SGD21-01

Room:303

Time:May 28 11:00-11:15

Re-examination of absolute gravity changes observed in Southeast Alaska
KAZAMA, Takahito1∗ ; FUKUDA, Yoichi1 ; SATO, Tadahiro2 ; OHTA, Yusaku2 ; MIURA, Satoshi2
1Graduate School of Science, Kyoto University, 2 AOB, Tohoku University

Ground gravity measurement is one of the most effective methods to monitor mass variations due to glacial isostatic adjustment(GIA) and present-day ice melting (PDIM). Meanwhile, observed gravity data often contains environmental disturbances suchas the effects of spatiotemporal mass variations associated with land water, atmosphere, and oceans, which should be corrected
accurately to retrieve the GIA/PDIM gravity signals.
For example, the GIA/PDIM-derived linear gravity decrease of the maximum of -5.6 micro-Gal/year was found from absolutegravity data, obtained at Southeast Alaska every summer in 2006-2008 (Sun et al., 2010). However, the new gravity datameasured at the same gravity sites in 2012-2013 was greater than expected from the regression lines of the linear gravity decreasesuggested by Sun et al. (2010) by up to 20 micro-Gal (Kazama et al., 2013), because of the excess snow loading associated withthe heavier-than-average snowfall in the wintertime of 2011-2012. Although Kazama et al. (2013) corrected the hydrological
gravity disturbances (including the excess snow loading effect) from the observed gravity data using the synthetic ground gravity
data created by the time series of satellite gravity (GRACE) and ground deformation (GPS), they did not take into account theatmospheric/oceanic gravity disturbances, which might distort their final results about the GIA/PDIM-derived gravity signal.
We were thus motivated to quantitatively evaluate the hydrological/atmospheric/oceanic gravity disturbances in the absolutegravity data measured at Southeast Alaska, in order to re-examine the gravity decrease rate due to GIA and PDIM. We firstestimate the atmospheric/oceanic gravity disturbances using the global model AOD1B (Flechtner, 2007), and the hydrologicaldisturbances using the satellite gravity time series collected by GRACE and some hydrological models (such as GLDAS (Rodell
et al., 2004) and G-WATER [3D] (Kazama et al., 2015)). We then retrieve the GIA/PDIM-derived gravity changes in 20062013 from the observed absolute gravity data by correcting for the above gravity disturbances, and compare the retrieved gravity
changes with those of the previous study (Sun et al., 2010).
Keywords: absolute gravity, Southeast Alaska, glacial isostatic adjustment, glacier, snow, soil moisture

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SGD21-02

Room:303

Time:May 28 11:15-11:30

Measuring the Difference between Two Local Vectors: the Gradient of Earth’s Gravity
Field and the Earth Surface Normal
CHEN, Wei-jun1∗
1

