# 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
Therefore, the NDVI increased rapidly and the slope values and differences are all greater than 0. From DOY 196 to DOY 227, the summer corn is in the heading stage. During this period, the average rainfall is 2.3 mm and the temperature continued to be in a higher range. The average highest temperature during the day reached 31.9 \({}^{\circ}\)C, with an average temperature of 26.0 \({}^{\circ}\)C. The water content in the vegetation increased, and the ET increase its maximum level from 16.1 to 24.9 mm/8 day and LE increase from 4.9 to 7.6 \(\times\) 10\({}^{6}\) J/m\({}^{2}\)/day, then they gradually decreased. Especially, there was an obvious rainfall and warming process on the DOY 198 to DOY 200 where the rainfall reached 28 mm and the average temperature increased by 5 \({}^{\circ}\)C. Likewise, the ET and LE increased rapidly from DOY 193 to DOY 201. It shows that the MOD16 product has high accuracy, which could reflect the changes of ET and LE on a regional scale, but also shows that the ET and LE are closely related to precipitation and temperature. The NDVI reached the maximum in the whole growing stage. The slope value and the difference were all greater than 0. However, it could be seen from the diagram that the NDVI gradient from DOY191-194 to DOY 194-195 NDVI is negative, indicating a small decrease in NDVI. The reason for this variation may be that the time difference between the three images is very small, and the influence of errors is therefore larger. We concluded that this stage was the key stage of high growth rate of summer maize. The LAI measured on the ground showed that the average LAI value increased from 2.5 (DOY 205, flare opening stage) to 3.4 m\({}^{2}\)/m\({}^{2}\) (DOY 224, tasseling and anthesis silking). From DOY 227 to DOY 246, the summer corn is in the milking stage, and it needs a larger leaf area for photosynthesis to transform the organic matter into corn grain. The photosynthesis of corn leaves depends on the adequate availability of suitable light, heat, and water. During this period, the precipitation in the study area reached the peak value, which averaged 6.8 mm, and the ET and LE are still at a higher stage but they are gradually decreasing. At the same time, the average highest temperature reached during the day was 29.4 \({}^{\circ}\)C, with an average temperature of 23.5 \({}^{\circ}\)C, and the day and night temperature difference was greater than 10 \({}^{\circ}\)C. These factors are beneficial to photosynthesis and the transformation of organic matter; therefore, the leaf area of the corn remained in a larger range. On the DOY 241, a continuous rainfall process can be seen, but at this point the temperature decreased. Then, the ET is increased by 1 mm/8 day and LE is increased by \(2\times 10^{5}\) J/m\({}^{2}\)/day. From DOY 246 to DOY 279, the summer corn was in the ripening stage. During this growing stage, the dry matter accumulation process of summer corn almost stopped, and the dry weight of the grains reached their maximum. Precipitation began to decline, the average precipitation dropped to 1.2 mm, the vegetation began to lose water, and the ET and LE also descended. The temperature and evaporation rates were reduced, and the average highest temperature during the day reached 23.7 \({}^{\circ}\)C, with an average temperature of 17.9 \({}^{\circ}\)C. The corn leaves began to turn yellow, leaf area decreased, and NDVI began to decline rapidly. The slope and differences were all below 0. From this time-series diagram, we can see that the summer corn grows quickly with the quick increasing NDVI at early growing stage, stable in the middle growing stage and decreases in the late growing stage. Moreover, the NDVI, ET and LE all increase after the rainfall in the early growing stage. Generally, this delay would be four to five days.