## 2 Materials and Methods
### Field-Measured CIs  
To validate the two versions of CI retrievals, we compiled a series of field-measured CI data (Figure 1) from various land cover types. First, 48 representative field-measured CIs (Table 1) were collected to validate the monthly MODIS CIs retrieved from the two product versions. These field-measured CIs were refined from the database of [PERSON] et al. (2016), who compiled a series of references ([PERSON] et al., 2017; [PERSON] et al., 2018; [PERSON] et al., 2018). These field CI data were measured by the tracing radiation and ar  
Figure 1: Distribution of collected field CI measurements for all IGBP classes at the global scale. The dots indicate 48 field-measured sites labeled with IDs listed in Table 1. The stars denote sites with seasonal profiles of field-measured CIs labeled with names in Table 2.  
chitecture of canopies (TRAC) instrument along transects of tens to hundreds of meters [25; 49; 77], which are usually considered to be the relatively appropriate data for comparisons with satellite-derived CIs [26]. A spatial representativeness evaluation using the variogram model based on high-resolution ETM+ images [78] was conducted for the compiled database, and 48 CI field measurements were ultimately selected (Table 1) and used to evaluate the MODIS CIs in this study. The field-measured CIs from these 48 sites are spatially representative of the MODIS CIs at a 500-m spatial resolution. Then, 7 sites with seasonal profiles of field-measured CIs (Table 2) were collected to validate the seasonal variation in the two versions of CI data. Two main sources of these field-measured sites are [PERSON] et al. [47] and Fang [79]. The Tonzi site is located in California, USA, with rainfall that is typically concentrated between October and May. This site is classified as oak savanna woodland, with scattered blue oak trees (_Quercus douglasii_) in the overstory and grasses and herbs in the understory [80]. The Radiation transfer Model Intercomparison (RAMI) pine site is located in Jarveslja, Estonia, with poor growth conditions. The dominant tree species is Scots pine (_Pinus sylvestris_), with herbs and moss in the understory [81]. The TP39 and TP74 sites are located in Norfolk, Ontario, Canada, and are dominated by white pine (_Pinus strobus_ L.), which were planted in 1939 and 1974. TP39 trees were thinned in 1983, which caused lower tree density and more understory vegetation species in this stand [82]. The Yatir site is located at the edge of the Negev and Judean deserts, Israel, with rainfall events usually occurring between November and March. The dominant tree species of this site is Aleppo pine (_Pinus halepensis_ Mill. ), and the forest consists of individual canopies for limited available water [83]. In the understory, sparse vegetation usually develops during the rainy season and disappears shortly thereafter [84]. The Honghe and Hailun sites are located in Heilongjiang Province, China [85]. The Honghe site is covered with paddy rice (_Oryza sativa_ L.) at Honghe farm, and the rice is usually transplanted in late May, with flowering in early July, grain filling in early August, and maturation in early September [86]. The Hailun site is planted with maize (_Zea mays_ L.), soybean (_Glycine max_ L.), and sorghum (Sorghum bicolor). Maize is usually planted in early May, with tasseling in late July, grouting in late August, and maturation in late September. Sorghum and soybean have similar growth patterns to maize, while the maturity stage of soybean normally occurs in early September [87]. The TRAC was used to measure field CIs along transects [77] at the TP39, TP74, and Yatir sites, while digital hemispherical photographs (DHP) taken by fisheye lens were used to retrieve field CIs at the Honghe [86], Hailun [87; 88], and RAMI pine [89; 90] sites. The upward-pointing digital images [91; 92] were used to estimate field CIs at the Tonzi site.