1. 測地VLBI技術による 高精度周波数比較 VLBI MEASUREMENTS FOR FREQUENCY TRANSFER
技術開発　（ハードウェア）
2009年度VLBI懇談会シンポジウム
「将来を見据えた研究協力を目指して」
12月5日（土）＠奥州宇宙遊学館
測地VLBI技術による 　　　　高精度周波数比較 VLBI MEASUREMENTS FOR FREQUENCY TRANSFER
瀧口 博士1，小山 泰弘1 ，市川 隆一1 ，後藤 忠広1 ，
石井 敦利1,2,3 ，Thomas Hobiger1 ，細川 瑞彦1
1情報通信研究機構，
2国土地理院， 3（株）エイ・イー・エス

2. Content Introduction Intercomparison between VLBI and other techniques
Previous study
Intercomparison : VLBI (IVS) vs. GPS (IGS)
Wettzell - Onsala
How stable are current VLBI systems?
Kashima34m – Kashima11m
Kashima11m – Koganei11m
Intercomparison between VLBI and other techniques
Can the VLBI measure the right time difference?
Kashima34m - Kashima11m
Artificial change by Line Stretcher & Trombone
Conclusions

3. Introduction Background
Development of frequency standard
Atomic fountains
Optical clocks
Time and frequency transfer technique
GPS Carrier Phase
TWSTFT
long averaging period
insufficient accuracy
2×10-15
@a few days
NICT-CsF1
….. developing
10-17～
@a few hours
improvements of highly precise time and frequency transfer techniques are strongly desired
NICT
　 optical clocks
….. developing
VLBI

4. Intercomparison : VLBI vs. GPS
Previous study
Intercomparison : VLBI vs. GPS
Wettzell-Onsala
VLBI vs. GPS CP
IVS and IGS data
GPS
+ GPS long period
( days, days)
GPS VLBI
VLBI
IGS: ●
IVS: □
Atomic Fountain
Onsala
Wettzell
Optical Clocks
Sweden
Onsala Space Observatory
103s
南北　920km
VLBI，GPS： 　同じH-maserをシェア
Germany
Fundamental Station Wettzell
VLBI is more stable than GPS
surpassing the stability of atomic fountain at 103s
VLBI stability : follows a 1/τ law very closely
2×10-11
at each site
VLBI and GPS
are sharing the H-maser
The geodetic VLBI technique has the potential for precise frequency transfer

5. How stable are current VLBI systems?
Previous study
How stable are current VLBI systems?
Kashima34m-Kashima11m
in summer
Kashima11m – Koganei11m
after removing linear trend
How stable are current VLBI systems?
→ surpassing the stability of atomic fountain at 2x104 , 105 s
　⇒ unstable than international baseline (Wettzell-Onsala)
　⇒ influence of temperature change
Measures to reduce the influence of the temperature change are necessary.
in winter

6. What’s Next ? Improve the station environment Intercomparison
The geodetic VLBI technique has the potential for precise frequency transfer
VLBI is more stable than GPS
surpassing the stability of atomic fountain at 103s （Wettzell-Onsala）
2x104 , 105 s （Kashima11-Koganei, Kashima34-Kashima11）
Improve the station environment
for Geodesy → for T&F transfer
Intercomparison
MARBLE
International
other techniques : GPS, DMTD, TWSTFT, TEC(ETS-8)
Calibrate instrumental delay

7. Intercomparison : VLBI vs. other techniques
NICT sites
Kashima34m – Kashima11m
Kashima11m – Koganei11m
239m
109km
Kashima
Kashima
Kashima Space
Research Center
H-maser, DMTD
VLBI
MARBLE
GPS
Koganei/Tokyo
Headquarters
VLBI Kashima11m
Koganei ★
GPS: kgni
VLBI
GPS
TWSTFT
TEC (ETS-8) ★
VLBI
Koganei11m
VLBI
Kashima34m
GPS : ksmv
GPS : ks34

8. Can the VLBI measure the right time difference?
Kashima34m – Kashima11m
Artificial time difference change
using Line Stretcher & Trombone
Intercomparison between VLBI, GPS and DMTD
DMTD
(6ps)
Trombone

