General introduction on payloads, ground segment and data application of Fengyun 3A

Abstract

Fengyun 3 series are the second-generation polar-orbiting meteorological satellites of China. The first satellite of Fengyun 3 series, FY-3A, is a research and development satellite with 11 payloads onboard. FY-3A was launched successfully at 11 a.m. on May 27, 2008. Since the launch, FY-3A data have been applied to the services on the flood season and the Beijing 2008 Olympic Games. In this paper, the platform, payloads, and ground segment designs are introduced. Some typical images during the on-orbit commission test are rendered. Improvements of FY-3A on Earth observations are summarized at the end by comparing them with FY-1D, the last satellite of Fengyun 1 series.

Keywords

Fengyun 3 / payloads / ground segment / data application

Historical review of Chinese meteorological satellites

Chinese meteorological satellite activities started in 1969. Since then, two parallel works have been advocated. They are receiving, processing, and utilizing foreign satellites, and programming, developing, and applying Chinese meteorological satellites (Fang et al., 2004).

Chinese meteorological satellites contain two systems (Li, 2001; Meng, 2004). They are the polar orbit series and the geostationary orbit series. Each satellite is named with an Arabic numeral and an alphabet. The Arabic numerals represent the satellite series, the odd being the polar orbit satellites and the even representing the geostationary satellites. The alphabet represents the sequence number within the series. So far, five polar orbit satellites and five geostationary satellites have been launched successfully (seen in Table. 1).

Specification of the FY-3A platform

Fengyun 3 series are the second-generation polar-orbiting meteorological satellites of China. To meet new and higher requirements in modern meteorological services, especially in numerical weather predictions, these series are designed to perform global, three-dimensional, quantitative, and multi-spectral observations under all weather conditions (i.e., cloud-free and cloudy conditions) with multiple sensors onboard (Fan, 2000; Zhang, 2001).

FY-3A is the first satellite of Fengyun 3 series. It was successfully launched on May 27, 2008 from the Taiyuan launch center. Compared with the single payload of Fengyun 1 series, the number of instruments onboard the satellite has increased to 11. Therefore, FY-3A turns over a new chapter in the history of Chinese meteorological satellites and satellite meteorology (Yang, 2008).

FY-3A is a research and development satellite. The designed lifetime of FY-3A is three years. FY-3A is located at 831 km altitude in the sun-synchronous, near-polar orbit. The attitude control adopted the three-axis stabilization techniques. The major technical specifications of the FY-3A platform are listed in Table 2 (National Satellite Meteorological Center, 2004; National Satellite Meteorological Center, 2008a).

Introduction of the FY-3A payloads

There are 11 payload instruments mounted on FY-3A. They are the visible and infrared radiometer (VIRR), infrared atmospheric sounder (IRAS), microwave temperature sounder (MWTS), microwave humidity sounder (MWHS), medium resolution spectral imager (MERSI), microwave radiation imager (MWRI), solar backscatter ultraviolet sounder (SBUS), total ozone unit (TOU), earth radiation measurement (ERM), solar irradiance monitor (SIM), and space environment monitor (SEM). Among them, the IRAS, MWTS, and MWHS make up the vertical atmospheric sounding system (VASS). The VIRR is the only instrument among them inherited from the formal FY-1 series platform. Other instruments are all first time in orbit.

The VIRR is a 10-channel VIS/IR radiometer for multi-purpose imagery with 1.1 km resolution at nadir. The swath of the VIRR is 2800 km. The MERSI is a 20-channel VIS/IR radiometer. There are 19 channels in VIS/NIR/SWIR bands and one in TIR band at 10.0-12.5 μm. Spatial resolution at nadir is twofold: 250 m (for four VIS/NIR channels and one TIR channel) and 1 km (for all other channels). Swath width is similar with VIRR at 2800 km. The MWRI is a 10-channel conical-scanning microwave radiometer at five frequencies. All frequencies are in double polarization. Spatial resolution is 9.5×15 km at 90 GHz and 30×50 km at 19 GHz. The swath of the MWRI is 1400 km. The IRAS is a 26-channel IR radiometer for temperature and humidity sounding. Spatial resolution is 17 km and swath width is 2250 km. The MWTS is a four-channel microwave radiometer for nearly-all-weather temperature sounding with the spatial resolution of 70 km at 54 GHz. The MWTS performs on cross-track scanning mode with swath of 2200 km. The MWHS is a five-channel microwave radiometer at four frequencies (one frequency in double polarization) for nearly-all-weather humidity sounding. The spatial resolution is 15 km at 183 GHz band. The swath width is 2700 km with cross-track scanning. The TOU and SBUS make up a suite of two UV spectro-radiometers. The TOU measures total ozone amount with six channels in the 308-360 nm range, with spatial resolution of 50 km with 3000 km swath. The SBUS measures ozone profile with channels in the range of 252-340 nm. Spatial resolution is 200 km at nadir viewing without side scanning. The ERM is a two-broadband channel radiometer for earth-reflected solar flux and earth-emitted thermal flux over total (0.2-50 mm) and short (0.2-4.3 mm) waveband. The ERM has two working modes. One is cross-track scanning mode with 28 km spatial resolution at 2° narrow field of view (NFOV); the swath width is 2300 km. The other is nadir viewing mode with 120° wide field of view (WFOV). The SIM is a three-channel radiometer over 0.2-50 mm wave band for the total incident solar flux. It views the sun near the north polar area. The SEM is the only in situ instrument to measure charged particles in solar wind.

