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20th ILRS Workshop, Oct. 11, 2016
1
Institute for Astronomical
and Physical Geodesy
Institute for Astronomical
and Physical Geodesy
Ranging the GNSS Constellation
Urs Hugentobler
Technische Universität München, Germany
20th ILRS Workshop
Potsdam, October 11, 2016
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20th ILRS Workshop, Oct. 11, 2016
2
Institute for Astronomical
and Physical Geodesy
GPS SLR Residuals
Springer 2000
-6 cm
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20th ILRS Workshop, Oct. 11, 2016
• Earth albedo causes a radial GNSS orbit error of 1-2 cm
• Antenna thrust causes a radial orbit error at a level of 1 cm
Rodriguez et al., 2010
Influence of Earth Albedo
2 cm
3
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
Improvements in Orbit Modeling and LRA Offsets
Urschl et al., 2007
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20th ILRS Workshop, Oct. 11, 2016
Flohrer et al., 2008
GPS SLR residuals in Sun-fixed reference frame, ROCK radiation pressure a
priori model.
SLR reveals significant systematic orbit errors
5
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
SLR bias below 1 cm for IGS CODE reprocessed orbits
Current GPS SLR residuals
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
What about new GNSS constellations?
Montenbruck et al. 2013
Montenbruck et al. 2013
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20th ILRS Workshop, Oct. 11, 2016
8
SLR Residuals of Galileo IOV Satellites
Institute for Astronomical
and Physical Geodesy
Montenbruck et al. 2015
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
Cause: different shape of satellites
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
Galileo SLR residuals
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20th ILRS Workshop, Oct. 11, 2016
11
Institute for Astronomical
and Physical Geodesy
old and new model… Inga
Galileo SLR residuals
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
New ECOM2 radiation pressure model
IGS MGEX project: http://mgex.igs.org/analysis/slrres.php
Galileo SLR residuals
Classical ECOM radiation pressure model
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
• SLR ranging to GPS and GLONASS has a long history. Independent orbit
validation helped to improve orbit models.
• Radiation pressure modelling crucially depends on details of satellite
structure and surface properties.
• SLR to satellites of the new GNSS constellations and satellites on new orbit
types thus plays an essential role for calibrating such models.
• For GEO the determination of satellite longitude with GNSS tracking data is
highly susceptible to biases. SLR can play an important role.
• For IRNSS satellites currently SLR are the only public tracking data allowing
the determination of precise orbits.
Conclusions 1
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20th ILRS Workshop, Oct. 11, 2016
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Monitoring of Satellite Clock Behaviour
Institute for Astronomical
and Physical Geodesy
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
Gravitational Redshift
E11
a = 29‘600 km
e = 0.00002
i = 55.4°
E14/18
a = 27980 km
e = 0.15725
i = 50.0°
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
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• SLR as tool for high precision time synchronization of stable GNSS clocks
combining Laser one-way with two-way, similar to ELT concept.
• Convince ESA for Galileo.
Laser Time Transfer to Galileo
ESA
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
• GNSS satellites are equipped with clocks of higher and higher stability.
• As GNSS-derived satellite clock corrections are highly correlated with radial
orbit errors.
• SLR thus plays an important role to separate temperature-induced
variations of the apparent satellite clocks from orbit errors and to
characterize the physical behavior of the clocks.
• This is also crucial for improving the determination of the gravitational
redshift parameter α beyond Gravity Probe A using the clocks onboard the
two Galileo satellites misplaced to eccentric orbits (Delva et al., 2015).
• It is time that SLR time synchronization of GNSS clocks plays a more
important role.
Conclusions 2
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20th ILRS Workshop, Oct. 11, 2016
Institute for Astronomical
and Physical Geodesy 18 18
GPS GLONASS Galileo BeiDou
GNSS is expanding
• Soon more than 100 satellites in the sky
• All equipped with SLR reflectors (GPS beginning with Block III SV-9)
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
• GNSS constellation is expanding, and in future all satellites will be equipped
with SLR reflectors.
• How to observe GNSS satellites with SLR to derive precise orbits?
• Covariance analysis with simulated SLR observations from
– 1, 6, and 17 SLR stations,
– three sets of normal points, at 30° elevation rising, culmination if
elevation above 60°, and at 30° elevation setting,
– or one set of normal points per station at high elevation,
– of full 24-satellite Galileo constellation.
• Good weather situation, observations of stations uncoordinated.
