Fig. 1. Overview of the study area

Fig. 2. Location distribution of apple tree samples in Luochuan County

Fig. 3. NDVI reference curve of fruit tree samples in Luochuan County

Fig. 4. Function fitting diagram of NDVI time series reconstruction based on reference curve

Fig. 5. Results of flowering monitoring by remote sensing in Yan'an City

Fig. 6. Proportion of initial flowering period in Yan 'an City

Fig. 7. Flower monitoring results by remote sensing in Luochuan， Xunyi， Liquan and Chengcheng counties

Fig. 8. Results of 2021 flower monitoring by remote sensing in Loess Plateau

Fig. 9. Regression equation

Fig. 10. Spatial distribution of flowering monitoring results and Sentinel data RGB display