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

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.

System-type-dependent centre-of-mass correction LAGEOS From Otsubo and Appleby, JGR, (m) 251 “Standard”257.6 r - nL sigma 242 w/o clipping 245 Ideal S.P. (<0.1 p.e.) p.e p.e p.e ps ps ps 244 1ns 242 3ns FWHM SinglePhoton C-SPAD PMT(LEHM) sigma sigma (n=2.0) 245 Hx

System-type-dependent centre-of-mass correction AJISAI SinglePhoton C-SPAD (m) 1010 “Standard” 1028 r - nL sigma 962 w/o clip 977 Ideal S.P. (<0.1 p.e.) p.e p.e p.e ps ps ps ns ns FWHM sigma sigma PMT(LEHM) 977(n=2.0) Hx From Otsubo and Appleby, JGR, 2003.

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?

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”

Riga 1884: PMT

McDonald 7080: PMT

Yarragadee 7090: PMT

Greenbelt 7105: PMT

Monument Peak 7110: PMT

Changchun 7237: APD

Beijing 7249: APD

Hartebeestoek 7501: PMT

Zimmerwald 7810 (423 nm): APD

Zimmerwald 7810 (846 nm): APD

Borowiec 7811: PMT

San Fernando 7824: PMT

Mt Stromlo 7825: APD

Riyadh 7832: SPAD? (No SCI Log)

Grasse 7835: APD

Shanghai 7837: APD

Simosato 7838: PMT

Graz 7839: APD

Herstmonceux 7840: APD

Potsdam 7841: PMT

Matera 7941: PMT? (No SCI Log)

Wettzell 8834: PMT+APD (?)

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 +/ 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” !!

System-type-dependent centre-of-mass correction ETALON SinglePhoton C-SPAD (m) 576 “Standard”613 r - nL sigma 552 w/o clip 558 Ideal S.P. (<0.1 p.e.) p.e p.e p.e ps ps ps ns ns FWHM sigma sigma PMT(LEHM) (n=2.0) 565 Hx From Otsubo and Appleby, JGR, 2003.