BDGIM: A new global ionospheric correction model for
BeiDou-3 system
Yunbin YUAN1, Zishen LI2*, Ningbo WANG2,3**, Xingliang HUO1
1 Institute of Geodesy and Geophysics (IGG-Wuhan), Chinese Academy of Sciences (CAS)2 Aerospace Information Research Institute (AIR-Beijing), CAS3 Institute of Astronomical and Physical Geodesy (IAPG), Technical University of Munich (TUM)
Olsztyn, Poland, BSS 2019
2 Aerospace Information Research Institute (AIR), CAS
• Background
• Status of BeiDou-3 satellite navigation System (BDS-3)
• Development and quality assessment of BDGIM
• Summary and Conclusions
Outlines
3 Aerospace Information Research Institute (AIR), CAS
Background (1/3)
Ionospheric delay errors on GNSS applications
Positioning TechniqueRequired IONO
QualityIONO Information Notes
Standard Point Positioning
(SF, 10-meter)50-70% Global broadcast models
Easy computation, few
transmitted parameters …
Wide Augmentation
Positioning (meter)85-90%
Grid-based wide area
augmentation ionospheric
correction
specific temporal and spatial
resolutions …
SF PPP
(sub-meter/dm)> 90%
Regional/global ionospheric
model
Real-time, high-rate, generated
from a set of dense GNSS
stations …DF PPP
(cm/dm)> 95%
Post-processing (mm) > 98% High-order ionospheric correctionSecond- and/or third-order
ionospheric corrections
4 Aerospace Information Research Institute (AIR), CAS
Background (2/3)
GNSS
satellite
Klobuchar
(50-60%)
NeQuickG
(70%)???
BDS
Requirements: limited broadcast parameters, high quality, computation efficiency
BDS-3: 25% (relative errors)
Problems to be handled
(1) better performance VS. Limited transmitted parameters
(2) Global service VS. Inhomogeneous sensing stations of OCX (mainland China)
Mathematical model
Observation data
Estimation method
Ionosphere
Users
5 Aerospace Information Research Institute (AIR), CAS
Background (3/3)
GPS Galileo BDS-2
Iono. modelsKlobuchar
(GPSKlob)NeQuickG
Klobuchar
(BDSKlob)
Algorithmcosine func. (day)
constant (night)Chapman Klobuchar-like
Singly-layer? 2D 3D 2D
Mapping func. Klobuchar n/a cosine
Par. number 8 3 8 (Civil users)
Update interval 2~7 days 24 hrs 2 hrs
Performance 50% 70% --
Comparison of GPS, Galileo and BDS-2/3 broadcast ionosphere models(CSNO, 2019)
BDS-3
BDGIM
SH
2D
cosine
9
2hrs
75%
6 Aerospace Information Research Institute (AIR), CAS
Status of BDS-3 (1/3)
BeiDou-3 Frequencies
Band Freq/MHz GPS Galileo BDS2 QZSS NAVIC BDS3
S 2492.028 Bs Bs
L
1575.420 L1 E1 L1 B1C
1561.098 B1-2 B1-2*
1278.750 E6
1268.520 B3 B3
1227.600 L2 L2
1207.140 E5b B2 B2b
1191.795 E5 B2a+b
1176.450 L5 E5a L5 L5 B2a
(Adapted from Yang 2018)
(Clock offset reference)
(New B1 frequency)
(…PPP…)
(New B2, … augmentation)
(Legacy B1 frequency)
7 Aerospace Information Research Institute (AIR), CAS
Status of BDS-3 (2/3)
BeiDou-3 Civil Signals
SignalFrequency
(MHz)
Signal
componentModulation
Observation
code
Service
type
B1 (B1-2) 1561.098 B1I BPSK(2) C2I OS
B1 (B1C) 1575.42 B1Cd BOC(1,1) C1D
B1Cp QMBOC(6,1,4/33) C1P
B2a 1176.45 B2ad BPSK(10) C5D
B2ap C5P
B3 1268.52 B3I C6I
(CSNO 2017a, 2017b, 2018, 2019)
8 Aerospace Information Research Institute (AIR), CAS
Status of BDS-3 (3/3)
BDS-3 COSPAR ID Launch date SVN PRN Manufacture Orbit Status
MEO-1 2017-069A 2017-11-05 C201 C19 CAST MEO Operational
MEO-2 2017-069B C202 C20
MEO-4 2018-018A 2018-02-12 C205 C22
MEO-3 2018-018B C206 C21
MEO-5 2018-062A 2018-07-29 C209 C23
MEO-6 2018-062B C210 C24
MEO-13 2018-072A 2018-09-19 C213 C32
MEO-14 2018-072B C214 C33
MEO-17 2018-093A 2018-11-18 C218 C36
MEO-18 2018-093B C219 C37
MEO-7 2018-003A 2018-01-11 C203 C27 SECM
MEO-8 2018-003B C204 C28
MEO-9 2018-029A 2018-03-23 C207 C29
MEO-10 2018-029B C208 C30
MEO-12 2018-067A 2018-08-24 C211 C26
MEO-11 2018-067B C212 C25
MEO-16 2018-078A 2018-10-15 C215 C35
MEO-17 2018-078B C216 C34
GEO-1 2018-085A 2018-11-01 C217 C59 CAST GEO Under test
9 Aerospace Information Research Institute (AIR), CAS
BDGIM ionospheric model
Development of BeiDou-3 BDGIM model
• Mathematical function: spherical harmonic (SH) expansion, widely used to describe
the variability of global VTECs.
