A linear method for the retrieval of sun-induced chlorophyll fluorescence from GOME-2 and SCIAMACHY data

P Köhler,J Joiner,L Guanter

doi:10.5194/amt-8-2589-2015

Abstract

Abstract. Global retrievals of near-infrared sun-induced chlorophyll fluorescence (SIF) have been achieved in the last few years by means of a number of space-borne atmospheric spectrometers. Here, we present a new retrieval method for medium spectral resolution instruments such as the Global Ozone Monitoring Experiment-2 (GOME-2) and the SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY). Building upon the previous work by Guanter et al. (2013) and Joiner et al. (2013), our approach provides a solution for the selection of the number of free parameters. In particular, a backward elimination algorithm is applied to optimize the number of coefficients to fit, which reduces also the retrieval noise and selects the number of state vector elements automatically. A sensitivity analysis with simulated spectra has been utilized to evaluate the performance of our retrieval approach. The method has also been applied to estimate SIF at 740 nm from real spectra from GOME-2 and for the first time, from SCIAMACHY. We find a good correspondence of the absolute SIF values and the spatial patterns from the two sensors, which suggests the robustness of the proposed retrieval method. In addition, we compare our results to existing SIF data sets, examine uncertainties and use our GOME-2 retrievals to show empirically the relatively low sensitivity of the SIF retrieval to cloud contamination.

Highlights

During the process of photosynthesis, the chlorophyll-a of photosynthetically active vegetation emits a small fraction of its absorbed energy as an electromagnetic signal (e.g., Zarco-Tejada et al, 2003)
The presented sun-induced fluorescence (SIF) retrieval method has been used to produce a global SIF data set from Global Ozone Monitoring Experiment-2 (GOME-2) data covering the 2007–2011 time period
The SIF retrieval has been implemented for SCIAMACHY data for the August 2002–March 2012 time span

Summary

Introduction

During the process of photosynthesis, the chlorophyll-a of photosynthetically active vegetation emits a small fraction of its absorbed energy as an electromagnetic signal (e.g., Zarco-Tejada et al, 2003). The first global SIF observations have been achieved in the last 4 years by studies from Joiner et al (2011), Frankenberg et al (2011a) and Guanter et al (2012) using data from the Fourier transform spectrometer (FTS) on board the Japanese Greenhouse Gases Observing Satellite (GOSAT). Frankenberg et al (2011b) and Guanter et al (2012) used two micro fitting windows around 757 and 770 nm by means of a reference solar irradiance data set. The method proposed by Frankenberg et al (2011a) relies on the physical modeling of the in-filling of several solar Fraunhofer lines by SIF using the instrumental line shape function and a reference solar irradiance data set.

Methods

Results

Conclusion