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IGS WS 2016
Estimation of satellite antenna phase center offsets for Galileo
Peter Steigenberger, Oliver Montenbruck German Space Operations Center (DLR/GSOC) Mathias Fritsche, Maik Uhlemann Deutsches GeoForschungsZentrum (GFZ) Rolf Dach, Lars Prange Astronomical Institute, University of Bern (AIUB) Ralf Schmid Deutsches Geodätisches Forschungsinstitut (DGFI-TUM)
IGS WS 2016 Slide 2
Galileo Phase Center Offset Estimation
• Phase Center Offset (PCO): center of mass → mean antenna phase center
• Global GNSS solutions including estimation of station coordinates, troposphere parameters, ERPs, and satellite orbits
PCO estimation: - NAPEOS@DLR - EPOS@GFZ
PCO validation: - NAPEOS@DLR - Bernese@AIUB
IGS WS 2016 Slide 3
Galileo In-Orbit Validation (IOV) Antenna
• Dual-band right-hand circularly polarized • Array of 45 photo-printed stacked patch elements
ESA
IGS WS 2016 Slide 4
Galileo Full Operational Capability (FOC) Antenna
• Similar to GIOVE-A antenna
• Dual-band right-hand circularly polarized
• Array of 28 stacked patch elements
• Launch anomaly of first pair of FOC satellites resulting in highly eccentric orbit
• Center of mass changes for GAL-201/202 due to orbit raising maneuvers
OHB
IGS WS 2016 Slide 5
Orbit Modeling
1. Empirical CODE Orbit Model (ECOM)
Constant plus sine and cosine terms in a Sun-oriented DYB frame
2. ECOM-2
Additional estimation terms:
D2 for GPS, D2 and D4 for Galileo
3. Box-wing model (BW)
“Cubicness” and “strechedness” parameters based on a+Z, a+X, and a-Z
4. Box-wing model and D0 constraint
Sun µ
Earth
Midnight
D
Y B
+Z
+X
ε
A+X
A-Z
A+Z +D +B
IGS WS 2016 Slide 6
Impact of Orbit Modeling on x-Offset Estimation (1)
ECOM
DLR GFZ
GAL-103
IGS WS 2016 Slide 7
Impact of Orbit Modeling on x-Offset Estimation (1)
0
60
-60
β an
gle
[deg
]
GAL-101 GAL-102 GAL-103 GAL-104 R
β
IGS WS 2016 Slide 8
Impact of Orbit Modeling on x-Offset Estimation (2)
GAL-103
Box-wing
DLR GFZ
GAL-103
ECOM-2
DLR GFZ
IGS WS 2016 Slide 9
Correlations between PCOs and Orbit Parameters
Orbit only Orbit+PCO Orbit+PCO D0 constrained
IGS WS 2016 Slide 10
Correlations between PCOs and Orbit Parameters
Orbit only Orbit+PCO Orbit+PCO D0 constrained
IGS WS 2016 Slide 11
Correlations between PCOs and Orbit Parameters
Orbit only Orbit+PCO Orbit+PCO D0 constrained
IGS WS 2016 Slide 12
Correlations between PCOs and Orbit Parameters
GAL-103
BW constr.
Orbit only Orbit+PCO Orbit+PCO D0 constrained
IGS WS 2016 Slide 13
Galileo IOV y-Offsets
GAL-103
BW
• No impact of orbit modeling on y-offset estimation
• Different approaches to form mean values agree within few mm
GAL-101 GAL-102 GAL-103 GAL-104
IGS WS 2016 Slide 14
Galileo FOC Horizontal PCOs
β=0°
|β|<5°
GAL-201
BW
IGS WS 2016 Slide 15
Mean Horizontal Galileo PCOs
• Significant x-offset bias for FOC satellites in eccentric orbit due to fuel consumption
• AC agree on the 1-2 cm level • Mean values per satellite group
rounded to 1 cm
IOV FOC FOCe
DLR GFZ
IGS WS 2016 Slide 16
Z-Offsets GAL-103 DLR GFZ
IGS WS 2016 Slide 17
Validation of MGEX and New PCOs
NAPEOS Bernese
IGS WS 2016 Slide 18
Summary and Outlook
• Pronounced β-dependent effects in horizontal PCO estimates, strong correlation with solar radiation pressure parameters
• Few cm level agreement for DLR/GFZ mean horizontal PCOs, 2-15 cm level agreement for z-offsets
• Appropriate orbit modeling essential for reliable and stable PCO estimation
• Update of conventional MGEX PCOs recommended, in particular for IOV
• Distinct differences in IOV and FOC phase residual maps
• Next step: estimation of satellite antenna PCVs
IOV
FOC
IGS WS 2016 Slide 19
Galileo FOC FM2 Main Antenna ESA - Anneke Le Floc'h
IGS WS 2016 Slide 20
GNSS Satellite Antenna Modeling
• Precise satellite orbits refer to the center of mass
• GNSS measurements refer to the actual phase center of the transmit antenna
• Phase Center Offset (PCO)
- Center of mass - Mean phase center
• Phase Center Variation (PCV) - Correction depending on the nadir angle n
(and the azimuth) of the observation direction as seen from the satellite
IGS WS 2016 Slide 21
The Galileo Satellites
Built by Astrium - 4 satellites launched in 2011 and 2012 - 3 operational satellites
Built by OHB - 2 satellites in eccentric orbit - 6 satellites in nominal orbit
IGS WS 2016 Slide 22
Impact of Orbit Modeling on x-Offset Estimation (1)
ECOM
DLR GFZ
GAL-103
0
60
-60
β an
gle
[deg
]
GAL-101 GAL-102 GAL-103 GAL-104 R
β