## 3 Results  
### Yield Estimation Basing on VIs  
In general, the accuracy of rice yield estimation models increases with a greater number of key growth stages involving in models, but introducing too many growth stages in models will not only make models more complex, but also weaken the interannual robustness of models [38]. Considering that rice spectral information at early growth stages is more easily affected by environmental factors such as water surface and soil background, it is better to estimate rice yield from the booting stage when rice leaves have basically covered the background [42]. Therefore, in this present study, the booting stage and the following three critical growth stages, i.e., the heading, filling, and ripening stages, were tested for yield estimation. The band locations for all selected VIs were shown in Table 3.  
As seen, band 1 from all types of vegetation indexes occurred in the red-edge region from 733 nm and 752 nm, but NIR bands were different at different growth stages. For NDVI and RVI at the booting stage, the NIR band was 768 nm; for NDVI at the ripening \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sensitive Bands** & **Booting** & **Heading** & **Filling** & **Ripening** \\ \hline \hline \multirow{2}{*}{NDVI} & band 1 & 740 & 733 & 752 & 748 \\  & band 2 & 768 & 832 & 880 & 792 \\ \multirow{2}{*}{Correlation coefficient} & band 1 & 740 & 748 & 752 & 748 \\  & band 2 & 768 & 832 & 880 & 792 \\ \multirow{2}{*}{Correlation coefficient} & 0.871 & 0.872 & 0.824 & 0.662 \\  & band 1 & 748 & 748 & 752 & 748 \\ \multirow{2}{*}{DVI} & band 2 & 800 & 840 & 864 & 816 \\ \multirow{2}{*}{Correlation coefficient} & 0.817 & 0.867 & 0.804 & 0.681 \\ \hline \hline \end{tabular} Note: band 1 is red and band 2 is NIR.  
\end{table} 
Table 3: Band locations of vegetation indices best suitable for yield estimation. stage, the NIR band was 792 nm. The NIR bands of the best vegetation indices at other growth stages were located between 800 nm and 880 nm. Correlation Analysis between Florescence Ratio Reflectance, Florescence Difference Reflectance and Rice Yield  
Taking the data of the P01 plot in 2019 as an example, the florescence difference reflectance and florescence ratio reflectance showed different spectral characteristics, but their variation trends were consistent (Figure 3). Most reflectance of florescence difference reflectance were positive, with the variation ranging from \(-0.05\) to \(0.15\). The maximum value appeared near 850 nm, and the minimum value occurred near 680 nm. The reflectance of florescence ratio reflectance fluctuated around 1, with most of them greater than 1. The maximum and minimum values appeared around 800 nm and 680 nm, respectively. Figure 3: (**a**) Time series florescence difference reflectance and florescence ratio reflectance (from 1 st day to 11 th day) (**b**) florescence difference reflectance and florescence ratio reflectance at the 7 th day of the flowering stage. It could be seen that the variation characteristics of the correlation coefficient curved between the florescence ratio reflectance, florescence difference reflectance and yield in the whole flowering stage were basically similar (Figure 4), with the peaks and troughs of the daily correlation coefficient curve highly coincident. The performance of florescence ratio reflectance was better than that of florescence difference reflectance. From the beginning of the flowering stage to the end of the flowering stage, the correlation coefficients increased at first and then decreased, and the best correlationship occurred around the seventh day of the flowering stage, at which showed the biggest correlation coefficient and stable band location. At the early flowering stage, the sensitive bands were mainly concentrated around yellow and red bands of 635 nm and 650 nm, and gradually extended to the red edge spectral region till the full flowering stage, and then completely moved to the near-infrared bands of 830-880 nm at the late stage of flowering.