Estimating COMPASS Orbits And Clocks And Applying To Real-Time Precise Positioning Services

Maorong Ge(maor@gfz-potsdam.de), Hongping Zhang, Xiaolin Jia, Shuli Song, and Jens Wickert

German Research Centre for GeosciencesGNSS Research Center, Wuhan UniversityXi’an Research Institute for Surveying And MappingShanghai Astronomical Observatory

Munich Satellite Navigation Summit, 13-16 March 2012, Munich, Germany

Motivation

COMPASS Constellation

WHU Tracking Network

EPOS-RT Software

Precise Orbit And Clock Estimation

Applying to Positioning And GPSMET

Real-time Precise Positioning Service

Summary

Contents

Three Phases:Phase I :Demonstration System, 2000

Phase II: Regional System, 2012

Phase III: Global System, 2020

What Can Be Achieved With Current COMPASS Constellation?

Motivation

COMPASS Constellation

Five GEOs:

Inclination 0º,longitudes: 60ºE to 160ºE, Altitude 36,000 km.

27 MEOs:

In 3 orbital planes,

Inclination 55.5º,

Altitude 21,500 km.

Three IGSOs.

COMPASS Constellations

Space Segment (Constellation)Phase II: 5 GEOs + 5 IGSOs + 4 MEOs

Phase III: 5 GEOs + 3 IGSOs + 27 MEOs

Current Constellation (Sept. 2011)3 GEOs + 4 IGSOs (Data available)

Tracking Network (Wuhan Uni)

A Global GNSS Network Dedicated To COMPASS Scientific Research

Data Available At Stations:

Beijing, Wuhan, Chengdu, Lasha, Shanghai, Urumuqi and Xi’an, Singapore and Perth Australia

Tracking Network (Wuhan Uni)

UR240

UA240BD/GPS四频OEM接收机

Recevier And Antenna

Data Availability

bj f1 cent chdu lasa pert sha1 sigp urmq xian 240 o - o - o o o - - 241 - o o - o o o - - 242 o o o - o o - - 243 o o o - o o o - - 244 o o o o o - o o - 245 o o o o o - o o - 246 - o o o o - o o - 247 - o o o o - o o - 248 - o o o o o o o o 249 - o - o o o o o o 250 o o - o o o o o o 251 o o - o o o o o o 252 o o o o o o o o o 253 o o o o o o o o o 254 o o o o o o o o o 255 o o o o o o o o - 256 o - o o o o o o - 257 o o o o o o o o o 258 - o o o o o o o - 259 o o o o o o o o o 260 o o o o o o o o o 261 o o o o o o o o o 262 o o o o o o o o - 263 o o o o o o o o - 264 o o o o o o o o - 265 o o o o o o o o - 266 o o o o o o o o - 267 o o o o o o o o - 268 o o o o o o o o -

EPOS-RT Software

Multi-TechnologyMulti-TechnologyGGNSS SLR NSS SLR VLBI VLBI ……

Multi-FunctionMulti-FunctionReal-time/Post-mission; Real-time/Post-mission; Static/Kinematic/Dynamic Static/Kinematic/Dynamic

EPOS-RT: Structure

Left Side: Post-Processing. Right Side: Real-Time

Data Processing

POD& PTDPOD& PTD

Real-Time PPP serviceReal-Time PPP service

Dynamical ModelsParameter COMPASS Satellite

Gravity EIGEN GRACE02S 12 x 12

Point mass Earth, Sun, Moon and Planets

Tides Solid Earth tidesPole tidesOcean tide

Relativistic effects Yes

Solar radiation Bern model with 9 model parameters

Velocity Breaks Only for maneuver modelling

Satellite Attitude: As GPSPCO/PCV: Not Available

Observation ModelsParameters Model Constraint

Observation LC and PC L1 0.02cycle, P1 1.0m

Sampling rate 60 seconds

Cutoff elevation 7 degree

Weight Elevation dependent elev > 30o, 1; else 2*sin(elev)

PCO/PCV Not available

Phase wind-up Yes

Tropospheric delay Saastamoinen model + process 10cm + 5 mm/sqrt(hour)

