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Volume 45 (1999)
- Issue 4 Pages 255-
- Issue 3 Pages 165-
- Issue 2 Pages 43-
- Issue 1 Pages 1-
Volume 45, Issue 3
Displaying 1-7 of 7 articles from this issue
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Taku Ozawa, Koichiro Doi, Kazuo Shibuya1999 Volume 45 Issue 3 Pages 165-179
Published: September 25, 1999
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSA pair of synthetic aperture radar (SAR) scenes over the Casey Bay region, Antarctica, was obtained using the C-band (5.7 cm wavelength) SAR sensor onboard the European Remote Sensing Satellite 1 (ERS-1). The two scenes were received at Syowa Station, using the 11 m S/X band paraboloid antenna, on 7 December and 10 December of 1991 for the 3-day ice-phase period of ERS-1. The interferometric processing of the two SAR scenes produced clear interferogram on the Zubchatyy Ice Shelf, which can be related to deformations by ocean tide. Although topographic fringes cannot be removed from the overall fringes, they can be considered as within 0.25 cycle, since the surface undulation of the Zubchatyy Ice Shelf is within 0-40 m height range. When we suppose that the obtained displacement fringes consist only of the vertical component, the calculated vertical change of the Zubchatyy Ice Shelf during 3 days can be estimated as 41.5 cm at maximum; this change is consistent with the ocean tide change of 35.2 cm predicted from the 0RI96 model by Matsumoto et al. (1995). At the transition zone between the ice sheet area and the ice shelf area, the grounding lines can clearly be identified by 1-3 km wide bands of dense displacement fringes in the interferogram. When appropriate values are adopted at the physical properties of ice, and thickness of ice shelf is assumed as 300 m in the deformation equation by Holdsworth (1977), the width of the transition zone results in around 45 m for the transient-creep model and around 230 m for the elastic deformation model, respectively. These values are smaller by a factor of 10-45 than the actually obtained values of about 2 km at the Zubchatyy Ice Shelf. Although refined analysis may be required with the combined use of different band/different look angle SAR scenes, SAP interferometry was shown to be a powerful tool for the studies of ice dynamics and ocean tide around Antarctica.View full abstractDownload PDF (8280K) -
Nobuyuki Kawano, Mizuhiko Hosokawa, Hideo Hanada, Michito Imae1999 Volume 45 Issue 3 Pages 181-203
Published: September 25, 1999
Released on J-STAGE: March 01, 2011
JOURNAL FREE ACCESSA new method for geodetic observations of a planet is proposed. Synchronized radio waves from two or more transmitters on the planet are received at an earth station, and the delays between the radio waves are measured within an error of 0.05 ns. The delays among the reference frequencies of the transmitters on the planet are monitored via an orbiter around the planet within an error of 0.05 ns. This new observation method has the potential to detect the tides and rotational variations of the planet such as Mars with the almost same accuracy as that in a VLBI observation on the Earth. In such precise observations, the relativistic effects influence on the delays so much that these effects are also considered in this paper. Observations for the period longer than a year by this method can reveal the internal structure and dynamics of the Mars.View full abstractDownload PDF (4743K) -
Toshiyuki Tanaka, Rika Shimatani, Yoshiteru Kono1999 Volume 45 Issue 3 Pages 205-214
Published: September 25, 1999
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSWe made a crustal density structure model along the Oga-Kesennuma profile in northeastern Japan ("O-K model") by combining the velocity structure model by explosion seismology with controlled sources and the gravity anomaly. This model suggests inland-like crustal structure extends to about 100 km offshore in the Pacific Ocean side. This tendency is consistentwith the result of inversion of travel time of natural earthquakes. After the crustal density structure model is procured, we can calculate the gravitational potential energy (GPE). If the isostatic compensation is valid, the geoidal height correlates with the GPE linearly. Therefore, we adopt a geoid model of Japan for the evaluation of the 0-K model. Consequently, in the wavelength of 100-200 km, a good consistency exists between the GPE value of the 0-K model and that of geoid. This confirms the validity of the 0-K model in this wavelength domain. Moreover, once the GPE distribution is obtained, we can estimate a crustal strain rate owed to lower crustal flow caused by the own weight. Actually, regarding sign, a good match between the strain rate expected from the GPE distributions and that from the geodetic data has been obtained. Under the assumption that the brittle-ductile transition depth is 15 km, rheologically dominant rock is anorthosite and lower crustal temperature is 1, 000 K (730°C), the estimated strain rates from the 0-K model are less than the observed crustal strain by the order of 104 On the other hand, if lower crustal temperature is 1, 200 K (930°C), the calculated strain rates from this model become an order of 102 of observed values. This result indicates the possibility of GPE-origin strain may be observed around volcanoes in the future.View full abstractDownload PDF (1957K) -
Gravitational Behavior of a Thin Spherical Cap of Axial SymmetryKyozo Nozaki1999 Volume 45 Issue 3 Pages 215-226
Published: September 25, 1999
Released on J-STAGE: July 05, 2011
JOURNAL FREE ACCESSThe author examined the gravitational behavior of a thin spherical cap of axial symmetry, which is one of the most fundamental elements of gravity correction. Suppose a spherical capwith a uniform density p, whose geometrical shape is defined by angular distance (or truncation angle) ψ and geocentric distances γ1 and γ2. Then the gravity g+ or g- due to the sphericalcap, at a radial distance γ+ or γ- (γ-<γ1≤γ≤ 2< +) on the symmetry axis, respectively, can be written as
g±=2πGpr± [Y±(t2, Ψ)-Y±(t1, Ψ)].
where, G: Newtonian gravitational constant, t1=γ11/γ±, t2=γ2/γ± and
Y± (t, Ψ)=[(±)(t2-tcosΨ+3cos>3Ψ-2)(t+1-2tcosΨ1/2+3)(cos3Ψ-cosΨ) ⋅ln | t-cosΨ+(t2+1-2tcosΨ)1/2 | ±t3]/3.
Double signs attached in the formulae should be taken in the same order (same hereinafter).A dimensionless parameter t=r/r±, the radius of curvature normalized by r±, takes t±=r/r±<1 for g+, and t-=r/r->1 for g-. In the above formula, setting t=t+Δt, Δt:2=t2-t1<<t, applying the Taylor's theorem and neglecting higher terms than or equal to (Δt)2, the gravity due to such a thin spherical cap with a thickness Δh:=r±Δt(or a spherical membrane)can be approximated by
g′±-2πGp⋅H±(t, Ψ)Δh,View full abstractDownload PDF (1203K) -
1999 Volume 45 Issue 3 Pages 227
Published: 1999
Released on J-STAGE: March 01, 2011
JOURNAL FREE ACCESSDownload PDF (44K) -
Masaki Murakami1999 Volume 45 Issue 3 Pages 229-239
Published: September 25, 1999
Released on J-STAGE: July 05, 2011
JOURNAL FREE ACCESSThe Geographical Survey Institute (GSI) is preparing the establishment of Japan's new geodetic datum, Japanese Geodetic Datum 2000 (JGD2000), and its realization, Geodetic Coordinates 2000, based on a geocentric system. This review paper focuses on historical background regarding the establishment of geodetic datums and the present situation of Japan'sdatum to help readers understand the idea of, and background for the move to the new geodetic datum.View full abstractDownload PDF (1443K) -
Torao Tanaka1999 Volume 45 Issue 3 Pages 241-247
Published: September 25, 1999
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSDownload PDF (2327K)
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