# Present and Future Marine Microwave Satellite Missions in China
## 2 Development of Marine Satellites in China
### Progress History of China's Marine Dynamic Environmental Satellites
The DCS receives buoy survey data in the coastal areas of China and other sea areas, and the AIS provides services for marine disaster prevention and mitigation, as well as marine fishery production activities. The data obtained by the HY-2B satellite have been found to be stable and continuous, and the data accuracy has been significantly improved when compared with the HY-2A satellite. The accuracy of the data regarding the sea surface heights, significant wave heights, and sea surface wind fields (wind speeds and directions) is similar to other orbital satellites, such as Jason-3 [23; 24], and the accuracy of the sea surface temperature data has been confirmed to be close to that of international satellite systems [6]. The radar altimeter is an active microwave remote sensor with a main objective to measure sea surface height, which lays the foundation for long-term ocean monitoring from space to an extent that will ultimately lead to improve understanding of the ocean's role in global climate change [25]. The main instrument parameters are listed in Table 1.  
The microwave scatterometer is dedicated to determine the wind vector field (including wind speed and direction) above the ocean surface. Its swath is about 1750 km and can cover above 90% of global open sea area within one day. The scatterometer adopts two pencil beams to measure the backscatter energy. To meet the requirements of wind vector retrieval with high precision and a wide swath, the following scatterometer specifications were proposed, as listed in Table 2([PERSON], 2018; [PERSON], 2018). The scanning microwave radiometer operated on HY-2A/B is a multi-channel radiometer (RM). Intended to obtain ocean parameters such as sea surface temperatures, sea surface winds, total water vapor and cloud liquid water content under all-weather conditions, the HY-2A/B RM is designed as a nine-channel instrument capable of receiving both horizontally and vertically polarized radiation, except on the 23.8 GHz channel, which only works with vertical polarization. The HY-2A/B satellite's RM instrument specification is listed in Table 3([PERSON], 2018; [PERSON], 2018). To more quickly obtain the dynamic environmental information of the majority of the global oceans, the HY-2C and HY-2D were designed with non-sun-synchronous inclined orbits, and only carry the payloads of radar altimeter, microwave scatterometer, calibration microwave radiometer (CMR), DCS, and AIS. The design about the main sensors on the HY-2C/D satellites is the same as that of HY-2A/B. The HY-2C \begin{table}
\begin{tabular}{l c} \hline \hline
**Parameter** & **Value** \\ \hline Frequency & 13.58 \& 5.25 GHz \\ Pulse-limited footprint & \textless{}2 km \\ Frequency bandwidth & 320 MHz \\ PRF & 2 KHz \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main parameters of the HY-2A/B radar altimeter. \begin{table}
\begin{tabular}{l c} \hline \hline
**Parameter** & **Value** \\ \hline Frequency & 13.256 GHz \\ Transmit power & 120 W \\ Pulse width & 1.5 ms \\ Swath & 1350/1750 km \\ Polarization & H/H/VV \\ Look angle & 34.8\({}^{\circ}\)/40.8\({}^{\circ}\) \\ Incidence angle & 41\({}^{\circ}\)/48\({}^{\circ}\) \\ Scanning mode & conically scanning \\ \(\sigma_{0}\) measurement accuracy & 0.5 dB \\ \(\sigma_{0}\) measurement range & \textless{}40\textless{}\textless{}\textgreater{}20 dB \\ Wind cell resolution & 25 km \\ Wind speed accuracy & \textless{}2 m/s \\ Wind direction accuracy & \textless{}20\({}^{\circ}\) \\ Mission lifetime & 3 years \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main parameters of the HY-2 scatterometer.