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IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 50, NO. 12, DECEMBER 2012
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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
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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
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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
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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
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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
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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.
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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.
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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.
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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.
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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.