Post on 21-Apr-2020
Time stability of the K-band catalog sources
K. Le Bail (1), A. de Witt (2), C. S. Jacobs (3), D. Gordon (1)(1) NVI, Inc., Greenbelt, MD, U.-S.
(2) SARAO/HartRAO, Krugersdorp, South Africa(3) Jet Propulsion Laboratory, California Inst. Technology/NASA, Pasadena, CA, U.-S.
24th Meeting of the European VLBI Group for Geodesy and Astrometry (EVGA)March 17-19 2019, Las Palmas, Gran Canaria, Spain
Acknowledgements:Copyright ©2019. All Rights Reserved.U.S. Government sponsorship acknowledged for work done at JPL-Caltech under a contract with NASA.The VLBA is managed by NRAO, funded by the National Science Foundation, and operated under cooperative agreement by Associated Universities.The authors gratefully acknowledge use of the VLBA under the USNO’s time allocation.This work supports USNO’s ongoing research into the celestial reference frame and geodesy.HartRAO is a facility of the National Research Foundation (NRF) of South Africa.The Hobart telescope is operated by the University of Tasmania and this research has been supported by AuScope Ltd., funded under the National Collaborative ResearchInfrastructure Strategy (NCRIS).
Outline
• K-band in ICRF3• Brief review on how to use the Allan variance to
determine noise floor of source time series• Noise floor of the latest GSFC K-band time series
solution and comparison with the latest GSFC S/X time series solution
2/17
K-band
• K-band in ICRF3See poster P306: A. de Witt et al., “The K-band (24 GHz) Celestial Reference Frame”.
3/17
K solutionJan 2019
S/X solutionJan 2019
Source # 906 4775
Session # 65 6271
Observation period
05/2002 –11/2018
08/1979 –01/2019
Source #(>10 sessions)
354 788
• This paper: Study of the latest GSFC time series solutions for K and S/X.
−80 −60 −40 −20 0 20 40 60 800
20
40
60
80
100
Declination (deg)
Sour
ce n
oise
(µas
)
ICRF3 decimation test − Right Ascension
S/X noise floorK noise floor
−80 −60 −40 −20 0 20 40 60 800
20
40
60
80
100
Declination (deg)
Sour
ce n
oise
(µas
)
ICRF3 decimation test − Declination
S/X noise floorK noise floor
310 common sources
K-band and S/X-bandPosition time series
• Different ways to study these time series:• Standard deviation => static quantity;• Noise floor using the Allan variance => takes into account the time variable.
4/17
1980 1985 1990 1995 2000 2005 2010 2015 2020−1
−0.5
0
0.5
1
RAcosDEC (mas) 0552+398
S/X Standard dev: 1.512 K Standard dev: 0.139
S/XK
1980 1985 1990 1995 2000 2005 2010 2015 2020−1
−0.5
0
0.5
1
DEC (mas) 0552+398
S/X Standard dev: 1.864 K Standard dev: 0.165
S/XK
1980 1985 1990 1995 2000 2005 2010 2015 2020−1
−0.5
0
0.5
1
RAcosDEC (mas) 3C120
S/X Standard dev: 4.686 K Standard dev: 0.166
S/XK
1980 1985 1990 1995 2000 2005 2010 2015 2020−1
−0.5
0
0.5
1
DEC (mas) 3C120
S/X Standard dev: 4.770 K Standard dev: 0.217
S/XK
Allan variance to determine noise floor (1/3)
• The Allan variance is a statistical tool that gives level and type of noise of time series.
• If !" "#$,& are the measurements and ' the sampling time, the Allan variance is:
() ' = $) !"+$ − -!" )
• The type of noise is determined by the slope of the curve
log10(Allan variance)=f(log10(sampling time))
• Cons: it has to be applied to regularly spaced time series.
