Journal of the Geodetic Society of Japan
Online ISSN : 2185-517X
Print ISSN : 0038-0830
ISSN-L : 0038-0830
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Volume 56, Issue 4
Displaying 1-8 of 8 articles from this issue
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TUTORIAL
  • Geophysics with GPS-TEC
    Kosuke Heki, Mamoru Sugawara, Masaru Ozeki, Ikuya Okazaki
    2010 Volume 56 Issue 4 Pages 125-134
    Published: 2010
    Released on J-STAGE: March 30, 2012
    DOIhttps://doi.org/10.11366/sokuchi.56.125
    JOURNAL OPEN ACCESS
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    Two carrier frequencies, L1 and L2, used in Global Positioning System (GPS) can be used to isolate ionospheric total electron contents (TEC) by taking the phase differences between the two carriers (L4). Here we review technical aspects of geophysical applications of TEC measurements. Topics include conversion of standard format raw GPS data files into L4 and TEC, and numerical techniques to isolate disturbance signals with various time scales. We also introduce typical examples of TEC change signatures of variety of geophysical phenomena, e.g. volcanic eruptions, earthquakes, solar flares, ionospheric hole formation by rockets and missiles, solar eclipse, and elusive precursory TEC changes before earthquakes.
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[SPECIAL ISSUE ON APPLICATION OF SYNTHETIC APERTURE RADAR TO GEODESY AND EARTH SCIENCES, PART I]
ORIGINAL PAPER
  • Atmospheric Noise Reduction in InSAR Analysis Using Numerical Weather Model
    Taku Ozawa, Shingo Shimizu
    2010 Volume 56 Issue 4 Pages 137-147
    Published: 2010
    Released on J-STAGE: March 30, 2012
    DOIhttps://doi.org/10.11366/sokuchi.56.137
    JOURNAL OPEN ACCESS
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    Atmospheric delay, one of the largest error sources in InSAR analysis, is often simulated as a linear function of the altitude (called “atmosphere-topography correction”). However, the applicable area is limited and it cannot treat a heterogeneous atmospheric distribution. We therefore attempted to reduce atmospheric noise using simulation from results of the 10 km-mesh numerical weather model (MSM: Meso-scale model) provided by the Japan Meteorological Agency. A radar propagation path was estimated using the ray-tracing technique in order to consider atmospheric heterogeneity. The average of residual standard deviations for interferograms employed for reducing atmospheric noise was 13 mm, which is almost the same as those for interferograms employed for atmosphere-topography correction. This result suggests that the accuracy of atmospheric delay correction using MSM results is the same level as that of the atmosphere-topography correction. This method is effective since this noise reduction can be applied everywhere in Japan. However, the noise component due to atmospheric heterogeneity could not be reduced, possibly due to inappropriate interpolation for temporal change and/or accuracy of MSM using smoothed topography. We therefore used CReSS, which is a detailed weather model, and estimated the detailed atmospheric data in the observation time. The result reproduced the local atmospheric noise distribution, demonstrating the effectiveness of such an approach.
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TECHNICAL REPORT
  • Correction of Unwrapping Errors Caused by Branch-Cut Algorithm
    Satoshi Okuyama
    2010 Volume 56 Issue 4 Pages 149-153
    Published: 2010
    Released on J-STAGE: March 30, 2012
    DOIhttps://doi.org/10.11366/sokuchi.56.149
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    This paper introduces a tool to correct misunwrapped region contained in interferograms which are unwrapped using branch-cut algorithm. Branch-Cut is one of the most common algorithms to unwrap interferograms, however, it is quite difficult to unwrap an interferogram without any errors. This fact makes the unwrapping time-consuming and painful process in the SAR interferometry analysis. Mod_unwrap is a GUI program that enables correcting unwrap errors in WYSIWYG style. Such tool is quite effective when the unwrapped interferogram contains many error regions.
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ORIGINAL PAPERS
  • Analysis of Crustal Deformation Associated with the 2008 Wenchuan, China, Earthquake Using ALOS/PALSAR data
    Mari Enomoto, Manabu Hashimoto, Yo Fukushima, Yukitoshi Fukahata
    2010 Volume 56 Issue 4 Pages 155-167
    Published: 2010
    Released on J-STAGE: March 30, 2012
    DOIhttps://doi.org/10.11366/sokuchi.56.155
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    We study crustal deformation associated with the Mw7.9 Wenchuan, China, earthquake of May 12, 2008 on the basis of ALOS/PALSAR images to estimate slip distribution. In addition to interferograms along the ascending tracks, we use the ScanSAR data along a descending orbit. The ScanSAR-ScanSAR interferogram has high coherence enough to discuss coseismic deformation, which implies up to 80cm range increase on the south side of the Long-Menshan fault.
