The first quantitative joint observation of typhoon by Chinese GF-3 SAR and HY-2A microwave scatterometer

The typhoon, as a mature tropical cyclone that develops in the western part of the North Pacific Ocean with high wind speed and heavy rainfall, is one of the most lethal and costly of natural disasters for the densely populated countries of East Asia. It can be easily detected by space-borne sensors operated at microwave, visible or infrared bands （Liu et al., 2014）. Synthetic Aperture Radar （SAR） is a kind of active imaging radar, which can detect the targets with high resolution at one-meter level. SARs can be used to extract the sea surface wind and the eyes of typhoons or hurricanes （Friedman and Li, 2000; Zhang and Perrie, 2012; Li, 2015; Jin et al., 2014; Liu et al., 2014）. As a pioneer project of Haiyang-3 （HY-3）, the Chinese C-band SAR satellite of Gaofen-3 （GF-3） was launched in August 2016 under China High-resolution Earth Observation System （CEOS）. GF-3 carries a multi-polarized C-band SAR with a highest spatial resolution of one meter, the most imaging modes in the word of twelve and a long designed lifespan of 8 years. Haiyang-2A （HY-2A）, which was launched in August 2011, is the first Chinese marine dynamic environment satellite with a main payload of Ku-band microwave scatterometer （Jiang et al., 2012; Ye et al., 2015）. One of the objectives of HY-2A scatterometer （HY-2A SCAT） is monitoring sea surface wind field of global ocean.

ONSET OF THE 1998 SUMMER MONSOON IN THE SOUTH CHINA SEA-EVIDENCE FROM SATELLITE MICROWAVE SCATTEROMETER

Weekly averaged winds observed by satellite microwave scatterometer on board ERS-2 are analyzed to reveal the onset process of the 1998 South China Sea (SCS) summer monsoon.The seatterometer data sets are firstly validated by field wind observation from a buoy located at 114.41°E,12.98°N during the same period.Results of the analysis suggest that in 1998,onset of the SCS summer monsoon started in the third week of May (May 18-May 2zi),and the summer monsoon was fully established in late May.Onset of the 1998 summer monsoon is associated with the eastward withdrawal of the North Pacific trade wind system,the development of Indian monsoon,and the occurrence of cross equatorial airflow.However,the SCS summer monsoon also shows its own independence in the mature phase.Local ocean-atmosphere and land-atmosphere interactions may also influence the onset and development of the SCS summer monsoon.

First six months quality assessment of HY-2A SCAT wind products using in situ measurements

The first Chinese microwave ocean environment satellite HY-2A, carrying a Ku-band scatteromenter （SCAT）, was successfully launched in August 2011. The first quality assessment of HY-2A SCAT wind products is presented through the comparison of the first 6 months operationally released SCAT products with in situ data. The in situ winds from the National Data Buoy Center （NDBC） buoys, R/V Polarstern, Aurora Australis, Roger Revelle and PY30-1 oil platform, were converted to the 10 m equivalent neutral winds. The temporal and spatial differences between the HY-2A SCAT and the in situ observations were limited to less than 5 min and 12.5 km. For HY-2A SCAT wind speed products, the comparison and analysis using the NDBC buoys yield a bias of-0.49 m/s, a root mean square error （RMSE） of 1.3 m/s and an increase negative bias with increasing wind speed observation above 3 m/s. Although less accurate of HY-2A SCAT wind direction at low winds, the RMSE of 19.19° with a bias of 0.92° is found for wind speeds higher than 3 m/s. These results are found consistent with those from R/Vs and oil platform comparisons. Moreover, the NDBC buoy comparison results also suggest that the accuracy of HY-2A SCAT winds is consistent over the first half year of 2012. The encouraging assessment results over the first 6 months show that wind products from HY-2A SCAT will be useful for scientific community.

The HY-2 satellite and its preliminary assessment

The HY-2 satellite was successfully launched on 16 August 2011.It carried four microwave instruments into space for operationally observing dynamic ocean environment parameters on a global scale.The HY-2 satellite altimeter provides sea surface height(SSH),significant wave height(SWH),sea surface wind(SSW)speed,and polar ice sheet elevation,while the HY-2 satellite scatterometer provides SSW fields.At the same time,other oceanic and atmospheric parameters such as sea surface temperature(SST)and wind speed,water vapor and liquid water content can also be obtained by its onboard scanning microwave radiometer.In this paper,we show the data processing methods of the HY-2 satellite’s payloads.The preliminary results show that wind vector,SSH,SWH,and SST conform to the designed technical specifications.