Regional gravitational field modelling by the spectral combination of satellite higher-order radial derivatives of the gravitational potential and a global geopotential model

In this contribution, we will discuss a problem of regional gravitational field modelling by the spectral combination of spaceborne first-, second- and third-order radial derivatives of the gravitational potential at the mean altitude of 250 km. Some of the mentioned measurements are not observable yet, so we will synthesize them from a global geopotential model over a test area. The main goal of a numerical experiment is to compute the gravitational field in a regional area from spatially restricted higher-order radial derivatives of disturbing potential, and two problems arise. The first is how to estimate local spectral properties, i.e., degree-order variances of local data, and the second is the effect of the omitted distant zone data, i.e., (spatial) truncation error. The spherical harmonic power spectrum from local data will be recovered by 2D-DFT, and the truncation error will be calculated from a global geopotential model. For this purpose, a mathematical model based on the spectral combination method of heterogeneous gravity field data and a global geopotential model is developed. The correctness of derived spectral weights suitable for spectral downward continuation will be verified by a closed-loop test and by direct comparison with the global solution. Moreover, different sizes of a data area (area covered by simulated satellite measurements) to minimize the truncation error and various truncation degrees of a global geopotential model will be tested.