Zero difference GPS ambiguity resolution at CNES-CLS IGS Analysis Center

Transcription

1 Zero difference GPS ambiguity resolution at CNES-CLS IGS Analysis Center S. Loyer, F. Perosanz, F. Mercier, H. Capdeville, J.C. Marty, F. Fund, P. Gegout 3, R. Biancale 08// G 0 ENSG, Marne-la-Vallée November 0 3

2 PRINCIPLES Equations for a satellite i and a receiver j Clock receiver (one per epoch) Ambiguities (one integer per pass) Code Noise ~m P = P = D D +e +γe + h + h p p Phase Noise ~ mm λ L λ L = = Geometric distance + propagation effects (except ionosphere) D +λ d D +λ d windup windup e γe Phase Wind-Up + h + h L L λ N λ N Ionosphere (first order) h = h i h j

3 PRINCIPLES Two code/phase linear combinations used Wide-Lane combination L WSB L NW cτ / λ cτ / λ WL f ( P P ) = N + ( cτ / λwl) ( cτ / λwl), W WSB Integer WL ambiguity (per pass) Wide-lane Satellite Bias (per epoch) Iono-Free & Narrow-Lane combinations γλl WRB WL λ γ ( L + N ) Wide-lane Receiver Bias (per epoch) w = D+ λ d c windup + t λ N c WRB N w = N N λwl = cm Narrow-Lane ambiguity λc ~0.7 cm Mesures Propagation model Iono-Free phase clocks differences γ = ( λ / λ ) 3

4 PRINCIPLES Problem Hardware delays destroy the integer property of the ambiguities Ideas Identify the wide-lane combination of these biases using the phase equations only: zero-difference ambiguities become integer the corresponding clocks ( phase clocks ) allow integer ambiguity fixing Solution :. Identify the (zero difference) Wide-Lane Satellite Biases. Wide-Lane combination of P, P, L, L observables allow to fix N-N to an integer value 3. Narrow-Lane combination of the L, L observables allow to fix N in a global solution (wavelength ~ 0.7 cm) The estimated phase clocks have the integer property 4

5 GRG PRODUCTS: STATION NETWORK 48 sites : 78 Primary IGS08 7 Glonass +GPS 4 collocated (VLBI or SLR or DORIS) 5

6 Wide-Lane combination L L f. WIDE-LANE SATELLITE BIASES ( P P ) = N + ( cτ / λwl) ( cτ / λwl), W WSB WRB Using a global network of stations and under some assumptions, the (relative) Wide-lane Satellite Biases (WSB = cτwsb / λwl) can be identified - Stable from day to day - Except satellite events - WSB file available at : 6

7 . WIDE-LANE ZERO-DIFFERENCE AMBIGUITY RESOLUTION Zero difference wide-lane residuals before and after correction with WSB values L ( P ) L f, P L L WSB f cτ / λ ( P P ) WL, WL cycle WL ambiguities NW=N N can be fixed to an integer value WRBs are the remaining fractional part (modulo WL cycle) 7

8 . WIDE-LANE ZERO-DIFFERENCE AMBIGUITY RESOLUTION Wide Lane: station MCM4 8

9 3. NARROW-LANE ZERO-DIFFERENCE AMBIGUITY RESOLUTION Phase residuals before Narrow-Lane resolution γλl λ γ ( L + N ) w = D+ λ d c windup + t λ N c 9

10 3. NARROW-LANE ZERO-DIFFERENCE AMBIGUITY RESOLUTION GRG products: Integer property of satellite clocks 0h 4+ hour arc 4h 0h Overlap of two successive clock solutions 4h hour overlapping 4+ hour arc Possible to estimate a continuous (phase) clock solution 0

11 METHODOLOGY FOR «INTEGER» PPP Apply WSBs to WL combinations Solve integer values of WL ambiguities: (N N) now fixed Input WL ambiguities in Iono-Free phase combinations First processing using integer satellite clock products (GRG) to estimate: - Positions - Tropospheric biases - Clock receivers - Float ambiguities (real values) Solve integer NL ambiguities using a bootstrapping method: - Find the best median pass and solve it - Update normal matrices of ambiguities - Find the next best pass and solve it - Second processing to estimate all parameters except ambiguities (fixed): phase are ambiguity-free and code measurements are no longer used!

12 INTEGER PPP: BENEFITS Position time series: BRUS Fixed Float Equivalent to DD processing: OHI-OHI3

13 INTEGER PPP: BENEFITS Post-processed High-frequency PPP (30s) BARH DOY 0 00 East-West 3

14 Seismology: Sendaï earthquake APPLICATIONS 4

15 Oceanography: Kerguelen islands APPLICATIONS Buoy VS tide gauge 5

16 CONTRIBUTIONS TO IGS Processing strategies closed to: Other analysis centers IERS Conventions ITRF008 derived products (ANTEX ) Daily Normal Equation 900 s sampling Weekly Normal Equation accumulation Solution: station coordinates & EOPs Consistent orbit solution 30 s sampling clock solution Name of products: GRG Web site: 6

17 CONTRIBUTIONS TO IGS WRMS of each ACs w.r.t. IGS final GPS orbit products Plots available at: Floating ambiguities Integer ambiguities Improved SRP model Acknowledgements to Jim Ray (NOAA) 7

18 CONTRIBUTIONS TO IGS GRG products are at the same level of quality/consistency as the other ACs Joined officially IGS ACs on May 00 (week 58) What about GLONASS? Joined IGS ACs on December 00 (week 66) Since week 660, hybrid GPS/GLONASS processing (WRMS decrease!) 8

19 CONCLUSIONS CNES-CLS contributes to the final IGS GPS products since May 00 Use of an alternative processing strategy: zero-difference ambiguity fixing Corresponding products are consistent with other ACs solutions We provide: SP3 orbits 30s phase clock files Corresponding Wide-lane satellite biases Loyer, S., F. Perosanz, F. Mercier, H. Capdeville, J.C. Marty (0), GPS products from the CNES-CLS IGS Analysis Center, Zero difference GPS ambiguity resolution, Submitted to Journal of Geodesy Satellite clocks keep the integer property of phase ambiguities : Continuous receiver (phase) clock solution (from day to day) Users of GRG orbits/clocks/wsb can make INTEGER PPP of isolated receivers: stations, mobiles like buoys, boats, planes,, LEO satellites 9

20 PROSPECTS: MULTI-GNSS GLONASS integer satellite clocks and GLONASS WSBs? Currently, GLONASS phase ambiguities are fixed in SD processing New GLONASS satellites will follow CDMA configurations: current GLONASS inter-frequency biases will no longer exist Use GALILEO data as soon as possible to make hybrid GPS/GLONASS/GALILEO processing (IGS MGEX campaign): GINS ready! 0

21 Ex: mobile processing in Antarctica DOP effects are reduced PROSPECTS: MULTI-GNSS GPS GLONASS