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Joint Discussion 6 Time and Astronomy

IAU XXVII GENERAL ASSEMBLY AUGUST 6, 2009 Rio de Janeiro, Brazil

VLBI MEASUREMENTS FOR FREQUENCY TRANSFER
Hiroshi Takiguchi (htaki@nict.go.jp), Yasuhiro Koyama , 1 1 1 ,2 ,3 Ryuichi Ichikawa , Tadahiro Gotoh , Asutoshi Ishii , 1 1 Thomas Hobiger , and Mizuhiko Hosokawa
1 2 1 1

National Institute of Information and Communications Technology, 3 Geographical Survey Institute, Advance Engineering Services Co., Ltd


Co n t e n t
Introduction
» Why VLBI is required? » Activities at NICT » Previous study : W ettzell - Onsala

Intercomparison between VLBI and other techniques
» Can the VLBI measure the right time difference?
Kashima34m - Kashima11m
Artificial change by Line Stretcher

Conclusions


Introduction
Development of frequency standard
Atomic fountains

Background
Time and frequency transfer technique
» GPS Carrier Phase 2· 10-15 @1day » TWSTFT

2· 10
NICT-CsF1
..... developing

-15

@a few days

2-4· 10

-15 @1day

Optical clocks

» long averaging period » insufficient accuracy
-17
improvements of highly precise time and frequency transfer techniques are strongly desired

10-16TM10
NICT optical clocks
..... developing

@a few hours

V LB I


A c t i v i t i e s a t N I CT
1. Developing a compact VLBI system
» MARBLE SYSTEM
Multiple Antenna Radio-interferometry of Baseline Length Evaluation
Diameter 1.65m

Future image

S/X-band
Front-fed paraboloidal reflector Az-El mounting · Max speed AzEl 5 deg/sec

Transportable
by few person Collaborating with GSI

2. Verifying the ability of VLBI frequency transfer
» to show the capability of the current VLBI system
Intercomparison between VLBI and other techniques À This study


Previous study

Intercomparison : VLBI vs. GPS
Wettzell-Onsala
VLBI vs. GPS CP IVS and IGS data
IGS: ò I VS: ü
GP S 100ps@1s

1.

+ GPS long period
(2007 91-105 15days, 106-124 19days)

VLBI 20ps@1s
Ato mic Fou nta in Op t ic a l Cl ock s

1

GPS VLBI

Onsala
Sweden Onsala Space Observatory

Wettzell

103s

at each site VLBI anThe geodetic VLBI technique d GPS are sharing theeH-mtasetral for precise has th po en i

Germany Fundamental Station Wettzell

frequency transfer

VLBI is more stable than GPS surpassing the stability of atomic fountain at 103s VLBI stability : follows a 1/ law very closely 2· 10-11 ¢ 20ps¸ @1s


Intercomparison : VLBI
NICT sites Kashima

vs. other techniques
Kashima34m ­ Kashima11m Kashima11m ­ Koganei11m
239m

109km

Kashima Space Research Center

Ka s h i m a

Koganei/Tokyo
Headquarters

VLBI
MARBLE

H-maser, DMTD

GPS
VL BI Kashima11m

Ko g a n e i GPS: kgni

VL BI Koganei11m

VLBI GPS TW STFT TEC (ETS-8)

ð

ð

GPS : ksmv

Please see the poser : JD06-p:21
Hosokawa et al., "Recent activities at NICT Space-Time Standards Group"

GPS : ks34

VL BI Kashima34m


Can the VLBI measure the right time difference?
Kashima34m ­ Kashima11m
» Artificial time difference change
using Line Stretcher » Intercomparison between VLBI, GPS and DMTD
34m

H-Maser
10MHz

11m

DMTD 6x10-12@1s (6ps)

34mE TR
Fr eq. Dist. Amp.

Fr eq. Dist. Amp.

GPS
l ine str etcher
+0~12 0ps

KSM V

OE EO

EO

Freq. Dis t. A mp.

Line Stretcher

A

B

DMTD

OE

GPS
KS 34


Differences with the normal observation
Normal Geodetic VLBI
» Observation
multiple sources antenna slew time different scan time 24 hours

This study
» Observation
one source : 3C84 no antenna slew time same scan time a f e w h o u rs

» Data Analysis
estimate clock parameter atmosperic delay station coordinates

» Data Analysis
estimate only clock parameter atmospheric delay : short baseline, one source station coordinates : fixed to a-priori coordinates


D at a an aly s is
VLBI
» CA L C » single » S/X io linear /SOLVE baseline nosphere-free combination

GPS
» NR Canada's PPP
IGS Rapid Orbit & Clock

» Precise Point Positioning
satellite clock interpolation clock offset / 30sec

clock offset / 10sec

» Time Defference clock offset / 10sec

» Time Defference
clock offset A ­ clock offset B / 30sec

vs. DMTD Time Difference / 1sec


DMT D
Line Stretcher A B 2 1 3 4 5 6 7

DM T D

1 2 3 4 5 6 7

" À" À Þ À Þ À Þ

# # # # # # #

Þ" À" Þ"


G P S vs. DM T D
DM T D GPS Line Stretcher A B

large difference opposite sense

1 2 3 4 5 6 7
after removing offsets

" À" À Þ À Þ À Þ

# # # # # # #

Þ" À" Þ"


V L B I v s . G P S a n d D M TD
DM T D GPS V L BI ( 14 % 5% . 7- #* % 5% . Q T Line Stretcher A B

D ( 14 % 5% D . MT 7- #* % 5% . PS G Q T V L BI

good agreement

1 2 3 4 5 6 7

" À" À Þ À Þ À Þ

# # # # # # #

Þ" À" Þ"

after removing offsets


Difference
GPS - DMTD V L BI - DM T D

Artificial change other parts
» VLBI vs. DMTD: larger difference atmospheric vari » GPS vs. DMTD:

Can the VLBI measure the right time difference? Þ YES

hour

» VLBI vs. DMTD: good agreement (<10ps) » GPS vs. DMTD: sometimes, opposite sense good agreement (<50ps) for short time range for longer time range due to the effect of ation good agreement


Co n c l u s i o n s
Can the VLBI measure right time difference?
» VLBI vs. GPS CP and DMTD » Artificial change
VLBI vs. DMTD: good agreement (<10ps) GPS vs. DMTD: sometimes, opposite sense

» The geodetic VLBI technique can measure the right time difference.


Acknowledgements
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.