# Investigating the Performance of Red and Far-Red SIF for Monitoring GPP of Alpine Meadow Ecosystems  
[PERSON]  
1 College of Geomatics, Xi'an University of Science and Technology, Xi'an 710054, China; [EMAIL_ADDRESS] (W.D. ); [EMAIL_ADDRESS] (X.J. )1  
[PERSON]  
2 Key Laboratory of Digital Earth Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China; [EMAIL_ADDRESS] (J.C.); [EMAIL_ADDRESS] (S.D. ); [EMAIL_ADDRESS] (L.L. )23 International Research Center of Big Data for Sustainable Development Goals, Beijing 100094, China 3  
[PERSON]  
2 Key Laboratory of Digital Earth Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China; [EMAIL_ADDRESS] (J.C.); [EMAIL_ADDRESS] (S.D. ); [EMAIL_ADDRESS] (L.L. )2  
[PERSON]  
2 Key Laboratory of Digital Earth Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China; [EMAIL_ADDRESS] (J.C.); [EMAIL_ADDRESS] (S.D. ); [EMAIL_ADDRESS] (L.L. )2  
[PERSON]  
2 Key Laboratory of Digital Earth Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China; [EMAIL_ADDRESS] (J.C.); [EMAIL_ADDRESS] (S.D. ); [EMAIL_ADDRESS] (L.L. )23 International Research Center of Big Data for Sustainable Development Goals, Beijing 100094, China 3  
[PERSON]  
1 College of Geomatics, Xi'an University of Science and Technology, Xi'an 710054, China; [EMAIL_ADDRESS] (W.D. ); [EMAIL_ADDRESS] (X.J. )1  
here are severely influenced by latitude, topography, and atmospheric circulation, making the growing environment of alpine meadows extremely harsh [3]. Previous studies have demonstrated the vulnerability of alpine ecosystems to major changes in climate [3; 5; 6; 7], which inevitably leads to changes in carbon fluxes in this ecosystem [4]. Gross primary productivity (GPP) is the sum of total organic carbon fixation through photosynthesis within the vegetation under natural light conditions, which is an important indicator of carbon fluxes [8; 9; 10]. Accurate estimations of the GPP of ecosystems is important for understanding the state of the ecosystem response to environmental variations and changes in carbon balance [11; 12]. Throughout recent decades, an increasing number of researchers have become accustomed to utilizing solar-induced chlorophyll fluorescence (SIF) as a promising approach on monitoring GPP [11; 13; 14]. SIF is an emission spectrum showing two emitting peaks in the red and far-red bands, which is a by-product of the photosynthesis process [11; 15; 16; 17]. Thereby, SIF is directly related to photosynthesis and could be treated as an indicator of GPP [15; 18; 19; 20; 21]. Most current studies on the association of SIF and GPP have focused on cropland, forest, grassland, and wetland ecosystems, and SIF-based GPP monitoring has demonstrated a strong ability to track changes in all of these ecosystems. Canopy far-red SIF (SIF\({}_{\text{Far-red}}\)) follows likeness seasonal and diurnal pattern of variation to GPP, which have been observed in crops [14; 22; 23; 24; 25], forests [26; 27; 28], and coastal salt marsh ecosystems [29]. In crop ecosystems such as wheat, maize, rice, and soybean, many studies have found that SIF\({}_{\text{Far-red}}\) showed an obvious linear relationship with GPP [24; 25; 30; 31], but this linear relationship is highly variable depending on the type of crop photosynthetic pathway [24]. Additionally, studies on grassland ecosystems based on the GOME-2 terrestrial chlorophyll fluorescence data product and FLUXNET GPP data have shown good linear relationships between SIF\({}_{\text{Far-red}}\) and GPP in multi-year data on monthly time scales but also variations in the correlations between SIF\({}_{\text{Far-red}}\) and GPP due to differences in the types of photosynthetic pathways of grasslands [32; 33].