## 3 Results
### Model Development and Validation
#### 3.1.3 Spatiotemporal Patterns of TSIF  
Figure 9 shows that TSIF captures well the _SIF_ signal in TROPOSIF observations, but provides more detailed information. TSIF shows the expected spatial and temporal variations. In January (the coldest month of winter, Figure 9a,b), because the area within MODIS tile grid H27V05 is dry and cold, the photosynthetic activity of all plants is limited, so both TSIF and TROPOSIF are very small. From February (the last month of winter, Figure 9c,d) to April (spring, Figure 9e-h), because the temperature gradually increases and vegetation show stronger and stronger photosynthetic activity, both TSIF and TROPOSIF increase gradually. During this period, the hotspot is observed in cropland located in the center of the images in the Sinusoidal coordinate reference system, and the hotspot spreads from the center to the upper left of the images (corresponding from the center to the north in the WGS84 coordinate reference system). Meanwhile, other plants such as DBF, SAV, and CNV show increasingly stronger photosynthetic activity. The right upper part of the images, corresponding to the Korean Peninsula in the WGS84 coordinate reference system, shows relatively small _SIF_ due to low temperatures. In May (spring) and June (summer), the DBF located at the bottom left of the images (Figure 9i-l) shows the strongest photosynthetic activity with the highest _SIF_ observed. During this period, most crops enter the mature and harvest stages. In July (summer, Figure 9m,n), when crops have been sown and enter the growing stage again, both DBF and croplands display active photosynthesis with the highest SIF. In fact, July is the month when almost all plants show the strongest photosynthesis due to high temperatures and sufficient precipitation. From August, photosynthesis starts to decrease for most plants, they show smaller _SIF_ compared to July, while croplands still show a hotspot from the upper left to the bottom right of the images (Figure 9o,p). In September (autumn), crops enter the mature stage again, showing lower _SIF_ compared to August. In October (autumn), crops enter their harvest stage and all plants show relatively low _SIF_ due to low temperatures. In November (autumn) and December (winter), all plants show low _SIF_ due to dry and cold weather, with the highest _SIF_ observed in cropland again.  
Figure 8: The boxplots of R\({}^{2}\) difference from different NN models with the numbers of layers changing from 1 to 4 and the numbers of neurons of the hidden layers changing from 8 to 64 (the absolute value of the training R\({}^{2}\) minus the validation R\({}^{2}\)). Each boxplot contains the R\({}^{2}\) difference specific to one date.  
As shown in Figure 10, we select several 3 \(\times\) 3 grids from TROPOSIF and the corresponding 60 \(\times\) 60 grids from TSIF and MCD12Q1 land cover classification for further analysis. Figure 10a,d,g show TROPOSIF data are too coarse to capture any details, but TSIF is able to show more details. For example, in Figure 10b, TSIF can distinguish OSH from ENF to some extent, in Figure 10h, TSIF can distinguish SAV from CNV clearly. In general, the downscaled TSIF can provide more details which will benefit many applications.