The joint use of gravity data and GPS/levelling undulations in geoid estimation procedures.

Coupled observations of GPS and levelling data are nowadays commonly available. In Italy, IGM has surveyed more than 1000 levelling points with GPS. On these GPS/levelling points, one can get thè geoid undulation by simply subtracting thè orthometric height from thè ellipsoidal height (Heiskanen and Moritz, 1993). This large and reliable data set of observed undulations can be used to check l'or thè precision of thè gravimetrie geoid estimate (Barzaghi et al., 2007). Also. theoretical and numerical method can be applied to merge this data set and gravity observations to get what we cali an integrated geoid estimate. In this way, gravity and observed undulations are both used to compute a joint estimate of thè undulation. Different approaches can be used. In this paper, we present two possible methods which bave been studied and applied to estimate thè integrated Italian geoid.