Range Bias vs Intensity 2005

Toshimichi Otsubo

Kashima Space Research CenterNational 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?

+

satellite

centre

(pulse transmittedfrom ground station)

(retroreflectedpulse)

cube corner reflectors

(imaginary pulse reflected

at centre)– Key error factor for TRF scale, GM, etc.

System-type-dependent centre-of-mass System-type-dependent centre-of-mass correctioncorrection

LAGEOSFrom Otsubo and Appleby, JGR, 2003.

0.25 0.24 (m)

251 “Standard”257.6r - nL

2453-sigma

242w/o clipping

245Ideal S.P. (<0.1 p.e.)

2491 p.e.

257100 p.e.

25610 p.e.

2561 ps

252100 ps

248300 ps

2441ns

2423ns FWHM

SingleSinglePhotonPhoton

C-SPADC-SPAD

PMTPMT(LEHM)(LEHM)

2502-sigma

2472.5-sigma

247249250252 (n=2.0)

245Hx

System-type-dependent centre-of-mass System-type-dependent centre-of-mass correctioncorrectionAJISAI

SingleSinglePhotonPhoton

C-SPADC-SPAD

1.00 0.95 (m)

1010 “Standard”1028r - nL

9763-sigma

962w/o clip

977Ideal S.P. (<0.1 p.e.)

9901 p.e.

1023100 p.e.

102010 p.e.

10221 ps

1017100 ps

1009300 ps

9931 ns

9763 ns FWHM

9852.5-sigma

9972-sigma

PMTPMT(LEHM)(LEHM)

977 (n=2.0)9879931002

985Hx

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 +/- 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” !!

System-type-dependent centre-of-mass System-type-dependent centre-of-mass correctioncorrectionETALON

SingleSinglePhotonPhoton

C-SPADC-SPAD

0.60 0.55 (m)

576 “Standard”613r - nL

5563-sigma

552w/o clip

558 Ideal S.P. (<0.1 p.e.)

5731 p.e.

613100 p.e.

60810 p.e.

6121 ps

607100 ps

598300 ps

5781 ns

5623 ns FWHM

5802-sigma

5642.5-sigma

PMTPMT(LEHM)(LEHM)

570575582593 (n=2.0)

565Hx

From Otsubo and Appleby, JGR, 2003.