VLBI MEASUREMENTS FOR FREQUENCY TRANSFER

Transcription

1 Joint Discussion 6 Time and Astronomy IAU XXVII GENERAL ASSEMBLY AUGUST 6, 2009 Rio de Janeiro, Brazil MEASUREMENTS FOR FREQUENCY TRANSFER 2 Hiroshi Takiguchi (htaki@nict.go.jp), Yasuhiro Koyama, Ryuichi Ichikawa, Tadahiro Gotoh, Asutoshi Ishii, Thomas Hobiger, and Mizuhiko Hosokawa National Institute of Information and Communications Technology, 3 Geographical Survey Institute, Advance Engineering Services Co., Ltd,2,3

2 Content Introduction» Why is required?» Activities at NICT» Previous study : Wettzell - Onsala Intercomparison between and other techniques» Can the measure the right time difference? Kashima34m - Kashimam Artificial change by Line Stretcher Conclusions

3 Introduction Development of frequency standard NICT-CsF.. developing Atomic fountains 2 few days Optical clocks Background Time and frequency transfer technique» GPS Carrier Phase 2 0» TWSTFT 2-4 long averaging period» insufficient accuracy NICT optical clocks.. developing 0-6 few hours improvements of highly precise time and frequency transfer techniques are strongly desired

4 Activities at NICT. Developing a compact system» MARBLE SYSTEM Multiple Antenna Radio-interferometry of Baseline Length Evaluation Diameter.65m S/X-band Front-fed paraboloidal reflector Az-El mounting Max speed AzEl 5 deg/sec Transportable by few person Collaborating with GSI Future image 2. Verifying the ability of frequency transfer» to show the capability of the current system Intercomparison between and other techniques This study

5 Previous study Intercomparison : vs. GPS. Wettzell-Onsala vs. GPS CP IVS and IGS data IGS: IVS: 20ps@s GPS 00ps@s Atomic Fountain + GPS long period ( days, days) GPS Onsala Sweden Onsala Space Observatory Wettzell Optical Clocks 0 3 s Germany Fundamental Station Wettzell at each site and The GPS geodetic technique are sharing has the H-maser potential for precise frequency transfer is more stable than GPS surpassing the stability of atomic fountain at 0 3 s stability : follows a / law very closely 2

6 Intercomparison : vs. other techniques NICT sites Kashima Kashima Space Research Center Koganei/Tokyo Headquarters Kashima34m Kashimam Kashimam Koganeim Kashima MARBLE GPS 239m 09km H-maser, DMTD Koganei GPS: kgni Koganeim GPS TWSTFT TEC (ETS-8) Kashimam GPS : ksmv GPS : ks34 Please see the poser : JD06-p:2 Hosokawa et al., Recent activities at NICT Space-Time Standards Group Kashima34m

7 Can the measure the right time difference? Kashima34m Kashimam DMTD (6ps)» Artificial time difference change using Line Stretcher» Intercomparison between, GPS and DMTD 34m Freq. Dist. Amp. OE 34mETR H-Maser 0MHz Freq. Dist. Amp. line stretcher +0~20ps GPS KSMV m EO EO Freq. Dist. Amp. Line Stretcher A B DMTD OE GPS KS34

8 Differences with the normal observation Normal Geodetic» 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

9 Data analysis» CALC/SOLVE» single baseline» S/X ionosphere-free linear combination clock offset / 0sec GPS» NR Canada s PPP IGS Rapid Orbit & Clock» Precise Point Positioning satellite clock interpolation clock offset / 30sec» Time Defference clock offset / 0sec» Time Defference clock offset A clock offset B / 30sec vs. DMTD Time Difference / sec

10 DMTD Line Stretcher A B DMTD

11 GPS vs. DMTD DMTD GPS Line Stretcher A B large difference opposite sense after removing offsets

12 vs. GPS and DMTD DMTD GPS Line Stretcher A B DMTD GPS good agreement after removing offsets

13 Difference GPS - DMTD - DMTD Can the measure the right time difference? Artificial change YES» vs. DMTD: good agreement (<0ps)» GPS vs. DMTD: sometimes, opposite sense other parts» vs. DMTD: good agreement (<50ps) for short time range larger difference for longer time range due to the effect of atmospheric variation» GPS vs. DMTD: good agreement hour

14 Conclusions Can the measure right time difference?» vs. GPS CP and DMTD» Artificial change vs. DMTD: good agreement (<0ps) GPS vs. DMTD: sometimes, opposite sense» The geodetic technique can measure the right time difference.

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