ON SOME PROBLEMS OF THE DOWNWARD CONTINUATION OF THE 5'-X-5' MEAN HELMERT GRAVITY DISTURBANCE

This research deals with some theoretical and numerical problems of th e downward continuation of mean Helmert gravity disturbances. We prove that the downward continuation of the disturbing potential is much sm oother, as well as two orders of magnitude smaller than that of the gr avity anomaly, and we give the expression in spectral form for calcula ting the disturbing potential term. Numerical results show that for ca lculating truncation errors the first 180 degrees of a global potentia l model suffice. We also discuss the theoretical convergence problem o f the iterative scheme. We prove that the 5' x 5' mean iterative schem e is convergent and the convergence speed depends on the topographic h eight; for Canada, to achieve an accuracy of 0.01 mGal, at most 80 ite rations are needed. The comparison of the ''mean'' and ''point'' schem es shows that the mean scheme should give a more reasonable and reliab le solution, while the point scheme brings a large error to the soluti on.