国家自然科学基金资助项目(40804001)

Based on mathematical induction,the general expression of stepwise estimation is established.In order to verify the performance of stepwise estimation,100 unsurveyed gravity anomaly are estimated by known airborne gravity anomaly using three-step estimation,four-step estimation,five-step estimation,and six-step estimation,respectively.The results show that the six-step estimation gives the best results and its computation efficiency is increased by at least 8 times in three cases(observation quantities is 1 133,2 636,3 686),respectively.At the same time,the six-step estimation is also the inflexion of the stepwise estimation.In the same case as stepwise estimation,the results of sequential estimation is identical to the stepwise estimation.But the computation efficiency is much lower than that of the common least square collocation.The main reason is that a lot of circulation computation decreases the efficiency of the algorithm although there are not more inversion operation in the program.The conclusion can be made that the stepwise estimation is recommended in practice and the sequential estimation should be carefully used.