GNSS ionosphere research activities at FCT/UNESP

João Francisgo Galera Monico, Paulo De Oliveira Camargo

FCT/UNESP - Presidente Prudente, SP.

Outline• Introduction• Developments on GNSS/Ionosphere

– Brazilian Ionospheric Model• Mod_ION• Mod_ION_FK/IG• Rinex_HO

• GNSS demands in Brazil• CIGALA & CALIBRA Projects• Final Comments

Ionosphere and GNSS• Ionospheric effects (delay and frequency dispersion & phase

scintillation and amplitude fading) are one of the main barriers to achieve high accuracy GNSS positioning and navigation.

• It affects the quality of positioning and navigation: PPP, relative carrier phase based positioning, DGNSS, GBAS and SBAS, mainly for users of one frequency receiver.

• Measurements made on two different frequencies allow the correction of the first order ionospheric delay by means of the widely used ionospheric-free linear combination (2nd order still has to be corrected).

Ionosphere and GNSS• Effects as ionospheric scintillations, may cause problems

such as:– signal power fading, – phase cycle slips, – receiver loss of lock, etc.,

• Such effects degrade the position quality provided by the satellite navigation systems (GNSS). This problem is still to be solved !

Developments on GNSS/Ionosphere at FCT/UNESP

• A Ion-model based on GNSS data has been under development since 1997;–Mod_Ion (in-house iono model) initially generated

coefficients for L1 users (Camargo et al., 2000)

• Mod_Ion expanded to generate Ionex files and Ionospheric maps from Brazilian GNSS data

• Real time: Mod_Ion_FK to generate the biases and a IG with respective GIVE are provided (Aguiar 2010).

n 4 m 4s s s s s s

1 2 j j 1 n*2 3 j j 1i 1 i 1j 2i 1 j 2i 10

VTEC a a B {a cos(i h ) a sin(i h )} a h {a cos(i B ) a sin(i B )}

2 2 2i 2i 1i 2iF f /(f f )

n 4s s s s s s s2 1 r r 1 2 j j 1 n*2 3

i 1j 2i 1

m 4s s s s

j j 1 P2 P1 r P2 P1 P21i 1j 2i 10

F(P P ) SF (a a B {a cos(i h ) a sin(i h )} a h

{a cos(i B ) a sin(i B )} F(R R ) F(S S ) F .

TEC s s TEC s s TECi 2r 1r i p2 p1 p2 p1 r i P21s

r

VTECF (P P ) + F [(S -S ) + (R -R ) ] + Fcos(z )

MOD_Ion - Fundamental (GPS & GLONASS)

Mod_Ion with inequality equation

• Problem: at some situations, even with calibrated equipments, negative values of TEC may be obtained.

• One solution: to apply inequality equation as follows:n 4

s s s1 2 j j 1

i 1j 2i 1

m 4s s s

n*2 3 j j 1 i 1j 2i 10

VTEC a a B {a cos(i h ) a sin(i h )}

a h {a cos(i B ) a sin(i B )} 0

GNSS Ionospheric Products

• TEC Maps

-75 -70 -65 -60 -55 -50 -45 -40 -35 -30

Longitude G eográfica (graus) + E stações G PS da RB M C

M apa do VTEC - 06/10/2001 - 01:00 U T

-35

-30

-25

-20

-15

-10

-5

0

5

Latit

ude

Geo

gráf

ica

(gra

us)

VTE

C (x

10E

+16

el/m

2)

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

BNC

ALDAR

Kalman Filter

Ionosphere Model:Polynomial

Function

Coeficients: dss and drr

Ionosphere Monitoring

dss, drr

VTEC, ROT, IPP

Real time ionosphere maps

GMT

IG & GIVE

Mod_ION_FK/IG (Aguiar, 2010)

BNC

Mod_ION_FK/IG

ALDAR

Kalman Filter

Ionosphere Model:Polynomial

Function

Coeficients: dss and drr

Ionosphere Monitoring

dss, drr

VTEC, ROT, IPP

Real time ionosphere maps

GMT

IG & GIVE

Grid Maps and GIVE/ Brazil

GIVEL1 Ionospheric Delay (m)

• November 22, 2009;• Real time processing;• 29 NTRIP stations.

