SLR towards mm accuracySLR towards mm accuracy

Stanisław SchillakStanisław Schillak

Space Research Centre of the Polish Academy of SciencesSpace Research Centre of the Polish Academy of Sciences Astrogeodynamic ObservatoryAstrogeodynamic Observatory

ILRS Fall 2005 WorkshopILRS Fall 2005 WorkshopEastbourne, 3 – 7 October 2005Eastbourne, 3 – 7 October 2005

Borowiec Borowiec

e-mail: sch@cbk.poznan.pl

AtmosphereAtmosphere 5 – 10 mm 5 – 10 mm

Is the Marini-Murray atmospheric model enough accurate for 1 mm ranging accuracy? Why not?

model is fixed and depend only on latitude and geodetic height, model is true only for short distance about 10 km, model don’t include changes of refraction coefficient from local conditions(winds, rapidly temperature and pressure changes etc.)

Are other better models?

How we can to control error value? Is it really several mm?

How we can to correct this error?

two-color ranging – we need to know distance between two colors for each measurement with accuracy several picoseconds, is detector for it?determination of the seasonal correction from orbital analysis? are the other methods?

How we can to eliminate this error?

new Lageos type satellite with prisms like in Larets or Westpac (returns only from one cube corner) additional advantage: more normal points for stations coordinates determination

strong signal – return will be from the nearest prism

determination corrections from a model of satellite signature

kHz lasers – identification of corner cubes, is it possible?

Satellite Center of MassSatellite Center of Mass 22 – 4 mm – 4 mm

11

22

33

44

Detector – stop signal strength variationDetector – stop signal strength variation

uncertainty of the photons distribution before detector for low signal: 100 ps 15 mm

40 ps 6 mm 10 ps 1.5 mm

is this effect important? new lasers with pulse width below 10 ps are necessary? short laser pulses are also important for spatial error

2.2. Detector delayDetector delay

is a model of Time Walk enough accurate for one mm accuracy? level of calibration is really the same as a mean level of satellite observation? how we can to control it?

1.1. Width of the laser pulseWidth of the laser pulse

3. Stability of stop pulse amplitude and shape3. Stability of stop pulse amplitude and shape

discriminator problem 30 ps - 4.5 mm

single photoelectron level?

ERRORS SOURCESERRORS SOURCES THE BEST SLR SYSTEM IN 2004 (mm)

BOROWIEC SLR SYSTEM IN 2004 (mm)

ENVIROMENTAL ERRORSENVIROMENTAL ERRORS  

•ATMOSPHERIC PROPAGATION (MODEL) ~5 ~5

•ATMOSPHERIC PROPAGATION (METEO) <1 <1

•SATELLITE CENTER OF MASS 2 2•REFERENCE POINT POSITION 1 3

SLR SYTEM ERRORSSLR SYTEM ERRORS  

•CALIBRATION PATH (SURVEY) 1 1•CALIBRATION PATH (METEO) <1 <1•SIGNAL STRENGTH VARIATION 2 5

•TEMPORAL VARIATION 1 2•SPATIAL VARIATION 1 2•MOUNT ECCENTRICITIES 1 1•TIMER 1 4•STANDARD FREQUENCY (RANGE) <1 <1

•SOFTWARE ERRORS <1 <1TIMING ERRORSTIMING ERRORS  

•UTC TIME SCALE 10ns 10ns•STANDARD FREQUENCY (EPOCH)) 100ns 100ns

•EPOCH REGISTRATION 100ns 100nsTOTALTOTAL 66 99

Systematic deviations per month (LAGEOS satellites)

   

ERRORS SOURCES

THE BEST SLR SYSTEM IN 2004

BOROWIEC SLR SYSTEMIN 2004

PARAMETERs

(mm)PARAMETER

s(mm)

STABILITY OF „STOP” PULSE Discriminator 30 ps 4.5 Discriminator 30 ps 4.5

DETECTOR’S TTS 25 ps 2.9 160 ps 12.4

LASER PULSE WIDTH 30 ps 1.9 40 ps 2.6

STABILITY OF „START” PULSE Discriminator <1 Discriminator <1

ELECTRONIC’S PRECISION ET 5 ps 0.7 TIC 25 ps 3.8

FREQUENCY JITTER Cesium <1 Cesium <1

EPOCH REGISTRATION 100 ns 0 100 ns 0

SATELLITE - LAGEOS CC   4.0   4.0

TOTAL – SINGLE SHOT 6.9 14.6

TOTAL – NORMAL POINT 100 pts/NP 0.7 20 pts/NP 3.3

Random errors - Random errors - LAGEOS satellites (single photoelectron)LAGEOS satellites (single photoelectron)

0

1

2

3

4

5

6

7

8

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Year

RM

S [

cm

]

0

20

40

60

80

100

120

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Year

Ra

w R

MS

[m

m]

Single shot precision of Single shot precision of LAGEOS-1 and LAGEOS-2 passes LAGEOS-1 and LAGEOS-2 passes

in the period in the period 1993.5 – 2003.51993.5 – 2003.5

Orbital RMS of normal points of Orbital RMS of normal points of LAGEOS-1 and LAGEOS-2 passes LAGEOS-1 and LAGEOS-2 passes

in the period in the period 1993.5 – 2000.51993.5 – 2000.5

BOROWIEC SLR (7811)BOROWIEC SLR (7811)

Orbital RMS LAGEOS-1 and LAGEOS-2

0

20

40

60

80

100

120

RM

S [

mm

]

LAGEOS-1

LAGEOS-2

Range BiasLAGEOS-1 and LAGEOS-2

-40

-20

0

20

40

60

80

RB

[m

m]

LAGEOS-1

LAGEOS-2

STATIONS

Stability of SLR stations coordinates1999 - 2003

0

5

10

15

20

25

30

35

40

45

50

1999 2000 2001 2002 2003

Years

Sta

bili

ty [

mm

]

186418847080709071057110712472107237724974037501780678107811782478327835783678377838783978407845784979418834

What is important for improvement of the station What is important for improvement of the station coordinates determination?coordinates determination?

STATIONSTATION

number of normal points per stationnumber of normal points per station

Precision of stations coordinates determination vs. number of normal points per orbital arc

0,01

0,1

1

10

100

1000

10000

0 200 400 600 800 1000 1200 1400 1600 1800

norm al points

data quality (single shot RMS, NP RMS, Range Bias, Time Bias)data quality (single shot RMS, NP RMS, Range Bias, Time Bias)

continuity of observationscontinuity of observations

rejection of normal points and passesrejection of normal points and passes

What is important for improvement of the station What is important for improvement of the station coordinates determination?coordinates determination?

ANALYSIS CENTERANALYSIS CENTER

rejection of normal points and passes

new models of the Earth gravity field: GRACE, GOCE

long term gravity variations

polar motion coordinates, below 1 day?

new stations coordinates: ITRF2004

geocenter motion

satellite-station perturbations (improvement or new effects)

new model of atmosphere

new precession-nutation model (IAU2000)

new celestial and terrestrial reference system (IAU2000)

near-real time monitoring of stations coordinates