Carl Zeiss AG

Even though concrete support is not yet available, it is widely believed or hoped, that earth quakes, which are generally
accidental events on our Earth surface, could be predicted by analyzing historical signals from kinds of geodetic measurements.
Directly or indirectly for such a purpose, many comparative analyses have been carried out for constructing an implicit or
explicit correlation between the temporal variations of selected measurements and the recorded earthquakes. For instance, in[1] the locally co-seismic and post-seismic variations of the Earth’s gravity field for three giant earthquakes (2004, 2010 and2011) are compared, with a frustrating but just normal conclusion that the observed discrepancies of gravity changes reflect thedifference in the settings of the studied earthquakes.
On another hand, based on the development of measurement techniques, geodetic measurements are continually reported withhigh quality. As an example, ITRF2008 [2] claims a believed origin accuracy at the level of 1 cm over the time-span of 26 year of
SLR observations. Integrating four measurement techniques, ITRF2008 provides an accuracy of 8 mm over more than 20 years.
With latest technical improvements, it is reasonable to expect even better accuracy in the coming release of ITRF2013 [3].
It seems that a gap between the high quality of geodetic measurements and the relatively less achievement by analyzing themdoes exist. Normally an accidental event like an earthquake is a local event which happens at a particular time moment covering aclose neighborhood of its epicenter. Geodetic measurements are often suffering from densely sampling the dynamical behaviors
on Earth. A typical velocity of plate tectonic movements which varies from 1-10 cm/year is indistinguishable from noise in mostof daily measurement systems, if the time span is set to be seconds, minutes, or even hours; The system reference of geodetic
observation is often set either as man-made satellites, or as natural space objects like lunar or extragalactic reference. These
references help us constructing a global coordinate system for geodetic observations with great successes. But still, they areneither convenient nor flexible for densely local observations.
In this paper a new geodetic measurement concept is suggested for local and short time-span observations. Other than goingto space pursuing a comparable scale than Earth radius, the suggested concept looks into the atomic scale, while a velocity of
1-10 cm/year is roughly equivalent to 317-3171 pm/s, which is the same scale for observing atomic structures. In this concept a
microscope for nano scale observation, e.g., scanning tunneling microscope [4], is required. The observation arm and the sample
holding arm are separately assembled as that the observation arm is fixed on the ground, and the sample holder is floating in the
air. The sample holder is designed as a long pendulum which keeps pointing to the earth gravity center. The local earth surface
normal, and the local gradient of the earth gravity field, are two vectors in the system. Within short time span like seconds it
is possible to measure the different temporal variations between them, based on the different earth dynamics of lithosphere andearth mass distribution.
Without systematic ambiguities like non-modeled forces in space, signal delay in ionosphere, as well as the tropospheredistortions, the suggested concept physically is promising for a new geodetic measurement.
References:[1] V. O. Mikhailov etc.: Comparative study of temporal variations in the earths gravity field using GRACE gravity models in
the regions of three recent giant earthquakes, 2014;[2] Z. Altamimi etc.: ITRF2008: an improved solution of the international terrestrial reference frame, 2011;[3] Z. Altamimi etc.: Status of ITRF2013 and early results, 2014;[4] C. J. Chen: Introduction to Scanning Tunneling Microscopy, 1993.

Keywords: Geodetic Measurement, Atomic scale, Plate movement, Velocity, Gradient of gravity field, Microscope

