graz in space 2008 graz slr systemsatellite laser ranging • range measurements to the satellites -...
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Graz in Space 2008
Graz SLR System
Daniel Kucharski
IWF / SatGeo
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Satellite Laser Ranging
• Range measurements to the satellites- time of flight of the ultrashort laser pulses- mm precision station-satellite- for: POD, science
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SLR – geodetic technique
‘time of flight’ measurement of the laser pulses
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SLR measurements
- scientific studies of the Earth / Atmosphere / Oceans systems, determination of the temporal mass redistribution, EOP
- determination of the geocentric positionof an Earth satellite (precise calibration ofradar altimeters)
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- allow to determine the stations’ positions, their tectonic motion with respect to the geocenter
- support research in fundamental physics. SLRmeasurements of LAGEOS 1and 2 have measured the Lense-Thirring “drag” of the referenceframe. A third LAGEOS-type satellite has been proposed forrelativity studies.
SLR measurements
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The satellites
Currently 35 objects
- active: altimetry, gravitometry, navigation
- passive: geodynamic
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LAGEOS-1 i 2
426 CCRs
60 cm diameter
Mass 411 kg, 405 kg
~6000 km above the surface
Fully passive, geodesy
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Ajisai
1436 CCRs + 318 mirrors
685 kg
Diameter 215 cm
1500 km above the Earth
Fully passive, geodesy
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GPS-35 i 36
Panels with 32 CCRs
Navigation system,
time transfer
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ERS-2, Envisat
9 CCRs
800 km above the ground
remote sensing and environmental monitoring
1200 km
altimetry, oceanography
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The Moon
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The Moon
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SLR stations on the world
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Graz SLR stationGRAZ The other
stations2 kHz 5 - 10 Hz
35 – 200 mJ
35 – 200 ps
532 nm
0.4 mJ
10 ps
532 nm
Laser pulse
Energy / puls
Puls width
Wavelength
High accuracy of the distance measurements
200 times more measurements per second -> POD
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LAGEOS-1 pass
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GPS 35: Average # of Pts/NP in 2004
845
357
215
155
129
95 67 62 46 32 30 30 20 18 12 7 30200400600800
1000
Gra
z
Mat
era
Gra
sse
Riy
adh
Mon
umen
t
Wet
tzel
l
Kog
anei
Mt S
trom
lo
McD
onal
dH
erst
mon
ceu
Yarr
agad
ee
Zim
mer
wal
d
Mai
dana
k 1
Sim
osat
o
Pots
dam
Cha
ngch
un
Bei
jing
Graz kHz SLR - statistics
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SLR Graz: Routine - Calibrations 2003-2005;10 Hz: 500 Returns; kHz: 10 000 Returns / CAL
-4
-3
-2
-1
0
1
2
3
4
2003 2003.5 2004 2004.5 2005 2005.5
Peak
min
us M
ean
[mm
] CAL Peak minus Mean [mm]
Graz kHz SLR - calibration
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Up Component: -3.53 ± 0.07 mm / year (≈100 k years until sea level)East Component: 22.15 ± 0.07 mm / yearNorth Component: 14.85 ± 0.10 mm / year
Graz station – position motion
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Graz kHz SLR – new applications
Satellite spin measurementsGravity Probe – B, 650 km, 75s AJISAI, 1500 km, 2sLAGEOS – 1, 2, 6000 km, 5000s, 600sETALON –1 , 2, 19000 km, 65 s
Atmospheric seeing measurementsmonitoring the atm. condition of the way of a laser pulse
Space debris trackinghelps to monitor them, POD
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Graz kHz SLR – Spin GP-BLense-Thirring “drag”
650 km
Only Graz kHz SLR station was able to measure the spin of the spacecraft
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Graz kHz SLR – Spin GP-B8 CCRs, 10cm dia.
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RMSLASER-OnBoard = 0.98 s
Graz kHz SLR – Spin GP-B
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Graz kHz SLR – Spin AJISAI
Spectral analysis of kHz SLR data
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Graz kHz SLR – Spin AJISAI
AJISAI SPIN RATE 2003/10 - 2005/06; corrected for apparent Spin 195 passes with >300 k points; ± 48 s around CA used (40 k min)
0.500
0.505
0.510
0.515
0.520
0.525
2003.8 2004.2 2004.6 2005.0 2005.4Year
Spin
Rat
e [H
z]
6-Retro
9 Retro
12 Retro
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Graz kHz SLR –LAGEOS-1
T=5775 s
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Graz kHz SLR – ETALON-1, 2
Real
obs.
Sim:
30 s
66 s
100 s
~70k returns/h
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Graz kHz SLR – ETALON-1, 2
Spin period of the ETALONs is increasing by a value of about 0.5 s/year
RMS ~1%
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Spin parameters - applicationImproving the accuracy of the perturbations’ models
The magnetic torque
( ) ( ) BBVBBVmagnetic ××′′−⋅×′=Γ ϖαϖϖα Bertotti and Iess, 1991
The gravitational torque
( )( )( )( )LnLnACLm
nalgravitatio ×⋅−−−=Γ 1cos343 2
2
2
ϑ Farinella et al., 1996
Solar radiation pressure causes a torque:
( )suncrossR
offset rscAhCI
×=Γ 0 Vokrouhlicky, 1996
Bertotti, B., and Iess, L. The rotation of LAGEOS, J. Geophys. Res., 96 (B1), 2431-2440, 1991
Farinella, P., Vokrouhlicky, D., Barlier F. The rotation of LAGEOS and ist long-term semimajor axis decay, J. Geophys. Res., 101 (B8), 17,861-17,892, 1996
Vokrouhlicky, D. Non-gravitational effects on LAGEOS’ rotation. Geophys. Res. Lett., 23, 3079-3082, 1996
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Graz kHz SLR – LAGEOS-2
Full 15 years spin period history,
Only Graz kHz system can measure L2 spin of more than 100s
Study of various perturbations and RE
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Graz kHz SLR – atm. seeing
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Laser Beam Backscatter is monitored by ISIT; => into PC;Real Time Image Processing: Determine Peak of Laser Beam;At 25 fps: Store peak coordinates in file;Post Processing: Get Area of Coordinates;FWHM of this area => Astr. Seeing (arc secs)Calibrate with standard astronomical methods
Graz kHz SLR – seeing
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- more accurate range measurements = improvement of POD (navigation systems HEO, LEO)
- much more scientific data: spin determination of various sat.
- kHz SLR allows to investigate the values of the SP and their changes, that gives an unique possibility to study the tiny petrurbating forces (RE)
- more information about the atmospheric conditions: seeing measurements over the station
Graz – the first kHz SLR system