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Range Bias vs Intensity 2005 Toshimichi Otsubo Kashima Space Research Center National Institute of Information and Communications Technology ILRS Fall 2005 Workshop, 5 Oct 2005

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Satelllite signature Transmitted pulse NOT equal to Return pulse –Multiple CCRs contributing to the return. –Where is the detection timing? –Key error factor for TRF scale, GM, etc.

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System-type-dependent centre-of-mass correction LAGEOS From Otsubo and Appleby, JGR, 2003. 0.250.24 (m) 251 “Standard”257.6 r - nL 245 3-sigma 242 w/o clipping 245 Ideal S.P. (<0.1 p.e.) 249 1 p.e. 257 100 p.e. 256 10 p.e. 256 1 ps 252 100 ps 248 300 ps 244 1ns 242 3ns FWHM SinglePhoton C-SPAD PMT(LEHM) 250 2-sigma 247 2.5-sigma 247249250252(n=2.0) 245 Hx

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System-type-dependent centre-of-mass correction AJISAI SinglePhoton C-SPAD 1.000.95 (m) 1010 “Standard” 1028 r - nL 976 3-sigma 962 w/o clip 977 Ideal S.P. (<0.1 p.e.) 990 1 p.e. 1023 100 p.e. 1020 10 p.e. 1022 1 ps 1017 100 ps 1009 300 ps 993 1 ns 976 3 ns FWHM 985 2.5-sigma 997 2-sigma PMT(LEHM) 977(n=2.0)9879931002 985 Hx From Otsubo and Appleby, JGR, 2003.

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Intensity-dependent Bias Are CoM corrections constant in the real world? –Big challenge for “mm accuracy” Systematic error harmful in the analysis stage –Likely to be elevation-angle-dependent –Directly contaminates station heights (Otsubo, 2004). –Short pulse: fully compensated by C-SPAD / CFD. –Long pulse: target signature (STRL < LAG < AJI) –The stronger, the shorter? Not so simple?

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Bias vs Intensity: Analysis Procedure Use of “Returns per NP bin” as intensity parameter –Strong signal High return rate –Weak signal Low return rate (Extreme: single photon) Orbit determination –Period: Jan 2004 to Jul 2005 (210 days) –Satellites: LAG1+LAG2, AJISAI, STARLETTE+STELLA –‘ concerto v4 ’ solved for orbits, station position & range bias –Stations: Top 20 in Quarterly Performance Card (Thanks Mark!) –Post-fit residuals sorted by “returns per NP bin”

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Riga 1884: PMT

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McDonald 7080: PMT

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Yarragadee 7090: PMT

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Greenbelt 7105: PMT

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Monument Peak 7110: PMT

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Changchun 7237: APD

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Beijing 7249: APD

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Hartebeestoek 7501: PMT

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Zimmerwald 7810 (423 nm): APD

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Zimmerwald 7810 (846 nm): APD

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Borowiec 7811: PMT

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San Fernando 7824: PMT

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Mt Stromlo 7825: APD

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Riyadh 7832: SPAD? (No SCI Log)

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Grasse 7835: APD

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Shanghai 7837: APD

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Simosato 7838: PMT

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Graz 7839: APD

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Herstmonceux 7840: APD

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Potsdam 7841: PMT

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Matera 7941: PMT? (No SCI Log)

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Wettzell 8834: PMT+APD (?)

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Discussions: 1 mm accuracy? Still things to do! “Bias vs Intensity”: overall summary –Up to +/- 5 mm for LAG1+LAG2 and STRL+STEL. –Up to +/- 10-15 mm for AJI. –Single photon systems behave superbly. –The result is most likely to be underestimated. –It has already affected TRFs for a long time. Necessity to eliminate the intensity dependence –Accurate vertical component is our strength! –Think “accuracy” instead of “single shot rms” or “# of returns.” –Let us see “High-Low Experiments” !!

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System-type-dependent centre-of-mass correction ETALON SinglePhoton C-SPAD 0.600.55 (m) 576 “Standard”613 r - nL 556 3-sigma 552 w/o clip 558 Ideal S.P. (<0.1 p.e.) 573 1 p.e. 613 100 p.e. 608 10 p.e. 612 1 ps 607 100 ps 598 300 ps 578 1 ns 562 3 ns FWHM 580 2-sigma 564 2.5-sigma PMT(LEHM) 570575582593(n=2.0) 565 Hx From Otsubo and Appleby, JGR, 2003.

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