Ionosphere effects on GNSS positioning: data collection, models and analyses João Francisgo Galera Monico, Paulo De Oliveira Camargo, Haroldo Antonio Marques, Heloisa Alves Da Silva UNESP – FCT – Presidente Prudente, SP. Bruno Bourgard Septentrio NV, Leuven. Luca Spogli INGV, Rome.

Outline Infra-structure available for GNSS research and applications in Brazil GNSS Services required in Brazil Brazilian Ionospheric Model –Mod_ION –Rinex_HO CIGALA Project –Objectives –Preliminary results Final Comments

Available Infra-structure in South America/Brazil

SIRGAS GNSS data SIRGAS-CON GNSS Network

Brazilian GNSS data (IBGE/INCRA) Brazilian Continuous GPS Network (RBMC). Some stations are operational since 1996 ~100 stations

RBMC Real Time – RBMC_IP Data of about 30 Brazilian GNSS stations are distributed in real time, using NTRIP protocol.

GNSS/GPS Active Network at São Paulo State – Real time data

Meteorological and GNSS stations Meteorological stations are required to be collocated with GNSS for GNSS/Met support –18 are available at São Paulo State (all stations were calibrated)

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!

São Paulo State Network RTK (VRS)

Preliminary results. LocalBase/RTKInitializationSartEnd N. points collected TUPÃ VRS (GNSS)1min 24 seg 13:07:01 as13:18:17205 ARAC (GNSS) 84,13km8 min 4 seg 13:24:52 as13:43:41205 VRS_S (GPS)2 min 23 seg 13:47:55 as14:08:33205 ARAC_S (GPS) 84,13 km12 min 19 seg 14:18:35 as14:44:30205

Ionospheric Index (I95) based on São Paulo State GNSS Network

Developments on GNSS/Ionosphere at FCT/UNESP

GNSS and Ionosphere A Ion-model based on GNSS has been under development at FCT/UNESP since 1997; –Mod_Ion (in-house iono model) generates Ionospheric maps and coefficients for L1 users Ionospheric Index (Fp) Ionex files from Brazilian GNSS data Real time ionosphere maps of TEC/ROT and of the correspondent delays on L1 (Aguiar – presentation on Nov 9 th ).

= > i = G, R k Ionospheric Regional Model (MOD_Ion) (GPS & GLONASS)

Mod_Ion with inequality equation Problem: at some situations, even with calibrated equipments, negative values of TEC are obtained. One solution: to apply inequality equation as follows:

GNSS Ionospheric Products TEC Maps

IONEX Files

2nd and 3rd order Ionosphere corrections In-house software was developed (RINEX_HO) GPS Solutions, Online First: 21 April 2011, DOI: /s , "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 Bipolar – IGRF and Differences

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

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 IS Monitoring Network in Brazil

CIGALA IS Monitoring Network in Brazil Continuous recording of : Amplitude scintillation index S 4 : standard deviation of received power normalized by its mean value Phase scintillation index σ Φ : 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)

Septentrio PolaRxS ISM receiver is the base of the CIGALA network (c) CIGALA Consortium

PolaRxS: facts  Track GPS, GLONASS, GALILEO, COMPASS, SBAS  L1, L2, L5, E5a, E5b signals, including GPS L2C, GLONASS L2C and Galileo E5 AltBOC  Very low phase noise OCXO  100Hz signal intensity and phase output for all signals  Computation of S 4,    TEC, spectral parameters,... for all satellites and signals  Interoperable ISMR file format  Multiple Interfaces: 4 RS232, USB, Ethernet  Rugged IP65 housing  Temperature range: -40C to 60C  Powering: 9-30V ; 6W

PolaRxS Phi60 Noise Floor <0.03rad 24-h Spirent simulation, Perfect GPS signal, L1

Receiver optimize for Maximum Tracking availability during Strong Scintillation Optimized ISM receiver Normal Receiver Simulated with CSM on Spirent Data bearing signals

Receiver optimize for Maximum Tracking availability during Strong Scintillation Optimized ISM receiver Normal Receiver Simulated with CSM on Spirent Pilot Signal (L2C)

Comparison with currently deployed GSV equipment Scintillation free mid- latitude location (Nottingham) GPS L1CA 24h recording S4: correlation coefficient = 0.9 Phi60: –PxS: –GSV: PRN19

Field Validation (C/N) CIGALA receivers PRU1 and PRU2 at Presidente Prudente February to April 2011 L1 L2

Field Validation (CCSTDDEV) CIGALA receivers PRU1 and PRU2 at Presidente Prudente February to April 2011 L1 L2

Using GLONASS for IS monitoring GPS and GLONASS orbits are complementary to increase spatial and temporal observability of the ionosphere GLONASS provides open signals on both L1 and L2 in all SV

Moderate Scintillation Occurrence (S4) observed using GPS vs. GLONASS INGV GBSC software is used to draw maps of rate of occurrence of S4>0.25 as a function of lat/long or lat/time Maps plotted for L1 observations between Feb and April 2011 Increased probability of scintillation clearly observable in EIA post-sunset Very good match between GPS and GLONASS observation => data can be merged GPS GLONASS EIA

Moderate Scintillation Occurrence (Phi60) observed using GPS vs. GLONASS GPS GLONASS INGV GBSC software is used to draw maps of rate of occurrence of Phi60>0.25 as a function of lat/long or lat/time Maps plotted for L1 observations between Feb and April 2011 EIA observable for GPS No match GPS and GLONASS observations

Understanding lack of Phi60 observability when using GLONASS signal Short term stability of the GLONASS satellite clock lower than GPS Small scale phase scintillation cannot be measured from single frequency observation Solution: Using differenced L1/L2 measurement to cancel the satellite clock effect

Strong Scintillation Event on Sept 25, 2011

S4 During Scintillation S4 reported continuously during scintillation S4 in L2 reported thanks to PRN15 (L2C) pass L1CA L2C

SigmaPhi during Scintillation L1CA L2C sphi reported continuously on ISM optimized receiver

Tracking robustness (Cycle Slips)  Phase tracking continuous during the whole event despites the very high S4 level  3 cycles slips seen on L1CA (PRN15)  No cycles slips on L2C!

Effect on Real Time Precise Point Positioning PPP service continuous during the whole event Up to 40cm error during event (service specification is 12cm 95%)

Brazil is a very challenge place for GNSS applications, mainly due to the Ionosphere behavior in the equatorial region; Several applications are already suffering the effects of such problem (IS) and will increase in the next two years; In the PA and aviation there is a need for more developments and tests; CIGALA network will continue collecting data after the final of the project (March 2012) and may provide data for scientific purpose. Final comments

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