CNTEC: A regional ionospheric TEC mapping
technique over China and adjacent areas

Ercha Aa, Wengeng Huang, Yanhong Chen, and Hua Shen
National Space Science Center, Chinese Academy of Sciences

Outline
1. TEC Global/Regional Ionospheric Maps
2. GNSS Data Processing and TEC Derivation
3. TEC RIMs Construction: Data Assimilation
4. Results Comparison and Validation

TEC GIM/RIMs
2.5o *5o *2 hour

Who provides Global Ionospheric Maps?
 Center for Orbit Determination of Europe (CODE) Jet Propulsion Laboratory (JPL) European Space Agency (ESA) Polytechnical University of Catalonia (UPC) Energy Mines and Resources Canada (EMR)

1o *1o *5 min MIT Automated Processing of GPS (MAPGPS)

What about typical Regional Ionospheric Maps?

N. America~2,700 Receivers[Tsugawa et al., 2007]

What about TEC RIMs over China?

Japan~1,200 Receivers[Tsugawa et al., 2011]

Europe~1,200 Receivers[Otsuka et al., 2012]Outline
1. TEC Global/Regional Ionospheric Maps
2. GNSS Data Processing and TEC Derivation
3. TEC RIMs Construction: Data Assimilation
4. Results Comparison and Validation

GNSS Data Processing & TEC Derivation• GNSS Receivers over China and adjacent areas (15o-55oN, 70o-140oE)~300+ Receivers
Crust Movement
Observation
Network of China(CMONOC)

International
GNSS
Service(IGS)Space
Environment
Prediction
Center (SEPC)

260+ Receivers

38 Receivers

9 receivers• TEC can be derived by combining the Pseudo-range and Carrier Phasemeasurements of the GPS dual frequency signals
Pseudo-range TEC

TECPCarrier Phase TEC( f L1 f L 2 ) 2c( f L1 f L 2 ) 2
PR
−PR
()
( L1λ1 − L2λ2 + b1λ1 − b2λ2 )
=TEC
L2
L1L
40.3( f L21 − f L22 )40.3( f L21 − f L22 )TEC= TECL + Brs=BrsN∑ (TECkP − TECkL ) sin 2 elkN∑ sin el=k 1=k 12k

fL1 = 1.575 GHz
fL2 = 1.227 GHz

GNSS Data Processing & TEC Derivation
Flow chart of the TEC derivation
DataAcquisition andUpdate

RINEX files(~300 stations)Navigation
files

Data
Input

Orbit
Parameters
Calculating

Observation
files

IPPs Position
Calculating

Cycle Slip
Removement

SystemConfiguration
Files

TEC derivation @ Ionospheric Pierce Points
StationLatitude

Longitude

SHAO

39.62

115.90

2-D Trail of IPPs

3-D Projection of IPP(TEC)

IPPs Vertical TEC

Receiver-Sat Slant TEC

Sat. andReceiver DCBs

VTEC andSTEC at IPPs

IPPs TEC over China and adjacent areas

Outline
1. TEC Global/Regional Ionospheric Maps
2. GNSS Data Processing and TEC Derivation
3. TEC RIMs Construction: Data Assimilation
4. Results and Validation

TEC RIMs Construction: Data Assimilation• The aim of DA scheme is to use measured observations in combination with adynamical system model to derive accurate estimates of the states of the system.
N. K. Nichols (2010)
Observation: TEC Measurements

Assimilation technique: Kalman Filter
Initial estimation
X: state variables
Z: observation vectors
dij: distance between i and j
Lij: iono-correlation lengthα¥β: associated coefficients

Model: International Reference IonospherePij = α X ib X bj e

− d ij / Lij

Rij = β z 2δ ij
1 cos2 (α ) sin 2 (α )=+L2ijLθ i Lθ j
Lϕ i Lϕ j

Time Update (“Predict”)
=xk− Axk −1 + Buk −1
1. Project the state ahead
Pk− APk −1 AT + Q
2. Project the error covariance =Measurement Update (“Correct”)
3. Compute the Kalman =gain
K k Pk− H T ( HPk− H T + R ) −1
 −
4. Update estimate
xk =xk + K k ( zk − Hxk− )5. Update the error covariance

P=( I − K k H ) Pk−k

TEC RIMs over China and Adjacent Areas (1o *1o *5 min)Outline
1. TEC Global/Regional Ionospheric Maps
2. GNSS Data Processing and TEC Derivation
3. TEC RIMs Construction: Data Assimilation
4. Results Comparison and Validation

Results Comparison and Validation
Cross-Validation with 8 GNSS Stations

Comparison with IRI and CODE TECDASubtle Structure√

Local Variation√

Climate Variation

IRI√

bjfs

shaowuhn

twtfurumxiaalhaz

kmin

Lat

39.6

31.1

30.5

24.9

43.6

34.2

29.6

25.0

Lon

115.9

121.2

114.4

121.2

87.6

109.0

91.1

102.8

CODE

√

The TEC data at each one of the 8 stations is
excluded from data assimilation process, this makes
the chosen data independent for comparison

Comparison with CODE GIMs
Analysis centers provide GIMs of TEC

5o *2.5o *120 min Center for Orbit Determination of Europe (CODE) Jet Propulsion Laboratory (JPL) European Space Agency (ESA) Poly-technical University of Catalonia (UPC) Energy Mines and Resources Canada (EMR)
RMSE=
NRMSE =1 N
∑ (TECmod − TECref )2
N i =1
1 N TECmod − TECref 2)∑ ( TECN i =1refComparison with Madrigal Database (1o *1o *5 min)
IRI TEC

Data Assimilation TECTECDA (IRI )– TECMadrigal @ Jan. 2014TECDA (IRI )– TECMadrigal @ Jul. 2013

Summary and Conclusion• A new technique has been developed to derive TEC over China andadjacent areas using CMONOC and IGS data, and a data assimilation
method based on Kalman filter scheme is used to assimilate the TEC data
into the background IRI model. Regional TEC maps over China andadjacent area (70oE-140oE and 15oN-55oN) are generated accordinglywith the resolution being 1o*1o and 5 min respectively.
• The accuracy and validity of data assimilation results have been verified
through the comparison with IRI, CODE, and Madrigal TEC data. The
data assimilation results are able to capture more subtle local
characteristics of TEC variation, and can get a smaller RMSE than thoseresults with no assimilation.
• The histogram and correlation analysis also indicate that considerable
systematic improvements can be obtained when GNSS data areassimilated into the background model, which demonstrates the viability
and effectiveness of the data assimilation method.