The paper summarized the capabilities, performance, and technical characteristics of the 4 payloads onboard the HY-2A satellite including radar altimeter, microwave scatterometer, scanning microwave radiometer and microwave calibration radiometer. The HY-2A satellite is marked as a significant breakthrough for microwave remote sensing technology of China, a milestone for China's own ocean dynamic environment satellite that plays a crucial role in maritime applications, and a role model for China's future ocean satellite missions.
HY-2A is China's first ocean dynamic environment satellite, and it is currently the only one satellite which is capable of all-weather, all-day synchronous access to the global sea surface altitude, available wave altitude, sea wind field, sea surface temperature, atmospheric water vapor, cloud liquid water and other remote sensing data. HY-2A satellite equips four kinds of active and passive microwave remote sensing load, adopts a new remote sensing system, realizes the localization of key parts and has certain characteristics of precision orbit determination, electromagnetic compatibility and high precision attitude control. As the first comprehensive type microwave remote sensing satellite, the realization of HY-2A engineering is significant. This paper is introduced about the aspects of system composition and functions, development stage, large-scale test, in-orbit test and application results show.
The HY-2A satellite, launched on October 16, 2011 is the first dynamic environments satellite in China, carrying the radar altimeter which continues the time series of centimeter lever ocean topography measurement. Orbit error is a major component in the overall error budge of all altimeter satellite missions. The HY-2A satellite carries DORIS deceiver, Dual frequency GPS receiver and Laser Retroreflector Array for Precise orbit determination (POD) to meet 10cm radial accuracy goal for the HY-2A satellite radar altimeter. First, the tracking system and method of POD for HY-2A satellite is introduced, then the solution strategy is showed, finally the results of the radial accuracy for HY-2A satellite are given in this paper.
HY-2A is the first satellite for oceanic dynamic environment measurement of China. As one of main payloads of HY-2A, HY-2A radar altimeter has obtained successive measurement data after the launch. The accuracy of HY-2A radar altimeter is better than 4 cm (at 20 m significant wave height) or 2 cm (at 4 m significant wave height), which is close to that of Jason-2 satellite altimeter. In this paper, the design and in flight preliminary results of HY-2A radar altimeter are introduced.
The HY-2A satellite was first launched in August of 2011,the microwave scatterometer as one of the main loads, is primarily applied in sea surface wind observation. HY-2A satellite scatterometer used two pencil beam circle scan system, and the radar worked in Ku band. The paper illuminates the scatterometer's system composition, main parameter, the in-orbit pretreatment and the results in observation to typhoon.
HY-2A satellite is China's first ocean dynamic environment satellite. The microwave radiometer is one of the four microwave payloads of the satellite, which is mainly used for measuring parameters including sea surface temperature, wind speed, water vapor and liquid water etc. The microwave radiometer is a conical scanning radiometer, real time calibration with cold sky and warm load on board, cover frequency from 6 GHz to 37 GHz. This paper introduced the design of instrument including system design, antenna design, receiver design and balance design etc.
Atmospheric correction microwave radiometer (ACMR) is one of the main payloads for correcting atmospheric path delay of radar altimeter on HY-2A satellite. After discussion and analysis on thermal vacuum calibration method of ACMR, microwave transfer functions and related coefficients were given, especially nonlinear coefficients derived from the test for correcting nonlinear responds between the input of antenna temperature and the output of voltage at each channel of ACMR. Meanwhile, antenna pattern correction algorithms for removing the effects of side-lobe and cross-polarization were derived and their coefficients were used for in-orbit data processing. The calibrated antenna temperatures were compared with the similar space-borne microwave radiometer on Jason-1 and Jason-2 satellite (JMR), launched by the NASA-French Space Agency Ocean Surface Topography Mission. The results of comparison showed that the data from ACMR were well matched to those from Jason-1 and Jason-2.
There are many factors affecting the height accuracy of satillite radar altimeter. The dry troposphere delays, wet troposphere delays, invert barometer delays, ionosphere delays, and sea state bias influence the computational accuracy directly. The error correction algorithms for the HY-2A satellite radar altimeter were conducted in this research. And, these algorithms were vertified using the more mature foreign satellite data such as Jason-1/2 and T/P. The results show that the HY-2A error correction algorithms can meet the accuracy requirements.
This paper describes the key technologies involved in the scatterometer data preprocessing, which include the geometric positioning algorithm and the radar backscatter coefficient calculation algorithm. The geometric positioning of space-borne scatterometer data is a process of obtaining the coordination of measuring pulse, which needs to consider the instrument scan geometry, spatial location, antenna pointing, earth curvature, rotation, and other factors. The traditional method of geometric positioning of space-borne scatterometer data depends on the satellite ephemeris with a low positioning accuracy. HY-2A satellite is equipped with a global positioning system(GPS) sensor to provide the location of the satellite platform with 1 s interval. Accordingly, the geometric relationship between sensor observation and ground surface can be established. The geographic coordination of the observation cell center, observation azimuth angle and incidence angle can be determined using this geometric relationship. The radar backscatter coefficient is calculated with a parameter substitution method.
