Real-Time Orbit And Clock Estimation Using PANDA

Software

Shi C, Lou YD, Zhao QL, Liu JNGNSS Research Center, Wuhan University, China

IGS Analysis Center Workshop 2008 2-6, June 2008, Miami, Florida, USA

Contents

• Introduction of PANDA software

• Strategy for Real-time POD• Strategy for Real-time Clock• Preliminary Results• Summary

Introduction of PANDA

PANDA : Positioning And Navigation Data Analyst

• To derive possible information from GNSS/SLR/ VLBI data in real-time and post-mission

• Developed at Wuhan University since 2001• Current Applications

– POD of GNSS&GEO (COMPASS, GPS)– POD of LEOs, CHAMP GRACE (Delft University), COSMIC

(JiaoTong Uni. Taiwan)– Huge Network (NEIS)

– PPP+Ambiguity-Fixing(GFZ, Nottingham Uni) – …..

PANDA System Structure

New Development: Real-Time

• PPP Based Positioning Service System– Real-time GPS orbits– Real-time GPS Satellite Clock Offsets– Precise Point Positioning

• Funded by – the Program 973 (No:2006CB701301)the Program 973 (No:2006CB701301)– Real-time Precise Positioning Service Prototype Real-time Precise Positioning Service Prototype

System (863)System (863)– Real-time POD for LEOs (863) Real-time POD for LEOs (863)

The Strategy For RT-POD

Two Steps: Generate NEQs of short ARCsCombine NEQs to estiamte orbits

NTRIP Data Cleaning

Last hourly NEQ

SRIF

Comb. NEQs for the last 1-N hours

Updated orbit and predicted orbit

Epoch-wise orbit update

Least Square Combinatio

Key Issues: Ambiguity-FixingWeight of predicted orbitsConstrained Parameter:

Orbit boundariesAmbiguitiesZTD, ERP

Parallel Combination

1h 2h 3h 12h Combined

Last hourly NEQ

Hourly NEQ

Combined NEQ

12h112h2h 12h 12h

1h 2h 3h 11h Combined 12h Combined 13h Combined

Last hourly NEQ

Hourly NEQ

Combined NEQ < 12h

Combined NEQ for orbits

Combine hourly NEQs Time-Consuming1. Save the combined NEQs of the last n-1,n-2, …,1 hours

2. Combined the last hourly NEQ with the saved combined NEQs

3. Only one combination (red) must be done in real-time

• Time-Saving• Fast restart with saved

(combined) NEQ

Orbital Boundary Constraints

1, 1, 1,1, 1( )k k k k k k

w k k k k w wv t t x x l P

kt 1kt 2kt

1 1 1

1 1 1

1 1 1

( ) ( )

( ) ( )

( ) ( )

k k k k

k k k k

k k k k

r t r t

r t r t

q t q t

1 1 0 1,( ) ( ) ( )k k k k k k kX t X t t t x

1 1 1 1 0 1( ) ( )k k k k kX t X t I x 1 1 1

! 1 11( , )

0 0

k k k

k k

k k kk k

k k

r r r

r r q

r r rt t

r r q

I

Juncture

Connected 1,k kwP

Not connected1, 0k kwP

Osculating orbital elements

1, 1, 1,1, 1( )k k k k k k

w k k k k w wv t t x x l P

, ,

1, 1 1 1, 1

k k k k k

k k k k k

N x W

N x W

NEQs:

Juncture constraint:

1 1 1( ) minT T Tk k k k k k w w wJ x v p v v p v v p v

1, 1, 1, 1,, 1, 1, 1, , 1

1, 1, 1, 1,11, 1, 1 1, 1

T k k T k k T k k k kkk k k k w k k k k w k k k w w

k k k k k k k kkw k k k k w k k w w

xN P P W P l

xP N P W P l

Solution with the Constraints

Stratgy For RT Clocks

Two approaches are developed:• Estimate SatClock Epoch-by-

Epoch(1hz)• Estimate SatClock Difference

between Epoch

Preliminary Results

The distribution of the 70 IGS stations for Real time satellite orbit determination (70stations)

Rinex data are inputted as stream through simulated real-time model

Test Network

Result of RT-POD vs IGS Finals

Max （ cm） Min （ cm） Mean （ cm）Radial 6.0 2.7 4.1

Cross 6.5 3.1 4.0

Along 10.6 4.6 7.3

Mean 7.5 3.6 5.4

Result of RT-POD

Difference between calculated real-time orbits (Hourly predicted orbits) and IGS final products

Result of RT-CLK vs IGS Finals

Statistics of the RMS values

max(ns) min(ns) mean(ns)

198 0.30 0.04 0.13

199 0.36 0.10 0.22

200 0.38 0.07 0.16

201 0.31 0.07 0.18

202 0.30 0.12 0.19

203 0.41 0.07 0.21

mean 0.18CPUT per epoch on IBM T60 notebook

RMS values of the difference between the calculated SatClock and IGS final products over the period day 198-203 of year 2006

Performance of the RT Production

Quality of the Real-time SatClock and SatOrbit for the day of year 2006

PPP Based on the RT Production

Epoch by Epoch

WUHN Station

RMS:

N: 2.87cm

E: 3.23cm

U: 7.96cm

• Real-time POD, 5cm• Real-time Clock, 0.18ns• PPP with the Products, 5, 10

cm

Summary

Thanks For Your Attention !