A theoretical research of the influence of ocean loading tide on the time variation of gravitational field

The ocean tide effects on the Earth's gravitational field can be considered as a kind of loading influence. In some sites, for example group of islands in the ocean and coastland, the ocean tides' loading influence on gravitational field can reach microgal size. Therefore it must be taken into account in the research of high precision gravitational field. This paper studies the theory and method for the influence of ocean loading tides on the gravitational field. In the deduction of the formulas, we avoid developing the point loading density into spherical harmonics, rather, we take directly the gravitational potential of ocean loading, introduce the height of ocean tides in this expression, and finally deduce the relevant formulas for ocean tide's influence on gravitational field. Furthermore, some problems that should be addressed when the accuracy reaches nanogal size are discussed. This study may provide a reference and basis for theoretical research in space geodesy.