Simple Simulation
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Simulation: 1 SLR Station
Institute for Astronomical
and Physical Geodesy
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Institute for Astronomical
and Physical Geodesy
Simulation: 6 SLR Station
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20th ILRS Workshop, Oct. 11, 2016
22
Institute for Astronomical
and Physical Geodesy
Simulation: 17 SLR Station
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20th ILRS Workshop, Oct. 11, 2016
23
Range of E01 for one SLR Station
Institute for Astronomical
and Physical Geodesy
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20th ILRS Workshop, Oct. 11, 2016
24
Institute for Astronomical
and Physical Geodesy
Ranges of all Galileo Satellites for one SLR Station
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20th ILRS Workshop, Oct. 11, 2016
25
Simulated SLR Observations: E=30°, Culmination
Institute for Astronomical
and Physical Geodesy
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
Simulated SLR Observations: E=30°, Culmination
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20th ILRS Workshop, Oct. 11, 2016
27
Simulated SLR Observations: 1 Station, 1 Day
Institute for Astronomical
and Physical Geodesy
1 sta 1 day
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
1 sta 1 day
Simulated SLR Observations: 1 Station, 1 Day
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20th ILRS Workshop, Oct. 11, 2016
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and Physical Geodesy
1 sta 1 day
Simulated SLR Observations: 1 Station, 1 Day
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20th ILRS Workshop, Oct. 11, 2016
30
Institute for Astronomical
and Physical Geodesy
1 sta 1 day
Simulated SLR Observations: 1 Station, 1 Day
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20th ILRS Workshop, Oct. 11, 2016
31
Institute for Astronomical
and Physical Geodesy
1 sta 3 day
Simulated SLR Observations: 1 Station, 3 Days
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20th ILRS Workshop, Oct. 11, 2016
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and Physical Geodesy
6 sta 1 day
Simulated SLR Observations: 6 Stations, 1 Day
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20th ILRS Workshop, Oct. 11, 2016
33
Institute for Astronomical
and Physical Geodesy
6 sta 3 day
Simulated SLR Observations: 6 Stations, 3 Days
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
17 sta 1 day
Simulated SLR Observations: 17 Stations, 1 Day
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20th ILRS Workshop, Oct. 11, 2016
35
Institute for Astronomical
and Physical Geodesy
17 sta 3 day
Simulated SLR Observations: 17 Stations, 3 Days
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
Formal Orbit Errors: 1 Station, 1 Day
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
Formal Orbit Errors: 1 Station, 3 Days
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20th ILRS Workshop, Oct. 11, 2016
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and Physical Geodesy
Formal Orbit Errors: 6 Stations, 1 Day
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20th ILRS Workshop, Oct. 11, 2016
39
Institute for Astronomical
and Physical Geodesy
Formal Orbit Errors: 6 Stations, 3 Day
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20th ILRS Workshop, Oct. 11, 2016
40
Institute for Astronomical
and Physical Geodesy
Formal Orbit Errors: 6 Stations, 1 Day, Culminations
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20th ILRS Workshop, Oct. 11, 2016
41
Institute for Astronomical
and Physical Geodesy
Formal Orbit Errors: 6 Stations, 3 Days, Culminations
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20th ILRS Workshop, Oct. 11, 2016
42
Institute for Astronomical
and Physical Geodesy
Formal Orbit Errors: 17 Stations, 1 Day
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20th ILRS Workshop, Oct. 11, 2016
43
Institute for Astronomical
and Physical Geodesy
Formal Orbit Errors: 17 Stations, 3 Days
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20th ILRS Workshop, Oct. 11, 2016
44
Institute for Astronomical
and Physical Geodesy
• Simple simulations demonstrate the capability of precise orbit determination
for GNSS satellites using a limited number of observations per station.
• Coordination of the observations between the stations is crucial to make
economic use of the observing system.
• Eventually SLR observations should not only be used for orbit validation but
combined with GNSS observations for determining precise orbits.
Conclusions 3
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20th ILRS Workshop, Oct. 11, 2016
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Institute for Astronomical
and Physical Geodesy
Space Geodetic Techniques
SLR
GNSS
DORIS
VLBI
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20th ILRS Workshop, Oct. 11, 2016
46
Institute for Astronomical
and Physical Geodesy
Space Geodetic Techniques
SLR
GNSS
DORIS
VLBI
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20th ILRS Workshop, Oct. 11, 2016
47
Institute for Astronomical
and Physical Geodesy
Space Geodetic Techniques
SLR
GNSS
DORIS
VLBI
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and Physical Geodesy
• SLR plays an important role since decades for validating GNSS derived
satellite orbits.
• For new GNSS constellations and new orbit types SLR proves to be
essential to calibrate new radiation pressure models.
• SLR allows to separate orbit- and temperature-induced variations of stable
onboard GNSS clocks.
• Eventually the role of SLR becomes even more important by contributing to
precise orbit determination of GNSS satellites.
• Coordination of the observation schedule between stations is crucial to
optimize the benefit-to-cost ratio.
• Integration of GNSS and SLR observations for precise product generation
has to be forced in the context of GGOS.
Conclusions
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20th ILRS Workshop, Oct. 11, 2016
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and Physical Geodesy
• For validation and calibration of radiation pressure models?
– one satellite block for a range of Sun-beta angles, i.e., one satellite
block per orbital plane
– good coverage along the orbit
• For determination of gravitational redshift parameter using Galileo E14/E18:
– good coverage of orbits of both satellites (as long as clock running on
H-maser)
• For BeiDou GEO satellites:
– coverage of all satellites
• For contributing to precise orbit products combined with GNSS
– coverage of full constellation
– coordination of observation schedule among SLR stations
How to track GNSS?
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20th ILRS Workshop, Oct. 11, 2016
Many thanks for
your attention!