Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 50, NO. 12, DECEMBER 2012 4975 The Capabilities and Applications of FY-3A/B SEM on Monitoring Space Weather Events Cong Huang, Jia-Wei Li, Tao Yu, Bing-Sen Xue, Chun-Qin Wang, Xian-Guo Zhang, Guang-Wei Cao, Dan-Dan Liu, and Wei Tang Abstract—The space environment monitor (SEM), onboard the Chinese meteorological satellites FengYun-3A/B, has the abilities to measure proton flux in 3–300-MeV energy range and electron flux in 0.15–5.7-MeV energy range. SEM can also detect the heavy ion compositions, satellite surface potential, the radiation dose in sensors, and the single events. The space environment information derived from SEM can be utilized for satellite security designs, scientific studies, development of radiation belt models, and space weather monitoring and disaster warning. In this paper, the SEM’s instrument characteristics are introduced, and the postlaunch calibration algorithm is presented. The applications in monitoring space weather events and the service for manned spaceflights are also demonstrated. Index Terms—Electron radiation effects, heavy ions, proton radiation effects, radiation monitoring, space technology. I. I NTRODUCTION T HE SPACE environment monitor (SEM) is onboard FengYun-3 (FY-3)A/B satellites which were successfully launched into orbit on May 27, 2008, and November 5, 2010, respectively. FY-3A/B are Chinese operational meteorological satellites in Sun-synchronous polar circular low-altitude (830 km) orbit with a 98◦ inclination, covering the midmorning and afternoon orbits. The SEM’s most important ability is to measure the intensities of high-energy charged particles, such as protons (3–300 MeV) and electrons (0.15–5.7 MeV). The high-energy charged particles may have effects on space environment and be a serious concern regarding the space weather disasters. For example, when the particles collide on a satellite, energetic electrons can induce the surface and deep dielectric charging and cause a possibility of disruption of satellite’s system, and the high-energy protons can penetrate the instruments [3]. Moreover, when these particles precipitate Manuscript received November 14, 2011; revised February 9, 2012 and May 14, 2012; accepted June 2, 2012. Date of publication August 20, 2012; date of current version November 22, 2012. This work was supported in part by the Chinese Ministry of Science and Technology (973 project) under Grants 2010CB951600, 2011CB811400, and 2012CB957800, by the National Hi-Tech Research and Development Program of China (863 Program) under Grants 2010AA122205 and 2012AA121000, and by the Natural Science Foundation of China under Grants 40890160, 40974093, 41004085, and 41074126. C. Huang, J.-W. Li, T. Yu, B.-S. Xue, D.-D. Liu, and W. Tang are with the Division of Space Weather, National Satellite Meteorological Center, Beijing 100081, China (e-mail: [email protected]). C.-Q. Wang, X.-G. Zhang, and G.-W. Cao are with the Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190, China. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TGRS.2012.2207388 into the ionosphere, energetic electrons and protons produce ionization in the mesosphere and low thermosphere [2], which may cause disturbances of radio communications. In addition, high-energy protons may be harmful for astronauts, particularly in the region of South Atlantic Anomaly (SAA). Therefore, it is necessary to monitor these particles, to investigate the causes of anomalies of satellite systems and degradation of radio communications and to support Chinese manned spaceflight missions. In the 1970s, some models called AP8/AE8 are developed to explain the mechanism of Van Allen radiation belt [12], [14]. However, AP8 and AE8 models only provide static-averageisotropic particle flux while the geomagnetic field migrates 0.3◦ every year. Therefore, the outputs of AP8/AE8 models may not be suitable for the requirements in the modern space missions. Monitoring the dynamic and anisotropic intensities of the energetic particles is of importance in the satellite security designs and manned spaceflight missions. Many satellite missions are developed for detecting the radiation belt [4], [6], [8], [9]. Currently, the National Oceanic and Atmospheric Administration (NOAA) Polar Orbiting Environmental Satellite (POES) series and China Meteorological Administration’s FY-3 series provide operational measurements of the energetic charged particle distribution in polar and Sun-synchronous orbits. The SEM aboard FY-3A/B is the first Chinese operational payload to monitor space environment, and it can also provide the information about heavy ion compositions, satellite surface potential, the radiation dose in sensors, and the single events (SEs). These space environment data can be used in satellite engineering and the space science studies. II. I NSTRUMENT D ESCRIPTION FY-3A/B satellites are observing the Earth from the Sunsynchronous orbits and passing from their ascending and descending nodes at the same local times. Their orbital periods are 102 min, and their approximate altitudes are 830 km. FY-3A/B satellites carry a SEM onboard to measure the intensities of the ions and electrons precipitating into the upper atmosphere, detect the satellite surface potential and