IONEX Files

2nd and 3rd order Ionosphere corrections• In-house software was developed (RINEX_HO)

• GPS Solutions, Online First: 21 April 2011, DOI: 10.1007/s10291-011-0220-1, "RINEX_HO: second- and third-order ionospheric corrections for RINEX observation files"  by H. A. Marques, J. F. G. Monico and M. Aquino

2nd and 3rd order Ionosphere corrections• The earth’s magnetic field

– Dipolar Approximation– International Geomagnetic Reference Field (IGRF) model

(IGRF11 model)– Corrected Geomagnetic Model from PIM (Parameterized

Ionospheric Model)

• TEC– From raw pseudoranges, from pseudoranges smoothed by

phase, or from Global Ionosphere Maps (GIM).

2nd order Ionosphere correctionsDipolar – IGRF and Differences

RECIFE/PE – RECF (28/10/2003)

Ionosphere irregularities Index (Fp )

Estação RECIFE/PE – RECF (21/11/2007)

Ionosphere irregularities Index (Fp )

GNSS demands in Brazil

Off shore applicationsAir Navigation

Positioning in generalPrecision agriculture

Rural Cadastre (50 cm or better – 1 sigma)

….

PA in Brazil is demanding 24 hours RTK service

Concerning Air Navigation, Brazilian authorities decided to invest in GBAS

instead of SBAS.

A system from Honeywell Aerospace is under certification at Rio de Janeiro

Airport (Galeão). (Cosendey presentation on Nov 09).

Challenges for such GNSS applications

Ionospheric Scintillation!

CIGALA Project“Concept for Ionospheric scintillation mitiGAtion for professional GNSS in Latin America”

Goal: Understand the cause and implication of IS disturbances at low latitudes, model their effects and develop mitigations through:– Research of the underlying causes of IS and the development of state-of-the-art models

capable of predicting signal propagation and tracking perturbations– Field measurement via the deployment in close collaboration with local academic and

industrial partners of multi-frequency multi-constellation Ionospheric Scintillation Monitoring (ISM) network

– Design and implementation of novel IS mitigation techniques in state-of-the-art GNSS receivers

– Field testing the mitigation techniques, leveraging the same partnership as during the measurement campaign.

CIGALA partners

CIGALA IS Monitoring Network in Brazil

Continuous recording of :• Amplitude scintillation index S4 : standard deviation of received power

normalized by its mean value• Phase scintillation index σΦ : standard deviation of

de-trended carrier phase, with Phi60 its 60” version• TEC (Total Electron Content)• Lock time• Code – Carrier Divergence• Spectral parameters of phase Power Spectral Density:

– Spectral slope p– Spectral strength T

• Raw high-rate I&Q correlation values (50Hz)

• 8 ISM stations• Latitudinal and longitudinal

distribution over Brazil• Two stations at São José dos

Campos (crest of EIA) and Pres. Prudente

• Data stored locally and sent to repository at UNESP, Pres. Prudente

• Data mirrored at INGV, Rome• Ended on Feb 2012, but the

network is still collecting data.

IS Monitoring Network in Brazil

ISMR Query Tool was developed

CALIBRA PROJECT• A follow up of the CIGALA Project

– Countering GNSS high Accuracy applications Limitations due to Ionospheric disturbances in BRAzil

Focus on high accuracy GNSS

positioning techniques

Better than 10cm

CIGALA/CALIBRA Network• Stations

equipped GNSS receivers PolaRxS-PRO,

• Five new stations will be installed for the CALIBRA Project.

• GNSS/Ionosphere developments at FCT/UNESP were presented;

• Brazil is a very challenge place for GNSS applications, mainly due to the Ionosphere behavior in the equatorial region;

• Several applications have suffered of the effects of such problem (IS);

• In the PA and aviation there is a need for more developments and tests;

• CIGALA/CALIBRA is collecting data that may provide more data for scientific and operational purposes.

Final comments

More information?http://gege.fct.unesp.br