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ESA UNCLASSIFIED - For Official Use
Phase Centre Calibration of the Galileo Satellite Navigation Antenna IGS workshop 2017, Paris (France) Antennas & Biases Session
F. Gonzalez (ESA) M. Söllner (Airbus) E. Schönemann (ESA) F. Dilssner (ESA) 05/07/2017
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 2
Summary
1. Introduction 2. Metadata information to correct phase measurements
• Antenna Phase Centre Offset (PCO) • Antenna Phase Centre Variation (PCV) • Antenna - User direction (attitude) • Antenna Reference Point (ARP) • Centre of Mass (CoM)
3. Galileo Metadata and IGS 4. Conclusions
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 3
Centre of Mass
Antenna Reference Point
Phase Centre Offset (E1, E5a, E5b, E5, E6)
Phase Centre Variation (E1, E5a, E5b, E5, E6)
Static
Dynamic
(θ,Φ)
Introduction – Galileo Antenna Metadata
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 4
Centre of Mass
Antenna Reference Point
Phase Centre Offset (E1, E5a, E5b, E5, E6)
Phase Centre Variation (E1, E5a, E5b, E5, E6)
Static
Dynamic
Phase Centre Variation Ionosphere-free (E1-E5a)
Dyn
amic
Sta
tic
Introduction – IGS Antenna data
(θ,Φ)
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 5
Antenna - types
Two antenna types GSAT01xx - EADS CASA GSAT02xx - Thales Alenia
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 6
Antenna – chamber calibration
• Individual for each navigation antenna by manufacturer • Directional in azimuth (Φ) and nadir (θ) • Each single frequency bands (E1, E5a, E5b, E5, E6)
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 7
CMRP(α) from measurements
in constant
distance from MRP
Farfield Sphere Segment with Radius r around MRP
MRP
PCO
r R(α)
R(α1)
R(α2)
d
Antenna – Phase Centre offset (PCO)
Delay pattern CFF on farfield sphere in distance r around MRP:
( ) ( ) rCrC MRPFF += αα ,
Range from PCO to sphere around MRP:
( ) ( )αα rdrR ˆ!"
−=
PCO: Find d, where R(θ) is most similar to CFF(θ,r)
( ) ( ) ( )ααα rdCdC MRPPCO ˆ, !""
+=
( ) ( )( ) ( ) 22,, dCdCdres PCOPCO
!!!αα −=Minimize
with
< > (weighted) averaging over α (field of view)
Note, α represents the observation direction (off-axis angle θ and azimuth angle ϕ)
( )
( )
( ) ( )( )22
22
22
coscos
cos,cos,
sinsinsinsin,
cossincossin,
θθ
θϕθθϕθ
ϕθ
ϕθϕθ
ϕθ
ϕθϕθ
−
⋅−⋅=
⋅
⋅⋅−=
⋅
⋅⋅−=
MRPMRP
MRP
MRP
CCdz
Cdy
Cdx
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 8
GALILEO-1 E11 E101 2011-060A TYPE / SERIAL NO
CHAMBER ESA 1 09-FEB-12 METH / BY / # / DATE
2.0 DAZI
0.0 14.0 1.0 ZEN1 / ZEN2 / DZEN
5 # OF FREQUENCIES
GALILEO-2 E18 E201 2014-050A TYPE / SERIAL NO
CHAMBER ESA 1 12-FEB-16 METH / BY / # / DATE
5.0 DAZI
0.0 20.0 0.5 ZEN1 / ZEN2 / DZEN
5 # OF FREQUENCIES
Antenna – Phase Center Variation (PCV)
• Azimuthal values [0°,360°] • Zenith values from 0° to 14° (GSAT01) and 20° (GSAT02) • All 5 single frequencies
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 9
Antenna – Phase Center Variation (PCV)
• Azimuthal values [0°,360°] • Zenith values from 0° to 14° (GSAT01) and 20° (GSAT02) • All 5 single frequencies (e.g. E1 signal).
0 2 4 6 8 10 12 14 16 18 20−8
−6
−4
−2
0
2
4NAVANT PCV
Nadir angle [deg]
[milli
met
res]
GSAT0101 (IOV)GSAT0201 (FOC)
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 10
Antenna - PCV Azimuthal components (GSAT01)
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 11
Antenna - User direction (attitude)
• Azimuthal correction requires Satellite yaw modeling (e.g. GSAT0101) • Orientation accuracy better than ground antennas1
1 Source: F.Dilssner, Galileo IOV Spacecraft Metadata and Its Impact on Precise Orbit Determination, EGU2017
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 12
Antenna Reference Point
• Antenna integrated on body frame • Physical point on the satellite [mm]
X Y Z
GSAT01 1375.5 600.0 1100.5
GSAT02 140.0 0.0 1215.0
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 13
Centre of Mass – dry measurement in stow
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 14
Centre of Mass – tank filling
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 15
Centre of Mass – Solar array deployment
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 16
Centre of Mass - Values
• Dynamic information. Value after any maneuver sent to ILRS • Agreement between S/C well below 1 cm
1205.0
1205.2
1205.4
1205.6
1205.8
1206.0
695 696 696 697 697 698 698
+X
[m
m]
Mass [Kg]
GSAT01
260
270
280
290
300
310
320
650 660 670 680 690 700 710 720
+X
[m
m]
Mass [Kg]
GSAT02 -01 -02
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 17
Metadata versus IGS
Galileo (GSAT_wwww.atx) IGS (IGS14.atx)
Source Measured on ground Estimated in space
Types Per single Satellite per family (IOV,FOC-L3,FOC)
Frequencies Single Frequency (E1,E5a,E5b,E5,E6)
Ionosphere-free (E1-E5a)
Data-static PCV – PCO (θ,Φ) PCO - ARP ARP - SRF
PCV – PCO (θ)
Data-dynamic CoM - SRF PCO – CoM
Attitude Normal + Modified Normal
Frame Satellite Reference Frame Antex
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 18
-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
101 102 103 201 202 203 204 205 206 207 208
Met
re
X
Y
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
101 102 103 201 202 203 204 205 206 207 208
Met
re
Z
Metadata versus IGS
• Accuracy of estimated in space affected by models accuracy (e.g. SRP) • Estimated in Space using NAPEOS versus measured on ground
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 19
Summary and conclusions Calibrated Metadata for Galileo antenna phase center corrections • Antenna Phase Centre Offset (PCO), Variation (PCV) and Reference Point (ARP) • Satellite Centre of Mass (CoM) and Attitude (user direction) Benefit • Tie GNSS phase measurements consistently to the spacecraft CoM • Especially relevant for GNSS-based realization of terrestrial scale, independent of SLR/VLBI • Galileo is the first GNSS disclosing the full range of metadata for each antenna and carrier frequency • Radial antenna offsets for other GNSS become accessible without the need to adopt any external scale Status • GSAT01 released during Initial Service Declaration (Dec-2016) • GSAT02 under release process. Recommendation • ANTEX format update to handle COM / ARP Location • https://www.gsc-europa.eu/support-to-developers/galileo-iov-satellite-metadata#2 • https://ilrs.cddis.eosdis.nasa.gov/missions/satellite_missions/current_missions/ga01_com.html
ESA UNCLASSIFIED - For Official Use ESA | 05/07/2017| Slide 20
THANKS for your attention