radiation dose in sensors, and record the SEs. A. SEM’s Particle Detector SEM has two detectors for detecting ion and electron, respectively. The detection principle of these two detectors is similar. The charged particles impact the sensors through the light-blocking layer and the collimator. These particles settle 0196-2892/$31.00 © 2012 IEEE 4976 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 50, NO. 12, DECEMBER 2012 Fig. 1. FY-3A/B SEM proton global distribution (from November 11 to December 11, 2010). The SAA region is shown clearly in the pictures. The SAA region is a part of inner radiation belt, and the cause of its formation is due to the geomagnetic field. It’s 3-D is shaped like a funnel, and its bottom can reach 200–300-km altitude. The high-energy charged particles are bound in this region, and the SAA region is harmful for the astronauts who are outside the orbital module. (a) Proton detections of 3–5 MeV. (b) Proton detections of 5–10 MeV. (c) Proton detections of 10–26 MeV. (d) Proton detections of 26–40 MeV. (e) Proton detections of 40–100 MeV. (f) Proton detections of 100–300 MeV. in the sensors and generate electric pulses. The amplitude and coincidence and anticoincidence of these pulses can be used to identify the particle type. The ion detector’s field of view is 60◦ , and it can measure the protons in six energy bands: 3.0–5.0, 5.0–10, 10–26, 26–40, 40–100, and 100–300 MeV [see Fig. 1(a)–(f)]. It can also detect the heavy ion compositions: He (12–110 MeV), Li (24–220 MeV), C (60–570 MeV), Mg (0.2–1.2 GeV), Ar (0.3–2.0 GeV), and Fe (0.5–2.0 GeV). The field of view of the electron detector is 40◦ , and it can measure electrons in five energy bands: 0.15–0.35, 0.35–0.65, 0.65–1.20, 1.20–2.00, and 2.00–5.70 MeV [see Fig. 2(a)–(e)]. These two detectors are set perpendicular to the satellite orbit plane (−Y -direction) and view the average flux with particles from 77◦ to 116◦ pitch angle. The detectors passed the ground tests using accelerator and radiation source and meet the calibration requirements from the simulation signals during the prelaunch period. B. SEM’s Surface Potential Detectors The surface potential detection is made from two instruments. One is turned on the satellite daytime orbit, and the other is on at the night. The measurement range of these detectors is from −300 to 3000 V. By analyzing the data collected by these detectors, we know the potential difference of the satellite surface that is regarded as the disturbance degree of the space particle radiation environment. C. SEM’s Radiation Dose Detectors The radiation dose detection is made from three instruments that are set at the payload module’s bottom toward +Y -direction (perpendicular to the orbit plane), the payload module’s +Y plane, the service module’s +Z (zenith) plane, respectively. The detectors collect the radiation dose HUANG et al.: CAPABILITIES AND APPLICATIONS OF FY-3A/B SPACE ENVIRONMENT MONITOR 4977 Fig. 2. FY-3A/B SEM electron global distribution (from November 11 to December 11, 2010). The high-energy electrons always exist in the SAA region and the polar region. The high-energy electron distribution of the polar region changes fast because of the effects of geomagnetic activities. The energetic electrons can go into the geostationary orbit along the geomagnetic field lines and cause the surface charging of synchronous satellites when space weather disasters occur. (a) Electron detections of 0.15–0.35 MeV. (b) Electron detections of 0.35–0.65 MeV. (c) Electron detections of 0.65–1.20 MeV. (d) Electron detections of 1.20–2.00 MeV. (e) Electron detections of 2.00–5.70 MeV. information from different positions of the satellite. These instruments are similar, and each one has two measurement ranges: 0–103 rd(Si) [high resolution, with the minimum response value of 13 rd(Si)] and 0–104 rd(Si) [low resolution, with the minimum response value of 33 rd(Si)]. D. SEM’s SE Detector The SE detector is a chip called 1750A (made in China), and this instrument’s aim is to test the validity of the 1750A’s radiation resistance and reinforce design. This detector can record the SE upset (SEU) and SEU’s spatial distribution in orbit. These records may help provide the basis for radiationhardened engineering of satellite. III. DATA VALIDATION In order to identify the validity of SEM’s proton and electron flux data, we use the Medium Energy Proton and Electron De- tector (MEPED) data from NOAA satellites to perform an intercomparison analysis. The POES satellites, also known as Television Infrared Observation Satellite Program/National Oceanic and Atmospheric Administration (TIROS/NOAA), have a Sunsynchronous circular polar low-altitude orbit (850 km) with a 98◦ inclination. MEPED has two sets of directional detectors and a set of omnidirectional detectors. The directional detectors measure protons in five energy bands: 30–80, 80–240, 240–800, 800–2500, 2500–6900, and above 6900 keV, and electrons in three energy bands: 30, 100, and 300 keV, for two viewing angles, 0◦ (MEPED-0) and 90◦ (MEPED-90) with respect to the zenith. The omnidirectional detectors measure the intensity of protons in four energy bands: 16–220 (the detection is shaded by the adjacent instruments, and the proton counts are not quite accurate in this range), 