03/000

15th International Laser Ranging Workshop 15th – 20th October2006

Canberra

Australian Government

Geoscience Australia

An Optimised Global SLR Network for Terrestrial Reference Frame Definition

Ramesh GOVIND

Overview• Introduction • Baseline Data and Solution • Simulated Data Set• COM Results• Simulation Study Summary• Global Simulation• Optimised Network Approach

Introduction

• Study to evaluate the contribution of an additional SLR station in northern Australia

• Measure: Earth Centre of Mass – a primary SLR product

• Site chosen: Tennant Creek– Same number of cloud free days as Yaragadee– Site options further north are limited by weather

Baseline Data and Solution

• 2005 Lageos-1, Lageos-2 • 52 Weekly arcs• Subset of the original 14-year solution from

Lageos-1 and Lageos-2 combination

Simulated Data Set

• Tennant Creek [S19º39’19.5”; E134º11’32.6”; 410.7m]

• Data simulated from the final orbits of the baseline solution for each respective week

• Noise added to the “perfect” data – 10 mm seed – same as the orbit fits for the baseline solution

• Data volume controlled to be within the weekly data from Yaragadee and Stromlo

Simulated Data Set

• Data Volume– 5-day week– Night operations only– 8-hour shift– Data losses due to weather not accounted

• Combined the 2 data sets for each weekly solution

Simulated Data Set

Lageos-1 No. of Observations

050

100150200250300350400450

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Week Number 2005

No

of N

orm

al P

oint

s

Moblas-5 Stromlo Tennant Crk

Simulated Data Set

Lageos-2 No. of Obseravtions

0

100

200

300

400

500

6001 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46

Week Number 2005

No

of N

orm

al P

oint

s

Moblas-5 Stromlo Tennant Crk

CoM Results

X-CoM Tennant Creek Simulated

-0.04

-0.03

-0.02

-0.01

0

0.01

53300 53400 53500 53600 53700 53800

MJD -- Weekly Arcs 2005

X-C

oM --

met

res

SLR Data SLR Data + Tck Sim

CoM Results

Y-CoM Tennant Creek Simulated

-0.02

-0.01

0

0.01

0.02

0.03

53350 53400 53450 53500 53550 53600 53650 53700 53750

MJD -- Weekly Arcs 2005

Y-C

oM --

met

res

SLR Data SLR Data + Tck Sim

CoM Results

Z-CoM Tennant Creek Simulated

-0.08

-0.06

-0.04

-0.02

0

0.02

53350 53400 53450 53500 53550 53600 53650 53700 53750

MJD -- Weekly Arcs 2005

Z-C

oM --

met

res

SLR Data SLR Data + Tck Sim

CoM Results

0 (2)0 (1)0 (2)Simulated-10 (10)2 (6)-1 (6)Baseline

Z-CoM-Mean(RMS); mm

Y-CoM-Mean(RMS); mm

X-CoM-Mean

(RMS); mm

Solution

•No “truth” to compare with•Mean and RMS of the 2 solutions compared

Simulation Study Summary

• additional SLR station in Australia (in the vicinity of Tennant Creek) and,

• operating at the same levels of productivity and precision as Mount Stromlo and Moblas-5)

• change in the determination of the Earth’s CoM by 7mm, -3mm 13mm in the X, Y, and Z components and, more importantly,

• showing a week-to-week consistency in the estimates.

Global Simulation

• New Approach for an optimised global network

• Structured

• Rational

Lageos-1 Observations Week 060702

15 observing stations

Lageos-1 Observations Week 060917

22 observing stations

Optimised Network Approach

• Lack of continuous tracking

• Stability of Geometry -- Changing network

Simulated Sites -- Distribution

22 observing stations

Optimised Network

• Current status– Simulated Lageos-1, Lageos-2 data for 11 stations

for all of 2005– First priorities in the study – Hawaii and Bangalore– Computations being done– Results pending