## 4 Results  
### Reconstructed Time Series of the Three VIs  
Noise and oscillations remained in the original time series of NDVI, EVI, and GCVI, which prevented them from illustrating the general and real growing trend of different crops over a full year. An appropriate reconstruction approach could rebuild a daily time series while removing noise and filling missing values to reveal the general trends of different crops and identify the differences among them. Figure 4 shows examples of the reconstruction results of the three VIs for seven typical crops or crop rotations that were summarized in Section 2 during a full year throughout the entire study region. Generally, they all achieved good reconstructed results in terms of R\({}^{2}\) (as shown in Table 3). For crop rotations of spring corn to vegetables and winter wheat to corn (Figure 4a,f), the reconstructed results exactly depicted the phenological characteristics of the two crops and exhibited a stable development trend in the NDVI, EVI, and GCVI time series. The group of peach trees, forest, and vineyards (Figure 4b,c,e) all had unimodal development curves in the three VIs because there was no rotation or changes in the middle year. By contrast, they had different rising/decline rates and smoothness of peaks because of their unique features, such as flowering and deciduous times, planting structure and density, and plant morphology. Greenhouse had relatively complex development curves for all three VIs' reconstructed results over a full year (Figure 4d), and the reasons can roughly be summarized in three categories: (i) the insulation materials that covered the outside of the greenhouse were different; (ii) numerous types of crops were planted in the greenhouse, and each crop had a different canopy reflectance; (iii) the greenhouse opposed the faster and unfixed phenological phase because it provided a superior temperature and humidity environment. The developing curve of vegetables planted on normal cropland generally had three peaks because vegetable farmers in our study region typically grow three seasons of vegetables, and the three reconstructed time series successfully characterized this feature (Figure 4g). Generally, the iterated S-G reconstruction approach produced the projected daily time series data of the three VIs for all planting conditions except the greenhouse, but the substandard reconstructed results of the greenhouse only demonstrated that its reconstruction was subject to the aforementioned factors rather than the unsuitableness of the reconstruction approach.  
From the view of the overall development trend of the reconstructed time series of the seven planting conditions (Figure 4), it was possible to distinguish the vineyard from crop rotations of winter wheat to corn and spring corn to vegetables, greenhouse, and vegetables according to the number of growing peaks during the entire year; the vineyard had only growing peak, but the other four plantingconditions had more than one. Although peach trees, forest, and the vineyard all had only one growing peak during the entire year, some differences still existed in the reconstructed time series of the VIs. For example, the vineyard developed slower than peach trees and forest during March and April in the NDVI case, and in the EVI case, the vineyard had the flattest development trend, and its values were lower than peach trees and forest after June. Both the development trend and the variations of the VIs values over the entire year made it possible to distinguish the vineyard from peach trees and forest.  
Figure 4: Example of the vegetation indices’ (VIs) time series reconstruction results for (**a**) spring corn-vegetables, (**b**) peach trees, (**c**) forest, (**d**) greenhouse, (**e**) vineyard, (**f**) winter wheat-corn, and (**g**) vegetables.