-1 White noise
0 Flicker noise
+1 Random walk
5/17
Allan variance to determine noise floor (2/3)
6/17
Allan variance to determine noise floor (3/3)
Real data: sources not observed regularly => difficulties in statistical determination due to gaps in between observations, number of observations,… We need to prepare the data, to preprocess the time series.• Step 1: Keep sources with 10 or more observations.• Step 2: Averaging (yearly, monthly and weekly) and interpolation.• Step 3: Allan variance processing for each source, each coordinate,
each averaged time series.• Step 4: Noise floor determination for each source and each
coordinate. We look at the noise type determined by the slope of the Allan variance curve:• If white noise or flicker noise, the noise floor is the lowest Allan variance.• If random walk, the noise floor is undefined.
7/17
Comparison of global solutions310 common sources
The K noise floors tend to be smaller than the S/X noise floors.
8/17
Standard deviationNoise floor determined by the Allan variance
500 1000 1500 20000
20
40
60
80
100
120
140
Source standard deviation (µas)
Sour
ce n
umbe
r
RAcos(DEC) − K−band
500 1000 1500 20000
20
40
60
80
100
120
140DEC − K−band
Source standard deviation (µas)
Sour
ce n
umbe
r
500 1000 1500 20000
20
40
60
80
100
120
140
Source standard deviation (µas)So
urce
num
ber
RAcos(DEC) − S/X−band
500 1000 1500 20000
20
40
60
80
100
120
140DEC − S/X−band
Source standard deviation (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
10
20
30
40
50
60RAcos(DEC) − K−band
Source noise floor (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
10
20
30
40
50
60DEC − K−band
Source noise floor (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
10
20
30
40
50
60RAcos(DEC) − S/X−band
Source noise floor (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
10
20
30
40
50
60DEC − S/X−band
Source noise floor (µas)
Sour
ce n
umbe
r
Comparison of global solutions310 common sources
Noise floor comparison in 10o declination bands
9/17
−80 −60 −40 −20 0 20 40 60 800
100
200
300
400
500
Declination (deg)
Sour
ce n
oise
floo
r (µa
s) RAcos(DEC)
S/X noise floorK noise floor
−80 −60 −40 −20 0 20 40 60 800
100
200
300
400
500
Declination (deg)
Sour
ce n
oise
floo
r (µa
s) DEC
S/X noise floorK noise floor
Comparison of partial solutions87 common sources from Nov 2016 to Nov 2018
• Focus on same period of observation: November 2016 to November 2018.
10/17
1980 1985 1990 1995 2000 2005 2010 2015
S/X sessionsK sessions
K solution Jan 2019 S/X solution Jan 2019 Common sources
Source # 901 4728 877Session # 44 391Source # (>10 sessions) 254 431 87
Comparison of partial solutions87 common sources from Nov 2016 to Nov 2018
11/17
2016.5 2017 2017.5 2018 2018.5 2019 2019.5−1
−0.5
0
0.5
1
RAcosDEC (mas) 0552+398
S/X Standard dev: 0.347 K Standard dev: 0.158
S/XK
2016.5 2017 2017.5 2018 2018.5 2019 2019.5−1
−0.5
0
0.5
1
DEC (mas) 0552+398
S/X Standard dev: 0.693 K Standard dev: 0.205
S/XK
2016.5 2017 2017.5 2018 2018.5 2019 2019.5−1
−0.5
0
0.5
1
RAcosDEC (mas) 3C120
S/X Standard dev: 0.319 K Standard dev: 0.183
S/XK
2016.5 2017 2017.5 2018 2018.5 2019 2019.5−1
−0.5
0
0.5
1
DEC (mas) 3C120
S/X Standard dev: 0.689 K Standard dev: 0.220
S/XK
Comparison of partial solutions87 common sources on period Nov 2016 – Nov 2018
The S/X noise floors tend to be smaller than the K noise floors.
