# Presentation: 424078

## Real-Time Orbit And Clock Estimation Using PANDA Software

- Shi C, Lou YD, Zhao QL, Liu JN
- GNSS 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 : P*ositioning *A*nd *N*avigation *D*ata *A*nalyst
- 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)
- Real-time Precise Positioning Service Prototype System (863)
- Real-time POD for LEOs (863)

## The Strategy For  RT-POD 

- Two Steps:
- Generate NEQs of short ARCs
- Combine NEQs to estiamte orbits

- Key Issues:
- Ambiguity-Fixing
- Weight of predicted orbits
- Constrained Parameter:
- Orbit boundaries
- Ambiguities
- ZTD, ERP

## Parallel Combination

- Combine hourly NEQs   Time-Consuming

- Save the combined NEQs of the last n-1,n-2, ...,1 hours
- Combined the last hourly NEQ with the saved combined NEQs
- Only one combination (red) must be done in real-time

- Time-Saving
- Fast restart with saved (combined) NEQ

## Orbital Boundary Constraints

**Juncture  **

- Connected

- Not connected

- Osculating orbital elements

## Solution with the Constraints

- NEQs:

- Juncture constraint:

## 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 |  |  | 0.18 |

- CPUT 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

## Summary

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

## Thanks For Your Attention !