gnss and time metrology: report from the cctf working
TRANSCRIPT
GNSS and Time Metrology:
Report from the CCTF Working
Group on GNSS
Pascale Defraigne, Chair, Royal Observatory of Belgium
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Current use of GNSS for UTC
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To date: all UTC(k) labs are connected via GPS, and 87% of the links are entirely based on GPS
GLONASS was used for some links during more than ten years
The accurate receiver calibration for GLONASS signals is still an issue. The GLONASS common view is used as back up for some links.
Galileo : data analysis shows a better performances than GPS in terms of code noise. - Calibration available since June 2020- Use in UTC – in test phase
BeiDou : transition from BDS-2 to BDS-3 (different signals and frequencies)- only a few receivers get the BeiDou 3 signals- Absolute calibration for BDS-3 just started
Current use of GNSS for UTC
Time transfer techniques in UTC
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Topics
• Calibration of GNSS equipment
• Time transfer with new GNSS
• Update on Circular T, Section 4
(UTC-Broadcast_UTCGNSS), to include all GNSS, with uncertainties
• Task Group on traceability to UTC from GNSS Measurements
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Hardware delay calibration
Latching pointd1
d4d3d2
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Calibration scheme
Absolutely
calibrated
BIPM reference
G1 reference
G1 referenceG1 reference
G1 reference
G2G2
G2
G2 G2G2
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Calibration trip
G1 reference
G2 G2
Traveling station
Traveling station
Traveling station
Uncertainties: 2.5 ns (or better)
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Calibration for GNSS hardware delays
G1 calibration trips:Since 1001-2018 all of them include Galileo
Excellent stability on GPS:
Ensemble Nr DIDP1 DIDP2 DIDC1 DIDP3
APMP (2018 – 2016) Ave 9 -0.1 -0.1 -0.2 -0.1
EURAMET (2018 – 2016) Ave 9 0.1 0.0 0.1 0.2
SIM (2018 – 2016) Ave 5 0.0 0.2 0.2 -0.2
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Stability of G2 calibration results
0
1
2
3
4
5
6C
S21
20
16
-20
18
DL0
4 2
01
6-2
01
9
DL0
5 2
01
6-2
01
9
ES0
3 2
01
2-2
01
6
ES0
4 2
01
2-2
01
6
ES0
3 2
016
-20
20
ES0
4 2
01
6-2
02
0
IF2
0 2
01
7-2
02
0
IT1
Z 2
01
6-2
01
6
IT2
_ 2
01
6-2
01
6
IT__
20
16
-20
16
IT0
8 2
01
9-2
02
1
IT0
9 2
01
9-2
02
1
IT1
0 2
01
9-2
02
1
IT1
1 2
01
9-2
02
1
IT1
2 2
01
9-2
02
1
MI0
4 2
01
5-2
01
9
NP
L1 2
01
7-2
01
9
RIT
1 2
01
6-2
01
9
SP0
2 2
01
6-2
01
9
SP0
5 2
01
6-2
01
9
SP0
1 2
01
6-2
01
9
ZA0
8 2
016
-20
18
BR
UX
20
17
-20
20
OR
4Z
20
17
-20
20
NTP
1 2
01
6-2
01
8
NTP
2 2
01
6-2
01
8
NTP
3 2
01
6-2
01
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difference between successive G2 calibrations (P3)
uB = 2.5 ns
(ns)
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G2 calibration status – June 2021
2020-2021
2019
2018
20172016
More than 5.5 yr
Age of last calibration
77
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67
31 labs
labs
labs
labs
labs labs
Improved information distributed to time laboratories. (July 2021)
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Progress in absolute calibration
GPS Intercomparisons
Galileo
Recent absolute calibrations agree within (peak-to-peak)4 ns for GPS 2.5 ns for Galileo
To date : absolute calibration by
ESA – CNES – JPL - VNIIFTRI
GNSS signal simulator
GNSS receiver
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Time transfer with new GNSS
Several studies carried out.The conclusions converge:• BeiDou-3 (B1C&B2a) provides similar
performances as GPS• Galileo code measurements are less
noisy, and provide short-term stability typically better than GPS P3, but not always at t ~ 0.25 day
→ Introduction of Galileo links in the computation of UTC, as backup to GPSPPP
