Abstract:

In traditional geodesy, geometric projection methods are commonly employed to reduce terrestrial elevation points to the reference ellipsoid, implicitly assuming that the external equipotential surface of the normal gravity potential is geometrically similar to the reference ellipsoid. From the perspective of physical geodesy, however, the flattening of the external equipotential surfaces of the normal gravity field varies with height in a non-uniform geometric manner, and the constant-flattening assumption adopted in the traditional expanding-ellipsoid method fails to accurately characterize this physical property. To address this issue, this paper proposes a method for constructing a local reference ellipsoid based on the equipotential condition of the normal gravity potential. By determining the normal distances from a specific normal gravity equipotential surface to the equator and the poles, a local reference ellipsoid is redefined for each height, so as to more faithfully represent the local geometric characteristics of the normal-gravity equipotential surface. Theoretical derivations and numerical analyses show that this local ellipsoid model can more accurately capture the variation of equipotential surfaces in the gravity field in high-altitude regions, and exhibits better physical consistency than the traditional reference ellipsoid model.

Key words: Earth's gravity field, normal gravity potential, local equivalent reference ellipsoid, ellipsoid transformation, high-altitude engineering survey