factors in survey regions in the waters surrounding Japan. The results to date show that the vicinities of Daito Ridge and the Ogasawara islands, which are south of Japan, are sea areas for which Japan could claim continental shelf beyond 200 nautical miles from its territorial sea baselines. Therefore, at present, JMSA is proceeding earnestly with analysis of the areas. In addition, hereafter, it intends to promote studies related to the possibility of establishing the outer limits of the continental shelf for the sea area in the vicinity of Minami Torishima Island.
Regarding sea areas for which studies have been completed, JMSA is preparing the basic data for submission to the "Commission on the Limits of the Continental Shelf." Furthermore, it has issued "Basic Maps of the Sea in Continental Shelf Areas," which use the survey data and are the basic data for marine control and development.
(3) Promotion of Marine Geodetic Survey
Nautical charts are prepared by each country respectively using its own geodetic datum determined through astronomical observations and other surveys. In recent years, along with the advancement in positioning systems using satellites, discrepancies in position caused by differences in geodetic systems (*Note 1) have become a problem. Therefore, the International Hydrographic Organization (IHO) is recommending that geographic coordinates indicated on nautical charts be based on a world geodetic system.
In response to this, Japan has worked to correct the position of the Japanese archipelago, as indicated using the current Japanese geodetic system, and to indicate it accurately based on the world geodetic system. Since 1982, JMSA has been participating in a joint international observation program using geodetic satellites, which NASA leads in promoting. It has conducted observations using satellite laser range systems at the Shimosato Hydrographic Observatory (the fiducial point for the Japanese mainland) in Wakayama Prefecture. As a result, it was revealed that according to the world geodetic system, the geographic coordinates for Japan are 465 meters northwest of the coordinates based on the Japanese system.
In addition, JMSA began to determine the positional relationship between the Japanese mainland and its remote islands' and other geographical features with high precision in FY 1987. It transports transportable laser range systems to these islands, etc., and conducts simultaneous observations with the Shimosato Hydrographic Observatory, the fiducial point
*Note 1: A geodetic system is a system of coordinates that indicates global position by first deciding such basic factors as the configuration of the earth. The Japanese geodetic system was built upon astronomical observations and triangulation surveys conducted during the early period of the Meiji Era (Japan's nautical charts are based upon this geodetic system). A world geodetic system would use satellites and be created so that it could be used jointly worldwide.
for the Japanese mainland. This accurately determines the position of the Japanese island group, which is the standard for territorial sea baselines, etc., using the world geodetic system.