35–235, 70–235, and 140–275 MeV. Low Earth orbit (LEO) charged particles mainly exist in the region of SAA and polar aurora belt. These particles are influenced by the geomagnetic activities and show anisotropy and complex temporal and spatial distributions. Due to the 4978 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 50, NO. 12, DECEMBER 2012 Fig. 3. FY-3A/B SEM particle pitch angle global distribution. From the figures, we can see that the SEM’s particle pitch angles are about 90◦ and those of MEPED are different. The different particle pitch angles cause different particle flux detections particularly for the electron detections in the polar region. (a) NOAA MEPED-00 pitch angle. (b) NOAA MEPED-90 pitch angle. (c) FY-3A/B SEM pitch angle. difference in instrument design and mounting direction, the particles detected by SEM and MEPED have different energy bands and pitch angles (see Fig. 3). Therefore, it is necessary to select the data with a close pitch angle and to perform the data normalization for intercomparison studies. Other SEM’s data (heavy ion compositions, surface potential, radiation dose, etc.) and their validations are checked according to space science theory and previous detections. A. Proton Flux Data In the space weather quiet period, high-energy protons are mainly present in the region of SAA and show stable distribution [7]. The proton counts of SEM and MEPED in SAA are selected during the space weather quiet period for a comparison (the geomagnetic index Ap should be less than five, which we define as quiet period of geomagnetic field). Considering the particle anisotropy and the variation with the space position, we choose the proton count data with the near detection position (average points flux near each longitude and latitude), the close particle pitch angle, and the closer observation time (the location difference is less than 1◦ at each Fig. 4. FY-3A SEM proton flux detections compared with POES MEPED’s data (from November 11 to December 11, 2010, using N17’s data). We choose the proton count data with the near detection position (average points flux near each longitude and latitude to avoid the effects of fluctuation), the close particle pitch angle, and the not-far observation time. The SEM results show a good relationship with MEPED that means that the SEM proton detections are valid. (a) Proton 3–5-MeV comparison. (b) Proton 35–275-MeV comparisons. latitude and longitude, the difference of observation time is less than 30 days, and the pitch angle difference absolute value is less than 10◦ ; see the details of selection in Appendix A). When the SEM proton detection energy bands are different from those from MEPED, we perform the data normalization so that the proton flux data from different satellites are fit in the same energy bands: 3–5 and 35–275 MeV. The proton flux is derived from the power law y = AxB , where y is the particle differential flux and x is the particle energy [5]. This equation can be applied to the proton detection data and to derive the values of A and B. This function is then used to get the proton flux in the ranges of 3–5 and 35–275 MeV (see the details of the fitting method in the Appendix). Fig. 4 shows the proton flux from SEM and MEPED (to each chosen point, MEPED’s flux is y, and SEM’s flux is x). The proton flux detected by SEM has a good relationship with that detected by MEPED. It is seen that the overall trends from two instruments agree well with a correlation coefficient greater than 0.9. HUANG et al.: CAPABILITIES AND APPLICATIONS OF FY-3A/B SPACE ENVIRONMENT MONITOR 4979 Fig. 5. FY-3A SEM electron flux detections compared with POES MEPED’s data (from November 11 to December 11, 2010, using N17’s data). The comparison solutions of the electron flux detected by SEM and MEPED are similar to that of the protons. Due to the fact that intensities of electrons are badly affected by geomagnetic activities, we select the electron data with more closer space position and observation time and low latitude in SAA. The electron flux detected by SEM has good relationships with the detections of MEPED, and the point variation trends are coinciding. However, the comparison points are less than that of protons because of strict selection criteria. (a) Electron 0.65–1.20-MeV comparisons. (b) Electron 0.35–0.65-MeV comparisons. (c) Electron 0.15–0.35-MeV comparisons. B. Electron Flux Data at Earth. The flux subroutines (also called “space ionizing radiation environment model”) of CREME require the inputs of the date, the range of nuclear charges considered, the type of orbit, and an “interplanetary weather index (M ).” Then, the model outputs the specified particle flux at the orbit that you are interested in. More details can be found at the Web site: https:// creme.isde.vanderbilt.edu. The electron intensities are strongly affected by the Earth geomagnetic field. In this paper, the electron data from SEM and MEPED collocated in space and time at low latitude in SAA are produced. Those data at high latitudes are excluded since they are highly affected by the geomagnetic field and precipitating particles from the aurora belt (http://poes.ngdc. noaa.gov/docs/status2008-01-10.pdf). The intercomparison of the electron flux is similar to that for proton. The