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Volume 36 (1990)
- Issue 4 Pages 219-
- Issue 3 Pages 143-
- Issue 2 Pages 73-
- Issue 1 Pages 1-
Volume 36, Issue 4
Displaying 1-6 of 6 articles from this issue
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Fumiaki KIMATA, Wahei USUI, Masaru NAKAMURA, Rikio MIYAJIMA, Takashi O ...1990 Volume 36 Issue 4 Pages 219-230
Published: December 25, 1990
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSWe repeated GPS measurements on two twelve observation points in the southern region of Chubu and Kanto district in March 1989 and January 1990 to detect the detailed mode of relative motion between the Philippine Sea and the Eurasian plates. The baseline lengths in this GPS network range from 40 km to 1150 km. In the 1989 campaign the satellite constellation over Japan was very poor and four satellites were visible for only several tens of minutes. The satellite visibility has been greatly improved in the campaign of 1990. The short term repeatability of baseline length is generally less than 0.2 ppm in the 1990 campaign, on the other hand it amounts to 2 ppm in the 1989 campaign because of poor satellite configuration. The strain change derived from GPS baseline measurements, except the lines extending from Hachijyo show the contraction of 0.5 ppm in NWN-SES and the extension of 1.5 ppm in ENE-WSW in the period from March 1989 to January 1990. Although the directions of contraction and extension agree with the result obtained from conventional geodetic survey repeated with 100-year interval, the strain rate does not agree. If we discuss GPS measurement with an accuracy of 0.1 ppm, many error sources have to be taken into consideration. Among them, errors in satellite broadcast ephemerides and satellite configuration are dominant sources. We processed the data by utilizing the broadcast orbits elements. The baseline determinations processed by using broadcast orbits which were obtained in different observation sessions in a day shows systematic differences ranging from 0.1 to 0.5 ppm.View full abstractDownload PDF (3941K) -
Atsushi YAMAMOTO, Ichiro TOMIZAWA, Takeo YOSHINO, Michito IMAE, Hiroo ...1990 Volume 36 Issue 4 Pages 231-241
Published: December 25, 1990
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSRelative positionings are carried out by a, simplified method to improve the precision of the time comparison only using GPS time comparison data. Positioning precision is obtained by the repeatability of positioning results to be a few meters. Precision is also evaluated by the closure errors to be approximately a few meters when the distance between stations is up to 1000 km. When the distance is about 100 km, the difference of positioning results between our method and the VLBI method is approximately lm. This shows the same level of uncertainties of ground surveys. Positioning precision of better than a few meter is required to carry out the time comparison via GPS with a precision of better than 10 nanoseconds (ns). As a result, the precision of our positioning method is sufficient to obtain a precision of 10 ns in time comparison via GPS.View full abstractDownload PDF (1077K) -
Naosuke SEKIGUCHI1990 Volume 36 Issue 4 Pages 243-252
Published: December 25, 1990
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSAssuming various types of the excitation functions of the polar wobble, simulated polar orbits are calculated for the respective excitation functions. About these polar orbits, the rotational periods and the mean square radii for respective examples are compared with the values calculated basing on the theory developed in the author's previous paper (SEKIGUCHI, 1990). The results are likely to support the validity of the present theory. In the case of harmonic oscillator, a parallel reasoning is also possible, and the similar simulations are performed.View full abstractDownload PDF (981K) -
Hiromi FUJIMOTO, Toshio FURUTA, Shimpei KAWACHI, Yuichiro ONO, Toshiyu ...1990 Volume 36 Issue 4 Pages 253-266
Published: December 25, 1990
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSGravity measurements were carried out over the Yatsugatake volcanic chain as a part of multi-disciplinary research of the volcanic chain, which lies near the junction of the Median Tectonic Line and the Itoigawa-Shizuoka Tectonic Line, central Japan. Maps of Bouguer anomalies were compiled from the observed gravity data together with other available data. Except for the gravity anomalies corresponding to the Akaishi Mountain, local gravity anomalies around the Yatsugatake volcanic chain are explained by shallow density structures estimated from geological maps. The Yatsugatake volcanic chain is estimated to be on the western border of the basement high of the Kanto Mountain. A negative gravity anomaly is observed over the western flank of the volcanic chain and close to the Itoigawa-Shizuoka tectonic line. The negative gravity anomaly is explained by a low density layer caused by depression in the basement under the western flank of the volcanic chain. Locally positive gravity anomalies found over the oldest rock in the central part of the volcanic chain indicate a small scale high-density structure.View full abstractDownload PDF (2999K) -
Eiki ONODERA1990 Volume 36 Issue 4 Pages 267-276
Published: December 25, 1990
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSThe Antarctic Circumpolar Current (ACC) is the only tonal ocean flow around the axis of Earth's rotation. It can directly exchange the angular momentum with Earth's rotational motion. The Trans-Polar Index (TPI), variations of the pressure at the sea surface and the air temperature in the Antarctic show correlations with variations of the length of day (lod). Excitations of the Earth's rotational speed are estimated by using variations of the tonal current of the ACC, which are derived from geostrophic balance approximation of the pressure difference at the surface along the meridian. The pressure difference along the meridian is obtained by two methods; one is from the TPI and another is derived from atmospheric temperature at the surface in the Antarctic and the surface pressure at Ushuaia, in front of the Drake Passage. From the estimated excitation of the Earth's rotational speed, the ACC has proved to contribute to the exchange of the angular momentum with the solid part of the Earth. The ACC has also proved to be coupled with the increasing and/or decreasing of the El Nino.View full abstractDownload PDF (903K) -
Katsumi NAKANE1990 Volume 36 Issue 4 Pages 277-278
Published: December 25, 1990
Released on J-STAGE: March 01, 2011
JOURNAL FREE ACCESSIn geodetic network, coordinates (unknown values) are nonestimable, while observation values are estimable. Observation values are, however, not estimable under the condition that more than two stations are held fixed in the network.View full abstractDownload PDF (151K)
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