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