Vol.51-4 CONTENTS
JGD2000 (vertical) -The New Height System of Japan-Tetsuro IMAKIIRE and Eiichi HAKOIWA AbstractJGD2000(vertical), the official height system and data set of Japan,is constructed using the newest leveling survey results and orthometric height system. This paper introduces the background and procedure of the construction of the new height system and data set, as well as the characteristics of the change of height around the Japanese Islands. The old height data set published in FY1969 was based on the normal orthometric height system, because not enough detailed gravity data was available. The detailed gravity data was used for the calculation of the new height data set. The newest results of leveling surveys are archived into "LAGSAS", the database of leveling surveys with analysis function, which supported the calculation of the height data of bench marks. Network adjustment is carried out with a single fixed point, the datum of leveling in Tokyo. As the Hokkaido network was directly connected to the main part of Japan for the first time by the leveling survey along the Seikan Tunnel, the Hokkaido network was also simultaneously adjusted in the nationwide adjustment. The height values of more than 20,000 bench marks have been determined and opened to the public. Evaluation of the calculation, such as inspection of loop closures, shows that the consistency of new height data set is satisfactory enough. Contents1. Introduction 1.1 Policy for building up the official height data set 1.2 Calculation 1.3 Evaluation and analysis 2. Calculation 2.1 The policy for the establishment of the new height data set 2.1.1 The strategy and procedure of calculation 2.1.2 Height of leveling datum 2.1.3 Determination of the weight for cross sea leveling 2.1.4 The datum value for isolated islands 2.2 Preparation for the calculation 2.2.1 Establishment of LAGSAS 2.2.2 Development of application program 2.3.1 Formulae used for the calculation 2.3.2 Nationwide network adjustment 2.3.3 Publication of the adjusted height 3. Evaluation and discussion 3.1 Systematic difference between orthometric height and normal orthometric height 3.2 Evaluation of the observation data and change of height system 3.3 Overview of calculation results 3.4 Discussion on the comparison between old and new height data 4. Conclusion Acknowledgement References |