## 2 Materials and Methods
### Materials  
The remote-sensing images used in this article are from PlanetScope satellites. PlanetScope small satellite constellation is the largest satellite constellation used for Earth observation in the world. The satellite consists of numerous Dove satellites equipped with remote-sensing observation equipment. The designed life expectancy of each satellite is about 3 years, which enables the satellite to be updated and replaced frequently. Currently, there are more than 170 satellites in orbit. Their products feature high temporal and spatial resolution and full coverage of the Earth. Specifically, the resolution of main image prod ucts acquired by the satellite sensor is about 3-4 m. The huge number of satellites and the extremely short revisit period enable it to cover any area of the world once a day [35; 36]. Specific parameters are shown in Table 1.  
In this study, the images obtained are 3B standard analytical products with 117 scenes in total. These images have been processed through atmospheric correction and ortho-rectification. They can be directly used for application and analysis. The number of images covered in the study area varies from 8 to 16 per month. The spatial resolution of the images is 3 m, and the bit depth is 16 bits. The information on the four spectral bands contained in the images is consistent with the parameter in Table 1. The time span of the whole dataset is from June 2021 to May 2022. PlanetScope's excellent temporal resolution enables the study  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter Name** & \multicolumn{2}{c}{**Parameter Information**} \\ \hline Image spectral range & Blue: 455–515 nm; Green: 500–590 nm; Red: 590–670 nm; NIR: 780–860 nm \\ Orbit name & International Space Station Orbit (ISS) & Solar Synchronous Orbit (SSO) \\ Orbit altitude & 400 km & 475 km \\ Orbit inclination & 51.6\({}^{\circ}\) & \(-\)98\({}^{\circ}\) \\ Latitude coverage & \(\pm\)52\({}^{\circ}\) (Season-related) & \(\pm\)81.5\({}^{\circ}\) (Season-related) \\ Image resolution & 3.0 m & 3.5–4.0 m \\ Image width & 20 km & 24.6 km \\ \hline \hline \end{tabular}
\end{table}
Table 1: PlanetScope satellite parameter information.  
Figure 1: Schematic diagram of the study area, Shangyu district, Shaoxing City, Zhejiang Province, China (the digital orthophoto map is processed on 10 adjacent images obtained by PlanetScope satellite on 17 May 2022).  
to select data with less cloud from more data and avoid the operation of cloud, fog, and aerosol removal. According to the statistical analysis of the preprocessed image, only the image in June has a relatively high cloud content, covering an area of 4.52% (56.43 square kilometers) of the study area, but most of them are thin clouds that account for 89%. In other months, the images in October 2021 and March 2022 contain clouds but only account for 0.04% and 0.03% of the study area, which has little impact on the time series NDVI study. Except for the images of the above months, the cloud cover of the images of all other months is 0. Such kind of data is conducive to land-cover classification.  
In addition, vector data of administrative divisions at the regional level need to be obtained as auxiliary data for subsequent data preprocessing, image masking, and other operations. Some ground samples in the study area were selected for field investigation and image shooting as auxiliary data. It is important to select validation data to test various precision indexes of LUCC accuracy.