electron flux data from different satellites fit in these energy bands: 0.15–0.35, 0.35–0.65, and 0.65–1.2 MeV are shown in Fig. 5. The electron flux detected by SEM is correlated with that detected by MEPED, and the trends agree well with a correlation coefficient greater than 0.9. However, the total number of data points used for electron comparison is smaller than that for protons because of strict selection criteria applied (the location difference is less than 0.5◦ at each latitude and longitude, the difference of observation time is less than 15 days, and the pitch angle’s difference absolute value is less than 5◦ ). The minimum response of surface potential detector is about 13 V. When the space environment is stable, the daytime detector shows a positive potential (maximum potential is about 16.7 V), and the nighttime detector shows a negative potential (minimum potential is about −21 V). These magnitudes are derived from the space science principle. The surface potential instrument of SEM aboard FY-3A satellite detected an obvious charging event induced by a geomagnetic storm on April 5, 2010 (see Fig. 7). The detector had a record of −50 V from the effects of charged particles. C. Heavy Ion Compositions E. Radiation Dose Data Heavy ion compositions at the LEO are needed for space weather forecast. The SEM’s heavy ion composition data are compared with Cosmic Ray Effects on Microelectronics (CREME) 1986 version (CREME86) model. The distributions of heavy ions detected by SEM are shown in Fig. 6 (The difference of panels Fig.6(a) and (b) is due to the data processing method. The method of He is more like protons although He is called “heavy ion,” so our data processing system produces the He map like the proton maps.), and the comparison details are shown in Table I. Overall, the composition detected from SEM falls within the range of the CREME86 model. The CREME86 model is the CREME model (1986 version). It is a software tool developed to investigate the effects of an ionizing radiation environment on the electronics inside a satellite, i.e., SEUs due to solar heavy ions. This model suite can perform SEU rate calculations, give the abundance and energy distribution of heavy ions, etc. The CREME86’s interplanetary flux outputs (galactic cosmic rays, anomalous cosmic rays, and solar energetic particles) are based on measurements In the past three years, the radiation dose detected by SEM increases with time in orbit, as shown in Fig. 8. The detections are accumulated dosage detections (day’s average in Fig. 8), and the sampling frequency of the detectors is 42 s. Both lowand high-resolution detectors show an increase in radiation dose. The radiation dose increases with time, and the trends reflect the characteristics of space environment. After the geomagnetic storm on April 5, 2010, the radiation dose showed a substantial growth (36 rd(Si)/day) due to the disturbance of charged particles in space environment. D. Surface Potential Data F. SE Record The SE detector has not recorded SEU events until now. According to the ground accelerator test, the linear energy transfer value of SEU is above 65 MeV/(mg/cm2 ). Thus, the radiation protection of 1750A is well designed, and there is little chance of SEU. In the ground test, the probability is calculated by CREME86 with aluminium of 3 mm thick at the worst 4980 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 50, NO. 12, DECEMBER 2012 Fig. 6. FY-3B SEM heavy ion compositions (from December 1 to 15, 2010). Due to the fact that public information about LEO heavy ion compositions is lacking, we test the validity of SEM’s heavy ion composition data by CREME86 model. The results coincide with the CREME86 model’s outputs. (a) CNO ion 60–570 MeV. (b) He ion 12–110 MeV. (c) Mg ion 0.2–1.2 GeV. TABLE I C OMPARISONS OF H EAVY I ONS (N OVEMBER 11–D ECEMBER 15, 2010) case cosmic ray level in FY-3A’s orbit. The SEU probability is 2.23 × 10−13 /(bit × day). The calculation is consistent with the ground accelerator test and the detection in orbit. IV. DATA A PPLICATIONS The space environment information provided by SEM is applied for space weather warning and forecast, service of manned spaceflight missions, the radiation-hardened designs of spacecraft, and some aspects of space science study. HUANG et al.: CAPABILITIES AND APPLICATIONS OF FY-3A/B SPACE ENVIRONMENT MONITOR 4981 detected by SEM in the aurora belt after a solar proton flare burst. SEM is the measurement in situ, and it takes 16 days to describe the whole picture of radiation belt with single satellite data. If space weather disaster occurs, FY-3A/B’s SEM can take intensive observations with combining two satellites’ data which describes the complete picture of radiation belt in about 10 days as shown in Fig. 10. B. Service for Man-Carrying Spaceflight Fig. 7. FY-3A SEM surface potential detections after a geomagnetic storm (on April 5, 2010). The charged particles cause about −50-V decrease in surface potential detections. The charged events occurred at the latitudes from 70◦ S to 80◦ S (the longitude of the position changed fast for the satellite is in the polar region) with the significant electron flux increasing (E1 and E2 fluxes even reached 2 × 105 , twice as much as usual). The minimum position is about at 73◦ S, 18◦ W. The man-carrying spaceflight is usually at the low altitudes (about 300 km), and the particle radiation always can cause a hazard for astronauts during their space walks. By calculating the particle distribution in SAA using SEM’s data (calculate the global particle distribution at the altitude of 300 km with the particle data of 830 km high and the geomagnetic field model), we can provide a time window for the astronauts to safely walk out the orbital module. In the service of Shenzhou VII manned spaceflight mission, the time window was forecasted successfully for astronauts’ space walk (see Fig. 11). C. Scientific Study of Interdiscipline Fig. 8. FY-3A SEM radiation dose detections (from June 25, 2008, to February 25, 2011). The differences of detections are due to instruments’ positions and orientations. The radiation dose detected by SEM is increasing stably in orbit. The radiation dose increased obviously after a geomagnetic storm on April 5, 2010, because of the charged particle disturbances in space environment. At present, scientific studies focus on the precipitating particle effect on the environment of the Earth. These particles produce odd nitrogen NOx when they precipitate into the Earth’s atmosphere. NOx is regarded as a catalyzer to destroy ozone [1]. Scientists have found that energetic particle precipitation (EPP) events were linked to significant ozone decreasing in the upper stratosphere at polar region [10], [13]. By altering stratospheric ozone content, EPP can influence the stratospheric radiative balance and may link to climate variability. Some calculations show about 2-K variations of air temperature in polar region that is caused by EPP effects [11]. The magnitude of the atmospheric response to EPP events can potentially exceed the influences from solar UV flux. The Total Ozone Unit (TOU) is also a payload of FY-3A/B. The detections by TOU and SEM are helpful for the global correlation analysis about ozone, and EPP may be one of the factors of the global climate change. V. C ONCLUSION AND D ISCUSSION A. Monitoring Space Weather Events When space weather events occur, the increasing number of the charged particles causes disturbances of space radiation environment, particularly at the polar region in LEO orbit. FY-3A/B cross the polar region 14 times per day and monitor the high-energy charged particle variations. While intense solar flares or geomagnetic storms occur, the number of precipitating charged particles increases fast, and the energetic protons appear at high latitude (high-energy protons usually exist in SAA and rarely present at high latitude). These protons are known as “killer particles” because they are harmful to LEO spacecrafts going through this region. Fig. 9 shows the solar proton event [(SPE), the proton energies are above 10 MeV] In this paper, we have presented the SEM instrument characteristics and the postlaunch scientific results. SEM aboard FY-3A/B satellites was calibrated during the prelaunch and met the requirements. The data are validated through the comparison with the measurement from NOAA POES MEPED. We confirm that SEM’s data are valid and are consistent with the knowledge of space science principles. However, it remains difficult for comparing the electron flux data detected by SEM with MEPED at high latitude due to the complex particle distribution induced by geomagnetic activities. The information about space environment can be used in space weather forecast and warning, satellite security designs, satellite malfunction analysis, and scientific studies. We hope that the data of SEM may be applied in more aspects of space science in the future. 4982 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 50, NO. 12, DECEMBER 2012 Fig. 9. FY-3A SEM proton detections about SPE at polar region. (a) is from August 29 to September 13, 2011. (b) is from January 15 to 31, 2012. SPEs caused by intense solar flares or corona mass ejection (CME) are always accompanied by those high-energy protons that appear at high latitude. The protons with particle energy over 10 MeV are called “killer particles.” These particles may damage the satellite and cause disruption of satellite’s system. The proton flux of 10–20-MeV energy band reached 5000 in the SPE caused by a solar flare with CME during the period of January 23–27, 2012, as shown in (b). (a) SPE detections in space weather quiet periods. (b) SPE detections in space weather disturbance periods. A PPENDIX A. How to Select Points and Do the Comparison First, we apply SEM’s data to match MEPED’s data by the constraints of the spatial location, the observation time, and the pitch angle. Then, we derive two data sets of chosen points. If there exist one point to several points, we do the average calculation of the several points to make the two data sets have one-to-one relationship. Second, we make grids that each grid has integer latitude and longitude (e.g., 1◦ S, 1◦ E; 1◦ S, 2◦ W; 1◦ S, 3◦ E; and so on). We average the points’ flux which points fall in the range of 0.5◦ near each grid and regard the average flux as the grid’s flux (this work is used to avoid the effects of fluctuation). Then, we have two grid flux data sets of SEM and MEPED. We plot SEM’s data as x and MEPED’s data as y to calculate the correlation