# Harmonizing Multi-Source Remote Sensing Images for Summer Corn Growth Monitoring
## 3 Results and Analysis
### Summer Corn Growth Monitoring Results Using Harmonized Time-Deries Images  
The harmonized time-series remote sensing images are the very ideal data source for summer corn growth monitoring because the growth difference can be reflected on the spectral variation and difference. In this study, we monitored the summer corn growth condition and changing using \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Model** & **R\({}^{2}\)** & **RMSE** & **_p-Value_** \\ \hline \multirow{2}{*}{DOY 178} & ESTARFM model & 0.55 & 0.09 & \textless{}0.01 \\  & Improved Kalman filter & 0.65 & 0.08 & \textless{}0.01 \\  & ESTARFM model & 0.82 & 0.08 & \textless{}0.01 \\  & Improved Kalman filter & 0.84 & 0.07 & \textless{}0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Accuracy assessment results using two image harmonizing methods. Figure 8: Spatial-temporal fusion results and predicted residuals of DOY 227: (**a**) the GF-1 image (R\(\backslash\)G\(\backslash\)B=Band 3\(\backslash\)2\(\backslash\)1); (**b**) the harmonized NDVI image by the improved Kalman filter; (**c**) the original GF-1 NDVI images; (**d**) the harmonized NDVI using ESTARFM model; (**e**) the \(\Delta PR_{K}\) of the Figure 8b,c; (**f**) the probability density distribution of \(\Delta PR_{K}\) in Figure 8e; (**g**) the \(\Delta PR_{K}\) of the Figure 8d,c; (**h**) the probability density distribution of \(\Delta PR_{K}\) in Figure 8g; (**f**) and (**h**) the X-axis is the \(\Delta PR_{K}\) value and the Y-axis represents the probability density of each \(\Delta PR_{K}\) value. time-series NDVIs from harmonized images. Moreover, the MODIS ET and LE products (MOD16) and meteorological data (rainfall, temperature in the corn growing season) were combined to analyse the summer corn growth behavior, in other words, how the summer corn growth status (i.e. NDVI) change with the change of rainfall, temperature and evapotranspiration. The time-series NDVI changing curve from DOY 156 to DOY 252 is used to analysis the summer corn growing and changing in study area. In addition, the changing slope and difference between neighboring NDVIs are calculated and used to quantize the summer corn growing and changing. The changing slope and difference of NDVI curve are calculated as follows:  
\[\text{Slop}_{DOY(k)}=\frac{\text{NDVI}_{\text{DOY}(k+1)}-\text{NDVI}_{\text{ DOY}(k-1)}}{\text{DOY}(k+1)-\text{DOY}(k-1)} \tag{14}\]  
\[\text{Difference}_{DOY(k)}=\text{NDVI}_{\text{DOY}(k+1)}-\text{NDVI}_{\text {DOY}(k-1)} \tag{15}\]  
Figure 9 is changing curve of time-series NDVI from harmonized remote sensing images over the summer corn fields. In addition, the simultaneous rainfall and daily temperature change curves from DOY 156 to DOY 252 are compared and analyzed synchronously. In study area, an interplanting system of winter wheat and summer corn was implemented in the study area to ensure two crops each year. From DOY 156 to DOY 174, the winter wheat was in the mature stage, while the summer corn was in the seeding and emergence stage. On DOY 156, the average rainfall was 1.4 mm, and the ET reaches 6.5 mm/8 day and LE reaches 2 \(\times\) 10\({}^{6}\) J/m\({}^{2}\)/day. From DOY 156 to DOY 174, the temperature increased continually, of which the average highest temperature during the day reached 29.8 \({}^{\circ}\)C, with an average temperature of 23.4 \({}^{\circ}\)C. The winter wheat began to turn yellow and dry, so the NDVI decreased and the slope value was therefore less than 0. From DOY 174 to DOY 195, the summer corn is in the jointing stage. During this period, the average rainfall was 2.8 mm. The rainfall on DOY 164 and DOY 196 was 0.08 mm and 1.17 mm, respectively. So the ET and LE increased continually. The temperature continued to increase, and the average highest temperature during the day reached 32.6 \({}^{\circ}\)C, with an average temperature of 26.5 \({}^{\circ}\)C. At this time, the climatic condition is favorable for the rapid growth of corn leaves.