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

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 OceanographyUniversity 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/NRCanGFZ/Nottingham/Wuhan

ClocksClocksEquipment biases, etc.Equipment biases, etc.AmbiguitiesAmbiguities

GIPSY 6.0 by JPL

Atmospheric corrections

Atmospheric corrections

Augmented PPP-RTK


Real-time PPP-AR system in Scripps for earthquake early warning

Generate Satellite Clocks

Generate Satellite Clocks

Generate Fractional-

Cycle Biases

Generate Fractional-

Cycle Biases

Predicted orbits from

IGS

Predicted orbits from

IGS

ITRF positions &

metadata(SOPAC)

ITRF positions &

metadata(SOPAC)

PPP client with accelerometersPPP client with accelerometers RTK UserRTK User

CRTNServerCRTNServer

75 stations used as reference stations which are located >200 km away from western US coast

Real-Time Data,

Various Servers

Real-Time Data,

Various Servers

Other UsersOther Users

Generate California-Based Troposphere and

Ionosphere Model

Generate California-Based Troposphere and

Ionosphere ModelRTCM3

Operational


Typical performance: fixed solutions for 25 days


Brawley swarm on Aug 26 2012

• 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)


Example: GPS waveforms in real time for Event 3 M5.5


Tightly-coupled GPS/Accelerometers based on PPP-AR

• Introduce raw accelerometer measurements into GPS data processing

• Loosely-coupled GPS/Accelerometers

Displacements and velocitiesDisplacements and velocities

GPS measurements

GPS measurements

Accelerometer measurementsAccelerometer measurements

Tightly coupledTightly

coupled

Displacements and velocitiesDisplacements and velocities

GPS-derived displaceme

nts

GPS-derived displaceme

ntsLoosely coupledLoosely coupled

GPS measureme

nts

GPS measureme

nts

Accelerometer measurementsAccelerometer measurements

GPS process

GPS process


Improvement of ambiguity resolution performance


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 4.6

Mw 5.4


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.


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


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


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


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)


How AFIF carrier-phase outperform pseudorange?

Session Sigma_L1 (mm)

Sigma_L2 (mm)

Sigma_L5 (mm)

Sigma_AFIF (mm)

1 0.7 1.8 0.6 136.7

2 1.0 2.7 1.0 207.1

3 1.5 6.3 1.5 466.6


Success rate & correctness rate of ambiguity fixing


Interrupt every 30 s


Multipath effects




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?


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?


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.

Documents

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