a proposed satellite laser ranging station in taiwan

A proposed satellite laser ranging station in Taiwan

Cheinway Hwang , Tingjung Lin, and Yishan Lee

Dept of Civil Engineering, National Chiao Tung University

1001 University Road, Hsinchu 300, Taiwan, ROC

1Department of Civil Engineering, NCTU

Benjamin Fong Chao, Institute of Earth Sciences,

Academia Sinica, Taipei, Taiwan, ROC

Ming Yang, Dept of Geomatics, National Cheng Kung University

No. 1, University Road, Tainan 701, Taiwan, ROC

TP Tseng, SPACE Research Centre, RMIT University, Australia

5th FORMOSAT-3 / COSMIC Data Users Workshop

And the International Conference on GPS Radio Occultation

April 13-15, 2011, Taipei, Taiwan

Introduction

• The primary objective :

(1) track current and future Taiwan satellites with corner-cube

reflectors for orbit improvement.

(2) Define the geocenter coordinate and join the international terrestrial

reference frame, serve as a reference station for plate tectonics of

Taiwan

(3) provide data for time-varying gravity/climate change research


(3) provide data for time-varying gravity/climate change research

• SLR and FORMOSAT-7 (COSMIC follow on)

potentially equipped with SLR reflectors, to be launched in late 2014.

The accuracy of SLR-derived ranges, is better than 1 cm, and can be

used to validate the accuracy of GPS-derived orbit, and calibrate

antenna offset and center-of-mass

SLR ground station- Argentina


Seeber (2003)

Example of corner-cube reflector: The CHAMP laser

retroreflector array


Telescope and Laser: can we reduce the size and

time-delay?Mobile and automated

SLR

•Mobile

•Small or no telescope

•Automated, real-time

Conventional SLR:

•Fixed

•Large telescope

•Manual operation


Validation of LEO GPS-derived Orbit:

Examples from GRACE and Jason-1


Examples from GRACE and Jason-1

Difference between GPS-derived orbit (one-D) and SLR

range for satellite GRACE A over 300 days, since DOY 100,

2007

(average RMS : 3.5 cm)


Difference between GPS-derived orbit and SLR ranges for

satellite (altimeter) Jason-1 over 170 days

8Department of Civil Engineering, NCTU(Scott et al., 2002)

SLR data processing: normal point reduction

• Subdivide the accepted fit residuals FR into fixed intervals (bins) starting from

0h UTC. The bin sizes for various satellites are listed at the end of this note.

• Compute the mean value and the mean epoch of the accepted fit residuals

within each bin i. Let ni be the number of accepted fit residuals within this bin.

• Locate the particular observation Oi with its fit residual FRi , whose

observation epoch ti is nearest to the mean epoch of the accepted fit residuals

in bin i.


in bin i.

• The normal point is computed as

• (10) Compute the RMS of the accepted fit residuals in each bin i from their

mean value :

where the summation over j is over the accepted points within the bin.

RMS of raw and filtered (normal-point) orbits for

COSMIC satellite FM5


Improving regional orbit of FORMASAT-7 using

SLR

11Department of Civil Engineering, NCTU XI ,YI ,ZI：Inertial Coordinate System

Near-real time orbit improvement for COSMIC2

satellites using SLR

Orbit error in radial, along-track and cross-track direction

(projection in the station-Leo direction)

• One-cycle-per-orbital-revolution (1CPR) empirical cofficients


：argument of latitude

, , ：empirical coefficients for the orbit errors in the

radial, along-track and cross-track direction

：time-dependent

• Adjustment model

：error vector in the distance between station and Leo due to orbit error

：real-time LEO state vector (based on real-time orbit)

：true LEO state vector


：true LEO state vector

：SLR observable

：SLR state vector

V ：residual vector of

Establishment of a reference frame of Taiwan

using SLR observations


Global and near-Taiwan ITRF stations (GPS, SLR,

VLBI, DORIS)


• SLR can be used to define geocenter coordinates and the

motion of geocenter, which can be expressed as a time

series of degree 1 harmonic coefficients in the Earth’s

gravity field model

1111 3 CRRCdx ==

==


R : the Earth’s radius

and :fully normalized potential coefficients

1111 3 SRRSdy ==

1010 3 CRRCdz ==

C S

Example of using SLR to solve for geopotential

coefficients and station coordinates by GEODYN II


Differences between the geocenter motions estimated

from SLR data of CHAMP and the result from ITRF2005

18Department of Civil Engineering, NCTU(Guo et al., 2008)

G P S

L E O


G P S G ro u n d S ta tio n L aser S ta tio n

Scenario 1: Ground Station to GPS (ground – high)

Scenario 2: LEO (Receiver) to GPS (low – high)

Combined scenario: Form three Layers (ground – LEO – GPS)(Zhu and Shih, 2003)

Scenario 1. Ground stations to GPS

- Usefulness: reference frame (site positions), EOP, trop., GPS orbits, ...

