# A Random Forest-Based Precipitation Detection Algorithm for FY-3C/3D MWTS2 over Oceanic Regions
## 2 Data and Methods
### Visible and Infrared Spin Scan Radiometer (VISSR)  
The Fengyun-2 (FY-2) meteorological satellite is a first-generation geostationary meteorological satellite developed in China. It can acquire daylight-visible cloud maps, day-night infrared cloud maps, and water vapor distribution maps with a high frequency. The VISSR is a visible/near-infrared scanning radiometer mounted on FY-2 that consists of one visible-band channel (0.55-0.99 \(\upmu\)m) and four infrared bands (3.50-4.00 \(\upmu\)m, 6.30-7.60 \(\upmu\)m,  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{**Channel Index**} & \multicolumn{2}{c}{**Center Frequency (GHz)**} & \multicolumn{2}{c}{**Polarization**} & \multicolumn{2}{c}{**Main Purpose**} \\
**MTWS3** & **MWTS2** & **MTWS3** & **MWTS2** & **MTWS3** & **MWTS2** & **MTWS3** & **MWTS2** \\ \hline \hline
1 & & 23.80 & & QH & & Cloud and \\  & & & & & & Precipitation \\
2 & & 31.40 & & QH & & Precipitation \\
3 & 1 & 50.30 & 50.30 & QV & QH & Temperature & Temperature \\
4 & 2 & 51.76 & 51.76 & QV & QH & Temperature & Temperature \\
5 & 3 & 52.80 & 52.80 & QV & QH & Temperature & Temperature \\
6 & & 53.246 \(\pm\) 0.08 & & QV & Temperature & Temperature \\
7 & 4 & 53.596 \(\pm\) 0.115 & 53.596 & QV & QH & Temperature & Temperature \\
8 & & 53.948 \(\pm\) 0.081 & & QV & Temperature & Temperature \\
9 & 5 & 54.40 & 54.40 & QV & QH & Temperature & Temperature \\
10 & 6 & 54.94 & 54.94 & QV & QH & Temperature & Temperature \\
11 & 7 & 55.50 & 55.50 & QV & QH & Temperature & Temperature \\
12 & 8 & 57.20344 (fo) & 57.209344 (fo) & QV & QH & Temperature & Temperature \\
13 & 9 & fo \(\pm\) 0.217 & fo \(\pm\) 0.217 & QV & QH & Temperature & Temperature \\
14 & 10 & fo \(\pm\) 0.3222 \(\pm\) 0.048 & fo \(\pm\) 0.3222 \(\pm\) 0.048 & QV & QH & Temperature & Temperature \\
15 & 11 & fo \(\pm\) 0.3222 \(\pm\) 0.022 & fo \(\pm\) 0.3222 \10.3-11.3 \(\upmu\)m, and 11.5-12.5 \(\upmu\)m). The VISSR completes full-disk images consisting of \(2288\times 2288\) pixels every hour, with substellar point resolutions of 5 km (infrared) and 1.25 km (visible/near-infrared) [(18)]. FY-2F is the sixth satellite in the FY-2 series and was launched on 13 January 2012; it orbits over the equator at 112\({}^{\circ}\)E. The meteorological satellite and polar-orbiting meteorological satellite of FY-2 complement each other and constitute the application system of China's meteorological satellite.  
Based on the observational data provided by the VISSR, real-time cloud images and dozens of retrieval products, such as clear-sky atmospheric radiation, atmospheric motion vectors, and sand-dust images, can be obtained. The cloud data retrieved from the FY-2F VISSR and used in this paper are shown in Figure 2, including the relative humidity profile (HPF) for 300-1000 hPa, the cloud classification results (CLC, with a total of 7 types: clear-sky sea surfaces, hybrid cells, high-level clouds, circumulus clouds, dense stratus clouds, cumulonimbus clouds, and stratocumulus clouds), the water vapor content in the upper tropospheric humidity (UTH), and the cloud-top temperature (CTT).  
Figure 2: Distribution of the FY-2F VISSR cloud retrieval product at 00:00 on 1 January 2018. (**a–f**) Relative humidity values at various levels from 300–1000 hPa; (**g**) cloud classification products; (**h**) cloud-top temperature; and (**i**) relative humidity values in the middle and upper levels of the troposphere.  
The FY-2F VISSR product and the FY-3E MWTS3 and NOAA-19 AMSU-A observations used in the experiments are obtained from the National Satellite Meteorological Center: [[http://www.nsmc.org.cn/nsmc/cn/home/index.html](http://www.nsmc.org.cn/nsmc/cn/home/index.html)]([http://www.nsmc.org.cn/nsmc/cn/home/index.html](http://www.nsmc.org.cn/nsmc/cn/home/index.html)) (accessed on 14 April 2025).