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

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1 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

2 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

3 TEC GIM/RIMs 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) 2.5 o *5 o *2 hour 1 o *1 o *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? Europe ~1,200 Receivers Japan [Otsuka et al., 2012] ~1,200 Receivers [Tsugawa et al., 2011]

4 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

5 GNSS Data Processing & TEC Derivation GNSS Receivers over China and adjacent areas (15 o -55 o N, 70 o -140 o E) Crust Movement Observation Network of China (CMONOC) ~300+ Receivers 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 Phase measurements of the GPS dual frequency signals Pseudo-range TEC ( f f ) TEC ( PR PR ) 2 L1 L2 P = 2 2 L2 L1 40.3( fl 1 fl2) Carrier Phase TEC c( f f ) TECL = ( L1λ1 L2λ2+ b1λ1 b 2λ2) 40.3( ) 2 L1 L2 2 2 fl 1 fl2 f L1 = GHz f L2 = GHz TEC = TEC + B N N P L 2 2 rs = ( k k )sin k sin k k= 1 k= 1 B TEC TEC el el L rs

6 GNSS Data Processing & TEC Derivation Flow chart of the TEC derivation TEC Ionospheric Pierce Points Data Acquisition and Update RINEX files (~300 stations) System Configuration Files Station Latitude Longitude SHAO Navigation files Data Input 2-D Trail of IPPs 3-D Projection of IPP(TEC) Orbit Parameters Calculating Observation files Sat. and Receiver DCBs IPPs Position Calculating Cycle Slip Removement VTEC and STEC at IPPs IPPs Vertical TEC Receiver-Sat Slant TEC

7 IPPs TEC over China and adjacent areas

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

9 TEC RIMs Construction: Data Assimilation The aim of DA scheme is to use measured observations in combination with a dynamical system model to derive accurate estimates of the states of the system. Observation: TEC Measurements N. K. Nichols (2010) Assimilation technique: Kalman Filter X: state variables Z: observation vectors d ij : distance between i and j L ij : iono-correlation length α β: associated coefficients Initial estimation P b b ij i j R = α X X e = βz δ d / L 2 ij ij cos ( α) sin ( α) = + 2 ij θi θ j ϕi ϕ j L L L L L ij ij Model: International Reference Ionosphere Time Update ( Predict ) 1. Project the state ahead x = Ax + Bu 2. Project the error covariance k k 1 k 1 T Pk = APk 1A + Q Measurement Update ( Correct ) 3. Compute the Kalman gain 4. Update estimate 5. Update the error covariance K = PH ( HPH + R) x = x + K ( z Hx ) T T 1 k k k k k k k k P= ( I KHP ) k k k

10 TEC RIMs over China and Adjacent Areas (1 o *1 o *5 min)

11 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

12 Results Comparison and Validation Comparison with IRI and CODE TEC Subtle Structure Local Variation DA IRI CODE Climate Variation Cross-Validation with 8 GNSS Stations bjfs shao wuhn twtf urum xiaa lhaz kmin Lat Lon The TEC data at each one of the 8 stations is excluded from data assimilation process, this makes the chosen data independent for comparison

13 Comparison with CODE GIMs Analysis centers provide GIMs of TEC 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) 5 o *2.5 o *120 min N 1 RMSE = ( TECmod TECref ) N i= 1 1 NRMSE = N N i= 1 TEC TEC ( ) TEC mod ref 2 ref 2

14 Comparison with Madrigal Database (1 o *1 o *5 min) IRI TEC Data Assimilation TEC TEC DA (IRI ) TEC Jan TEC DA (IRI ) TEC Jul. 2013

15 Summary and Conclusion A new technique has been developed to derive TEC over China and adjacent 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 and adjacent area (70 o E-140 o E and 15 o N-55 o N) are generated accordingly with the resolution being 1 o *1 o 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 those results with no assimilation. The histogram and correlation analysis also indicate that considerable systematic improvements can be obtained when GNSS data are assimilated into the background model, which demonstrates the viability and effectiveness of the data assimilation method.

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