Chlorophyll Fluorescence From GOSAT Data

First global retrievals of sun-induced chlorophyll fluorescence (F₈) have been achieved in the last years by using data from the Fourier transform spectrometer (FTS) onboard the Japanese Greenhouse Gases Observing Satellite (GOSAT). The high spectral resolution (approximately 0.025 nm) of the FTS enables measurements of F₈ by the evaluation of the in-filling of solar Fraunhofer lines around 755 nm. This study presents a new F₈ retrieval algorithm (GARLiC, for GOSAT retrieval of chlorophyll fluorescence) and compares its results to F₈ from two previously implemented approaches. GARLiC is intended to simplify some of the assumptions of existing retrieval approaches without a loss in retrieval accuracy. We show that GARLiC F₈ retrievals are comparable to the previously used methods. We also assess the effect of clouds on F₈ retrieval from GOSAT data through the analysis of the effect of different cloud filter thresholds on F₈ time series. Our results show a low sensitivity of Fraunhofer-line-based F₈ retrievals to cloud contamination.