- weakness: scale, geocenter (especially, z-direction)

Scenario 2. LEO to GPS

- Usefulness: orbit, gravity, occultation, ....

CHAMP (GRACE、FORMOSAT-3) is a (low altitude) satellite, its dynamic orbit is

sensitive to gravity, including 1st. degree term (geocenter). And at the same time is a


sensitive to gravity, including 1st. degree term (geocenter). And at the same time is a

flying receiver (station).

Combined together to form 3 layers(at different height)

Ground--LEO--GPS

Solving orbits of GPS and LEO, ground station coordinates, EOP, etc.(incl. gravity)

together simultaneously. Overcome the weakness of each individual scenario.

Solution is more homogeneous and consistent.

SLR and GPS Data from CHAMP and GRACE strengthen

the reference frame

Estimated geocenter variation in Z-directions

DAY 020502 030502 040502 050502

ground only 16.2 ±±±±13.0 3.8 ±±±±11.7 -39.4 ±±±±13.1 19.4 ±±±±12.1

unit: mm


ground+LEO -7.7 ±±±±4.2 7.3 ±±±±4.7 -0.5 ±±±±4.7 0.9 ±±±±4.7

(Zhu and Shih, 2003)

Time-varying gravity recovery using

combined GPS and SLR observations


1. Restitution of the orbits of GPS satellites from GPS ground tracking data.

2. Determination of the orbits of CHAMP and GRACE satellites from space

receiver GPS data based on fixed GPS ephemerides and clocks from step 1.

3. Simultaneous determination of orbits of the GPS and LEO satellites and

recovery of gravity field model coefficients, EOPs, and station positions from

GPS ground and LEO space-borne data in the same solution. Attitude,


GPS ground and LEO space-borne data in the same solution. Attitude,

accelerometer, thruster, and K-band data can also be added if required. This is

the one-step or integrated procedure.

4. SLR data can be added with some realistic weighting.

)()( 332211

1

332211 UcUcUcNcNcNcX ++++=−

Time series of delta C20 from CSR RL04 and SLR solutions from

September 2006 to December 2007


The possible locations of the Taiwan SLR station

• Low cloud cover rate

• Avoid aviation safety

• Accessibility to station


• Power supply

Comparison of possible locations of Taiwan SLR

station

Ali Mountain

weather station((((阿里山氣象站阿里山氣象站阿里山氣象站阿里山氣象站))))

Kunyang at

Provincial high

14((((昆陽昆陽昆陽昆陽))))

Mt. Hehuan

(合歡山主峰合歡山主峰合歡山主峰合歡山主峰))))

Mt. Small-

Snowy((((小雪山雷達站小雪山雷達站小雪山雷達站小雪山雷達站))))

Height 2413m 3070m 3390m 2997m

Administrative Chiayi Nantou Nantou Taichung


Administrative

division

Chiayi Nantou Nantou Taichung

Accessibility

(transportation)

Good Good Good Bad

Power supply Good Average Average Unknown

Difficulty in site

construction

Unknown Easy Easy Hard

man-made

interference

Low High Average Very Low

Ali Mountain weather station

((((阿里山氣象站阿里山氣象站阿里山氣象站阿里山氣象站))))


Advantage：Good maintenance and stable power supply

Disadvantage：1. The weather-induced disasters may interrupts road access

2. Less suitable space for site construction

Kunyang

((((昆陽昆陽昆陽昆陽))))


Advantage： Entrance limitation in snowing season

Disadvantage： High man-made interference

Mt. Hehuan

(合歡山主峰合歡山主峰合歡山主峰合歡山主峰))))


Advantage： Vehicle control

Disadvantage：Too many tourists

Mt. Small-Snowy

((((小雪山雷達站小雪山雷達站小雪山雷達站小雪山雷達站))))


Advantage：Very low man-made interference

Disadvantage：High construction difficulty

Conclusions and suggestions

• Data from the Taiwan SLR station can be applied to precise orbitdetermination/validation, determinations of geocenter coordinate andtemporal gravity (primary). Other applications are fundamentalphysics, solid/ocean tides, time-transfer and alternative trackingwhen GPS fails (secondary).

• An NSC proposal (2011-2014) was submitted to develop theories and


• An NSC proposal (2011-2014) was submitted to develop theories andcomputer programs for SLR applications.

• The success of the proposed Taiwan SLR station will depend onmany parties in Taiwan, including NSPO, NSC, MOI and academicinstitutions.

a proposed satellite laser ranging station in taiwan

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