Test and Analysis of Upward Continuation Models for Earth Surface Gravity with Regard to the Effect of Topographic Height

Upward continuation plays an important role in approximation of the external gravity field of the earth and in accuracy evaluation of airborne gravity data. This paper reviews the available models for upward continuation including approximate spherical solution and rigorous formulas, and makes a comprehensive comparison and analysis of their properties as well as the applicability of different models. The Ultra-high-degree geopotential model and point mass methods are suggested to be used for the realization of "downward continuation comes before upward" procedure combining the remove-restore technique, paying attention to the stability of the downward continuation solution before the upward continuation. Real numerical computations were carried out to evaluate the effects of topographic height on upward continuations. The performance of different models with regard to the effect of topographic height were compared and analyzed. The accuracy of the upward continuation model was estimated. Some useful conclusions are obtained. in rugged mountainous areas, the maximum rms value of terrain effect on upward continuation can reach several tens mGal(10^-5m/s²). Even if the continuation height is greater than 10 km, the effect of topographic height on upward continuation can exceed 3 mGal. The accuracy of upward continuation model was estimated to be about±1 mGal. The modified Poisson integral model, in which the downward continuation is accomplished using a ultra-high-degree geopotential model and terrain information, is therefore recommended for upward continuation due to its simple computation procedure, high stability, and reliability.