coefficient of two data sets, the fitting line slope, and the standard deviation. B. Algorithm of Fitting Different Energy Bands for Electrons We select MEPED electron directional (MEPED-0, in the low-latitude region) detections (0.03–1.1, 0.1–1.1, and 0.3–1.1 MeV) to do intercomparison with SEM electron detections (0.15–0.35, 0.35–0.65, 0.65–1.2, 1.2–2.0, and 2.0– 5.7 MeV). We define the MEPED-0 fluxes of 0.03–1.1, 0.1–1.1, and 0.3–1.1 MeV as f1 , f2 , and f3 , respectively. The energy spectrum equation follows the power law y = axb , where y is the differential flux and x is the median of the energy range (by logarithmic transformation of the equation). There are two arrays as follows: f1 − f2 f2 − f3 f3 , , y= 0.1 − 0.03 0.3 − 0.1 1.1 − 0.3 lg0.03+lg0.1 lg0.1+lg0.3 lg0.3+lg1.1 2 2 2 . x = 10 , 10 , 10 (1) Then, we fit the two arrays and derive the values of a and b. Integrating the function to derive the fluxes (f ) in SEM’s energy bands ⎡ 0.35 ⎤ 0.65 1.2 b b b ⎢ 0.15 ax Δx, 0.35 ax Δx, 0.65 ax Δx, ⎥ ⎥. f = ⎢ 2.0 5.7 ⎣ ⎦ b b ax Δx, ax Δx 1.2 (2) 2.0 Because 1.2–2.0 and 2.0–5.7 MeV are out of the energy range of MEPED-0 detections, the fitting fluxes may deviate the truth values. We only apply the fitting fluxes of first three energy bands (0.15–0.35, 0.35–0.65, and 0.65–1.2 MeV) in the comparison with SEM. HUANG et al.: CAPABILITIES AND APPLICATIONS OF FY-3A/B SPACE ENVIRONMENT MONITOR 4983 Fig. 10. Global radiation belt map combined by FY-3A and FY-3B in 10 days (from November 12 to 21, 2010). The space weather monitoring is a whole observation. When we observe an intense solar flare or CME toward the Earth, we know that the particles from the Sun will reach near-Earth space environment soon and go along the geomagnetic field lines into the polar region (the cause of aurora). When protons with the particle energy over 10 MeV occur in the polar region, we define that the space weather event is a space weather disaster and start to combine the pictures. (a) Electrons: 0.35–0.65 MeV. (b) Protons: 10–26 MeV. Fig. 11. FY-3A SEM’s data applied in manned spaceflight missions. We calculate the time window that tells what period is appropriate for astronauts to do space walk (the period from hh:mm to hh:mm is a safe time window, etc). The calculation is based on the SAA region detections, the geomagnetic model (International Geomagnetic Reference Field model), and the spacecraft orbit forecast. First, we use IGRF model and the SAA detections of SEM (830-km altitude) to calculate the SAA region’s shape at 300-km altitude (the charged particles are bound by the geomagnetic field, so we can apply IGRF model to construct a 3-D grid by interpolation method). Then, according to the calculation of the SAA region’s shape at 300-km altitude and the spacecraft orbit forecast data, we know when the spacecraft runs in and out of the SAA region that is dangerous for astronauts who are outside the orbital module. 4984 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 50, NO. 12, DECEMBER 2012 C. Algorithm of Fitting Different Energy Bands for Protons 1) To 35–275-MeV Energy Band: MEPED proton omnidirectional detections have four energy bands: 16–220, 35–235, 70–235, and 140–275 MeV. We exclude the detections of 16–220 MeV in the comparison due to that the detections in this energy band are shaded by the adjacent instruments, which resulted in the proton counts that are not quite accurate in this range. We define the fluxes of 35–235, 70–235, and 140– 275 MeV as P1 , P2 , and P3 , respectively. The flux of 35– 275 MeV (MEPED) is Ptotal . We have the equation Ptotal = 0.849(P1 − P2 ) + 0.341(P2 − P3 ) + 0.341 × P3 . This equation is mentioned in the readme file on http://poes.ngdc.noaa. gov/data/. Then, we derive Ptotal of each grid of MEPED proton detections. SEM proton detections have six energy bands: 3–5, 5–10, 10–26, 26–40, 40–100, and 100–300 MeV. With higher energy, particles show more isotropic characteristics. Thus, we choose the last four energy bands (10–26, 26–40, 40–100, and 100– 300 MeV) to do the comparison with MEPED’s omnidirectional detections of 35–275 MeV. We define the fluxes of 10–26, 26–40, 40–100, and 100–300 MeV as f1 , f2 , f3 , and f4 , respectively. The fitting flux of 35–275 MeV (SEM) is ftotal . To each grid of SEM detections, we fit the values of f1 , f2 , f3 , and f4 with the energy spectrum equation y = AxB (the power law). The method is similar to the electrons. Then, we derive the values of A and B. We integrate this function (y = AxB ) from 35 to 275 MeV to derive ftotal and compare ftotal with Ptotal . 