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SGD21-03

Room:303

Time:May 28 11:30-11:45

VLBI application for Frequency Transfer and Development of GALA-V System (V)SEKIDO, Mamoru1∗ ; TAKEFUJI, Kazuhiro1 ; UJIHARA, Hideki1 ; KONDO, Tetsuro1 ; MIYAUCHI, Yuka1 ;TSUTSUMI, Masanori1 ; KAWAI, Eiji1 ; HASEGAWA, Shingo1 ; TAKIGUCHI, Hiroshi1 ; ICHIKAWA, Ryuichi2 ;HANADO, Yuko1 ; KOYAMA, Yasuhiro3 ; WATABE, Ken-ichi4 ; SUZUYAMA, Tomonari4 ; FUKUZAKI, Junyou5 ;KOMURO, Jun-ichi6 ; TERADA, Kenjro7 ; NAMBA, Kunitaka7 ; TAKAHASHI, Rumi7 ; OKAMOTO, Yoshihiro7 ;AOKI, Tetsuro7 ; IKEDA, Takatoshi81National Institute of Information and Communications Technology, Space-Time Standards Laboratory, 2 Global ICT Strategy
Bureau Technology Policy Division, The Ministry of Internal Affairs and Comm., 3 National Institute of Information and Communications Technology, International Relations Office, 4 AIST, National Metrology Institute of Japan, Frequency Measurement
Systems Section, 5 Geospatial Information Authority of Japan, 6 NICT, Outcome Promotion Department, Development support
Section, 7 NICT, Outcome Promotion Department, Information System Section, 8 National Institute of Information and Communications Technology, Network Architecture Laboratory
1. Introduction
NICT is conducting a development of the new broadband VLBI system for distant frequency comparison. This project, named
GALA-V, is intended to make precise frequency comparison between atomic frequency standards by VLBI observation of celestial radio sources with 3 ? 14 GHz. Advantages of using VLBI technology with respect to the two way satellite time andfrequency transfer (TWSTFT) are simultaneous multi station comparison by single VLBI session and freedom of from availability of communication satellites. Additionally VLBI method is not affected by precision of orbit information of GNSS satellites.
From the view point of broadband observation system, ours is semi-compliant with the VGOS (VLBI2010 Global Observing
System), which is under development as next generation geodetic VLBI system in international VLBI community. Thus thissystem is not only useful for distant frequency comparison, but also for precise geodesy.
NICT has originally developed broadband feed for Kashima 34m radio telescope. And small diameter broadband VLBI antennas and data acquisition systems were installed at NICT Koganei and National Metrology Institute of Japan (NMIJ) in Tsukuba,
where standard time UTC[NICT] and UTC[NMIJ] are maintained, respectively. By joint use of the 34m antenna and two small
antenna systems, measurements of UTC[NICT]-UTC[NMIJ] have been performed.
For contribution to geodesy, we have made a series of test experiments between Ishioka VGOS station, which is establishedby GSI in 2014, and Kashima 34m antenna. In January 2015, we have successfully observed super broadband signal over 8GHz
frequency range and cohelently synthesized for the first time. Additionally, the first international broadband VLBI experiment
was successfully performed among Kashima 34m, Westford 18m antenna at MIT Haystack observatory, and GGAO station at
NASA/GSFC.
2. VLBI Frequency Comparison between NMIJ and NICT.
Small diameter antenna systems of GALA-V have been installed at NICT Koganei, where Japan Standard Time (JST) is
maintained, and NMIJ, where atomic time standards are developed. Since accurate measurement result of difference between
UTC[BIPM] and UTC[NICT], UTC[NMIJ] are regularly reported to BIPM (Bureau International des Poids et Mesures), thus
NICT-NMIJ is good test bed for development of VLBI system for frequency comparison. Further long term comparison andemployment of broadband system will be tested in this year.
3. Super broadband VLBI observation with Ishioka VGOS Geodetic Station of GSI
The GSI has established a new VGOS 13m diameter antenna (hereafter Ishioka 13m antenna) at Ishioka geodetic station in
2014. This antenna is domestically the second largest telescope with broadband receiver. We have conducted a super broadband
VLBI experiments between Kashima 34m antenna and Ishioka 13m antenna. Signal from celestial radio source was observedby six observation bands (1GHz bandwidth) allocated in 6-14GHz frequency range. The data was acquired by newly developed
direct-sampling technique. After correlation processing of the data, signal was synthesized coherently over 8GHz bandwidth.
This was the first achievement and theoretical delay precision reaches to several tens of femto seconds! Of course precision inreal measurement is degrade by a number of causes. Further evaluation of actual delay precision will be made.
4. The First International VLBI Experiment with Broadband Systems.
The GALA-V project is not only developing original new technology such as direct-sampling data acquisition technique, butalso keeping compatibility with VGOS system is in the scope for joint international observation. In January 2015, we have successfully made the first international VLBI experiment with broadband feed between Kashima 34m antenna, and Westford 18m

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SGD21-03

Room:303

Time:May 28 11:30-11:45

antenna, and GGAO 12m antenna. The observation data were exchanged between Japan and U.S.A. through high speed networkof JGN-X, APAN, and Internet2.