From the view point of data application, the payload instruments on the FY-3A can be analogous to those sensors that are well-used in the world. In fact, the VIRR is the expanded AVHRR instrument, and the MERSI is the MODIS-similar sensor. Both of these optical imagers can provide surface characteristics (including cloud surface, land surface, and ocean surface) and aerosol information. The VASS set is made up of ATOVS-similar instruments for atmospheric sounding. The MWRI is the AMSR-similar instrument except for the low frequency at 6.9 GHz. The SBUS and TOU are the SBUV-similar and TOMS-similar sensors, respectively, which can provide ozone profile and total ozone amount separately. The ERM is the CERES-similar instrument inherited from ERBE. The detailed specifications of these 11 payload instruments and their data applications are listed in Table 3 (National Satellite Meteorological Center, 2004; National Satellite Meteorological Center, 2008a).

FY-3A ground segment design

The Chinese meteorological satellite engineering system comprises five parts: satellite segment, launch pad segment, launch vehicle segment, measurement and control segment, and ground segment (Li, 2008). The ground segment responds to data receiving, data pre-processing, and data processing. It is the key to sustaining and promoting satellite data application in the meteorological services (Xu et al., 2006).

The FY-3A ground segment includes the data processing center, operation and control center, ground receiving center, and data archiving center. They are composed of 10 technical systems and one airborne-based field experiment (National Satellite Meteorological Center, 2006). The technical systems are the Data Acquisition System (DAS), Computer and Network System (CNS), Operation Control System (OCS), Data Pre-Processing System (DPPS), Products Generation System (PGS), Quality Control System (QCS), Utilization Demonstration System (UDS), Archive and Service System (ARSS), Monitoring and Analysis System (MAS), and Simulation and Technical Supporting System (STSS). The purpose of the airborne-based field experiment is to test the engineering model of the payload instruments. The FY-3A ground segment framework is shown in Fig. 1.

The FY-3A ground segment has five ground stations to receive the satellite direct-broadcasting data. Four of them are inside China and the last one is located near the northern polar region. Such distribution, especially the ground station in the polar region, guarantees that global data can be received and collected within about three hours. The ground stations receive all of the L-band HRPT data, X-band MPT data, and DPT data. Table 4 shows the information of current ground stations built for FY-3A.

Data application and demonstration

There are five systems in the FY-3A ground segment related directly with data application. They are the DPPS, PGS, ARSS, MAS, and UDS. Thereinto, the DPPS generates level 1 products with geolocation and calibration information, and the PGS produces level 2 products to provide geophysical and geochemical information through retrieval algorithms. The ARSS responds to data archiving and data distribution. The MAS provides users a special toolkit to analyze satellite data. The UDS responds to promote the utilization and demonstration of FY-3A data into meteorological services. Figure 2 shows the relationship among the DPPS, PGS, ARSS, MAS, and UDS. Table 2 lists the level 2 products generated from the PGS currently covering the atmosphere, land, ocean, cryosphere, radiation, and space environment (National Satellite Meteorological Center, 2008b).

Since the launch, FY-3A data have been applied to global weather system monitoring, typhoon monitoring, sea and inland water body monitoring, fire monitoring, aerosol and air quality monitoring, the monitoring of hot-island effect in cities, global sea shelf monitoring, global ozone monitoring, etc. It is noted that FY-3A is still on its on-orbit commission test phase. However, FY-3A has served the Beijing 2008 Olympic Games and the flood season in 2008 at the same time.

Figure 3 is the global mosaic image in MERSI channels 3, 2, 1 with 250 m resolution acquired on the same day. The intertropical convergence zone (ITCZ), tropical depression, and subtropical high pressure can be seen clearly. As indicated in Fig. 4, when typhoon Fung-wong was monitored by MERSI on 27 July, 2008, the typhoon hole inside and the spiral cloud outside can be distinguished. Figure 5 shows the ozone hole monitored from TOU on November 1, 2008. The region on the cold color side corresponds to the ozone hole in the image.

Conclusions

In comparison with FY-1 series, the principal improvements in FY-3A include: 1) atmospheric sounding capacity, 2) microwave imaging capacity, 3) optical imaging with spatial resolution from 1 km to 250 m, 4) atmospheric composition detecting capacity, 5) radiation budget measuring capacity, and 6) global data acquisition from within one day to within two to three hours.

The number of instruments on board the satellite has increased to 11. FY-3A has evolved from single imaging to comprehensive earth environment observations, from optical to microwave remote sensing, with resolution having been increased from kilometer to hectometre-category, and receivable both in China and up to the polar region. Therefore, FY-3A turns over a new chapter in the history of the Chinese meteorological satellites and satellite meteorology.

The FY-3A satellite provides global air temperature, humidity profiles, and meteorological parameters such as cloud and surface radiation required in producing weather forecasts, especially in making medium numerical forecasting. The FY-3A satellite monitors large-scale meteorological disasters, weather-induced secondary natural hazards and environment changes, and provides geophysical parameters for scientific research in climate change and its variability, climate diagnosis, and predictions. The FY-3A satellite renders global and regional meteorological information for aviation, ocean navigation, agriculture, forestry, marine activities, hydrology, and many other economic sectors.

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