Journal of the Geodetic Society of Japan

Clarification and Application of Environmental Effects on Geodetic Observations

Atsushi Mukai

2008 Volume 54 Issue 1 Pages 1-13
Published: March 25, 2008
Released on J-STAGE: September 07, 2010

DOIhttps://doi.org/10.11366/sokuchi1954.54.1

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The observations of gravity and crustal strain changes are disturbed by environmental noises such as meteorological variations. The atmospheric effects on gravity observations can be estimated in the order of 1, μgal using a spatial integration of global meteorological data. Spatial dense meteorological data are obtained by the interpolation of grid data such as JANL and GANL. The atmospheric temperature is of importance for the interpolation of the atmospheric density. In particular, the temperature changes in the convective boundary layer (CBL) have large signal levels within the diurnal band. The effects of atmospheric tides should be estimated by considering the thermal effects of CBL. A major part of the atmospheric effects in the regions that are 10 degrees away from the site is attributed to the atmospheric variations within a horizontal scale larger than a few 100 km. The atmospheric effects at a distance from the site can be easily estimated with a precision of 0.1 μgal by using the spherical surface harmonic expansions of the meteorological data. Strain changes induced by groundwater penetration with a known pressure source can be used to estimate the hydraulic conductivity of the surrounding crust. Water injection experiments were repeatedly performed at the 1800m-deep borehole in order to investigate the healing process of the Nojima fault. When the hydraulic parameters were estimated using the strain changes induced by water injection, the hydraulic conductivity and coefficient of specific storage decreased at a rate of 5 and 11 %lyear, respectively. These decreases might be caused by the closure of fractures, suggesting the healing of the Nojima fault. Elastic factors were estimated using the tidal strains observed at the 800m-deep borehole. After 1998, the obtained Young's moduli increased, indicating the gradual hardening of the surrounding crust. This increase might be caused by the closure of fractures, and it is in good agreement with the decrease in the hydraulic conductivity, as estimated from the injection experiments. The estimation of the elastic factors using the tidal strains is one of the effective procedures used to examine the variations in geological structures.

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Geodynamics of the Antarctic Continent Focus on the First Stage of Geodetic Studies in 1990s

Katsutada Kaminuma

2008 Volume 54 Issue 1 Pages 15-30
Published: March 25, 2008
Released on J-STAGE: March 01, 2011

DOIhttps://doi.org/10.11366/sokuchi1954.54.15

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The Japanese Antarctic station, Syowa (69.0°S, 39.6°E) was established for International Geophysical Year (IGY) in East Ongul Island, Lutzow-Holm Bay, East Antarctica on Jan. 29, 1957. Since then Japanese Antarctic Research Expedition (DARE) has carried on many scientific items in and around Syowa Station. JARE has carried out geographical surveys in the area and had published more than 100 sheets of geographical maps. The station geophysics such as gravity, geomagnetism, seismology etc. has been observed during the last half century. The observation of tide gauge was started in 1966 and has been continued four decades. Syowa Station was nominated one of the A stations of the International Absolute Gravity Baseline Network (IAGBN) in 1987 . The absolute gravity measurements have repeated and obtained the absolute gravity value as g=982524.3269 mGal ± 0.0001 mGal. A super conductivity gravity meter (SG) was installed at Syowa Station in 1993. Free oscillation of the earth incessantly excited by coupling between atmosphere and geosphere was found using the data of SG at Syowa Station. Since 1990 the geodetic Very Long Baseline Interferometry (VLBI) observations were made on baselines among Syowa Station, O'Higgins Station in Antarctica, Stations in Australia, South Africa and Japan. The dynamics of the Antarctic plate become to be discussed by the data of VLBI and GPS. The relation between crustal uplift of the Antarctic continent and seismic activity are discussed.

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RFI Mitigation at a 2 GHz Band by Using a Wide-band High-temperature Superconductor Filter

Eiji Kawai, Junichi Nakajima, Hiroshi Takeuchi, Hiromitsu Kuboki, Tets ...

2008 Volume 54 Issue 1 Pages 31-37
Published: March 25, 2008
Released on J-STAGE: September 07, 2010

DOIhttps://doi.org/10.11366/sokuchi1954.54.31

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Since 2002, severe radio frequency interference (RFI) due to a third-generation mobile phone system (IMT-2000) has occurred at the S-band (2.2 GHz) of a 34-m antenna located at the Kashima Space Research Center, National Institute of Information and Communications Technology (NICT: formerly the Communications Research Laboratory) in Japan. It has become difficult to continue observations on the S-band due to saturation of the down converter by the RFI signals. To mitigate this RFI, a new high-temperature superconductor (HTS) band-pass filter was developed. The characteristics of the HTS filter include a sharp frequency cutoff, wide bandwidth, and low losses. Since the LNA of the S-band receiver was not saturated, we installed the filter in the LNA output to avoid

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[title in Japanese]

Kazuhiro Ozawa, Takeshi Kataoka

2008 Volume 54 Issue 1 Pages 39-42
Published: March 25, 2008
Released on J-STAGE: September 07, 2010

DOIhttps://doi.org/10.11366/sokuchi1954.54.39

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