1. No category

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).
MOD_Ion - Fundamental (GPS & GLONASS)
TEC
i
F
VTEC
TEC
s
s
TEC
(P  P ) 
+
F
[(S
-S
)
+
(R
-R
)
]
+
F
 P 21
i
p2
p1
p2
p1 r
i
cos(zs ) r
s
2r
s
1r
Fi  f 2i2 /(f1i2  f 2i2 )
VTEC  a1  a 2 B 
s
n 4
 {a jcos(i
i 1
j 2i 1
F(P  P )  SF (a1  a 2 B 
s
2
s
1 r
s
r
s
m4
 {a cos(i
i 1
j 2i 10
j
h )  a j1 sin(i h )}  a n*23h 
s
s
n 4
 {a cos(i
i 1
j 2i 1
j
s
m4

i 1
j 2i 10
{a jcos(i Bs )  a j1 sin(i Bs )}
h s )  a j1 sin(i h s )}  a n*23h s 
Bs )  a j1 sin(i Bs )}  F(R P2  R P1 )r  F(SsP2  SsP1 )  FP21.
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:
VTEC  a1  a 2 Bs 
 a n*23h 
s
n 4

i 1
j 2i 1
{a jcos(i h s )  a j1 sin(i h s )}
m4

i 1
j 2i 10
{a jcos(i Bs )  a j1 sin(i Bs )}  0
GNSS Ionospheric Products
Mapa do VTEC - 06/10/2001 - 01:00 UT
• TEC Maps
5
140
0
130
110
-5
100
90
-10
80
70
-15
60
50
-20
40
30
-25
20
10
0
-30
-35
-75
-70
-65
-60
-55
-50
-45
Longitude Geográfica (graus)
-40
-35
-30
+ Estações GPS da RBMC
VTEC (x 10E+16 el/m2)
Latitude Geográfica (graus)
120
Mod_ION_FK/IG (Aguiar, 2010)
Kalman Filter
ALDAR
Ionosphere Model:
Polynomial
Function
Coeficients: dss
and drr
dss, drr
Ionosphere
Monitoring
VTEC, ROT, IPP
BNC
Real time ionosphere
maps
GMT
IG & GIVE
Mod_ION_FK/IG
Kalman Filter
ALDAR
Ionosphere Model:
Polynomial
Function
Coeficients: dss
and drr
dss, drr
Ionosphere
Monitoring
VTEC, ROT, IPP
BNC
Real time ionosphere
maps
GMT
IG & GIVE
Grid Maps and GIVE/ Brazil
•November 22, 2009;
•Real time processing;
•29 NTRIP stations.
L1 Ionospheric Delay (m)
GIVE
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 corrections
Dipolar – IGRF and Differences
Ionosphere irregularities Index (Fp )
RECIFE/PE – RECF (28/10/2003)
Ionosphere irregularities Index (Fp )
Estação RECIFE/PE – RECF (21/11/2007)
GNSS demands in Brazil
Off shore applications
Air Navigation
Positioning in general
Precision 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)
IS Monitoring Network in Brazil
ISMR Query Tool was developed
• 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.
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.
Final comments
• 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.
More information?
http://gege.fct.unesp.br