Post on 25-Sep-2020
Status Report of the
IGS Clock Products
2015 September 17 – 18
Michael J. ColemanClock Products CoordinatorInternational GNSS ServiceU.S. Naval Research Laboratory
Washington, DC, USA
Consultative Committeeon Time and Frequency
Bureau International
des Poids et Mesures
Sevres, Cedex, France
Existing IGS Core Products
SERIES Product Interval AccuracyIssue
Latency
Time
Ultra Rapidgps orbits 15 min ∼ 3.0 cm Daily atgps clocks ∗ 15 min ∼ 150 ps 03:00 09:00 3 – 9
(igu)polar motion 6 hrs ∼ 40 µas 15:00 21:00 Hourslength of day 6 hrs ∼ 10 µs utc
Rapidgps orbits 15 min ∼ 2.5 cmgps clocks † 5 min ∼ 75 ps (rms) Daily at 17 – 41
(igr)polar motion 1 day ∼ 40 µas 17:00 utc Hourslength of day 1 day ∼ 10 µs
Finalgps orbits 15 min ∼ 2.5 cmglonass orbits 15 min ∼ 5.0 cm Weekly ongps clocks † 5 min ∼ 75 ps (rms) Wednesday 11 – 17
(igs)polar motion 1 day ∼ 30 µas or Thursday Dayslength of day 1 day ∼ 10 µs
* Only satellite clocks are reduced in the Ultra Rapid products.
† Both satellite and station clocks are reduced but not all IGS network station clocks.
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 2 / 12
Production Line
Timescale
Generation
Analysis Center
Coordinator
Kevin Choi, NGS
Analysis Centers
Data
Centers
IGNInstitut
GeographiqueNational
KAISKorean Astronomyand Space Science
Institute
CDDISCrustal DynamicsData Information
Systems
SIO
USNO WHU (Wuhan University)
GOP (Geodetic Observatory Pecny)
CODE Center for Orbit Determination in Europe
SIO (Scripps Institute of Oceanography)
JPL (Jet Propulsion Lab) ESOC
NRCan (Natural Resources Canada)
GFZ (GeoForschungsZentrum)MIT
NGS (National Geodetic Survey)
GRG (Groupe de Recherches en Geodesie Spatiale)
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 3 / 12
IGS Time
The current IGS timescale is formed for both the IGS rapid and final products and isderived using a standard Kalman Filter approach.
Kalman Filter was introduced in IGS2.0 version. This second version wasimplemented in 2011 with repreocessing computed from 2010.
Specifications for IGST
Consists of an average of 50 – 60 positively weighted member clocks.
Timescale is generated and exchanged with the IGS data clock reference for theRapid and Final products.
Stability performance as low as E-16 for longer averaging intervals.
Steers to UTC via AMC2 or USNO. Goal is towards UTC(USNO).
Timescale Features
Institutes a harmonic component into model for all satellite clocks.
Automated break detection responds to phase and frequency breaks in clockdata as well as day–by–day boundaries.
Steering achieved using Linear Quadratic Gaussian Steering Algorithm.
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 4 / 12
General IGS Clock Model
Filter uses a four state clock model for all station clocks. The total phase stateincorporates additional white noise process.
For satellite clocks, two fixed period harmonics are estimated and added to thetotal phase state. Hence, some clocks have 8 states.
∫
dt
White Noise
⊕
∫
dt
White Noise
⊕
∫
dt
White Noise
⊕
uf
r
up
f
uθ
pur
NoiseWhite
Drift Frequency Phase
θ
⊕
∼
∼
(a1 + ua1 ) cos(2πω1t) + (b1 + ub1) sin(2πω1t)
(a2 + ua2 ) cos(2πω2t) + (b2 + ub2) sin(2πω2t)
Periodic #1
Periodic #2
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 5 / 12
IGS(R)T Offset from UTC
52000 53000 54000 55000 56000 57000−50
0
50
Nan
osec
onds
UTC−GPST (Circular T) IGST−GPST IGRT−GPST
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
52000 53000 54000 55000 56000 57000−50
0
50
Nan
osec
onds
UTC−IGS(R)T*
UTC−IGST UTC−IGRT
52000 53000 54000 55000 56000 57000−50
0
50
MJD
Nan
osec
onds
IGRT − IGST
* Assumes that GPS Time via Circular T is equivalent to GPST
U.S
. Nav
al R
esea
rch
Labo
rato
ry 0
4−S
ep−
2015
, 17:
51
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 6 / 12
GPS Clock Frequency Weight Contribution
2010 2011 2012 2013 2014 2015 20160
20
40
60GPS Clock Contribution to IGS(R)T
Clock
Weight%
IGRIGS
2010 2011 2012 2013 2014 2015 20160
20
40
60
80Size of IGS(R)T Clock Membership
Number
ofClocks
GPS
IIF
Broadcast
Start
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 7 / 12
Ground Stations Reduced in Combinations
These tables show some common stations that are weighted in the timescale over thefirst 257 days of year 2015.
