Range Bias vs Intensity 2005 Toshimichi Otsubo Kashima Space Research Center National Institute of...

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.