Theoretical Centre-of-mass Theoretical Centre-of-mass Corrections for LAGEOS, ETALON and Corrections for LAGEOS, ETALON and

AJISAIAJISAI

Toshimichi OTSUBOCommunications Research Labo

ratory, Kashima, Japan

Graham M APPLEBYNatural Environment Research

Council, Monks Wood, UK

Laser Workshop 2003, Koetzting, 28-31 Oct 2003.

See Otsubo and Appleby, JGR, 108, B4, 2201, Apr 2003.See Otsubo and Appleby, JGR, 108, B4, 2201, Apr 2003.

Satellite signature effectSatellite signature effect

• Multiple reflectors contributing to the satellite Multiple reflectors contributing to the satellite response.response.

• System-dependent detection timing.System-dependent detection timing.– Single photonSingle photon– C-SPADC-SPAD– MCP-PMTMCP-PMT

• Key error factor to achieve accurate GM and TRF Key error factor to achieve accurate GM and TRF scale.scale.

+

satellite

centre

(pulse transmittedfrom ground station)

(retroreflectedpulse)

cube corner reflectors

(imaginary pulse reflected

at centre)

LAGEOS(1&2)US+Italy 1976, 92Altitude 5900 kmDiameter 0.60 m426 CCRs

ETALON(1&2)USSR 1989Altitude 19000 kmDiameter 1.294 m2134 CCRs

AJISAIJapan 1986Altitude 1500 kmDiameter 2.15 m1436 CCRs

Response from single reflectorResponse from single reflector

• 3 factors to be considered.3 factors to be considered.–Effective reflection area (Effective reflection area (aa))–Reflectance (Reflectance (ee))–DiffractionDiffraction

• How to compute the intensity.How to compute the intensity.∝ae … diffraction neglected.… diffraction neglected.∝a2e … simple diffraction model.… simple diffraction model.

[Neubert, 1994; Otsubo, 1999]

∝ane … this study.… this study.

42.0

8.5AJ IS AI

fused silican=1.46

no coatingon back faces

(front)

17.1

LAGEOS

fused silican=1.46

no coatingon back faces

38.1

27.8

27.0

ETALON

fused silican=1.46

alminium coatingon back faces

19.1

(side)

← ← Effective reflection Effective reflection areaarea

ReflectancReflectance →e →

LAGEOS n=1.1LAGEOS n=1.1 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)

Centre-of-mass correctionCentre-of-mass correction

245Hx

Extracted from Otsubo and Appleby, JGR, 108, B4, 2201, Apr 2003.Extracted from Otsubo and Appleby, JGR, 108, B4, 2201, Apr 2003.

AJISAI n=1.2AJISAI n=1.2

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

Centre-of-mass correctionCentre-of-mass correction

985Hx

Extracted from Otsubo and Appleby, JGR, 108, B4, 2201, Apr 2003.Extracted from Otsubo and Appleby, JGR, 108, B4, 2201, Apr 2003.

ETALON n=1.3ETALON n=1.3

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)

Centre-of-mass correctionCentre-of-mass correction

565Hx

Extracted from Otsubo and Appleby, JGR, 108, B4, 2201, Apr 2003.Extracted from Otsubo and Appleby, JGR, 108, B4, 2201, Apr 2003.

Discussions Discussions (personal opinions)(personal opinions) for mm ranging for mm ranging

• Avoid the intensity-dependent bias ON-SITE!Avoid the intensity-dependent bias ON-SITE!– Likely to become the elevation-angle-dependent Likely to become the elevation-angle-dependent

bias, which can significantly degrade the station bias, which can significantly degrade the station height determination.height determination.• C-SPAD does NOT compensate the satellite C-SPAD does NOT compensate the satellite

returns. 1 cm for LAGEOS, 4-5 cm for AJISAI returns. 1 cm for LAGEOS, 4-5 cm for AJISAI and ETALON.and ETALON.

• MCP+CFD seems ok at 1-cm level, but not at MCP+CFD seems ok at 1-cm level, but not at 1-mm level.1-mm level.

– Try the on-site shot-by-shot experiment.Try the on-site shot-by-shot experiment.– kHz laser? Go for STRICT single photon!kHz laser? Go for STRICT single photon!

Range residuals vs Intensity Range residuals vs Intensity (Otsubo and Genba, DC Workshop, 2002)(Otsubo and Genba, DC Workshop, 2002)

Range residuals vs Intensity Range residuals vs Intensity (Otsubo and Genba, DC Workshop, 2002)(Otsubo and Genba, DC Workshop, 2002)

Range residuals vs Intensity Range residuals vs Intensity (Otsubo and Genba, DC Workshop, 2002)(Otsubo and Genba, DC Workshop, 2002)

Discussions Discussions (personal opinions)(personal opinions) for mm for mm analysisanalysis

• Better adjust the range bias for a while.Better adjust the range bias for a while.– 1-mm accuracy is still a challenge.1-mm accuracy is still a challenge.

• Impossible to model the CoM correction for multi-phoImpossible to model the CoM correction for multi-photon (esp. MCP+CFD) systems at 1-mm accuracy.ton (esp. MCP+CFD) systems at 1-mm accuracy.

• Many other systematic error sources.Many other systematic error sources.– Accept a constant offset bias. Too risky to fix it to 0 mAccept a constant offset bias. Too risky to fix it to 0 m

m. m. – Tight constraints can be applied if necessary.Tight constraints can be applied if necessary.– A different story when all stations do the single photon.A different story when all stations do the single photon.

SummarySummary

• Stations, Stations, Eliminate any systematic range errors.Eliminate any systematic range errors.

• Analysts,Analysts,Not assume zero range bias.Not assume zero range bias.

• English speakers,English speakers,Is the word “bias” appropriate? Probably Is the word “bias” appropriate? Probably negative impression to non-SLR people. negative impression to non-SLR people.

Satellite Signature Effect Satellite Signature Effect in GLONASS SLR Datain GLONASS SLR Data

Toshimichi OTSUBOCommunications Research Labo

ratory, Kashima, Japan

Graham M APPLEBYPhilip GIBBS

Natural Environment Research Council, Monks Wood, UK

Laser Workshop 2003, Koetzting, 28-31 Oct 2003.

GLONASS CCR ArrayGLONASS CCR Array

Old typeOld type- 396 CCRs.- 396 CCRs.

- Until GLO-80.- Until GLO-80.

New type New type (except GLO-8(except GLO-88)8)

- 132 CCRs.- 132 CCRs.

- Since GLO-84.- Since GLO-84.

Effective array size estimatioEffective array size estimationn- for 2001.- for 2001.

- estimated by concerto ver 3.- estimated by concerto ver 3.

- bias - bias

elevation dependentelevation dependent

average average ～ ～ (eff array size) x (eff array size) x 0.15 .0.15 .

old

old

NEW

Effective array size Effective array size estimationestimation- for 2002.- for 2002.

NEW

NEW

NEW

SummarySummary

• GLONASS CCR Design GLONASS CCR Design Large flat array is probably not the best idea. It causes the Large flat array is probably not the best idea. It causes the elevation-dependent range error. ~ 2 cm on average.elevation-dependent range error. ~ 2 cm on average.

New CCR array at least halved the signature effect. < 1 cm New CCR array at least halved the signature effect. < 1 cm on ave.on ave.

• Return energy vs signature effectReturn energy vs signature effectDifficult in observing new GLONASSes esp in daytime?Difficult in observing new GLONASSes esp in daytime?

What is the best array pattern for such high orbiters? What is the best array pattern for such high orbiters? How about in the GALILEO project?How about in the GALILEO project?