Keywords: Very Long Baseline Interferometory, Time and Frequency Transfer

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SGD21-04

Room:303

Time:May 28 11:45-12:00

Improvement of the accuracy in seafloor acoustic ranging by estimating the spatio-temporal
temperature variation
YAMAMOTO, Ryusuke1∗ ; KIDO, Motoyuki2 ; OSADA, Yukihito1
1Graduate School of Science, Tohoku University, 2 International Research Institute of Disaster Science, Tohoku University

Direct-path seafloor acoustic ranging is widely used to detect crustal deformation. The idea is simply to monitor a baseline
length by multiplying sound speed to the round-trip time between transducer and transponder installed on the seafloor. A transducer transmits the acoustic wave and a transponder record. Sound velocity is a function of temperature, pressure and salinity,
among which the temperature is most effective on seafloor. Thus, evaluation of temperature field plays a key roll on this measurement.
In the past studies, time-varying uniform temperature field is assumed employing a simple average of measured temperature
at the both ends of the baseline. This results in large apparent fluctuation in measured baseline length, especially during rapid
temperature change. So, we tried to infer the spatio-temporal temperature field by applying a simple advection model of temperature field..
We proposed an equation of temperature T(x,t) which linearly interpolates between measured temperature data for both x(space) and t (time). Typical change in the temperature is thought to be associated with the semidiurnal tide, so field advection
is postulatedas simple 12-hours harmonic oscillation with arbitrary phase and amplitude. Measured temperature at both ends arebasically in coherent with certain time-lag. Any individual deviation at each site can be consistently formulated by linear interpolation in time and space. We assessed the formulation by inverting a given temperature field using synthetic temperature data.
If there are temperature data at three sites, the formula can be easily expanded to 2-D temperature field by linear interpolation
between the two baselines..
We also tried to apply the formula to real data. In 2007, the acoustic ranging test was conducted at Kumano-nada [Osada, Y.,
M. Kido, and H. Fujimoto, Ocean Engineering , 2012]. Significant improvements in the stability of apparent baseline length were
found when the advection vector is clear from the original temperature data. Base on this result, the formula is effective if thesampling frequency of temperatures is high enough (about 30 min. to 1 hour), while the acoustic ranging itself can be infrequent.
Currently, we only verified the formula for the time windows in where the advection vector is clear. Without knowing advection, the formulation cannot be applicable. The advection is estimated based on coherency and time-lag between the temperaturesat the both ends of the baseline, however, it is not possible to estimate it for time window with smaller temperature variation or
non-coherent behavior. The best way to know temperature field is dense measurement along the baseline. Although the advectionof temperature field is not always equivalent with flow of water, it should be valuable to introduce currently meter or to makerough estimate from time varying attitude of the instrument. In the different point of view, it could be worth to utilize the finescale assimilated ocean model, JCOPE-T (provided by Application Laboratory, JAMSTEC), which can predict local temperature
variation.
Keywords: Seafloor geodesy, Acoustic ranging, Seafloor temperature, Tidal current, Extensometer

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SGD21-05

Room:303

Time:May 28 12:00-12:15

Noise assessment of the kinematic GNSS analysis for GPS/Acoustic observation by precisely controlled movable table data
OHTA, Yusaku1∗ ; KIDO, Motoyuki2 ; DEMACHI, Tomotsugu1 ; HINO, Ryota1
1Graduate School of Science, Tohoku University, 2 International Research Institute of Disaster Science, Tohoku University