2) To 3–5-MeV Energy Band: With lower energy, particles show more anisotropic characteristics. Therefore, we select MEPED directional (MEPED-0, in the low-latitude region) detections (800–2500 and 2500–6900 keV, these two energy bands) to do the intercomparison with SEM’s detections of 3–5 MeV. The method is similar to that of 35–375 MeV. We fit the flux values of 800–2500 and 2500–6900 keV with the power law equation (y = AxB ) to derive the values of A and B and integrate the function to derive each grid’s flux of 3–5 MeV. Then, we compare each grid’s flux of MEPED-0 with SEM in the energy band of 3–5 MeV. D. About the Proton Contamination in the Electron Channel About the proton contamination issue stated in the POES’s documentation (http://poes.ngdc.noaa.gov/docs/sem2_docs/ 2006/SEM2v2.0.pdf), we have mentioned that, in Section II-A paragraph 1, “These particles settle in the sensors and generate electric pulses. The amplitude and coincidence and anticoincidence of these pulses can be used to identify the particle type.” The instruments can identify the particle type by the threshold value of the particle energy deposition in the layer, i.e., the instruments’ electronic characteristics. According to the instrument design working reports, the simulation also shows that the proton contamination effects can be neglected in the energy bands of electrons in the ground test of prelaunch period. In other words, to avoid the proton contamination is an electronic characteristic design in sensor’s hardware. For example, if the electrons of 2 MeV have the same settle energy to that of the 10-MeV protons in the sensors. First, the sensor’s design can get rid of the 10-MeV protons and let the electrons of 2 MeV go into the telescope in the front according to the differences of the particle energy. Then, the design of coincidence–anticoincidence electrocircuit has the ability to distinguish the particle’s type due to the different pulse responses of protons and electrons. Although the two methods cannot eliminate the effect of proton contamination completely, it will reduce the influence to an acceptable level. Mentioned earlier is the hardware solution to avoid the proton contamination for FY-3’s SEM electron data. In the comparison work, we define that the POES’s data to public are a standard source (POES’s data have been cross-calibrated). We did not do any other operation with POES’s electron data. We select space weather quiet period, and the inner radiation belt (SAA) is very stable. The proton contamination will bring a stable system error (not random) between POES’s MEPED and FY-3’s SEM. The system error can be corrected by fitting method in the postlaunch calibration of SEM’s data. The correction coefficient is added into the SEM product process. After those solutions and with the strict selection criteria, we think MEPED and SEM can be compared together and the electron flux comparisons are reliable. ACKNOWLEDGMENT The authors would like to thank S.-J. Wang’s group, the SEM instrument research team, who are with the Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, China, for their help. Thanks to T. Yu’s work as the corresponding author. R EFERENCES [1] G. Brasseur and S. Solomon, Aeronomy of the Middle Atmosphere, 3rd ed. Dordrecht, The Netherlands: Reidel, 2005. [2] M. V. Codrescu, T. J. Fuller-Rowell, R. G. Roble, and D. S. Evans, “Medium energy particle precipitation influences on the mesosphere and lower thermosphere,” J. Geophys. Res., vol. 102, no. A9, pp. 19 977– 19 987, Sep. 1997. [3] H. Du and Z. H. Ye, Space Environment Handbook for LEO Spacecraft [S], vol. 402. Beijing, China: National Defence Industry Press, 1996. [4] H. H. Heckman and G. H. Nakano, “Low-altitude trapped protons during solar minimum period,” J. Geophys. Res., vol. 74, no. 14, pp. 3575–3590, Jul. 1969. [5] R. Gubby and J. Evans, “Space environment effects and satellite design,” J. Atmos. Solar-Terr. Phys., vol. 64, no. 16, pp. 1723–1733, Nov. 2002. [6] W. N. Hess, The Radiation Belt and the Magnetosphere. New York: Blaisdell, 1968. [7] X. L. Li, D. N. Baker, and S. G. Kanekal, “Long term measurements of radiation belts by SAMPEX and their variation,” J. Geophys. Res. Lett., vol. 28, no. 20, pp. 3827–3830, 2001. [8] C. E. Mcllwain, “Coordinates for mapping the distribution of magnetically trapped particles,” J. Geophys. Res., vol. 66, no. 11, pp. 3681–3691, 1961. [9] T. G. Northrop and E. Teller, “Stability of the adiabatic motion of charged particles in Earth’s field,” Phys. Rev., vol. 117, no. 1, pp. 215–225, Jan. 1960. [10] C. E. Randall, V. L. Harvey, G. L. Manney, Y. Orsolini, M. Codrescu, C. Sioris, S. Brohede, C. S. Haley, L. L. Gordley, J. M. Zawodny, and J. M. Russell, “Stratospheric effects of energetic particle precipitation in 2003–2004,” Geophys. Res. Lett., vol. 32, pp. L05802-1–L05802-4, 2005. [11] E. Rozanov, L. Callis, M. Schlesinger, F. Yang, N. Andronova, and V. Zubov, “Atmospheric response to NOy source due to energetic electron precipitation,” Geophys. Res. Lett., vol. 32, pp. L14811-1–L14811-4, 2005. [12] D. M. Sawyer and J. I. Vette, “AP8 trapped proton environment for solar maximum and solar minimum,” NASA, Washington, DC, CA, NSSDC/WDC-A-R&S Rep. NASA-GSFC, 76-06, 1976. HUANG et al.: CAPABILITIES AND APPLICATIONS OF FY-3A/B SPACE ENVIRONMENT MONITOR [13] A. Seppälä, M. A. Clilverd, and C. J. Rodger, “NOx enhancements in the middle atmosphere during 2003–2004 polar winter: Relative significance of solar proton events and the aurora as a source,” J. Geophys. Res., vol. 112, no. D23, pp. D23 303-1–D23 303-11, 2007. doi:10.1029/2006JD008326. [14] J. I. Vette, “The AE 28 trapped electron model environment,” NASA, Washington, DC, CA, NSSDC/WDC-A-R&S Rep. NASA-GSFC, 91-24, 1991. Cong Huang was born in Jilin, China, in 1978. He received the B.Sc. and Ph.D. degrees in astrophysics from Peking University, Beijing, China, in 2001 and 2006, respectively. Since 2006, he has been with the Division of Space Weather, National