June 12-14, 2013, Ottawa, Canada From dual- to triple-frequency PPP: method, problems and application in California Jianghui Geng, Yehuda Bock Scripps Institution of Oceanography University of California San Diego

Precise point positioning: reaching full potential Precise point positioning ambiguity resolution (PPP-AR) PPP-AR has been developed since 2008 –“Uncalibrated phase delay” by GFZ/Nottingham/Wuhan –“Integer clock” or “decoupled clock model” by CNES/NRCan –Single receiver ambiguity resolution by JPL –etc. CNES/NRCan GFZ/Nottingham/Wuhan Clocks Equipment biases, etc. Ambiguities GIPSY 6.0 by JPL Atmospheric corrections Augmented PPP-RTK

Precise point positioning: reaching full potential Real-time PPP-AR system in Scripps for earthquake early warning Generate Satellite Clocks Generate Fractional- Cycle Biases Predicted orbits from IGS ITRF positions & metadata (SOPAC) ITRF positions & metadata (SOPAC) PPP client with accelerometers RTK User CRTN Server CRTN Server 75 stations used as reference stations which are located >200 km away from western US coast Real-Time Data, Various Servers Other Users Generate California- Based Troposphere and Ionosphere Model RTCM3 Operational

Precise point positioning: reaching full potential Typical performance: fixed solutions for 25 days

Precise point positioning: reaching full potential Brawley swarm on Aug PBO and SCIGN real-time GPS stations in the vicinity of Brawley Swarm of August 26, 2012, operated at 1 Hz during event WLA (Wildlife Liquefaction Array) is accelerometer run by Jamie Steidl (UCSB), continuously at 200 Hz, ~ 5 km from P506 4 events (GPS time) 19:20:15 (M4.6) 19:31:35 (M5.4) 20:58:05 (M5.5) 23:33:25 (M4.6) Collocation of GPS/Accelerometers P506/WLA (8km) P494/WES (35km)

Precise point positioning: reaching full potential Example: GPS waveforms in real time for Event 3 M5.5

Precise point positioning: reaching full potential Tightly-coupled GPS/Accelerometers based on PPP-AR Introduce raw accelerometer measurements into GPS data processing Loosely-coupled GPS/Accelerometers Displacements and velocities GPS measurements Accelerometer measurements Tightly coupled Displacements and velocities GPS-derived displaceme nts Loosely coupled GPS measureme nts Accelerometer measurements GPS process

Precise point positioning: reaching full potential Improvement of ambiguity resolution performance

Precise point positioning: reaching full potential Brawley Seismic Swarm: Comparison of seismogeodetic and broadband seismometer velocity waveforms P494/WES (80 m apart), 35 km from hypocenter Mw 5.5 Mw 4.6 Mw 5.4

Precise point positioning: reaching full potential Solutions in dual-frequency PPP for fast convergence Partial solution: rapid re-convergences/Cycle-slip repair Unsatisfactory solution: precise ionosphere products, e.g. dense augmentation network, ionosphere tomography, etc.

Precise point positioning: reaching full potential Triple-frequency PPP Enable rapid ambiguity resolution for triple-frequency PPP –Triple-frequency means various combinations of frequencies for long wave- length observable –Resolve ambiguities for long-wavelength observable –Using the resolved long-wavelength observable to constrain the ambiguity resolution of short-wavelength observable

Precise point positioning: reaching full potential A method for triple-frequency PPP Basic carrier-phase equation: Step 1: resolve extra-wide-lane ambiguity with a wavelength of 5.8m Step 2: resolve wide-lane ambiguity with a wavelength of 3.4m, but the noise is amplified by 100 times. –Wide-lane ambiguity resolution can still be very efficient Step 3: with ambiguity-fixed ionosphere-free (AFIF) wide-lane carrier-phase, resolve narrow-lane ambiguity (0.1m wavelength) AFIF observations

Precise point positioning: reaching full potential Data simulation GSS8000 hardware simulator by Spirent Septentrio receiver Troposphere delay: RTCA06 Ionosphere delay: Klobuchar Receiver antenna level pattern is applied –Elevation-dependent attenuation Use default satellite orbit and satellite clocks Land mobile multipath effect –Rural environment –<15°, reflected signals only –<40°, allow reflected signals

Precise point positioning: reaching full potential How AFIF carrier-phase outperform pseudorange? Position accuracy with ionosphere-free pseudorange (Dural-frequency PPP) Position accuracy from ambiguity-fixed ionosphere-free carrier-phase (triple-frequency PPP)

Precise point positioning: reaching full potential How AFIF carrier-phase outperform pseudorange? SessionSigma_L1 (mm) Sigma_L2 (mm) Sigma_L5 (mm) Sigma_AFIF (mm)

Precise point positioning: reaching full potential Success rate & correctness rate of ambiguity fixing

Precise point positioning: reaching full potential Interrupt every 30 s Interrupt every 120 s Multipath effects Interrupt every 30 s Interrupt every 120 s

Precise point positioning: reaching full potential Question 1: optimum combination? Do we have to use ionosphere-free combinations or not? –How residual ionospheric delays affect hardware bias estimation? –What if the residual ionospheric delays are small enough? What are the optimum combinations? –Which combinations are used depends on not only PPP users, but also satellite clock providers –How to define satellite clock products in future for multi-frequency and multi-constellation GNSS? What if we have 4, 5 … frequencies? –Do we have to look for the optimum again and again?

Precise point positioning: reaching full potential Question 2: A general way to PPP? Do we have to manually look for the optimum combinations? –We can use raw observation equations –LAMBDA method Multi-frequencies: the problem is how b_1, b_2 … B_1, B_2 …affect the clock, ionosphere parameters? Can multi-frequency clocks be used for dual-frequency data processing?

Precise point positioning: reaching full potential Summary and conclusions Dual-frequency PPP-ambiguity resolution improves positioning accuracy, but not convergence speed to ambiguity-fixed solutions. Triple-frequency PPP can speed up convergences to ambiguity-fixed solutions from a few tens of minutes to a few minutes. Potential of multi-frequency PPP has not been exploited, especially in how to design a general way to do multi-frequency PPP. Satellite clock product may need to be re-defined to accommodate the future multi-frequency signals.