The routine wind fields retrieval algorithm for China's microwave scatterometer onboard HY-2A (HY2-SCAT) was developed. By introducing a two-step search schema into the wind retrieval process, which included a coarse-search and an optimal-search, the efficiency of wind retrieval was greatly improved. Circular median filter was applied to remove the ambiguities, and the NCEP wind field was used as a background to re-initialized wind field consists of ambiguous wind vectors, so that the ambiguity removal skill can be largely enhanced. Wind vectors observed by HY2-SCAT were evaluated by comparison with NDBC buoy observations and ASCAT observations. The RMS difference was less than 2 m/s or less than 10 % for the comparison of wind speeds and the RMS difference was less than 20 degree for the comparison of wind direction, which indicated that the wind products provided by HY2-SCAT can meet the requirements for science and routine meteo users.
HY-2A scanning microwave radiometer cold shy calibration method and Geophysical parameters retrieval algorithm were studied. According to HY-2A satellite scanning microwave radiometer on observation and scanning design principle and observation geometry, the earth's signal into cold reflector based on the earth observation data of microwave radiometer was corrected, and cold sky reflector weight coefficient matrix by the ground observation brightness temperature to correction cold sky observation signal was established. Based on the sea surface temperature, sea surface wind speed, moisture content and cloud liquid content and microwave radiometer radiative transfer model, HY-2A scanning microwave radiometer model theory brightness temperature under different conditions of each frequency and polarization was calculated, and a linear regression model was established to fit different geophysical parameters retrieval coefficient, using multiple linear regression algorithm retrieving HY-2A microwave scanning radiometer geophysical parameters, compared to international microwave radiometer data, and the product accuracy was obtained.
Advanced microwave atmospheric sounder (AMAS) is the new generation of microwave humidity sounder onboard FY-3(C/D) satellite, and is inheritance and development of MWHS onboard FY-3(A/B) satellite. Based on 150 GHz (horizontal and vertical polarization) and 183.31 GHz (horizontal polarization, three-channel) of MWHS, the AMAS still operated in cross-orbited scanning and used for deriving atmospheric temperature and humidity of the vertical distribution, rainfall, etc. The observation channels are advanced as 89 GHz (vertical polarization), 118.75 GHz (horizontal polarization, eight-channel), 150 GHz (vertical polarization), 183.31 GHz (horizontal polarization, five-channel).This paper mainly introduces the design and structure of AMAS and describes its performance requirements. Test results show that the performance indicators of AMAS meet the design requirements.
The microwave temperature sounding (MWTS) is a multi-channel passive microwave radiometer. It is designed for Chinese meteorology satellite (FY-3), which is in a circular sun synchronous orbit. As an introduction, this paper describes the operational and functional parameters of MWTS. The system consists of antenna subsystem, receive subsystem, signal processing and control subsystem, calibration subsystem, mechanical scanning subsystem, etc. The MWTS consists of four channels with channels center at 50.30 GHz, 53.596 GHz, 54.94 GHz and 57.29 GHz. It can provide a vertical temperature profile of the atmosphere.
In this paper, the method for FY-3A/MWHS calibration in-orbit has been introduced. Radiometric calibration of FY-3A/MWHS on orbit has been performed based on the T/V test results and surface lab performances test results. It is confirmed that the system of radiometric calibration for MWHS is successful, and performs well on orbit. The variations among space views and warm target views in the interval of scan lines are generally within 20 counts. And the temperature fluctuation of warm target is within 0.5 K in a single pass. Due to the accuracy of the nonlinearity parameters, the radiance calibration of MWHS agrees well with NOAA-17/AMSU-B. The brightness temperature differences between FY-3 MWHS and NOAA-17/AMSU-B at simultaneous cross overpass points are less than 1.5 K. That is the foundation of quantitative application for the data of FY-3A/MWHS in numerical weather prediction(NWP). The method of calibration and validation for FY-3A/MWHS will be a good demo for the other passive microwave sounder in the future.
Considering the characteristics of Fengyun-3(FY-3) satellite lifespan on orbit increased from 3 years to 5 years, the risk of extending lifespan was analyzed, and the reliability of scan driver system and receiver system which were critical items of microwave radiation imager was evaluated, taking corresponding measures from design and improving crafts reliability. Microwave radiation imager operates normally on orbit and provides effective reliability assurance according to these methods. Finally, the ideal of accelerated lifespan test was put forward at last.
In this paper, algorithms of retrieving physical temperature and effective temperature from CE-1 lunar microwave sounder (CELMS) brightness temperatures are developed. The influences of physical temperature on microwave radiation are analyzed. These retrievals provide important information for evaluating other lunar surface parameters.