No abstract

A three-dimensional geodetic measurement of the 1.24-km Haystack-Westford base line vector was performed to verify the accuracy of previously published radio interferometric measurements. The differences between the geodetic and the very long base line interferometry (VLBI) measurements of the base line length, the horizontal X and Y components, and the vertical Z component were -4, 2, 4, and -19 mm, respectively. After a correction was applied to the VLBI determination of the vertical component to account for a recently measured, repeatable gravitational flexure of the Haystack antenna, the discrepancy in this component was reduced to -6 min. Other possible repeatable flexures in the two antennas, which have not yet been measured, could either further reduce or increase this discrepancy.