Report

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. Local Base/RTK Initialization TUPÃ VRS (GNSS) ARAC (GNSS) 84,13km VRS_S (GPS) ARAC_S (GPS) 84,13 km 1min 24 seg 8 min 4 seg 2 min 23 seg 12 min 19 seg Sart 13:07:01 as 13:24:52 as 13:47:55 as 14:18:35 as End N. points collected 13:18:17 13:43:41 14:08:33 14:44:30 205 205 205 205 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 9th). Ionospheric Regional Model (MOD_Ion) (GPS & GLONASS) • • Fi TEC (P s 2r P ) s 1r VTEC s cos( z ) r TEC + Fi s s [(S p2 -S p1 ) + (R p2 -R p1 ) r ] + Fi TEC P 21 = > i = G, Rk Fi f 2 i /(f 1i f 2 i ) 2 2 2 n4 VTEC a1 a 2B s m 4 {a j cos(i h ) a j 1 sin(i h )} a n*2 3 h s s i 1 j 2i 1 s {a jcos(i B ) a j 1 sin(i B )} s s i 1 j 2i 10 n4 F(P P ) r S F (a 1 a 2 B s 2 s 1 s r s {a j cos(i h ) a j 1 sin(i h )} a n*2 3 h s s s i 1 j 2i 1 m4 i 1 j 2i 10 {a j cos(i B ) a j 1 sin(i B )} F(R P 2 R P1 ) r s s F(S P2 S P1 ) F P 21 . s s 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: n4 VTEC a1 a 2B s {a j cos(i h ) a j 1 sin(i h )} s s i 1 j 2i 1 m4 a n*2 3 h s i 1 j 2i 10 {a j cos(i B ) a j 1 sin(i B )} 0 s s 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: 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 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 IS Monitoring Network in Brazil • 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 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) 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 S4, sf , 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 Normal Receiver Optimized ISM receiver 60 10 8 Loss-of-lock probability [%] Loss-of-lock probability [%] 50 40 30 20 10 0 20 6 4 2 0 20 1 15 10 1 15 0.8 0.8 10 0.6 5 PLL bandwidth [Hz] 0.6 5 0.4 S4 level PLL bandwidth [Hz] Data bearing signals Simulated with CSM on Spirent 0.4 S4 level Receiver optimize for Maximum Tracking availability during Strong Scintillation Normal Receiver Optimized ISM receiver 60 10 8 Loss-of-lock probability [%] Loss-of-lock probability [%] 50 40 30 20 10 0 20 6 4 2 0 20 1 15 0.8 10 1 15 0.8 10 0.6 5 PLL bandwidth [Hz] 0.6 5 0.4 S4 level PLL bandwidth [Hz] 0.4 S4 level Pilot Signal (L2C) Simulated with CSM on Spirent Comparison with currently deployed GSV equipment • Scintillation free midlatitude location (Nottingham) • GPS L1CA • 24h recording • S4: correlation coefficient = 0.9 • Phi60: – PxS: 0.0292 – GSV: 0.0547 PRN19 Field Validation (C/N) L1 • CIGALA receivers PRU1 and PRU2 at Presidente Prudente • February to April 2011 L2 Field Validation (CCSTDDEV) L1 • CIGALA receivers PRU1 and PRU2 at Presidente Prudente • February to April 2011 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 GPS EIA GLONASS EIA • 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 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 L2C L1CA PRU2, Sep-25, 2011 PRU2, Sep-25, 2011 1.4 1.4 PRN2 PRN15 PRN15 1.2 PRN26 S4 from L2C (elevation mask of 20 deg) S4 from L1CA (elevation mask of 20 deg) 1.2 1 0.8 0.6 0.4 0.2 0.8 0.6 0.4 0.2 0 0 0 • • 1 0.5 1 UTC time [hours] 1.5 2 0 0.5 1 UTC time [hours] S4 reported continuously during scintillation S4 in L2 reported thanks to PRN15 (L2C) pass 1.5 2 SigmaPhi during Scintillation L2C L1CA PRU2, Sep-25, 2011 PRU2, Sep-25, 2011 1.5 1.5 PRN15 PRN2 PRN15 Phi60-L2C [rad] (elevation mask of 20 deg) Phi60-L1CA [rad] (elevation mask of 20 deg) PRN26 1 0.5 0.5 0 0 0 0.5 1 UTC time [hours] • 1 1.5 2 0 0.5 1 UTC time [hours] sphi reported continuously on ISM optimized receiver 1.5 2 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! PRU2, PRN15, Sep-25, 2011 carrier phase 0.5 nav bit error 0.4 0.3 Detrended L1 carrier phase [cycles] 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 1500 2000 2500 UTC time [hours] 3000 Effect on Real Time Precise Point Positioning PRU2, Sep-25, 2011 1.4 PRN2 PRN15 1.2 S4 (elevation mask of 20 deg) PRN26 1 0.8 0.6 0.4 0.2 0 0 0.5 1 1.5 2 2.5 3 UTC time [hours] 434 433.8 PPP Height [m] 433.6 433.4 433.2 433 432.8 432.6 0 0.5 1 1.5 UTC time [hours] 2 2.5 3 PPP service continuous during the whole event Up to 40cm error during event (service specification is 12cm 95%) Final comments • 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. More information? http://gege.fct.unesp.br