Acta Geodaetica et Cartographica Sinica ›› 2025, Vol. 54 ›› Issue (9): 1561-1571.doi: 10.11947/j.AGCS.2025.20250102

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Theoretical foundation of gravity field and improvement of classical concepts for geodetic height datum unified in the terrestrial reference system

Chuanyin ZHANG1,2,3(), Tao JIANG1,2,3(), Baogui KE1,2,3   

  1. 1.State Key Laboratory of Spatial Datum, Chinese Academy of Surveying and Mapping, Beijing 100036, China
    2.Beijing Fangshan Satellite Laser Ranging National Observation and Research Station, Beijing 100036, China
    3.Chinese Academy of Surveying and Mapping, Beijing 100036, China
  • Received:2025-03-12 Revised:2025-07-15 Online:2025-10-10 Published:2025-10-10
  • Contact: Tao JIANG E-mail:zhangchy@casm.ac.cn;jiangtao@casm.ac.cn
  • About author:ZHANG Chuanyin (1968—), male, PhD, researcher, PhD supervisor, majors in geodesy and geodynamics. E-mail: zhangchy@casm.ac.cn
  • Supported by:
    The National Key Research and Development Program of China(2021YFB3900200);Basic Scientific Research Operating Expenses Project of Chinese Academy of Surveying and Mapping

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Abstract:

The current theory of geodetic height datum were mainly established during the era of traditional terrestrial geodesy, and have difficulty adapting to the rapid development of the Earth's gravity field and satellite geodesy. This paper strictly follows the principles of geometric and physical geodesy and the uniqueness and precise measurability requirements of geodetic elements and concepts, and deduces the theoretical and logical relationship among the height datum, the terrestrial reference system and the gravity field concisely and clearly by conducting scientific research on the theoretical foundations and implementation principles necessary for unifying the elements of physical geodesy into the terrestrial reference system, and then re-examines some classical concepts of the height datum. The paper presents the following main results and their specific geodetic evidences. ①It is demonstrated that whether it is the orthometric height, normal height or geopotential number system, the height starting datum surface is the geoid if the deformation of the geoid is ignored, and it is pointed out that the analytical orthometric height is more suitable for the purpose of the height datum than other types of orthometric heights. ②The theoretical foundation of the gravity field for the geodetic height datum unified in the terrestrial reference system is improved, and the geodetic datum conditions and technical implementation principles for the GNSS replacing leveling technology are derived. ③The theoretical method of Earth's center of mass and shape polar positioning based on space geometric and physical geodesy is derived. Which neither relies on geophysical assumptions or geodynamic protocols, nor on the principle of earth rotation and its dynamics, but rather realizes scientifically the positioning and orientation of the terrestrial reference system only based on the theory of geodesy. ④It is demonstrated that the surfaces of orthometric equi-height are parallel to the geoid and the normal gravity field can be fully determined with only three parameters. Thus the trouble of coordination and consistency between the geoid defined by the Gaussian convention and the gravity geoid has been effectively solved.

Key words: terrestrial reference system, height system, height datum, theory of Earth's gravity field, geodesy, uniqueness and precise measurability, analytical orthometric height, geoid

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