12/17
Standard deviationNoise floor determined by the Allan variance
500 1000 1500 20000
5
10
15
20
25
30
35
40
Source standard deviation (µas)
Sour
ce n
umbe
r
RAcos(DEC) − K−band
500 1000 1500 20000
5
10
15
20
25
30
35
40DEC − K−band
Source standard deviation (µas)
Sour
ce n
umbe
r
500 1000 1500 20000
5
10
15
20
25
30
35
40
Source standard deviation (µas)
Sour
ce n
umbe
r
RAcos(DEC) − S/X−band
500 1000 1500 20000
5
10
15
20
25
30
35
40DEC − S/X−band
Source standard deviation (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
5
10
15
20RAcos(DEC) − K−band
Source noise floor (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
5
10
15
20DEC − K−band
Source noise floor (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
5
10
15
20RAcos(DEC) − S/X−band
Source noise floor (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
5
10
15
20DEC − S/X−band
Source noise floor (µas)
Sour
ce n
umbe
r
Comparison of partial solutions87 common sources on period Nov 2016 – Nov 2018
Noise floor comparison in 10o declination bands
13/17
−80 −60 −40 −20 0 20 40 60 800
100
200
300
400
500
Declination (deg)
Sour
ce n
oise
floo
r (µa
s) RAcos(DEC)
S/X noise floorK noise floor
−80 −60 −40 −20 0 20 40 60 800
100
200
300
400
500
Declination (deg)
Sour
ce n
oise
floo
r (µa
s) DEC
S/X noise floorK noise floor
Comparison of partial solutions31 common sources in VLBA sessions UD sessions for K-band, UF-UG sessions for S/X
• UD sessions: 24-hour VLBA sessions at K-band.
• UF001 and UG002 sessions: 24-hour VLBA sessions at S/X band. Goals: improving the precision of ICRF3, ICRF3 maintenance, and future updates of the ICRF at radio frequencies. Approximately 3300 of the weakest ICRF3 sources will be re-observed during these sessions.
14/17
K solution Jan 2019
S/X solution Jan 2019
Source # 819 4145
Session # 27 40
Source #(>10 sessions)
149 132
2016.5 2017 2017.5 2018 2018.5 2019 2019.5−1
−0.5
0
0.5
1
RAcosDEC (mas) 0552+398
S/X Standard dev: 0.214 K Standard dev: 0.150
S/XK
2016.5 2017 2017.5 2018 2018.5 2019 2019.5−1
−0.5
0
0.5
1
DEC (mas) 0552+398
S/X Standard dev: 0.209 K Standard dev: 0.209
S/XK
31 common sources
Comparison of partial solutionsUD vs. UF-UG sessions (31 common sources)
The K noise floors tend to be smaller than the S/X noise floors.
15/17
Standard deviationNoise floor determined by the Allan variance
500 1000 1500 20000
5
10
15
Source standard deviation (µas)
Sour
ce n
umbe
r
RAcos(DEC) − K
500 1000 1500 20000
5
10
15DEC − K−band
Source standard deviation (µas)
Sour
ce n
umbe
r
500 1000 1500 20000
5
10
15
Source standard deviation (µas)
Sour
ce n
umbe
r
RAcos(DEC) − S/X−band
500 1000 1500 20000
5
10
15DEC − S/X−band
Source standard deviation (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
5
10
15RAcos(DEC) − K−band
Source noise floor (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
5
10
15DEC − K−band
Source noise floor (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
5
10
15RAcos(DEC) − S/X−band
Source noise floor (µas)
Sour
ce n
umbe
r
100 200 300 400 5000
5
10
15DEC − S/X−band
Source noise floor (µas)
Sour
ce n
umbe
r
Comparison of partial solutionsUD vs. UF-UG sessions (31 common sources)
Noise floor comparison in 10o declination bands
16/17
−80 −60 −40 −20 0 20 40 60 800
100
200
300
400
500
Declination (deg)
Sour
ce n
oise
floo
r (µa
s) RAcos(DEC)
S/X noise floorK noise floor
−80 −60 −40 −20 0 20 40 60 800
100
200
300
400
500
Declination (deg)
Sour
ce n
oise
floo
r (µa
s) DEC
S/X noise floorK noise floor
Conclusion
• K-band time stability• The K-band observations have reached a level of stability equivalent to the
level of current S/X observations. They benefited from the history of the S/X observations.
