Abstract: Compass Geostationary Earth Orbit(GEO)satellites observations are used tostudy medium-scale traveling ionospheric disturbances(MSTIDs).Themethod to exactionos-(下转第1429页)1412 第38卷第12期 翟振和等:利用级数展开法确定区域大地水准面的重力位Local Geoid Gravitational Potential DeterminationUsing the Series Expanding MethodZHAI Zhenhe1,2 SUN Zhongmiao2 WANG Xingtao2 LIU Xiaogang2(1 Institute of Geography Spatial Information,Information Engineering University,66Middle Longhai Road,Zhengzhou 450052,China)(2 State Key Laboratory of Geo-information Engineering,1Middle Yanta Road,Xi’an 710054,China)(3 State Key Laboratory of Astronautic Dynasmics,28P.O.Box 505,Xi’an 710043,China)Gravitational potential can be expressed as a mathematical series,in which the firstsection is geoid potential-W0.This method was used to determine the Baltic Sea geoid poten-tial by using the GPS station data(1997-04).The results show that the first rank term com-puted by EGM2008is almost equal to the results computed by WGD2000(complete to degreeand order 360)while the difference is about a quantity of 10-3.The second rank term has aquantity of 10-5and can be omitted.In the case of changeless geocentric coordinates,the de-termination of W0is largely affected by changing height data,so it is important to accuratelydetermine the height of the GPS station.The W0value(62 636 857.23±０．４８ｍ2·s-2)ofBaltic sea study site is obtained by using five set of GPS stations and an EGM2008modelwith degree and order of 360.