## 3 Results
### Development of Florescence Difference Index (FDI) and Florescence Ratio Index (FRI)  
In this study, florescence ratio reflectance, florescence difference reflectance, first derivative florescence ratio reflectance and first derivative florescence difference reflectance from 500-900 nm of 62 bands constructed florescence spectral indices in three types of all two-band combinations, and the correlation between these indices and yield were as in Figure 6. The indices with high correlation coefficients were identified as the florescence spectral indices more suitable for yield estimation.  
In general, the first derivative florescence ratio reflectance and the first derivative florescence difference reflectance were better related to yield than the raw florescence ratio and difference reflectance. Additionally, the first derivative florescence ratio reflectance performed better than the first derivative florescence difference reflectance.  
For the first derivative florescence ratio reflectance, the types of band combinations with larger correlation coefficients were very diverse, including ratio, normalized and difference combinations: ratio combination of red-edge and red bands, ratio combination of red-edge and green bands, normalized combination of red-edge and red-edge bands, difference combination of NIR and red-edge bands. For the first derivative florescence difference reflectance, the larger correlation coefficients were obtained by normalized combinations, including the normalization combinations of NIR and red-edge bands, NIR and NIR bands, NIR and yellow bands, red and yellow bands, and yellow and yellow bands (Figure 7). Compared with the second part of the study, it was found that the denominators in the ratio combination of the first derivative ratio reflectance were always within the sensitive band range, but numerators were not. Most of the bands in the ratio combination and difference combination were within the range of sensitive bands. Additionally, the two bands in a normalization combination of the first derivative difference reflectance basically consisted of a highly sensitive band and a less sensitive (at least generally sensitive) band. The combination of a highly sensitive band and a less sensitive band, such as FRI3 and FRI4, gave the best results. On the basis of band combination analysis, five combinations of the ratio derivative reflectance and of the difference derivative reflectance highly correlated with yield were selected as the florescence difference index (FDI) and florescence ratio index (FRI) for yield estimation. (Table 4).  
Figure 5: Correlation between rice yield and the first derivative florescence difference reflectance (FDFDR), rice yield and the first derivative florescence ratio reflectance (FDFRR) at the 7 th day of flowering.  
Figure 6: Correlation analysis of sensitive bands in the florescence ratio reflectance (FRR), the florescence difference reflectance (FDR), the first derivative florescence ratio reflectance (FDFRR) and the first derivative difference reflectance (FDFDR).  
Figure 7: The combinations of high correlation florescence indices in the florescence ratio reflectance (FRR), the florescence difference reflectance (FDR), the first derivative florescence ratio reflectance (FDFRR) and the first derivative florescence difference reflectance (FDFDR).