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