## 2 Materials and Methods
### Data Sources and Preprocessing  
In this study, the time series of satellite remote sensing data used were mainly the Level-I SAR data from S-1A in 2022 and the Level-1 C product data from S-2A. The S1 satellite is the first environmental satellite in the Copernicus global monitoring program. S-1 is a constellation of two polar-orbiting satellites, A and B, which are part of the European Space Agency (ESA, Paris, France)'s Copernicus Earth observation satellite series. S-1A and S-1B were launched on 3 April 2014 and 25 April 2016, respectively. The orbital period of an individual satellite is 12 days. The standard revisit period of the two-satellite network is 6 days, with the fastest revisit time being between 1 and 3 days. The satellites are equipped with a 5.404 GHz C-band SAR with a maximum coverage width of 400 km, featuring four imaging modes: SM (Strip Map), IW (Interferometric Wide Swath), EW (Extra-Wide Swath), and WV (Wave). The SM, IW, and EW modes support single polarization (HH/VV) as well as dual polarization (HH + HV/VV + VH). The WV mode, on the other hand, represents single polarization, i.e., it supports HH/VV only. This study employed the IW GRD ground distance multi-view imagery, with a width of 250 km and a ground resolution of 5 m by 20 m (Table 2). The S-2 satellite is the second satellite belonging to the Global Environment and Safety Monitoring program. Launched on 23 June 2015, it carries a multispectral imager (MSI) at an altitude of 786 km, covering 13 spectral bands over a width of 290 km. The ground resolutions are 10 m, 20 m, and 60 m, respectively. Each satellite is revisited every 10 days. Both satellites are complementary and revisit during the same week. A large number of studies have reported that the growth stage period is effective in identifying fruit trees; it is a longer period rather than a point in time, which can be categorized into the branch growth, bud differentiation and anthesis, fruit growth and ripening, and harvest periods [2]. Hence, specific screening stages are required for the growth stage period. During the critical growth stage period of fruit trees, frequent cloud \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Satellite** & **Resolution** & **Work Pattern** & **Flight Direction** & **Polarization Scheme** \\ \hline Sentinel-1A (GRD) & 10 m & Interferometric & & & & & & \\   Sentinel-2A (Level-IC) & 10 m & / & Ascending & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Sentinel-1 and Sentinel-2 data parameters. \begin{table}
\begin{tabular}{c|c|c|c|c|c|c|c|c|c|c|c} \hline \hline
**Jan.** & **Feb.** & **Mar.** & **Apr.** & **May** & **Jun.** & **Jul.** & **Aug.** & **Sep.** & **Oct.** & **Nov.** & **Dec.** \\ \hline Litchi & & & & & & & & & & & & \\ \hline Citrus & & & & & & & & & & & & \\ \hline Longan & & & & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The growth periods of litchi, citrus, and longan in the study area. cover limits access to clear-sky observations and visible light data. However, microwave data are less affected by cloudy and rainy weather, providing coverage throughout the entire growth stage period. For the 2018 and 2022, 68 images (Table 3) were downloaded from the European Space Agency (ESA, Paris, France) Copernicus Open Access Hub based on the temporal coverage of the available S-1 SAR imagery and S-2 optical multispectral imagery. These two years data were used to map the spatial distribution of fruit trees. The processing of the satellite data was largely based on the SNAP 9.0.0 (European Space Agency, Paris, France) platform developed by the ESA.