# Crop Water Content of Winter Wheat Revealed with Sentinel-1 and Sentinel-2 Imagery
## 2 Materials and Methods
### Sentinel-1/2 Imagery  
The Sentinel-1A and -1B satellites are a European polar orbit C-band radar imaging system. The revisit period for one-satellite constellation is twelve days and the two-satellite constellation revisit period is six days. The optimal image resolution is \(5\times 5\) m and the maximum width is 400 km. The revisit period for each Sentinel-2 satellite is ten days and the Sentinel-2A and -2B two-satellite revisit period is five days. The main payload of the Sentinel-2 satellites is a MSI instrument with 13 bands and a spectral range between 0.4 and 2.4 \(\mathrm{\SIUnitSymbolMicro m}\). The width is 290 km and the spatial resolutions are 10 m (four bands), 20 m (six bands), and 60 m (three bands). The Sentinel-1 satellite images were acquired on 25 May 2017 and the Sentinel-2 satellite images were acquired on 28 May 2017 from the ESA website ([[https://scihub.copernicus.eu/](https://scihub.copernicus.eu/)]([https://scihub.copernicus.eu/](https://scihub.copernicus.eu/))). The Sentinel-1 satellite images were ground range detected products of the interference wide swath mode and included two polarization modes (VH, VV) (Table 1).  
The Sentinel-1 images were pre-processed, as follows: orbit calibration, thermal noise removal, radiation calibration, speckle noise removal, and geocoding. Pre-processing was conducted using the ESA's SNAP software ([[http://step.esa.int/main/download/](http://step.esa.int/main/download/)]([http://step.esa.int/main/download/](http://step.esa.int/main/download/))). From the Sentinel-2 satellites, we acquired level-1C image products (top of atmosphere reflectance in fixed cartographic geometry combined UTM projection and WGS84 ellipsoid). Level-1C images are a set of tiles each with an area of 100 km\({}^{2}\). Pre-processing of the Level-1C Sentinel-2 images included radiometric calibration and atmospheric correction. The L2A data processing plug-in Sen2 cor released by ESA to pre-process the images ([[http://step.esa.int/main/third-party-plugings-2/sen2](http://step.esa.int/main/third-party-plugings-2/sen2) cor/]([http://step.esa.int/main/third-party-plugings-2/sen2](http://step.esa.int/main/third-party-plugings-2/sen2) cor/)) was used in this study.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{6}{c}{**Sentinel-1 Imagery**} \\ \hline Date & \begin{tabular}{c} Acquisition \\ Time (UTC) \\ \end{tabular} & Imaging Mode & \begin{tabular}{c} Frequency \\ (GHZ) \\ \end{tabular} & \begin{tabular}{c} Spatial \\ Resolution (m) \\ \end{tabular} & \
\begin{tabular}{c} IncidenceAngle \\ (\({}^{\circ}\)) \\ \end{tabular} &
25 May 2017 & 10:20:58 & VH, VV & 5.045 & \(5\times 20\) & 42.45 & Ascending \\ \hline \multicolumn{6}{c}{**Sentinel-2 Imagery**} \\ \hline Date & \begin{tabular}{c} Acquisition \\ Time (UTC) \\ \end{tabular} & \begin{tabular}{c} Spatial \\ Resolution (m) \\ \end{tabular} & \
\begin{tabular}{c} Orbit \\ Direction \\ \end{tabular} &
\begin{tabular}{c} Spectrum \\ range (um) \\ \end{tabular} & Width (km) & FOV (\({}^{\circ}\)) \\ \hline
28 May 2017 & 03:16:29 & 10–60 & Descending & 0.4–2.4 & 290 & 20.6 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Sentinel-1 and Sentinel-2 data used in this study.