    We jointly invert these data and GPS displacements to estimate slip distribution and dip angle of the source fault simultaneously. The optimal dip angle is estimated to be 48 degrees for the combination of three datasets, while 58 degrees for only InSAR ascending data. The maximum slip is 5m for only ascending data, while it exceeds 8m for the combined datasets. This discrepancy may be attributed to the geometry of the source fault to the line-of-sight direction of SAR, suggesting that enough information cannot be retrieved by only ascending images. It is important to note that thrust component is relatively large in the southwestern part, while dextral slip is prevailing in the northeastern part, in the slip distribution obtained from the joint inversion. These characteristics are consistent with those of surface ruptures detected by field surveys.
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  • Relationship between two Solomon Islands Earthquakes in 2007 (M8.1), 2010 (M7.1), and Seismic Gap along the Subduction Zone, Revealed by ALOS/PALSAR
    Yousuke Miyagi, Taku Ozawa
    2010 Volume 56 Issue 4 Pages 169-177
    Published: 2010
    Released on J-STAGE: March 30, 2012
    DOIhttps://doi.org/10.11366/sokuchi.56.169
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    On January 3, 2010 (UTC), an M7.1 earthquake occurred in the Solomon Islands subduction zone where the Australian, Woodlark, and Solomon Sea plates subduct northeastward beneath the Pacific plate. ALOS/PALSAR observed the epicentral area both before and after the earthquake, and a crustal deformation associated with the earthquake was detected using the DInSAR technique. With the geodetic data, we inferred a thrust-type seismic fault that caused the 2010 earthquake. On April 1, 2007 (UTC), an M8.1 interplate earthquake occurred in the subduction zone between the Pacific Plate and the Australian Plate, about 50km northwest of the 2010 earthquake. Miyagi et al. (2009) estimated a slip distribution of the seismic fault mainly from the PALSAR/DInSAR data and suggested that most of the seismic gap was filled by the 2007 earthquake. However, a small seismic gap related to an Mw7.0-sized earthquake still remained. After fault modeling of the 2010 earthquake, we concluded that the 2010 earthquake filled the remnant seismic gap supposed by Miyagi et al. (2009). The distribution of Coulomb failure stress change in the epicentral area after the 2007 earthquake suggested the possibility that the 2010 earthquake was triggered by the 2007 earthquake.
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  • Detection of Landslide Displacement at the Hakusan volcano from Interferometric Analysis of ALOS/PALSAR data
    Hitoshi Michinaka, Yoshihiro Hiramatsu
    2010 Volume 56 Issue 4 Pages 179-194
    Published: 2010
    Released on J-STAGE: March 30, 2012
    DOIhttps://doi.org/10.11366/sokuchi.56.179
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    A continuous landslide about 10 cm per year has been observed for about 30 years around the Jinnosuke valley of the Hakusan volcano from GPS and/or EDM observations. To reveal the spatial coverage of the landslide around the Jinnosuke valley, we generate 23 differential SAR interferograms (15 Ascendings and 8 Descendings) around the Jinnosuke valley of the Hakusan volcano using 15 SAR acquisitions of PALSAR data from 2006 to 2009. The raw SAR data are processed by using the JAXA/SIGMA-SAR. We apply a linear relationship between altitudes and phase difference changes to remove the effect of the propagation delay on the entire interferogram due to the vapor in the atmosphere. We find the interferometric fringes of the displacement on surface due to the landslide in three interferograms between June and October in 2007 and 2009. The occurrence of the landslide over several hundred meters to 2 km squares is recognized around the Jinnosuke and the Senzai valleys. The horizontal displacement of the landslide is several to 25 cm per year. The estimations around the Jinnnosuke valley are coincident with GPS and EDM observations. Comparison of the two interferograms which were acquired in 2007 shows that the whole area of the landslide has not changed temporally while we can find the difference in the areas with large displacement between the two. We, thus, consider that the local landslide occurs independently in time and space due mainly to a seasonal change in underground water channel.
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