Gravity tide observations were carried out at VERA four stations. LaCoste-Romberg gravimeters D73 and G457 were used in the observations of three stations, and a superconducting gravimeter was used at Mizusawa station. The major purpose of the observations is to verify the tidal displacement model used in VERA geodetic VLBI and astrometry VLBI observations. The tidal analysis results were compared with a model calculation by GOTIC2. The results of three stations except Ogasawara show good agreement between the observations and the model estimations. The differences are estimated less than 0.2% in tidal factors. If those differences come from the ambiguity of Love number h, it is estimated to be less than 1%. This ambiguity of h is corresponding to the maximum error of 3 mm in the vertical displacement model. The difference of M₂ factor at Ogasawara is nearly twice as large as that of other stations, but it is only 0.2%. A slightly large difference between observation and model at Ogasawara station might be caused by local geology and/or ocean tide model error. Still, the error for the displacement model used in VERA is negligible small enough to affect analyses results.

We have developed a new broadband VLBI system GALA-V for distant frequency comparison project. The GALA-V broadband VLBI observation system is designed to be compatible with the concept of the next generation geodetic VLBI system: VGOS (VLBI Global Observing System). The GALA-V system contains advanced technologies, such as (1) unique broadband feed, which enables upgrading standard Cassegrain telescope to broadband radio telescope, (2) RF direct sampling and broadband bandwidth synthesis. We have originally developed broadband feed (NINJA Feed), which has been installed to Kashima 34-m antenna, and we have successfully realized high-gain large diameter broadband antenna with Cassegrain optics. The combination use of RF-Direct sampling technique and broadband bandwidth synthesis have achieved stable high precision group delay measurement. The GALA-V system demonstrated sub-pico second precision delay measurement by one second of VLBI observation of extragalactic radio source with Kashima 34 m - Ishioka 13 m baseline. Our project is targeting to make precision frequency comparison and geodetic measurements with transportable small diameter antennas. We have conducted a series of broadband VLBI experiments between two small telescopes installed at NICT (Tokyo) and NMIJ (Tsukuba) for measurement of clock difference between UTC (NICT) and UTC (NMIJ). These experiments demonstrated that broadband observation enables one pico-second or better delay precision measurement even by using small diameter radio telescopes. Weighted RMS of post-fit delay residual of a pair of 1.6 m & 2.4 m antennas was about 14 psec in the session on 25th Nov., which is the same level with the best precision current geodetic VLBI observation with large diameter antennas. The experiment results suggest that analysis errors of broadband VLBI are no more limited by delay measurement precision, but totally dominated by atmospheric delay uncertainty.

The latest Geodetic Reference Frame （GRF） ITRF2014 has been available since Jan. 2016. In ITRF2014, Post Seismic Deformation （PSD） models were introduced in coordinate time series models to account for coseismic and postseismic deformations caused by major earthquake. PSD models are indispensable in modeling coordinate time series of Japanese GNSS observation network （GEONET） stations since they are subject to active crustal deformations. In this paper, we developed Bayesian method to estimate PSD models that was composed of non-linear functions based on ensemble Marcov Chain Monte Carlo （MCMC） method. We compared the estimated PSD model and PSD model of ITRF2014 products at TSKB station, which is one of IGS GNSS stations. We found that standard deviation of differences between the estimated PSD model and observation was as small as （E, N, U） ＝ （7.9, 13.2, 1.6） mm, indicating that the estimated PSD models sufficiently explain observation data. We also evaluated prediction capability of the PSD model in Miyako station, which had been severely impacted by the 2011 off the Pacific coast of Tohoku Earthquake. We estimated the PSD model of Miyako station with observations spanning two years from the earthquake （fitting period） and compare estimated PSD model with observations for post-fitting period. As a result, we found that the differences were smaller than 1 cm for horizontal component and 2 cm for vertical component from end of fitting period to 2 years later if Log＋Exp＋Log model was employed.

It is important for precise gravity measurement to calibrate the frequency of a rubidium oscillator as a time frequency standard. We demonstrate simple on-site frequency measurement by using a time frequency calibration tool (FT-001A) with a GPS common view method. We equipped one at the Full Range Seismograph Network of Japan (F-net) Ishigaki (IGK) station, Okinawa, Japan, and measured frequency variation of the internal rubidium oscillator of gPhone gravimeter (#133). As a result, we could measure its frequency with uncertainty of approximately 10^-12 (0.01 mHz) on the gravity station 2,000 km apart from AIST Tsukuba where UTC(NMIJ) is maintained.

We changed the observation frequency band adopted by the geodetic VLBI (Very Long Baseline Interferometry) observations bounded within the VERA (VLBI Exploration of Radio Astrometry) network from S/X- to K-band (2.2 and 8.2 GHz to 22 GHz) aiming at improving precision of the antenna coordinates. Since performance of the VERA observing system has been demonstrated best in K-band, fringe detection sensitivity increases by a factor of 8.9 in comparison with that in X-band, leading to reduction of scan length needed for fringe detection. Thanks to the sensitivity improvement, the number of scans increased to more than 800, i.e., the number that is twice of that of geodetic VLBI using S/X bands in VERA. 90 radio sources which are sufficient in quantity to be used for regular observations have been secured, and more than a half of the sources have higher peak flux density in K-band than in X-band. Experimental observations were carried out for two years from January 2006. The coordinates of the VERA antenna reference points and the baseline lengths were estimated with errors of a few mm. The increase in the number of scans thus led effectively to reduction of the standard deviations of the estimated coordinates of antennas by typically 1.64 times in one session. The distribution of post-fit residual delays in K-band and in X-band is similar. The magnitude of error in K-band is 7.14 picoseconds smaller than that in X-band. The inaccuracy of a coherence loss factor is one of the candidates of the additional error sources. Secular variations were detected from the time series of observed baseline lengths. In these baseline lengths and their temporal variations, clear differences are not found between S/X- and K-band.