Correcting Clear‐Sky Bias in Gross Primary Production Modeling From Satellite Solar‐Induced Chlorophyll Fluorescence Data,Journal of Geophysical Research: Biogeosciences

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Correcting Clear‐Sky Bias in Gross Primary Production Modeling From Satellite Solar‐Induced Chlorophyll Fluorescence Data
Journal of Geophysical Research: Biogeosciences ( IF 3.7 ) Pub Date : 2020-09-09 , DOI: 10.1029/2020jg005822
Zhaoying Zhang _{1,

2,

3} , Yongguang Zhang _{1,

4} , Yao Zhang _{5,

6} , Jing M. Chen ₃

Affiliation

Satellite solar‐induced chlorophyll fluorescence (SIF) has been demonstrated the potential to monitor photosynthesis, quantified as gross primary production (GPP), for large areas. However, satellite SIF retrievals are only reliable for clear‐sky conditions, creating overestimation in estimating GPP for all‐sky conditions, called clear‐sky bias. Clouds can reduce the total radiation and increase the diffuse radiation, which can have counteracting effects on photosynthesis since plants are more efficient in using diffuse radiation. To mitigate this uncertainty in estimating global GPP from satellite SIF, we propose a clear‐sky bias correction approach that considers both the increase in light use efficiency (LUE) and the decrease in photosynthetically active radiation (PAR) under cloudy conditions. An enhancement factor (α) of LUE under cloudy conditions is first parameterized from FLUXNET data set, which is found to converge to 1.21 among all vegetation types. Then, a correction factor of clear‐sky bias is developed to account for the variations of LUE under cloudy conditions, which is used to estimate global terrestrial GPP in 2019 with spaceborne SIF retrievals from TROPOspheric Monitoring Instrument (TROPOMI). We estimate global annual terrestrial GPP of 135.47 ± 3.36 and 142.03 ± 3.53 PgC/year, respectively, with and without correcting clear‐sky bias. This approach is also able to identify regions with large uncertainties in GPP estimation from satellite SIF data due to the effects of clear‐sky bias, such as eastern America, western Europe, and southern China. Our results highlight the importance of considering clear‐sky bias in estimating terrestrial photosynthesis from satellite SIF data.

更新日期：2020-09-16

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