9. Differences with the normal observation
Normal Geodetic VLBI
Observation
multiple sources
antenna slew time
different scan time
24 hours
Data Analysis
estimate clock parameter atmosperic delay station coordinates
This study
Observation
one source : 3C84
no antenna slew time
same scan time
a few hours
Data Analysis
estimate only clock parameter
atmospheric delay : short baseline, one source
station coordinates : fixed to a-priori coordinates

10. Data analysis VLBI GPS CALC/SOLVE NR Canada’s PPP single baseline
S/X ionosphere-free linear combination
clock offset / 30sec
Time Defference clock offset / 30sec
GPS
NR Canada’s PPP
IGS Final Orbit & Clock(30s)
Precise Point Positioning
satellite clock interpolation
clock offset / 30sec
Time Defference clock offset A – clock offset B / 30sec
vs. DMTD Time Difference / 1sec

11. DMTD Time Difference 42 ps 0 ⇒ Max 211 ps 50メモリ DMTD 37.9 39.7 46.9
38.8
26.7
-22.5
-45.0
-43.3
-55.1
-43.7
207.9
-210.1
214.2
-215.3
216.8
-210.6
203.8
-212.3
Time Difference
DMTD 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
42 ps 5 6 12 14 16 18 4 7 11 13 15 17 3 8
0 ⇒ Max 2 9 1 10
211 ps
50メモリ

12. GPS vs. DMTD Time Difference 19 ps 62 ps 44 ps rms：GPS-DMTD DMTD 37.9
39.7
46.9
38.8
26.7
-22.5
-45.0
-43.3
-55.1
-43.7
207.9
-210.1
214.2
-215.3
216.8
-210.6
203.8
-212.3
GPS
61.7
66.3
62.1
54.6
44.3
-43.7
-53.0
-54.0
-72.0
-65.3
268.0
-263.0
273.0
-283.0
277.3
-274.3
269.3
-279.0
GPS-DMTD
23.8
26.7
15.2
15.8
17.7
21.2
8.0
10.7
16.9
21.6
60.1
52.9
58.8
67.7
60.6
63.7
65.6
66.7
Time Difference
DMTD
GPS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
19 ps
after removing offsets
GPS-DMTD
62 ps
44 ps

13. VLBI vs. GPS and DMTD Time Difference 9 ps 43 ps 30 ps rms：VLBI-DMTD
37.9
39.7
46.9
38.8
26.7
-22.5
-45.0
-43.3
-55.1
-43.7
207.9
-210.1
214.2
-215.3
216.8
-210.6
203.8
-212.3
VLBI
48.3
48.2
60.8
48.5
27.3
-30.2
-53.1
-43.0
-62.6
-54.5
243.8
-244.0
256.6
-251.3
262.6
-258.5
259.0
-254.6
VLBI-DMTD
10.4
8.5
13.9
9.7
0.6
7.7
8.2
0.3
7.5
10.7
35.8
33.9
42.4
36.0
45.9
47.9
55.3
42.3
Time Difference
DMTD
GPS
VLBI 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
9 ps
after removing offsets
GPS-DMTD
VLBI-DMTD
43 ps
30 ps

14. VLBI vs. GPS and DMTD Time Difference DMTD GPS VLBI DMTD GPS VLBI
-43.3
-54.0
-43.0
DMTD
GPS
VLBI
GPS-DMTD
VLBI-DMTD

15. Conclusions Can the VLBI measure right time difference?
VLBI vs. GPS CP and DMTD
Artificial change
VLBI vs. DMTD: rms 　　 ↑good agreement
GPS vs. DMTD:
The geodetic VLBI technique can measure the right time difference.

16. How stable are current VLBI systems?
Kashima34-Kashima11
　・3C84 tracking data
　・integrate 10s per 10s
　・obs. delay – a priori
VLBI

17. Acknowledgements Thank you very much for your attention.
IVS and IGS for the high quality products
GSFC, JPL, NRC Canada
for VLBI and GPS analysis software
Thank you very much for your attention.