A Broadband VLBI experiment with transportable station between Japan and Italy~RF Direct sampling and a new observation scheme using closure delay relation~

Abstract:

We have developed a broadband VLBI (very long baseline interferometry) system stimulated by the concept of the VLBI Global Observing System (VGOS). The new broadband VLBI system was implemented in the Kashima 34 m antenna and in two transportable stations utilizing 2.4 m diameter antennas. The transportable stations have been developed as a tool for intercontinental frequency comparison but are equally useful for geodesy. To enable practical use of such small VLBI stations in intercontinental VLBI, we have developed the procedure of node-hub style (NHS) VLBI: In joint observation with a large, high sensitivity hub antenna, the closure delay relation provides a virtual delay observable between node stations. This overcomes the limited sensitivity of the small diameter node antennas, while error sources associated with large diameter antennas, such as gravitational deformation and delay changes in necessarily long signal cables, are eliminated. This scheme has potential to mitigate radio source structure effect, though it need further investigation. We have performed VLBI experiments utilizing this approach over 8700 km baselines among Medicina, Koganei, and Kashima. We used the Vienna mapping function (VMF3) for atmospheric delay corrections including its anisotropic components. The performance of NHS VLBI scheme with broadband 2.4 m diameter antenna pair and Kashima 34 m antenna was evaluated to be comparable with IVS-R1/R4 via baseline length repeatability (Fig.1).

This presentation describes the system components, signal processing procedure, experiment, and results in terms of baseline repeatability. This NHS VLBI scheme can be applied at VGOS observation stations, and it may become a tool for improving the global distribution of geodetic VLBI station and also for collocation with other space geodetic technique.

Figure 1. Baseline length repeatability of 2.4 m diameter antenna pair with NHS VLBI scheme (▼), and those of IVS-R1 and R4 sessions (□). Solid line is polynomial to represent baseline length repeatability examined by Teke et al.(2008).