Observation requirements for precise determination of local (quasi)geoid

Many geodetic-related observations nowadays require a precise local geoid height that is as accurate as sub-centimeters. Here, we develop a method to combine global Earth Gravitational Model (EGM), Digital Terrain Model (DTM), as well as highly accurate local gravity and Global Navigation Satellite System (GNSS) observations to achieve this goal. We carried out several observation campaigns to obtain high space resolution and high accuracy gravity and GNSS data. Firstly, we analyze the accuracy of the commonly used methods such as those that use EGM only or use EGM and DTM combined. Then we test our method with a synthetic earth that was developed with EGM, DTM, and local high-resolution topography. Our results should that, the high degree EGM-only geoid has a mean error of tens of centimeters; the geoid from combined EGM and DTM can achieve accuracy of several centimeters; and if we want to have a local geoid with deviations less than sub-centimeter, high accurate observations with space resolution as high as 1"x1" are needed.