Stations with IGS & UTC (Partial List)
Station IGST IGRT
IGS UTC Location Days wp wf Days wp wf
BJNM NIM Beijing CHINA 59 4.31 4.30 0 -- --
IENG IT Torino ITALY 38 2.31 0.89 239 3.77 3.85
NIST NIST Boulder CO USA 0 -- -- 212 4.80 4.80
OPMT OP Paris FRANCE 223 4.37 4.38 1 4.86 4.96
PTBB PTB Braunschweig GERMANY 233 4.44 4.44 249 4.85 4.84
SFER ROA San Fernando SPAIN 225 4.36 2.21 6 5.16 3.53
SPT0 SP Boras SWEDEN 130 3.69 3.68 194 4.66 4.66
TWTF TL Chung-Li TAIWAN 119 4.32 4.31 113 5.07 5.07
USNO USNO Washington DC USA 73 3.58 1.09 58 4.37 4.36
WAB2 CH Bern SWITZERLAND 231 1.64 1.97 238 2.13 0.11
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 8 / 12
Case Observation: IENG Rapid Product Estimates
Data is mostly present for the rapid product.
U.S. Naval Research Laboratory, 01−Sep−2015 16:35:17
−1.5
−1
−0.5
0
0.5
1
1.5
2
phas
e (n
s)
0
2
4
6
ph. s
igm
a (n
s)
Sigmas
0 5 10 15 20 25 300
5
10
MJD − 57235
wφ (
%)
−6
−4
−2
0
2
4
6
8
freq
uenc
y (n
s/da
y)
−0.06
−0.04
−0.02
0
0.02
0.04
0.06
drift
(ns
/day
2 )
phase + WHPH + periodic(− 0.0061t2− 0.019t+ 19) phase (− 0.0061t
2− 0.019t+ 19) frequency (− 0.0051t
1+ 0.081) drift ( 0.058) 2 phase reset(s)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1AUG2015
Filter States & SigmasIENG
01−Aug−2015 through 31−Aug−2015
0
5
10
fr. s
igm
a (n
s/da
y)
0
0.1
0.2
0.3
0.4
dr. s
igm
a (n
s/da
y2 )
0
0.5
1
wf (
%)
0
0.5
1
wd (
%)
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 9 / 12
Case Observation: IENG Final Product Estimates
Data is largely absent for the final product.
U.S. Naval Research Laboratory, 11−Sep−2015 09:40:44
−0.1
−0.05
0
0.05
0.1
0.15
0.2
0.25
phas
e (n
s)
0
5000
10000
15000
ph. s
igm
a (n
s)
Sigmas
0 5 10 15 20 250
1
2
MJD − 57235
wφ (
%)
−5
0
5
10
freq
uenc
y (n
s/da
y)
−0.04
−0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
drift
(ns
/day
2 )
phase + WHPH + periodic(− 1t2+ 23t− 1.2e+02) phase (− 1t
2+ 23t− 1.2e+02) frequency (− 1.6t
1+ 18) drift ( 0.39)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30AUG2015
Filter States & SigmasIENG
01−Aug−2015 through 29−Aug−2015
0
50
100
150
fr. s
igm
a (n
s/da
y)
0
0.5
1
dr. s
igm
a (n
s/da
y2 )
0
0.5
1
wf (
%)
0
0.5
1
wd (
%)
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 10 / 12
Proposed Improvements
UTC(k) Laboratory Inclusion
UTC labs occasionally fall from IGS(R)T due to Analysis Center computationchanges and/or drop outs. This is especially more prominent in IGR.
Request that Analysis Centers utilize some collection of UTC(k) labs to allowimproved IGS(R)T stability and UTC steering (as best possible / if possible).Request at next Governing Board Meeting in [ December 2015 @ AGU ]
Goal via steering to these references is to maintain
∣
∣utc – igs(r)t∣
∣ < 10 ns
Satellite Clock Models
Improvements to the initialization of clock states and covariances are beingtimescale filter. This will assist with false starts for GPS clocks and/or resets.
Increase the contribution of GNSS clocks in IGS(R)T; in particular, includefrom Galileo, Glonass and Beidou as data becomes available after MGEXproject complete. [ Longer term timeline ]
GPS (in future, GNSS) clocks are nearly always part of the IGS combinations.
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 11 / 12
IGS Information / Contact
For more information on the IGS core products, experiments and working groups:
www.igs.org
For suggestions or requests for the Clock Products:
michael.coleman@nrl.navy.mil
M. Coleman (IGS // US NRL) IGS Clock Products 2015 September 17 – 18 12 / 12