(~20 links in 12/2020 )
Guang et al 2020 Metrologia 57 065023
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Revised section 4 for Circular T
GOAL :Provide a validation of tGNSS – “UTC” → quantify UTC – “UTC”
Current situation :
- Only GPS and GLONASS
[UTC-UTC(USNO)_GPS] = C0', [TAI-UTC(USNO)_GPS] = 37 s + C0'
[UTC-UTC(SU)_GLONASS]= C1', [TAI-UTC(SU)_GLONASS]= 37 s + C1’
- No specified uncertainty
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G1 laboratories - laboratories regularly calibrated
and monitored by the BIPM,- directly calibrated differentially against
an absolutely calibrated station- Geographically distributed over the world
Revise section 4 for Circular T
Naming Convention : “UTC” → Broadcast_UTCXXX (xxx= BDS GAL GLO GPS)
Pivot UTC(k)
UTC – Broadcast_UTCXXX
= [UTC(k) – Broadcast_UTCXXX ]GNSS– [UTC(k) – UTC]circular T
NIST NIMOPNICT
Uncertainties
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Uncertainties on UTC-Broadcast_UTCGNSS
1. GNSSTIME – Broadcast_UTCGNSS from different satellites
2. The uncertainties in the solution UTC(k)-GNSST due to multipath, and satellite clocks and orbits in the navigation messages.
3. Receiver calibration
4. Uncertainty on UTC-UTC(k) for the pivot UTC(k)
5. Differences between single-frequency and dual-frequency solutions.
GPST – Broadcast_UTCGPS
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Uncertainties on UTC-Broadcast_UTCGNSS
Final uncertainty Budget:BeiDou Galileo GLONASS GPS
Calibration 2.6 2.4 3.8 2.6
Broadcast value dispersion
3.0 0.5 1.7 1.3
Code noise and multipath
1.5 0.7 3.5 0.9
UTC-UTC(k) pivot 2.2 2.2 2.2 2.2
Total 4.8 ns 3.4 ns 5.9 ns 3.7 ns
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Traceability to UTC using GNSS measurements
Increasing use of GNSS for synchronization& increasing demand for traceability
Need for guidelines on - how the user can get UTC from GNSS (including equipment and calibration)- and how traceability can be obtained when using GNSS for synchronization to UTC (UTC from Signal in Space or UTC from UTC(k) )
Task force of the GNSS WG, with the help of the WG on MRA.
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Task Force on Traceability to UTC
using GNSS measurements
CCTF survey → some questions on the traceability to UTC using GNSS
Answers : from the UTC(k) laboratories + stakeholders (telecom, IT, Science,TF equipment manufacturers, standardization bodies, …)
Observations from the answers received ➢ The term „traceability“ is used with different connotation in the various user groups. often ignoring the definition of (metrological) traceability in the Vocabulaire International de Metrologie (VIM). ➢ Traceability and accuracy are sometimes not clearly distinguished.➢ GNSS signals are employed for getting a reference for frequency, for epoch,
for time-of-day, with quite different accuracy requirements.
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Task Force on Traceability to UTC
using GNSS measurements
Final Goals : - Produce unified guidelines on how to get traceability to a realization of
UTC through GNSS measurements
- Different options are on the table,- Work in progress
- Disseminate the information to the end user, via e. g. RMOs, ICG, GNSS providers, GNSS stakeholders
Pascale Defraigne, [email protected]
Thank You• Gérard Petit (BIPM)• Andreas Bauch (PTB) • Giancarlo Cerretto (INRIM) • Michael Coleman (U.S. NRL) • Jérôme Delporte (CNES) • Héctor Esteban (ROA) • Johann Furthner (DLR) • Marina Gertsvolf (NRC) • James Hanssen (USNO) • Ryuichi Ichikawa (NICT) • Artem Karaush (VNIIFTRI) • Paul Koppang (USNO) • Alexander Kuna (UFE) • Judah Levine (NIST) • Zhiqiang Yang (NIM) • Shinn-Yan Lin (TL) • Andrey Naumov (VNIIFTRI) • Jerzy Nawrocki (AOS) • Bijunath Patla (NIST) • Daniele Rovera (LNE-SYRTE) • Pierre Uhrich (LNE-SYRTE) • Pierre Waller (ESA) • Michael Wouters (NMIA) • Wenjun Wu (NTSC)