• The strength of the S/X data set is in its broad diversity of baselines and sessions.
• Comparing the VLBA sessions UD (K-band) and UF-UG (S/X-band), it seems to show the K-band statistic stability is better than the S/X-band statistic stability.
• We need more K-band observations to continue monitoring and comparing the stability of the frame realized by the K-band observations.
17/17
• Thanks to the VLBA, K-band observations have increased greatly in the past two years, prompting many studies. At the EVGA2019:• Benedikt Soja: Ionospheric calibration for K-band celestial reference frames.• Hana Krásná: Earth orientation parameters estimated from K-band VLBA
measurements.• Aletha de Witt: The K-band (24 GHz) Celestial Reference Frame.
And more…
• Structure?
18/17
1980 1985 1990 1995 2000 2005 2010 2015 2020−1
−0.5
0
0.5
1
RAcosDEC (mas) 3C418
S/X Standard dev: 0.732 K Standard dev: 0.191
S/XK
1980 1985 1990 1995 2000 2005 2010 2015 2020−1
−0.5
0
0.5
1
DEC (mas) 3C418
S/X Standard dev: 0.853 K Standard dev: 0.227
S/XK
2016.5 2017 2017.5 2018 2018.5 2019 2019.5−1
−0.5
0
0.5
1
RAcosDEC (mas) 3C418
S/X Standard dev: 0.227 K Standard dev: 0.189
S/XK
2016.5 2017 2017.5 2018 2018.5 2019 2019.5−1
−0.5
0
0.5
1
DEC (mas) 3C418
S/X Standard dev: 0.283 K Standard dev: 0.219
S/XK
Noise floor comparison on individual sources
19/17
Standard deviation
0 500 1000 1500 20000
500
1000
1500
2000
RAcos(DEC)
S/X source standard deviation (µas)
K so
urce
sta
ndar
d de
viat
ion
(µas
)
0 500 1000 1500 20000
500
1000
1500
2000
DEC
S/X source standard deviation (µas)
K so
urce
sta
ndar
d de
viat
ion
(µas
)
0 100 200 300 400 5000
100
200
300
400
500
RAcos(DEC)
S/X source noise floor (µas)
K so
urce
noi
se fl
oor (µa
s)
0 100 200 300 400 5000
100
200
300
400
500
DEC
S/X source noise floor (µas)
K so
urce
noi
se fl
oor (µa
s)
0 100 200 300 400 5000
100
200
300
400
500
RAcos(DEC)
S/X source noise floor (µas)
K so
urce
noi
se fl
oor (µa
s)
0 100 200 300 400 5000
100
200
300
400
500
DEC
S/X source noise floor (µas)
K so
urce
noi
se fl
oor (µa
s)
0 500 1000 1500 20000
500
1000
1500
2000
RAcos(DEC)
S/X source standard deviation (µas)
K so
urce
sta
ndar
d de
viat
ion
(µas
)
0 500 1000 1500 20000
500
1000
1500
2000
DEC
S/X source standard deviation (µas)
K so
urce
sta
ndar
d de
viat
ion
(µas
)
0 500 1000 1500 20000
500
1000
1500
2000
RAcos(DEC)
S/X source standard deviation (µas)
K so
urce
sta
ndar
d de
viat
ion
(µas
)
0 500 1000 1500 20000
500
1000
1500
2000
DEC
S/X source standard deviation (µas)
K so
urce
sta
ndar
d de
viat
ion
(µas
)
Noise floor determined by the Allan variance
0 100 200 300 400 5000
100
200
300
400
500
RAcos(DEC)
S/X source noise floor (µas)
K so
urce
noi
se fl
oor (µa
s)
0 100 200 300 400 5000
100
200
300
400
500
DEC
S/X source noise floor (µas)
K so
urce
noi
se fl
oor (µa
s)
(157
/142
sour
ces)
Entir
e pe
riod
(310
sour
ces)
(74
sour
ces)
2-yr
per
iod
(87
sour
ces)
(24/
28 so
urce
s)VL
BA se
ssio
ns(3
1 so
urce
s)