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Abstract:
It is important to understand how sun‐sensor geometry affects satellite sun‐induced fluorescence (SIF) in order to take full advantage of these measurements, particularly given their close relationship with gross primary production (GPP). A recent paper by Li et al. (2018) (hereafter L2018) presented results on the relationship between Orbiting Carbon Observatory‐2 (OCO‐2) SIF and GPP from 64 flux sites. Similar to Sun et al. (2017), this study suggested a nearly universal linear relationship between SIF and GPP across biomes although higher slopes were found for C4 plants. Their results differ from previous studies suggesting that slopes vary with biome (Guanter et al., 2012; Zhang et al., 2016). We argue that the nearly universal relationship discussed by L2018 may be complicated by the fact that three observation modes from the OCO‐2 instrument with different geometries.
