BDGIM: A new global ionospheric correction model …bss2019.uwm.edu.pl/sites/default/files/uploads/1._yunbin...BDGIM: A new global ionospheric correction model for BeiDou-3 system

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)

**[email protected]

*[email protected]

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


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


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


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%


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)



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)



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


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



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



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)



Global vTEC map reproduced by re-estimated BDGIM model (Wang et al., 2019)



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


Validation results during BeiDou-3S (experimental) test period


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: %)



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



BDGIM performance – regional assessment

Ionospheric correction percentage of

the individual ionospheric model with

respect to GPS TECs over China

Yuan et al. (2019)



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



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


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]

Documents

BDGIM: A new global ionospheric correction model …bss2019.uwm.edu.pl/sites/default/files/uploads/1._yunbin...BDGIM: A new global ionospheric correction model for BeiDou-3 system