Ionospheric delay Eliminated by using LC and PC

Satellite clock Broadcast + Wite noise 300 m

Receiver clock Range estimating + White noise 300 m

Station displacement

Solid earth, pole tide, ocean loading

Station coordinate Constraint to GPS derived value Accordingly

Ambiguity Estimated and fixed to integer

Relativistic effects Yes

ERP Solve for x-pole y-pole and rates and LOD

Almost fixed

Three-Day Solution

Three-Day Sliding Window With One-Day Step-size. Orbit Overlap 48 h, Sol. 1 and 2, or Sol 2 and 3 24 h, Sol. 1 and 3, or Sol 2 and 4 1 h, Sol. 1 and 4 (Blue parts)

Estimation (Green), Predicted (Blue)

Sol. 1

2

3

4

Orbit Comparison

RMS increases along with time-lag GEO has significant larger RMS On average GEO 6 m, IGSO 1 m

Time-lag of

the solutions

Large RMS in Along- Tracking, 23 m

Constant Bias ! < 1 m in Cross-Tracking

& Radial

(Unit dm) Along Cross Radial 3D C01 233 7 18 234 C03 81 1 23 84 C04 177 3 24 179 C06 14 13 4 20 C07 18 9 13 24 C08 32 8 14 36 C09 15 8 5 18 Mean 81 7 14 83

Orbit Comparison

Systematic Bias Except C04Orbit Related ?STD 0.5 ns (15 cm)

Clock Comparison

• ZTD RW process with PD• Better than 10 mm in Horizontal• 4 cm bias in vertical, 1-2 cm STD

Static PPP With Estimated Orb&CLK

• MEAMGPS-COMPASS = -13 mm, STD=14 mm

• Both PCO&PCV for Sat. and Rec. not available

ZTD Estimated vs GPS Derived

Position: 100 m + 1 m per sqrt (minute)Epoch not shown if nsat <=4 After 1-2 hour to 1 dm, Stay at cm-levelFluctuation at 20:00, repeated daily (?)

Kinematic PPP (Forward)

Epoch not shown if nsat <=4 Bias 12, 6, -8 mm, STD 45, 27. 74 mm (ENU) Fluctuation at 20:00 ?

Kinematic PPP (+Backward)

East North Up

Mean 0.012 0.006 -0.008 STD 0.045 0.027 0.074

EPOS-RT For Real-Time PPP Service

RT Orbit

RT Clock

RT PPPGPS receivers

SRIF(Orb)

BNC BNC2SRIF SRIF(Clk)

SRIF2BNS

BNC2SRIF SRIF(PPP)

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IGS Hourly DataIGS Hourly Data

RT PPPGPS receivers

BNC2SRIF SRIF(PPP)

OBS StreamingOBS Streaming

NTRIP ProductsNTRIP Products

NTRIP ProductsNTRIP Products ORB/CLK/UPDORB/CLK/UPD

Hourly DataHourly Data RT ORBRT ORB

Pos&Time

ZTD/STD

Pos&Time

ZTD/STD

Co

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IGS Real-Time Analysis Center at GFZ

Orbit Prediction

Three-Day Sliding Window With One-Day Step-size. Orbit Integration To The Fourth Day (1D Pred.) The Step-size Can Be To 1 h For A Faster Update

depending on the data availability

Prediction (Green with Data, Yelllow=Predicted

Compared With Estimated OrbitsMajor Bias in Along-track Direction,

Especially for GEOsSTD Are Similar, Smallest in Radial.

Quality of Predicted Orbits

Clocks are estimated epoch-wise by fixing the predicted orbits. Both clocks&orbits are used for simulated real-time positioningURA should be compared

Quality of Estimated Clocks

Simulated Real-Time PPP

Very similar to that with estimated orbits&clocks

Decimeter accuracy achievable

Fluctuation at 20:00 ?

• 3D-rms 16 m for GEOs and 2.4 m for IGSOs. Large bias in along-track, small and similar errors in radial of 1.8 m for GEO and IGSO.

• Static Daily PPP: 1 cm/3cm, Bias due to PCO/PCV

• Kinematic PPP: 5, 3 and 7 cm in ENU

• Simulated RTPPP service: 1-2 dm.

• To be improved with the full constellation of Phase II.

Summary