The seafloor geodetic observation techniques are extremely important for understanding of the spatial and temporal heterogeneity of the interplate coupling. Especially, GPS/Acoustic (hereafter GPS/A) techniques have been developed for practical use
in the past ten years, which allowed offshore measurement just above the expected strong coupling region in the plate boundary.
The conventional observation style of the GPS/A is campaign style, which repeatedly observed by the research vessel. Recently,
several groups have proposed continuous style GPS/A observation based on the moored buoy system.
The one of key technique of GPS/A observation is high-rate sampling precise/accurate positioning of floating section (e.g.
research vessel, moored buoy) based on kinematic GPS analysis. A required precision/accuracy is typically smaller than several
tens mm in the horizontal components even though it depend on the required precision by user. On the other hand, true positionof such moving body is generally unknown.
Based on these backgrounds, we developed the precisely controlled movable table for the assessment of the precision/accuracyof the kinematic GPS (GNSS) analysis. The developed precise movable table consists of uniaxial small electric actuator device
and its control unit. The maximum movable stroke of the actuator is 200mm, and the resolution of moving step is 0.1mm/pulse.
We implemented a several moving pattern to the developed table. One of the moving patterns is modeled upon the research vessel. We used the velocity data obtained by 10Hz GPS Doppler measurement in the actual research vessel. We applied high-passfiltering after the integration of velocity data to the displacement. Obtained displacement strongly reflects the ship rolls and/or
pitches, so we used this data as true value of the moving body. Based on the developed movable table, we tested the precision of
the kinematic GPS analysis. We used the dual-frequency GNSS (GPS and GLONASS) receiver with 10Hz sampling for the test.
For the test, we compared with real-time kinematic PPP time series and known movable table motion. As a preliminary result,obtained 10Hz time series by real-time kinematic PPP time series shows the good agreement with known movable table motion
during the short period of time (<several hundred seconds). In contrast, the large discrepancy clearly appeared between bothtime series in the long period of time. It caused by the high noise level of kinematic PPP time series in the low frequency band.
These experiments should be important for understanding of the noise property of the kinematic GNSS analysis for the moving
body.

Keywords: kinematic GNSS, moving body

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SGD21-06

Room:303

Time:May 28 12:15-12:30

The effect of snowfall on the solution of GEONET (2)
IMAKIIRE, Tetsuro1∗ ; MUNEKANE, Hiroshi1 ; SATO, Yudai1
1

Geospatial Information Authority of JapanThe routine solutions of geodetic coordinate of observation stations of GEONET, F3 solution, are fundamental data for thestudies of crustal deformation and tectonics and widely utilized for a variety of purposes. As GEONET data is available freely,
researchers can discuss the crustal deformation or tectonics without carrying out GNSS observation or baseline analysis. However, it should be noted that the coordinates provided by GEONET may include errors caused by various noise sources or factors.
One of the significant error sources is the effect of snowfall, especially the stuck of the snow on the radome of GEONET sites.
We reported that the effect of heavy snow fall on the February 2014 caused notable perturbation on the GEONET solution in
Yamanashi prefecture, on the 2014 fall meeting of the Geodetic Society of Japan. We investigated other GEONET sites on samedate and those sites on other heavy-snowy days with abnormal F3 solution. We will report how snowfall affected the GEONET
solution on those cases, combining the GEONET solutions and he meteorological data in time series.
Keywords: GEONET, GNSS, positioning, error, snowfall

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SGD21-07

Room:303

Time:May 28 12:30-12:45

Development of a new precise positioning technique using multi-GNSS signals
KAMAKARI, Yuki1∗ ; FURUYA, Tomoaki1 ; MANDOKORO, Motomu1 ; TSUJI, Hiromichi1 ; TANAKA, Kazuyuki1 ;MIYAGAWA, Kohei1 ; SATO, Yudai1 ; HATANAKA, Yuki1 ; MUNEKANE, Hiroshi1 ; KAWAMOTO, Satoshi1
1

GSI of Japan

Geospatial Information Authority of Japan (GSI) is developing and standardizing new precise positioning techniques which
deal with multiple GNSS constellations, GPS, QZSS, GLONASS, Galileo, and Beidou, in order to mainly encourage effective
surveys at places where it is currently difficult to carry out them using only GPS satellites.
In FY 2014, we examined analysis methods to correct Inter System Bias and to using single/double differences between Beidou
and other GNSS. Moreover, in case of using Beidou, we need to correct Inter-satellite-type Bias which is 1/2 cycle shift between
GEO and MEO, IGSO. In addition, we obtained multi-GNSS data in five cities and evaluated the effects and problems using
multi-GNSS signals.
This presentation shows results of FY 2014.

Keywords: GNSS, Geodetic Survey, Beidou

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