Graz in Space 2008 Graz SLR System Daniel Kucharski IWF / SatGeo
Satellite Laser Ranging Range measurements to the satellites - time of flight of the ultrashort laser pulses - mm precision station-satellite - for: POD, science
SLR geodetic technique time of flight measurement of the laser pulses
SLR measurements - scientific studies of the Earth / Atmosphere / Oceans systems, determination of the temporal mass redistribution, EOP - determination of the geocentric position of an Earth satellite (precise calibration of radar altimeters)
SLR measurements - allow to determine the stations positions, their tectonic motion with respect to the geocenter - support research in fundamental physics. SLR measurements of LAGEOS 1 and 2 have measured the Lense- Thirring drag of the reference frame. A third LAGEOS-type satellite has been proposed for relativity studies.
The satellites Currently 35 objects - active: altimetry, gravitometry, navigation - passive: geodynamic
LAGEOS-1 i 2 426 CCRs 60 cm diameter Mass 411 kg, 405 kg ~6000 km above the surface Fully passive, geodesy
Ajisai 1436 CCRs + 318 mirrors 685 kg Diameter 215 cm 1500 km above the Earth Fully passive, geodesy
GPS-35 i 36 Panels with 32 CCRs Navigation system, time transfer
ERS-2, Envisat 9 CCRs 800 km above the ground remote sensing and environmental monitoring 1200 km altimetry, oceanography
The Moon
The Moon
SLR stations on the world
Graz SLR station Laser pulse GRAZ The other stations 2 khz 5-10 Hz Energy / puls Puls width Wavelength 0.4 mj 10 ps 532 nm 35 200 mj 35 200 ps 532 nm High accuracy of the distance measurements 200 times more measurements per second -> POD
LAGEOS-1 pass
GPS 35: Average # of Pts/NP in 2004 Potsdam Graz 12 845 Matera Grasse Riyadh Monument Wettzell Koganei Mt Stromlo McDonald Herstmonceu Yarragadee Zimmerwald Maidanak 1 Simosato 357 215 155 129 95 67 62 46 32 30 30 20 18 Changchun Beijing 7 3 1000 800 600 400 200 0 Graz khz SLR - statistics
Graz khz SLR - calibration SLR Graz: Routine - Calibrations 2003-2005; 10 Hz: 500 Returns; khz: 10 000 Returns / CAL 4 Peak minus Mean [mm] 3 2 1 0-1 -2-3 CAL Peak minus Mean [mm] -4 2003 2003.5 2004 2004.5 2005 2005.5
Graz station position motion Up Component: -3.53 ± 0.07 mm / year ( 100 k years until sea level) East Component: 22.15 ± 0.07 mm / year North Component: 14.85 ± 0.10 mm / year
Graz khz SLR new applications Satellite spin measurements Gravity Probe B, 650 km, 75s AJISAI, 1500 km, 2s LAGEOS 1, 2, 6000 km, 5000s, 600s ETALON 1, 2, 19000 km, 65 s Atmospheric seeing measurements monitoring the atm. condition of the way of a laser pulse Space debris tracking helps to monitor them, POD
Graz khz SLR Spin GP-B Lense-Thirring drag 650 km Only Graz khz SLR station was able to measure the spin of the spacecraft
Graz khz SLR Spin GP-B 8 CCRs, 10cm dia.
Graz khz SLR Spin GP-B RMS LASER-OnBoard = 0.98 s
Graz khz SLR Spin AJISAI Spectral analysis of khz SLR data
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) Spin Rate [Hz] 0.525 0.520 0.515 0.510 0.505 6-Retro 9 Retro 12 Retro 0.500 2003.8 2004.2 2004.6 2005.0 2005.4 Year
Graz khz SLR LAGEOS-1 T=5775 s
Graz khz SLR ETALON-1, 2 Real obs. Sim: 30 s ~70k returns/h 66 s 100 s
Graz khz SLR ETALON-1, 2 Spin period of the ETALONs is increasing by a value of about 0.5 s/year RMS ~1%
Spin parameters - application Improving the accuracy of the perturbations models The magnetic torque ( ϖ B) Vα ( B ϖ ) B Γmagnetic = Vα ϖ B Bertotti and Iess, 1991 The gravitational torque m Γ nal = 3 2 2 1 2 4L ( C A)( 3cos ϑ )( n L)( n L) gravitatio Farinella et al., 1996 Solar radiation pressure causes a torque: I hc A c ( s r ) 0 R cross Vokrouhlicky, 1996 Γoffset = sun 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
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
Graz khz SLR atm. seeing
Graz khz SLR seeing 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 the first khz SLR system - 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