# Retrieval of Cloud Ice Water Path from FY-3F MWTS and MWHS
## 2 Satellite Data and ERA5 Data  
### Satellite Data  
FY-3F satellite was successfully launched in August 2023 and is carrying onboard MWTS-III and MWHS-II. FY-3F is the seventh satellite in the Fengyun-3 series and the third satellite in the sun-synchronous dawn-dusk orbit [12]. As a dawn-orbit satellite, FY-3F has taken over the in-orbit operational mission of FY-3C, enhancing Earth system observation capabilities while continuing to conduct global imaging and vertical atmospheric sounding. The MWTS-III used in this study, compared to its predecessor, the Microwave Temperature Sounder -II (MWTS-II), includes two additional window channels with center frequencies of 23.8 GHz and 31.4 GHz, providing horizontal resolutions of 75 km and 65 km, respectively. These channels can detect precipitation, surface emissivity, liquid water, and water vapor [13]. MWTS-III is a total power radiometer with a scanning range of \(\pm\)53.35\({}^{\circ}\) from the zenith direction, covering a width of 2700 km, and achieving a total field of view (FOV) of 98% within each scan line [14]. The MWHS-II on board FY-3F is the second instrument of the 03 batch, capable of retrieving vertical information on atmospheric humidity and temperature through four detection frequency bands and fifteen detection channels, with a horizontal resolution of 15 km. MWHS-II on FY-3F has adjusted the frequency of the window channel from 150 GHz to 166 GHz. Using the 166 GHz and 89 GHz window channels, IWP over the ocean can be retrieved. Channels 11 to 15, with center frequencies on the 183.31 GHz water vapor absorption line, can be used to retrieve water vapor distribution in different vertical layers of the atmosphere [15].  
The European Meteorological Operational Satellite Program (METOP) is a crucial component of the European Polar System (EPS) space segment operated by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), providing real-time data to multiple European meteorological services, the National Oceanic and Atmospheric Administration (NOAA), and other international agencies. The third METOP satellite (METOP-C) was launched on 7 November 2018, carrying MHS and AMSU-A [16; 17]. AMSU-A is a total power microwave radiometer with 15 channels operating in the frequency range of 23.8 GHz to 89 GHz. It uses a step-scan mode with a swath width of 2343 km for each channel, consisting of 30 FOVs per scan line and a scan period of 8 s. Each FOV in AMSU-A does not overlap with its adjacent FOV [18; 19; 20]. MHS has five frequency channels ranging from 89 GHz to 190 GHz. It includes two window channels at 89 GHz and 157 GHz, as well as three water vapor channels near 183.3 GHz, primarily used for observing tropospheric water vapor and cloud-rain information. MHS is a cross-track scanning instrument, with each scan containing 90 consecutive FOVs, covering a range of approximately 49.5\({}^{\circ}\) on both sides of the satellite orbit, and an antenna beamwidth of 1.11\({}^{\circ}\) at the half-power point, resulting in a swath width of 2348 km. Its spatial resolution at the nadir is approximately 17 km, enabling it to obtain detailed atmospheric information [21]. Table 1 presents the parameter specifications for each microwave channel utilized in this study.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Instrument**} & **Center Frequency** & **Bandwidth** & \multirow{2}{*}{**Polarization**} & **3-db** \\  & **(GHz)** & **(MHz)** & & **Beamwidth (\(\cdot\))** \\ \hline MWTS-III & 23.8 & 270 & QH & 2.20 \\  & 31.4 & 180 & QH & 2.20 \\  & 23.8 & 270 & QV & 3.30 \\  & 31.4 & 180 & QV & 3.30 \\  & 89 & 180 & QH & 2.00 \\  & 166 & 1500 & QH & 1.10 \\  & 183.31 \(\pm\) 7 & 200 & QV & 1.10 \\  & 89 & 180 & QV & 1.10 \\  & 157 & 2800 & QV & 1.10 \\  & 190.311 & 2000 & QV & 1.10 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Microwave sounding instrument channels used in the cloud ice water algorithms.