• Problem: too many parameters to be transmitted (e.g. with degrees 15)
• Solution: parts to be estimated using BeiDou observation data, other parameters be
predicted with pre-determined periodicities
10 Aerospace Information Research Institute (AIR), CAS
BDGIM ionospheric model
Development of BeiDou-3 BDGIM model
9
0
1
vtec i i
i
T A A
1 2
BDGIM (Number of broadcast parameters: 9) Klobuchar (Number of broadcast parameters: 8)
Comparison of ionospheric TEC map produced by BDGIM and GPS
Klobuchar on the 80th day of 2012, respectively
Term #1 is calculated on the basis of coefficients predicted at user receivers
Term #2 is computed using the 9 coefficients transmitted in BeiDou nav. messages
(see also CSNO, 2019)
0
=5nscos 2
( )
tday
I t
n
AMPPER
tDC
DC
D ightC
GPS Klobuchar model
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BDGIM ionospheric model
Ionospheric VTEC computation using BDGIM
16 9
F 021
40.28 10ion i i
i
T M A Af
─ slant ionospheric delay along sat-to-receive signal path (in meter)ionT
FM ─ mapping function, cosine function with an assumed iono. height at 400 km
f ─ center frequency of the carrier phase (in Hz)
1~ 9i i ─ nine iono. parameters transmitted in BeiDou navigation message
1~ 9iA i ─ Legendre function depending on geomagnetic latitude and longitude
0A ─ predicted iono. delay at user receiver (depending on time and user location)
(CSNO, 2019)
12 Aerospace Information Research Institute (AIR), CAS
BDGIM ionospheric model
Global vTEC map reproduced by re-estimated BDGIM model (Wang et al., 2019)
13 Aerospace Information Research Institute (AIR), CAS
BDGIM ionospheric model
Validation results during BeiDou-3S (experimental) test period
Schemes TEC Data for Model Coef. Estimation TEC Data for Model Validation
1 [S1, R+C] Mainland China, BeiDou TECs #1 BeiDou TECs within China
#2 GPS TECs within China
#3 GPS TECs on global scales2 [S2, R+G] Mainland China, GPS TECs
3 [S3, G+G] Mainland China (12) + Oversea stations (4)
GPS TECs
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Validation results during BeiDou-3S (experimental) test period
BDGIM ionospheric model
Schemes
China and nearby regions Overseas (NH) Overseas (SH)
BDS TEC GPS TEC GPS TEC GPS TEC
S1, R+C 74.4 80.2 83.5 62.4
S2, R+G 76.5 82.2 81.9 66.3
S3, G+G 77.2 82.7 80.4 75.7
Correction percentage compared to independent BDS/GPS TECs (unit: %)
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BDGIM ionospheric model
Distributions of the sites selected for the
validation of BDGIM over China
Normalized histograms of model TEC errors with respect
to GPS TECs over China for DOY 060-181, 2015
BDGIM performance – regional assessment
Yuan et al. (2019)
BDGIM overperforms
GPS and BDS-2 Klobuchar models
by
17.9 and 12.2%, respectively, over China
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BDGIM ionospheric model
BDGIM performance – regional assessment
Ionospheric correction percentage of
the individual ionospheric model with
respect to GPS TECs over China
Yuan et al. (2019)
17 Aerospace Information Research Institute (AIR), CAS
BDGIM ionospheric model
BDGIM performance – global assessment
Yuan et al. (2019)
Distributions of the selected monitoring
(crosses) and test sites (dots) used for BDGIM
coefficient estimation and validationBias and STD of the differences between model TEC estimates
and GPS-derived TECs at each individual test site
BDGIM overperforms
GPSKlob, and NeQuickG
by
18.2, and 6.7%, respectively
18 Aerospace Information Research Institute (AIR), CAS
BDGIM ionospheric model
BDGIM performance – global assessment
Yuan et al. (2019)
RMS and correction percentage of
different ionospheric models with respect
to GPS TECs at the individual test site
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Summary and conclusions
BeiDou-3 constellation under very quick construction (new frequency bands,
new civil signals, freq. standards, satellite links, compatible to GPS/Galileo
L1/L5…), which is scheduled to provide FOC global service by 2020.
A new broadcast ionospheric model, BDGIM, is designed for BeiDou-3.
We (CAS) plan to release BDGIM C code program late this year (NOT CSNO
official one).
Zukunft denken
Thinking the Future
Thanks for your attention
In case of any questions, please feel free to contact:[email protected] / [email protected]