Multi-technique approach for deriving a VLBI signal extra-path variation model induced by gravity: the example of Medicina.  

P. Sarti1, C. Abbondanza1, M. Negusini1, L. Vittuari2
1Istituto di Radioastronomia, Istituto Nazionale di Astrofisica, Italy
2DISTART,Università di Bologna, Italy

Oral presentation 

Since the beginning of VLBI activities, gravitational deformations have been identified as crucial factor on VLBI data analysis; in spite of that, they have been largely disregarded: if neglected, they can introduce to a various extent errors in the estimate of geodetic parameters, such as station heights and tropospheric delays. Deformations induced by gravity may modify the length of path travelled by incoming radio signal as the pointing elevation of the antenna varies; with this investigation we present the most recent results of the multi-technique approach that we have successfully applied to the 32 m VLBI antenna at Medicina (Italy): a combination of terrestrial and laser scanning observations and a Finite Element Model (FEM) allowed to quantify the amount of signal path variation and to formulate an elevation dependent model for correcting VLBI observable. Being connected to structural deformative patterns, signal path variation is strictly peculiar to the VLBI antenna: in the case of Medicina, it is showed to increase of about 2 cm, from horizon to zenith. Such correction models may be regarded as analogous to those introduced in GPS data analysis to correct PCV.