Theoretical Centreofmass Corrections for LAGEOS, ETALON and AJISAI

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Theoretical Centre-of-mass Corrections for
LAGEOS, ETALON and AJISAI
See Otsubo and Appleby, JGR, 108, B4, 2201, Apr
2003.

• Toshimichi OTSUBO
• Communications Research Laboratory, Kashima,
  Japan
• Graham M APPLEBY
• Natural Environment Research Council, Monks Wood,
  UK

Laser Workshop 2003, Koetzting, 28-31 Oct 2003.
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Satellite signature effect

• Multiple reflectors contributing to the satellite
  response.
• System-dependent detection timing.
• Single photon
• C-SPAD
• MCP-PMT
• Key error factor to achieve accurate GM and TRF
  scale.

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ETALON(12) USSR 1989 Altitude 19000 km Diameter
1.294 m 2134 CCRs
AJISAI Japan 1986 Altitude 1500 km Diameter 2.15
m 1436 CCRs
LAGEOS(12) USItaly 1976, 92 Altitude 5900
km Diameter 0.60 m 426 CCRs
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Response from single reflector

• 3 factors to be considered.
• Effective reflection area (a)
• Reflectance (e)
• Diffraction
• How to compute the intensity.
• ?ae diffraction neglected.
• ?a2e simple diffraction model.
• Neubert, 1994 Otsubo, 1999
• ?ane this study.

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• ? Effective reflection area

Reflectance ?
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Centre-of-mass correction
Extracted from Otsubo and Appleby, JGR, 108, B4,
2201, Apr 2003.

• LAGEOS n1.1

0.25
0.24 (m)
251 Standard
257.6 r - nL
247
249
250
252
(n2.0)
Single Photon
245 Hx
245 3-sigma
242 w/o clipping
250 2-sigma
247 2.5-sigma
C-SPAD
245 Ideal S.P. (lt0.1 p.e.)
249 1 p.e.
257 100 p.e.
256 10 p.e.
PMT (LEHM)
248 300 ps
244 1ns
256 1 ps
242 3ns FWHM
252 100 ps
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Centre-of-mass correction
Extracted from Otsubo and Appleby, JGR, 108, B4,
2201, Apr 2003.

• AJISAI n1.2

1.00
0.95 (m)
1010 Standard
1028 r - nL
977
(n2.0)
987
993
1002
Single Photon
985 Hx
976 3-sigma
962 w/o clip
985 2.5-sigma
997 2-sigma
C-SPAD
1023 100 p.e.
1020 10 p.e.
977 Ideal S.P. (lt0.1 p.e.)
990 1 p.e.
PMT (LEHM)
1009 300 ps
976 3 ns FWHM
1022 1 ps
1017 100 ps
993 1 ns
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Centre-of-mass correction
Extracted from Otsubo and Appleby, JGR, 108, B4,
2201, Apr 2003.

• ETALON n1.3

0.60
0.55 (m)
576 Standard
613 r - nL
570
575
582
593
(n2.0)
Single Photon
565 Hx
552 w/o clip
556 3-sigma
580 2-sigma
564 2.5-sigma
C-SPAD
558 Ideal S.P. (lt0.1 p.e.)
613 100 p.e.
573 1 p.e.
608 10 p.e.
PMT (LEHM)
607 100 ps
598 300 ps
612 1 ps
562 3 ns FWHM
578 1 ns
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Discussions (personal opinions) for mm ranging

• Avoid the intensity-dependent bias ON-SITE!
• Likely to become the elevation-angle-dependent
  bias, which can significantly degrade the station
  height determination.
• C-SPAD does NOT compensate the satellite returns.
  1 cm for LAGEOS, 4-5 cm for AJISAI and ETALON.
• MCPCFD seems ok at 1-cm level, but not at 1-mm
  level.
• Try the on-site shot-by-shot experiment.
• kHz laser? Go for STRICT single photon!

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Range residuals vs Intensity (Otsubo and
Genba, DC Workshop, 2002)
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Range residuals vs Intensity (Otsubo and
Genba, DC Workshop, 2002)
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Range residuals vs Intensity (Otsubo and
Genba, DC Workshop, 2002)
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Discussions (personal opinions) for mm analysis

• Better adjust the range bias for a while.
• 1-mm accuracy is still a challenge.
• Impossible to model the CoM correction for
  multi-photon (esp. MCPCFD) systems at 1-mm
  accuracy.
• Many other systematic error sources.
• Accept a constant offset bias. Too risky to fix
  it to 0 mm.
• Tight constraints can be applied if necessary.
• A different story when all stations do the single
  photon.

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Summary

• Stations,
• Eliminate any systematic range errors.
• Analysts,
• Not assume zero range bias.
• English speakers,
• Is the word bias appropriate? Probably
  negative impression to non-SLR people.

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Satellite Signature Effect in GLONASS SLR Data

• Toshimichi OTSUBO
• Communications Research Laboratory, Kashima,
  Japan
• Graham M APPLEBY
• Philip GIBBS
• Natural Environment Research Council, Monks Wood,
  UK

Laser Workshop 2003, Koetzting, 28-31 Oct 2003.
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GLONASS CCR Array
New type (except GLO-88) - 132 CCRs. - Since
GLO-84.
Old type - 396 CCRs. - Until GLO-80.
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old
Effective array size estimation - for 2001. -
estimated by concerto ver 3. - bias
elevation dependent average (eff array size)
x 0.15 .
old
NEW
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NEW
Effective array size estimation - for 2002.
NEW
NEW
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Summary

• GLONASS CCR Design
• Large flat array is probably not the best idea.
  It causes the elevation-dependent range error.
  2 cm on average.
• New CCR array at least halved the signature
  effect. lt 1 cm on ave.
• Return energy vs signature effect
• Difficult in observing new GLONASSes esp in
  daytime?
• What is the best array pattern for such high
  orbiters?
• How about in the GALILEO project?