Fy-3 Meteorological Satellites and the Applications

FY-3 is the second generation polar-orbiting meteorological satellite of China. The first satellite named FY-3A of this series was launched on 27 May, 2008. The first operational satellite named FY-3C of this series was launched on 23 September, 2013. The new generation satellites are to provide three-dimensional, quantitative, multi-spectral global remote sensing data under all weather conditions, which will greatly help the operational numerical weather prediction, global climate change research, climate diagnostics and prediction, and natural disaster monitoring. They will also provide help for many other fields such as agriculture, forestry, oceanography and hydrology. With the above-mentioned capability, the FY-3 satellites can make valuable contributions to improving weather forecasts, global natural-disaster and environmental monitoring. 1 Missions of FY-3 Satellites To meet new and higher requirements in modern meteorological services, especially in Numerical Weather Predictions (NWP), the FY-3 series was designed to perform global, three-dimensional, quantitative and multi-spectral observations under all weather conditions with multiple sensors on board. As a new generation of polar orbiting meteorological satellite, The FY-3 series is divided into two phases, one is experimental and the other is operational. It consists of two experimental and at least four operational satellites. The FY-3 series is expected to have a service life until 2020 [1]. The first two satellites in the FY-3 series, named FY-3A and FY-3B, are Research and Development (R&D) satellites. After the successful launch


Missions of FY-3 Satellites
To meet new and higher requirements in modern meteorological services, especially in Numerical Weather Predictions (NWP), the FY-3 series was designed to perform global, three-dimensional, quantitative and multispectral observations under all weather conditions with multiple sensors on board.
As a new generation of polar orbiting meteorological satellite, The FY-3 series is divided into two phases, one is experimental and the other is operational.It consists of two experimental and at least four operational satellites.The FY-3 series is expected to have a service life until 2020 [1] .The first two satellites in the FY-3 series, named FY-3A and FY-3B, are Research and Development (R&D) satellites.After the successful launch-ing of FY-3C, China has completed the transition from R&D satellite to operational satellite of the second generation polar-orbiting meteorological satellites.FY-3C is equipped with 12 payloads, inherited from the FY-3A/B with upgrading of some crucial instruments, and has enhanced sounding and imaging capabilities.Figure 1 shows the FY-3 meteorological satellite.
Two groups of FY-3 satellites are put into operation, one in a morning orbit and the other in an afternoon orbit.The FY-3 satellites will alternately take morning orbit or afternoon orbit, so that FY-3A and FY-3C are the morning-orbit satellites, and FY-3B is the afternoon-orbit one.The FY-3 satellites' core capabilities are optical imaging observations at global medium resolution and atmospheric temperature and humidity sounding using both high-precision optical and microwave instruments, which are essential for weather forecasting and disaster monitoring [2] .The two orbital satellites have the capability to make more complete and integrated Earth observations.
The missions of FY-3 are listed as follows [3] .
To provide global measurements of three-dimensional temperature and moisture sounding of the atmosphere, and to measure cloud and precipitation parameters in support of NWP.
To provide global imagery of large-scale meteorological and hydrological disasters as well as biosphere and environment anomalies.
To derive geophysical parameters to support research activities in global and regional climate change.
To provide global and local meteorological information for specialized meteorological users working in services of aviation, marine, etc.

