Centre-of-mass correction issues: Toward mm-ranging accuracy Toshimichi OTSUBO [email protected]...
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Transcript of Centre-of-mass correction issues: Toward mm-ranging accuracy Toshimichi OTSUBO [email protected]...
Centre-of-mass correction issues:Centre-of-mass correction issues:Toward mm-ranging accuracyToward mm-ranging accuracy
Toshimichi OTSUBO [email protected]
National Institute of Information and Communications Technologyand
Graham M [email protected]
NERC Space Geodesy Facility
10 June 2004, 14th International Laser Ranging Workshop (San Fernando)
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Difficult challenge:We want to achieve mm accuracyusing targets designed for cm accuracy.
+
s a te llite
c entre
(pu ls e trans mittedfrom a ground s ta tion)
(re tro -re flec tedpuls e )
c o rne r c ube
re flec to rs
(imagina rypu ls e re flec ted a t the c entre )
c entre -o f-mas s c o rrec tion x 2
Very Important:High “accuracy” is NOT equivalent to small single-shot rms.
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)
Response functionResponse function
Red: n=1.0Green: n=2.0Blue: best-fit
LAGEOS
AJISAI
ETALON
Centre-of-mass correction
for high energy system … approx. at leading edge
for single photon system … approx. at centroid
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.
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.
The most guilty “error”The most guilty “error” … intensity-dependent range bias … intensity-dependent range bias
C-SPAD users:“C-” does NOT mean “compensated” for actual targets!Control the return energy (preferably at single-photon).
MCP-PMT users:Probably not so serious as C-SPAD, but not sure at 1-mm accurate level.
Likely to be elevation-angle-dependent error
We should test at each station! cf: following 2 speakersWilkinson and Appleby (C-SPAD at Herstmonceux)Carman, Noyes and Otsubo (MCP+CFD at Yarragadee)
Apr 03To
Feb 04
ResidualResidualanalysisanalysis
Apr 03To
Feb 04
ResidualResidualanalysisanalysis
Apr 03To
Feb 04
ResidualResidualanalysisanalysis
Apr 03To
Feb 04
ResidualResidualanalysisanalysis
Apr 03To
Feb 04
ResidualResidualanalysisanalysis
Apr 03To
Feb 04
ResidualResidualanalysisanalysis
Apr 03To
Feb 04
ResidualResidualanalysisanalysis
Apr 03To
Feb 04
ResidualResidualanalysisanalysis
Residual analysis “bias vs intensity 2003-04”: suResidual analysis “bias vs intensity 2003-04”: summarymmary
The intensity dependency is underestimated in this analysis.Intensity-dependent Elevation-angle-dependent absorbed in parameter estimation
Overall verdictsSingle photon systems (Hx, and Zimm also?) behave very good.MCP systems also good, but a few mm trend seen.C-SPAD systems have “the stronger, the shorter” trend.
… typically p-p 5 cm for AJISAI, p-p < 1 cm for LAGEOSGraz kHz … difficult to tell too many “9999” data.
Very Important:DO NOT be relieved even if your station looked ok.
How guilty of corrupting geodetic resultHow guilty of corrupting geodetic resultis intensity-dependent range bias?is intensity-dependent range bias?
Adding artificial bias to raw LAG1 NP data (50 days: 21 Apr to 9 Jun 03)Station: Yarragadee (7090), Hartebeesthoek (7501) and Graz (7839)Intensity = number of single-shot returns per NP bin
StrongWeak 25% 25%
48 shots/bin 223 shots/binYarragadee
109 shots/bin 322 shots/binHartebeesthoek
65 shots/bin 234 shots/binGraz
+5 mm -5 mm
How guilty of corrupting geodetic How guilty of corrupting geodetic result is intensity-dependent range result is intensity-dependent range bias?bias?
Orbit determination with Pos+RB estimation,with and w/o introducing artificial biasDifference
artificial-original
Height +7.4 mm
Range bias (orig +5.1 mm)
+4.2 mm
Height +8.4 mm
Range bias(orig +8.9 mm)
+4.8 mm
Height +6.0 mm
Range bias(orig +0.1 mm)
+4.9 mm
Yarragadee
Hartebeesthoek
Graz
-5 mm
+5 mm
Conclusions: mm accuracy from cm targets? Conclusions: mm accuracy from cm targets?
LAGEOS is a “large” satellite now!
Eliminate the intensity-dependent bias!
C-SPAD does not fully compensate for satellite returns.MCP systems are more robust, and single-photon systems are the most.
Intensity robustness should be TESTED at EVERY station (cf. following 2 speakers)Strong-Weak test for LAGEOS, AJISAI and any LEO with small CCR array. Please report at the future workshops!
This bias contaminates the geodetic solutions.
Do not go for small single-shot rms.Do not go for many single-shot returns.
For the single photon systems, we can calculate the centre-of-mass corrections.