In this paper, it is pointed out theoretically that the ground surface tilt is not observed by only tiltmeter, but must be determined by both tilt and gravity earth tide data.

Using this model, the airborne gravity measurement test data is downward continued based on least squares collocation and is compared with known ground gravity data.

This paper discusses the problem of gravity field determination by application of such a new gravity boundary condition as the disturbing gravity by use of GPS.