Payloads of FY-3 Satellites
There are 11 instruments on FY-3A/B, including three imaging remote sensors VIRR, MERSI and MWRI, three sounding instruments IRAS, MWTS and MWHS, two ozone instruments SBUS, TOU, two Earth radiation budget instruments ERM, SIM, and one space environment monitoring instrument SEM.The payloads have nearly 100 remote-sensing channels in the spectral range, from ultraviolet to Visible (VIS), Infrared (IR) and microwave [4] .FY-3C is equipped with all of the 11 payloads, but MWTS is upgraded to MWTS-II, MWHS to MWHS-II, and a new payload, GNSS Occultation Sounder (GNOS), is on board FY-3C.MWTS-II will increase the channels from 4 to 13, and MWHS-II will increase the channels from 5 to 15. GNOS will improve the measured temperature and moisture profiles in the upper atmosphere.
(1) Imaging Instruments VIRR and MERSI are the two optical imagers.VIRR is the only payload inherited from the FY-1 series to perform the successive observations operationally.MERSI is the upgrading to VIRR.It has 20 visible and infrared channels.MERSI holds 5 channels of 250 m spatial resolution at nadir and the other 15 channels of 1 km.It improves the optical imaging capacity of the FY meteorological satellite from kilometer to hundredmeter resolution.MWRI is a 10-channel conicalscanning microwave radiometer at five frequencies.All frequencies are dually polarized.The soil moisture, land surface temperature, land surface emissivity at microwave, snow depth, snow water equivalent, etc., can be retrieved quantitatively from the microwave frequency difference or the polarization difference of MWRI measurements.
(2) Sounding Instruments IRAS is the primary sounder on FY-3.It has 26 channels.The first 20 channels are almost the same as the HIRS/3, while the other six enable the IRAS to measure aerosols, carbon dioxide content and cirrus.MWTS/ MWTS-II is a 4-channel/13-channel passive scanning microwave sounder capable of temperature sounding in cloudy regions.MWHS has the primary purpose of moisture sounding in cloudy regions.MWHS/MWHS-II has 5/15 higher frequency channels.Its products are atmospheric humidity profiles and precipitation intensity and cloud-ice-water thickness.GNOS is a new payload for FY-3C.The goals for FY-3 GNOS mission include (a) providing all-weather data for operational weather prediction, atmospheric physics study and climate research, (b) monitoring electron density profiles for predictive models, magnetospheric studies and radio communication, (c) exploring the relationship between troposphere and stratosphere exchange.
(3) Ozone Instruments SBUS and TOU, are new sensors for measuring atmospheric ozone distribution.TOU is a 6-channel spectrometer with wavelengths from 308 to 360 nm and a resolution of 50 km at nadir.SBUS is a 12-channel spectrograph with wavelengths ranging from 252 to 380 nm.The spatial resolution of the ozone profile is around 200 km at nadir.The typical products of SBUS and TOU are global vertical ozone profiles and total column ozone.
(4) Earth Radiation Instruments ERM is two broadband channel radiometers for Earth-reflected solar flux and Earth-emitted thermal flux over short and total wavebands.It has separate wide-FOV and narrow-FOV observation units.Its products are solar radiation flux and outgoing long-wave radiation flux.SIM provides long-term constant solar observations, offering reliable scientific data for studying variations in the solar energy output at various time scales.Its primary product is the solar constant.
(5) Space Environment Monitoring Instruments SEM on board FY-3 is a modified version of that on board FY-1, with improved accuracy and measuring capacity for high-energy particles.SEM can effectively monitor the space environment and the charged particle flux, record impacts of space weather events on the satellite, and provide important data for space weather monitoring and warning.
In the future, the instruments including MERSI-II, SIM-II, and ERM-II would be improved.The advanced MERSI-II will increase the channels from 20 to 25 after merging the VIRR channels.And five new payloads will be developed.The Hyperspectral Infrared Atmospheric Sounder (HIRAS) is an instrument to improve the measured temperature and moisture profile instead of the IRAS.Ozone Mapping Spectrometer (OMS) is an instrument to detect the ozone and other atmospheric chemicals as well, instead of the suite of TOU and SBUS.Wind Radar (WindRAD) will measure the sea wind.Greenhouse Gases Absorption Spectrometer (GAS) will measure CO 2 and CH 4 globally.The subsequent FY-3 satellites would be equipped with all of these instruments.

Data Sharing and Service
Fengyun satellite data is provided to both domestic and international users via the following ways.
Direct Broadcast Service.Users with appropriate receiving equipment can directly receive data transmission of each operational Fengyun satellite.
DVB-S Dissemination System.The CMACast system uses the DVB technology to disseminate real-time products to subscribers.
Internet.The Fengyun Satellite Data Service Network (Website: http://satellite.cma.gov.cn) is one of the ways to download real-time or historical products.
FTP Service.For users demanding for large bulk data in real-time or near-real-time, the system initiatively pushes the data to user-specified FTP servers.
Manual Service.If large volume data is requested and has been approved by China Meteorological Administration, manual service is also available.
The website has become one of the main accesses to FY-3 satellites data for global users.Users can easily obtain data, use the Web GIS platform to browse the satellite imagery, customize the content and format of the required data after a quick registration.

Data Assimilation in NWP
The application of meteorological satellite data assimilation in NWP can greatly improve the accuracy of weather forecasts.Payloads on board the FY-3 satellites include four instruments of particular interest for NWP: IRAS, MWTS, MWHS and MWRI.Data from the four instruments were introduced into the ECMWF Integrated Forecasting System to assess the data quality and the influence of the data on analyses and forecasts.An overview of the data quality for the key channels of the four FY-3A instruments, in terms of the standard deviations of the first-guess departures after variational bias correction (VarBC) and quality control, is given in Figure 2. Also shown for comparison are the equivalent statistics for the corresponding MetOp-A instruments and, for the case of the MWRI instrument, the equivalent AMSR-E statistics.The statistics were obtained over one month.The results show that the data from the four instruments in FY-3 meet the requirements for application in NWP assimilation, and preoperational testing has shown that the FY-3 data deliver measurable forecast improvements in the NWP model [5] .

Natural Disaster and Environmental Monitoring
The  meteorological information for aviation, ocean navigation, agriculture, forestry, marine activities, hydrology, and many other economic sectors.All monitoring results and analysis were promptly provided by CMA to the public and government for decision making.

FY- 3
series represents in fact a new chapter in the history of the Chinese meteorological satellites and satellite meteorology.The FY-3 satellites monitor largescale meteorological disasters, weather-induced secondary natural hazards and environment changes, and provide geophysical parameters for scientific research in climate change and its variability, climate diagnosis, and predictions.The examples are shown from Figure 3 to Figure 12.The FY-3 series renders global and regional