Satellite Meteorological Center, Beijing, as a Research Associate. His research interests are the space environment monitoring of low Earth orbit satellites, the space weather forecast model building, the observation data assimilation, and the climate change induced by space weather. He is the author or coauthor of more than ten Science Citation Index and Index Scientific Technical Proceedings papers published in astrophysics and space physics journals and presented at international conferences. He is also the coauthor of three books of teaching materials. Dr. Huang is a member of Asia Oceania Geosciences Society and was the recipient of the Best Oral-Report Award of the Seventh China Space Weather Symposium in 2009. Since 2010, he has been the Academic Secretary of the Space Weather Society which belongs to Chinese Meteorological Society. Jia-Wei Li was born in China in 1977. He received the Ph.D. degree in space physics from the University of Science and Technology of China, Hefei, China, in 2006. Since 2006, he has been with the National Satellite Meteorological Center, Beijing, China, as a Research Associate. His main efforts are on the space weather monitoring instruments onboard FengYun series meteorological satellites, including the instruments capability designing, and the data processing, calibration, application, and data analysis. Tao Yu was born in Hubei, China, in 1975. He received the Ph.D. degree in space physics from the Chinese Academy Sciences, Beijing, China, in 2003. Since 2003, he has been with the National Satellite Meteorological Center, Beijing, as a Research Fellow. His research interests are in the area of ionosphere research and the ionosphere model building with the observation data assimilation. He is the author or coauthor of more than 30 Science Citation Index and Index Scientific Technical Proceedings papers published in astrophysics and space physics journals and presented at international conferences. Bing-Sen Xue was born in China in 1966. He received the Ph.D. degree in space physics from the University of Science and Technology of China, Hefei, China, in 2008. Since 2008, he has been with the National Satellite Meteorological Center, Beijing, China, as a Chief Forecaster for space weather with the job title of Research Fellow. His research interests are in the main area of space weather forecast method. He is carrying on the application of FengYun series satellite data in space environment monitoring the effects induced by space weather. He has got several results and applied them into forecast practices, such as the forecast of relativistic electron enhancement forecast and deep charging estimation for FengYun satellites. His research on geomagnetic storm forecast algorithm and its following effects on satellite are undergoing as well. 4985 Chun-Qin Wang was born in China in 1978. She is currently working toward the Ph.D. degree in astrophysics at the Chinese Academy of Sciences (CAS), Beijing, China. Since 2001, she has been with the National Space Science Center, CAS, as a Research Associate. She is engaged in observation data analysis and focusing on data of magnetosphere energetic particle. Her research interests are dynamic changes in radiation belt. Xian-Guo Zhang was born in Shandong, China, in 1979. He received the Ph.D. degree in space physics from Peking University, Beijing, China, 2007. He is currently with the National Space Science Center, Chinese Academy of Sciences, Beijing, as an Associate Professor. His research interests are the space environment monitoring and the dynamic changes in radiation belt. Guang-Wei Cao was born in Shandong province, China, in 1981. He received the M.Sc. degree in space physics from the Graduate University of Chinese Academy of Sciences, Beijing, China, in 2007. Since 2007, he has been with the National Space Science Center, Chinese Academy of Sciences, Beijing, as an Engineer. His research interests are the space environment monitor designing and the space dust detector designing. Dan-Dan Liu was born in Hubei, China, in 1979. She received the B.Sc. degree in electronic information engineering and the M.Sc. degree in space physics from Wuhan University, Wuhan, China, in 2003 and 2006, respectively. Since 2006, she has been with the Division of Space Weather, National Satellite Meteorological Center, Beijing, China, as a Research Assistant. Her research interests are the neural network application in the space weather forecast, the radio wave propagation in ionosphere, and optimization analysis in power consumption. She is the author or coauthor of more than ten Science Citation Index, The Engineering Index, and Index Scientific Technical Proceedings papers published in space physics and wireless communication journals and presented at international conferences. She is also the coauthor of three books of teaching materials. Wei Tang was born in Shanxi, China, in 1980. He received the B.Sc. degree in space physics from Peking University, Beijing, China. Since 2002, he has been with the National Satellite Meteorological Center, Beijing, as a Forecaster for space weather with the job title of Research Assistant. His interests are in the area of space weather forecast and the application of FengYun series satellite data of space environment.