Report of Hydrographic And Oceanographic Researches

No.45 (March, 2009)
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Contents

Original Papers

  1. abstract pdf Re-estimation of the velocity of Simosato from analysis of LAGEOS SLR data
    Mariko SATO, Hiroshi MATSUSHITA, Masayuki FUJITA and Arata SENGOKU , p.1
  2. abstract pdf Submarine topography in the east sea of Minami-Tori Shima Island, North West Pacific Ocean
    Mitsuhiro OIKAWA, Taisei MORISHITA , p.13
  3. abstract pdf Effect of the frequency of undersea sound velocity measurement on seafloor positioning in seafloor geodetic observation
    Hiroaki SAITO, Mariko SATO , p.23
  4. abstract pdf Introduction of characteristics of NOAA-MCSST analysis data compared with the observation data and its effective use - Construction of automatic making system of the detailed SST maps -
    Keizo SHUTTA , p.34
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Abstracts

Re-estimation of the velocity of Simosato from analysis of LAGEOS SLR data

Mariko SATO, Hiroshi MATSUSHITA, Masayuki FUJITA and Arata SENGOKU

Simosato Hydrographic Observatory in Wakayama Prefecture has been carrying out Satellite Laser Ranging (SLR) observation for AJISAI, LAGEOS-1, LAGEOS-2, and other geodetic and Earth-observation satellites, since 1982. More than 26,000 passes have been obtained. In this report, we re-estimated the velocity of Simosato from LAGEOS SLR data for 15 years. As a result, the velocity of 2.9cm/year in direction to 294oN relative to the Eurasian plate was obtained. This velocity is close to the subduction velocity of the Philippine Sea plate. This indicates that the interplate coupling at this region is strong. In addition, our result is consistent with other researches using SLR data (e.g., ITRF2000, ITRF2005 SLR rescaled).

Submarine topography in the east sea of Minami-Tori Shima Island, North West Pacific Ocean

Mitsuhiro OIKAWA, Taisei MORISHITA

Japan Coast Guard has carried out the bathymetric surveys in the eastern sea of the Minami-Tori Shima Island, NorthWest Pacific Ocean since 1998 to 2008. The precise bathymetric data acquired in these surveys reveal the details of the submarine topography, and clusters of small conical volcanoes were discovered. The cluster which is located at southeast of Minami-Tori Shima Island is the largest (80km x 50km) in this area. Almost all cones which belong to the cluster are hundred meters in height and less than 10km in diameter. Considering the size and the shape of the cones, the cones are considered not to be formed by landslide or hotspot. The morphological characteristics are very similar to petit spot volcanoes near Japan Trench, northwestern Pacific Plate. More than one cluster are found out on the survey area, therefore there is a possibility that more small cones cluster exist on (northwestern) Pacific Plate.

Effect of the frequency of undersea sound velocity measurement on seafloor positioning in seafloor geodetic observation

Hiroaki SAITO, Mariko SATO

As part of consideration of improving the observation efficiency, we have evaluated the effect of reducing the frequency of undersea sound velocity measurement on the horizontal components of the position of a seafloor reference point. As a result, it was suggested that balanced distribution of acoustic measurement points would enable us to reduce the present frequency of undersea sound velocity measurement to about one-fourth, keeping the present accuracy of seafloor positioning. After this, if the distribution of acoustic measurement points is more balanced by sailing-observation that can control observation lines, the undersea sound velocity measurement would be more efficient.

Introduction of characteristics of NOAA-MCSST analysis data compared with the observation data and its effective use - Construction of automatic making system of the detailed SST maps -

Keizo SHUTTA

Detailed dataset of 1.13km square mesh was developed using NOAA satellite SST (sea surface temperature) data (MCSST : Multi-Channel SST analysis data) which our department receives in real-time, and the dataset was verified in comparison with an enormous amount of data observed around inshore Japan. Then by using MCSST analysis data I performed to construct a system which automatically outputs SST maps and numerical analysis data around inshore Japan, and from these outputs I developed some products distributed to Hydrographic and Oceanographic Department of Regional Coast Guard everyday.

Regarding the accuracy of MCSST analysis data, I verified the data by comparing with data observed at SST observation stations, which were scattered in the Setonaikai (the Inland Sea of Japan) and I proved the validity by checking correlation maps of daily and seasonal variations between MCSST analysis data and observation data. I also examined sea area characteristics of SST in the Uwakai Sea where the influence of open sea was received easily and in the area from the Iyonada Sea to Osaka bay where the influence was not received directly. As a result, I proved the validity of SST information made from MCSST analysis data.

The observation data for comparative verification had the period of 2 years (2004-2005). MCSST analysis data used here was mapped around the Setonaikai, and was fitted into the area of the Setonaikai. That meant observation data corresponded to MCSST data averaged in 5' pixel x 5' pixel (about 5km x 5km) over centering on the point corresponding to the observation point. Generally, MCSST analysis data was considered to be varied around inshore area and narrow sea area, but by averaging MCSST analysis data into 5opixel x 5opixel conparatively stable data could be obtained. Still, there were many points where the data was lack or the value was unusually low because of cloud cover, so I also examined the validity of data composite period. As a result, it was indicated that it was possible to make a valid SST map by compositing daily MCSST analysis data and the map accuracy was good enough in a narrow sea region for example the Setonaikai although there were slight variations depending on season.

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